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Curiosity at Whitebark Pass: The Curiosity rover at Gale Crater continues to find interesting things. On June 7, it sent a MAHLI close-up image of light-colored rocks at a place the rover team calls “Whitebark Pass.” The rover is continuing to study the area, but I must say, the rocks imaged resemble quartz, a mineral conventional thinking says should not be on Mars. Hmmmm. See it for yourself here:

Chang’e 6 News: On June 1, the Chinese National Space Agency successfully landed the Chang’e 6 spacecraft in Apollo Crater on the Moon’s far side. It returned images of its surroundings, deployed instruments and a mini-rover that took a selfie of the lander, collected rock, soil, and drilled samples, and, on June 4, lifted off successfully. It’s presently en route to Earth, and is due to rendezvous with a vehicle already in Earth orbit that will transfer the samples to Earth. For more on this mission, see:

Water Under Martian Polar Regions? Well, Maybe Not: ESA’s Mars Express spacecraft carried an imaging radar system capable of penetrating deeply into the martian surface, and very deeply into Mars’ polar caps. Unexpectedly-strong radar returns from the cap implied a material that could reflect radar waves was present at depth, and that the most likely reflector candidate was liquid water.

Liquid water is still in the running (sorry), but recent research at Cornell “show that small variations in layers of water ice -- too subtle for ground-penetrating radar instruments to resolve -- can cause constructive interference between radar waves. Such interference can produce reflections whose intensity and variability match observations to date -- not only in the area proposed to be liquid water, but across the so-called south polar layered deposits.”

Other research in the past three years has also indicated that a large liquid body underground on Mars may not be the cause of the large radar return.


For a summary of this work, see here; for the paper in Science Advances, see here.

Jim Green’s Gravity Assist Podcast of the Week: For some time now, I’ve been re-running installments of NASA’s Gravity Assist podcast, hosted by Jim Green, former NASA Chief Scientist. This week, I’ll spotlight Episode 32 of Season 5, entitled “Finale: Thanks for All the Gravity Assists,” which originally aired on 8/12/2022. It’s the final episode of this wonderful five-season podcast. I’m going to keep this story up for a few weeks yet.

The episode begins with a summary of Gravity Assist by Liz Landau, the lead producer of the series. Jim’s guests this time are Liz and Manny Cooper, the podcast’s audio engineer. Jim starts off by asking both of them how they came to work for NASA.

Liz is a Public Affairs Officer at NASA HQ, long versed in writing for NASA’s website, editing, and other podcast production. She got into the field by taking a course in science communications, a subject she hadn’t known existed, at Princeton. The course really put her “on this path to communicate to the public my enthusiasm for science and all of the amazing activities that are going on in space exploration.” She worked at CNN, then at JPL, and finally to HQ, where Gravity Assist became her regular program.

Manny said that what he really liked about the GA podcast was “getting to learn things that I wouldn’t necessarily learn in my field. Being exposed to, you know, the science behind, you know, growing food and, and Space. What, what does another planet sound like? What are some of the things that astronauts think about when, you know, launching, what you know, they’re thinking about when they’re on the ISS? I t’s all interesting things. So, getting to learn stuff like that is, is really, really amazing.”

Jim then shifted gears and talked a bit about himself and the origin of the Gravity Assist podcast. I want to share what he said with you. 

“In 2017, the Office of Communication came to me and said they’d like to do a podcast, and would like to know if I would be the host. And I said, ‘Yeah, I’d love to be the host!’ Not only that, I know what to call it. Let’s call it Gravity Assist. And, of course, initially, from the Office Communication, they were puzzled by that name, but it really has its roots in an experience that I had the year before. In fact, the name comes from my interaction with people in a town called Mars, Pennsylvania, the mayor of Mars was putting on this big huge parade celebrating the planet Mars as a theme for his parade.

“He had asked me what the celebration could be about. And I said, let’s make it you know, the Mars New Year. And this is when the year on Mars starts. It’s a perfect timing for it, with the Mars calendar.

“(The town) had this fabulous parade. Kids were dressed up as Martians. And I said, ‘Well, can I bring some NASA employees up and we’ll be there and enjoy the celebration too, and talk about what we know about Mars?’ Well, he loved that idea. And so I brought about 100 NASA people up. It was great. We had displays and rovers and everything. And I had a little boy in the, in the town, follow me around all day. In fact, I had him hand out stuff and we chit-chatted all kinds of things that he wanted to know.

And we just had a really wonderful time (the boy). I even ran rovers over on top of him, you know. Which was fun to do. And he enjoyed it. Well, about nine months later, I received an email from his father. And I had given the little boy my card. And so it wasn’t hard for his father to get a hold of me. And he said that his son was really blossoming in school. He was getting great grades in math and science and building the Juno spacecraft out of Legos. His son was really getting into space. And so his father said, he wanted to thank me for giving his son a Gravity Assist.

I got it immediately. I thought, ‘Wow, who would have thought that, you know, Jim Green, scientist, could really inspire or get people motivated, to be more involved in Space to understand how they might fit into the future? I’m not Carl Sagan, you know, I’m not people like Neil DeGrasse Tyson and, and really put it out there on a regular basis. But I did love the name. And I really wanted to know how other scientists get involved in the business we’re in. And that’s really where the name comes from, that one event that happened to me.”

What a wonderful way to end a wonderful podcast series. It is up to all of us to follow Jim’s lead and provide a Gravity Assist to the next generation of STEM students!

As Only WE Can!

Why Venus is SO Dry: Venus and Earth likely have similar bulk compositions, and both planets likely received a lot of volatile-rich material during their accretion process. Yet the surface of Venus appears to be very dry, with 100,000x less water than Earth. What happened to all Venus’ water? Many scientists believe that Venus started life more Earth-like than it is now, but for reasons unknown (but super important for understanding Earth’s future!!) Venus suffered a runaway greenhouse effect that made its surface environment absolutely hellish. But that doesn’t explain the lack of water observed today. Recent computer modeling of Venus’ atmosphere led scientists to a hypothesis that might explain the dryness. High in the venusian atmosphere, the model shows that CO2 and H2O can combine to form HCO+, a short-lived molecule that attracts an electron and splits, with some H escaping Venus’ gravity in the process. If the modelling is correct, there should be a lot of HCO+ in Venus’ atmosphere, but nobody has flown a mission to Venus with the necessary detector to test the new hypothesis, and NASA’s planned DAVINCI mission isn’t slated to carry one, either. For more information, see the summary here. And no, Carrie Nation is not the scientist involved…

Venus Might Not Be So Hellish After All, At Least Aloft: The surface conditions on Venus are not conducive to life: a dense atmosphere of CO2 and temperatures hot enough to melt lead. Cooler temperatures prevail at high altitude in the venusian cloud deck, but the chemistry of those clouds is somewhat off-putting due to sulfuric acid. However, recent research conducted at MIT finds that 19 amino acids that are key building blocks for life on Earth could be stable under the conditions in the clouds; “concentrated sulfuric acid is not a solvent that is universally-hostile to organic chemistry.” For a summary of this research, see here; for the paper in Astrobiology, see here.

NASA’s Dragonfly mission is a “Go!” Success often begats success, and no better example can be found than the just-now-approved Dragonfly helicopter mission to Saturn’s moon, Titan. The enormous success of the Ingenuity helicopter on Mars has shown that vertical flight on another Solar System body is feasible, and Titan has a much denser atmosphere than Mars has. Johns Hopkins’ Advanced Physics Laboratory will build the spacecraft and APL scientist Elizabeth Turtle will be the Principal Investigator. “Dragonfly’s goal is to characterize the habitability of the moon’s environment, investigate the progression of prebiotic chemistry in an environment where carbon-rich material and liquid water may have mixed for an extended period, and even search for chemical indications of whether water-based or hydrocarbon-based life once existed on Titan.” The mission will launch in July, 2028, and arrive at Titan in 2034. For more information about the mission, see here; for more about the “Go” announcement, see here.

The Voyagers Keep on Voyaging! The Voyager mission was originally scheduled to last only four years, sending both probes past Saturn and Jupiter. NASA extended the mission so that Voyager 2 could visit Neptune and Uranus; it is still the only spacecraft ever to have encountered the ice giants. Both spacecraft are so far out there is nothing to photograph, at least after Voyager 1 sent back the Solar System “Family Portrait” in 1990 (which showed Earth as a “pale blue dot”). JPL’s Ed Stone was the Project Scientist for the Voyager project, taking leadership in 1972. He recently retired (October, 2022) after serving fifty years as the guy in charge of the Voyager program! 

 The Voyagers’ mission was extended again to give additional value to the overall Voyager program. Astronomers and heliophysicists wanted to know about the conditions at/near/past the “heliopause,” the spherical region around the Sun where the solar wind is stopped by the interstellar medium. Both Voyagers have their Cosmic Ray Subsystem, Low-Energy Charged Particles” detector, and Magnetometer instruments in operation, and Voyager 2’s Plasma Science instrument is still operating, too. Collectively, these instruments are providing valuable information on the nature of the heliopause and interstellar Space.

Availability of electrical power will limit the remaining operational lifetimes of the Voyagers. Both spacecraft have three radioisotope thermal generators aboard, which generate electricity from the heat of radioactive decay (for more on RTGs, see here). Alas, all the Voyager RTGs have only a few years at most before their power output decays too low to operate, even though NASA recently made alterations to the Voyager operation plan that will add some years to the Voyagers’ operations. For more info, see here. After that, they will become V’gers.

The Voyagers have grossly exceeded pre-mission expectations, but their success has not been free of glitches, especially as the spacecraft age. 

A while back there were news items about problems with communicating with Voyager 2. An inadvertent command caused its main communication antenna to lose lock on Earth. It could not receive commands or transmit data back to Earth. The Deep Space Network was able to detect a carrier wave signal showing that the spacecraft was still operational, but misaligned. NASA then broadcast a “reorient yourself” command with a signal powerful enough for Voyager 2’s misaligned antenna to still receive. The spacecraft performed the desired maneuvers (it does so quarterly as SOP, to ensure precise alignment) and full communications were restored

Voyager 1 had a serious communications problem five months ago. It could send and receive signals from Earth, but a failed computer chip in its internal Flight Data System resulted in sending out messages with no science or engineering data. For more on the details of the problem, see here.

An amazing amount of engineering sleuthing identified the problem area and devised an ingenious work-around. The new code required to restore the system was sent out to Voyager 1 on April 18. Waiting to see if the change worked must have tried the engineers’ patience, because the round-trip time for signals from Earth to Voyager and back would take almost two days! But on April 12, meaningful data was being received successfully. Both spacecraft can now continue to be useful in learning about interstellar Space for at least a few more years.

As only NASA can!

Solar Max and Mars: The Sun’s 11-year electromagnetic activity cycle is approaching its maximum. Such activity not only produces higher levels of auroral activity, it also can endanger satellite electronics and even astronauts in Space, or on the Moon or Mars. The Mars Atmosphere and Volatile EvolutioN satellite (MAVEN), which has been in Mars orbit for a decade, will monitor the effect of solar activity to help NASA prepare for Mars exploration by humans. For more about it, see: MAVEN the cat approves. (So does her brother, LADEE!)

Is Europa Active Enough for internal tides to cause volcano-tectonic activity at the base of its sub-surface ocean, as is apparently the case with Saturn’s moon, Enceladus? Two studies reported at March’s Lunar and Planetary Science Conference suggest Europa has insufficient geothermal energy to drive the geochemical conditions that may be conducive to the development of life. For more on this topic, see here.

Io, On the Other Hand may have been volcanically active over the lifetime of the Solar System, according to a recent study that used data from the ALMA radio telescope complex in Chile to analyze the isotopic content of gases in Io’s atmosphere, particularly molecules containing chlorine and sulfur. Heavy isotopes of both elements are more abundantly present at Io than anywhere else in the Solar System, suggesting that volcanism on Io has been present in quantity for billions of years. For a summary of this research, see here; for the abstract of the paper in Science, see here.

An Amazing Comparison: The Universe Today website recently showed a Perseverance photo of layered sedimentary deposits of the delta of Jezero Crater on Mars side-by-side with a photo of a Jurassic-age delta deposit in the Atacama Desert. OK, without looking at the caption, or the sky, can you tell which is which? Me neither. See: The Atacama, the driest place on Earth that isn’t covered by ice, has been used by NASA and ESA to test Mars rovers and instrumentation. Could the instruments now on Mars or planned for future missions detect biosignatures or the remnant chemistry of life? They have a difficult time finding evidence of life in the Atacama, even though it’s teeming elsewhere on our planet. Hmmm…

Curiosity at Gediz Vallis:Perseverance and Ingenuity have been getting most of the press about roving Mars, but let’s not forget Curiosity! It’s been steadily exploring in Gale Crater, climbing steadily up Mt. Sharp, an eroded deposit of lake sediments. It recently reached the rim of Gediz Vallis, what appears to be an ancient river were the water flowed for an extended period. Curiosity will explore the area for a number of weeks. The layered terrain its traversing is quite spectacular. For more information about Gediz Vallis, see:

UPDATE on Mars Sample Return Mission: The Perseverance rover has been collecting samples from interesting areas as it explores the interior of Jezero Crater on Mars. The plan is for a follow-up mission by NASA/ESA that would land by the rover and return the cache of samples to Earth for detailed analysis, a high-priority scientific objective. Such a mission is “one of the most technically complex, operationally demanding, and ambitious robotic science missions every pursued (i.e. expensive) and therein lies the rub. Two independent review boards have been advising about changes in the mission profile, including a delay, to reduce costs significantly. One of the consequences of all this is serious layoffs at JPL, Goddard, and Marshall NASA centers. NOTE: Jim Green has an idea to get the samples back at lower cost; see the item in the “Of Special Interest” section above!

NASA’s Inspector General released their analysis on February 28. For more about it, see the piece on the Aviation Week website here:

MSR is not the only NASA Planetary mission facing funding difficulties. The VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, And Spectroscopy mission had been accepted and planned for launch in 2027, but NASA had to put it on hold, cutting its funding in the 2024 budget request. It’s an important mission, especially since we need to know about potential climate tipping points in our wildly-different-although-a-lot-alike “fraternal twin” planet. Spurred by blowback from the scientific community, NASA found the money to put VERITAS back on track, but with a launch date slip to 2031. For more on this issue, see:

Three New Moons: Three new moons have been found in the Solar System recently; one at Uranus and two at Neptune, bringing their moon totals to 28 and 16, respectively. The one at Uranus, S/2023U1, is the first new moon to be found at Uranus in 20+ years. Score one for the Magellan Telescopes at Las Campanas Observatory in Chile!

The two new moons at Neptune had been seen before, but not often enough to calculate an orbit. The brighter of the two was also found at LCO, and the fainter moon, only a few miles across, was first seen with the Subaru and Gemini North Telescopes atop Mauna Kea. For more information on the discovery of these three, see:

Mars Volcanoes: Just Basalt?  Planetologists have known about the impressive giant basalt volcanoes in the Tharsis region of Mars since Mariner 9’s visit in 1971. They are the largest volcanic structures in the Solar System, and a clearly basaltic lavas akin to Hawaii. Geologists had not found examples of more explosive volcanoes with magma higher in silica, until perhaps now. Recently-reported detailed examination of the volcanic terrains of the martian highlands has found examples of more explosive, higher-silica volcanoes in the distant martian past. If that is true, it is evidence for some sort of crustal recycling, perhaps caused more by vertical tectonic motion than horizontal, like Earth’s. For a summary of this development, see here; for the paper in Nature Astronomy, see here.

The Kuiper Belt May be Bigger than Previously Thought: The New Horizons spacecraft that became the first (and only) to fly by Pluto, in 2015, continues to make interesting observations. The most recent results are observations of very small particles, “the tiny frozen remnants of collisions between larger KBOs.” Theoretical studies indicate that the number of such collisions should decrease at the distance NH is from the Sun; the greater amount of small impacts suggests that the Kuiper Belt is larger and extends further from the Sun than previously known.

The dust counter aboard NH making the observations is the first instrument NASA has flown that was designed, built, and operated by students (all at UC Boulder)! A number of KBOs have been found recently farther than they were expected to be, corroborating the students’ results. The outer boundary of the Kuiper Belt had been thought to be on the order of 50 AU, but it looks like it may be considerably further out than that. For more information about this, see:

The Incredible Shrinking Moon: Some bodies in the Solar system actually suffer a (small) change in diameter due to internal movements of material. One example is Uranus’ moon, Miranda, which has an enormous vertical cliff and other surface disruptions that could have arisen from incomplete differentiation. [Differentiation in a rocky body is when less-dense material is overlain by more-dense material. Such a body would try to turn itself inside-out internally, with the heavy stuff sinking to the middle. This is how planetary cores are thought to form.] Another example is Mercury, where pictures from the MESSENGER orbiter show a surface beset with compressional faulting, indicating a surface that is contracting slightly everywhere because Mercury is shrinking slightly. [If you are having trouble mentally-visualizing this, think about the change the surface of a grape goes through as it dries to become a raisin.]

The Earth’s Moon might have to be added to that list. The Lunar Reconnaissance Orbiter has been producing high-resolution images of the lunar surface for years, and the Apollo landings left seismometers on the lunar surface that recorded a number of Moonquakes. The seismometers were far enough apart for selenologists to determine the location of the quake’s epicenter – near the lunar south pole. Its severity equated to a magnitude 5 Earthquake on the Richter Scale, and it lasted for hours! Detailed scrutiny of LRO data from that area shows the same sort of compressional faulting seen on Mercury, as well as some faults that were likely created by the Moonquake Apollo equipment detected.

For a summary of this issue, see here; for the paper in The Planetary Science Journal, see here. [BTW, the lead author of the paper is my good friend Tom Watters, who is an expert in global tectonics. He also is the one that identified compressional tectonic features on Mercury.]

D/H Clues on Eris and Makemake: The JWST doesn’t just look at the most distant objects in the Universe, it also makes interesting discoveries much close to home. One such is the study of the composition of two dwarf planets in the Kuiper Belt, Eris and Makemake. Icy-surfaced bodies have a lot of hydrogen that JWST can detect, but there is also deuterium, the isotope of hydrogen that has a neutron in its nucleus. The ratio of deuterium to hydrogen yields information about the origin and geologic history of objects with icy surfaces. The JWST is capable of measuring the D/H ratio on bodies in the outermost Solar system, where the material could be coming from water or frozen methane. Theoretical predictions show that the D/H ratio is highest for the oldest materials, and is less for younger stuff. The D/H ratio for Eris and Makemake is intermediate in size, indicating that the surfaces are not ancient, but rather have probably been affected by internal geological processes, which could also produce nitrogen on their surface, as also seen on Eris. “Models developed for this study additionally point to the formation of geothermal gases on Saturn's moon Titan, which also has abundant methane. Furthermore, the inference of unexpected activity on Eris and Makemake underscores the importance of internal processes in shaping what we see on large KBOs and is consistent with findings at Pluto.” For more info on this interesting development, see here and here for a summary and here for the abstract and excerpts from the paper in Icarus.

Mimas Joins the “Moons with Subsurface Oceans Club!” Wow! When planetary scientists first saw close-up images of Jupiter’s moon, Europa, and Saturn’s moon, Enceladus, they were deeply suspicious that both had a deep, liquid ocean with a thick ice cover. That proved to be correct, with the reason for them having an underground ocean was the same tidal heating mechanism proposed for Jupiter’s moon, Io, which was proven so dramatically when Voyager 1 fly by it (see more of that story here). Subsequent studies have shown that two of Jupiter’s other large moons, Ganymede and Callisto, also have large underground bodies of liquid (mostly) water. Saturn’s large moons, Titan and Enceladus do, too. The Cassini spacecraft even flew through plumes of water spewing from cracks on the surface of the latter (and found chemistry akin to that of “black smoker” hot springs in deep ocean locales on Earth – which by the way teem with life). And there is strong evidence that dwarf planets Ceres and Pluto; Neptune’s large moon, Triton; and several of the moons of Uranus have them, too. All these bodies make quite a club!

A moon doesn’t have to be big to have enough internal heating from tidal forces to make an underground ocean (but it helps). It turns out that a small moon can, too, provided it’s close enough to larger bodies to be subject to sufficient tidal stresses. Planetologists analyzing the motion of Mimas, a small but close-in moon of Saturn, also has underground liquid water. [Mimas was noteworthy when the first up-close pictures of it were acquired, because it has one giant crater that makes it a dead ringer for Star Wars’ Death Star, which was fresh on everyone’s mind when the fly-by took place.]

But wait, there’s more! Detailed tracking of the Cassini spacecraft provides data that indicates that the subsurface ocean on Mimas is very, very young, geologically speaking, only a few million years old.

For more on Mimas and its hidden ocean, see: and

Ancient Asteroid Impact in Antarctica: Antarctica is a mecca for meteorite recovery, not because it has some sort of special attraction for Solar System debris, but rather its ice cover makes it easier to find meteorites there. Stony meteorites look a lot like terrestrial rocks, especially if they have had time to get weathered. That’s why most meteorites recovered long after they fell are made of easier-to-notice iron, even though irons make up only a few percent of the total meteorites impacting Earth.

Meteorite researchers recently (2/1) published a paper in Earth and Planetary Science Letters about a cluster of small meteorites recently discovered in Antarctica. Detailed chemical analysis shows that they all are from the same parent meteor, and their distribution suggests that a single asteroidal body suffered an airburst prior to impact, scattering the resulting debris. Such airbursts aren’t uncommon; examples include Tunguska in 1908 and Chelyabinsk in 2012. The chemical analysis also indicates that the airburst took place between 2.3 and 2.7 million years ago, making it only the third prehistoric examples of meteor airbursts; the other two occurred between 430,000 and 480,000 years ago, also over Antarctica.

For a summary of this finding, see here; for the paper in EPSL, see here. For a paper describing the earlier airbursts found, see here.

SLIM Pickins’: The Japanese Space agency has joined the Moon Soft Landing club (USA, Russia, China, and India) with their Smart Lander for Investigating the Moon spacecraft, aka “Moon Sniper,” which landed on January 20. The mission had been slated for a 2021 launch, but was delayed by a series of technical problems. JAXA lost contact with the lander after it touched down, and it took a few days for them to restore communications. Apparently SLIM had two of its landing rockets malfunction just before touchdown, which caused the lander to tumble when it hit, rolling onto its communications antenna and solar panels. The silver lining was that the landing site was spot on to that planned. JAXA has been managing SLIM’s battery power carefully, especially after getting images from it that showed what had happened. The Sun set at SLIM’s location on February 1; JAXA hopes that the low Sun hit the solar panels enough to acquire more data, but SLIM was not designed to survive the lunar night. For more on this mission, see: and:

More Evidence from Jezero! The Perseverance rover recently completed its 1000th sol on the martian surface. It has been exploring the floor of Jezero Crater and the delta and lacustrine (lake) deposits within, finding both carbonates and phosphates, indicative of a past environment quite conducive to biological activity. For more info on this mission and its ongoing success, see:

But Wait, There’s More Evidence from Jezero! The Jezero landing site was deemed the most important single place to have a rover explore, because it was rather obvious from orbital data that a lake had once existed in the crater and a river had brought in (at least some of) the water that filled it, building a large delta in the process. Curiosity was not sent there because the landing site was a bit risky, a similar once-filled lake site at Gale Crater was chosen instead. Jezero’s scientific potential, and our improved confidence in the sky-crane landing system, made it the target for the Perseverance rover.

Assessing the potential for paleo-life requires more than data acquired from orbit or even from looking at surface features; being able to determine subsurface details is important. Percy carries a ground-penetrating radar and has been examining the edges of the delta deposits for some time now. The data show that the crater’s original floor had experienced some erosion before the lake was established, and two distinct periods of deposition and two distinct periods of erosion of lake sediments. The sedimentation pattern reveals that there were large-scale changes in the martian surface environment. For a summary of this work, see:; for the paper in Science Advances, see:

More Evidence from the Moon! Apollo astronauts did a great job in returning a large quantity of lunar rocks and “soil” from the Moon for detailed study back here on Earth. But it is one thing to describe that material in detail, and another much more difficult to understand how it came to be. One problem that has proved vexing for decades was the odd (compared to Earth) composition of lunar basaltic rocks. We’ve long known that heat from the Moon’s formation and radioactive decay was sufficient to melt the upper layer of the Moon, forming a “magma ocean” that filled low-lying areas, creating the lunar “seas.” However, samples of lunar basalt had a higher-than-expected titanium component in their make-up, and more recent surveys from orbit show that high-Ti basalts are common and widespread on the lunar surface. Geologic modeling of the creation of such high-Ti-yet-low-density material failed to match the in-hand rock compositions. Until now. New high temperature testing shows that a reaction in the cooling magma ocean between the iron content of the liquid magma and the magnesium in the surrounding solid rock could adequately create the chemical and physical processes required to explain the chemistry of the returned samples. For more info on this work, see:; for the paper in Nature Geoscience, see:

More Evidence from Enceladus! Saturn’s icy moon, Enceladus, is known to have a subsurface liquid ocean, as does many of the moons in the outer Solar System. The Cassini spacecraft actually sampled material from the plumes of geysers erupting from fissures on its surface, finding chemistry similar to that surrounding deep-ocean “black smokers” hot springs on Earth, abodes to a great variety of life that does not require oxygen. Now, recent analysis of those data shows the presence of hydrogen cyanide, toxic yes, but “critical to processes driving the origin of life.” For a summary of this exciting work, see here; for the abstract of the paper in Nature Astronomy, see here. We live in exciting times!

Mars Odyssey at 22, Still Going Strong! Its very name is a play on the year of its launch (2001, A Mars Odyssey!), but in spite of it being in Mars orbit for 22 years, it is still producing interesting scientific data. One of the instruments aboard Mars Odyssey is called THEMIS (THermal EMission Imaging System), a device that detects thermal infrared radiation. Normally, THEMIS data have been used to measure the resistance of martian surface materials to temperature change, usually a function of the size of the particles of matter covering the surface. THEMIS is fixed to the spacecraft, and in normal operation only points straight down. That’s good for looking at the surface, and that’s good for assessing how much water and dust are in the martian atmosphere directly beneath the spacecraft, as designed. But Odyssey scientists and mission controls are clever folk, and they figured out a way for the orbiter to turn sideways and have THEMIS look at the horizon, rather than straight down. They were hoping to be able to see a cross-section of the atmosphere and derive information of its water/dust composition as a function of altitude. It worked! And since Odyssey orbits about 250 miles above Mars, the views coming back from these maneuvers give a pretty good view of what Mars might look like if the ISS were orbiting Mars, not Earth. You can see the image that was produced and learn more about it at:

The Principal Investigator of THEMIS is Phil Christensen of Arizona State University. Twenty years ago, PI’s rarely released data to the public in (near) real-time, but Phil is a big believer in public participation in the process of scientific inquiry, and made THEMIS data available for display at the National Air and Space Museum soon after it was returned to Earth. It was a fun exhibit to watch in the former Exploring the Planets gallery!

MAVEN at 9: Still Going Strong! The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has been on a decade-long quest to study how and at what rate water and gases are lost from the martian atmosphere to Space. Part of its instrumentation is devoted to measure conditions of the solar wind and its effect on the martian atmosphere. Recently, a large disruptive flare resulted in a zone of charged particles in the solar wind that carries only 1% of the number of charged particles it does normally. The solar wind was essentially turned off, and the martian atmosphere responded by expanding greatly. Being able to study a complex system with one of its principal components “turned off” is proving to be quite valuable in understanding the system as a whole. For a summary of this work, see here; for more on the MAVEN mission, see here; and for more on how my wife’s cat came to be named for MAVEN the mission, see here. MAVEN the cat, like MAVEN the mission, is nine years old!

Mars Has Auroras (!): Data from ESA’s Trace Gas Orbiter’s UVIS-NOMAD instrument show a greenish emission that “is due to the recombination of oxygen atoms created in the summer atmosphere and carried by the winds towards the high winter latitudes," explains Lauriane Soret, a researcher at LPAP. "There, the atoms recombine on contact with CO2 to reform an O2 molecule in an excited state that relaxes and emits light in the visible range." For a summary of this work, see here:

In addition, the United Arab Emirates’ orbiting Mars mission, Hope, has observed martian auroral activity, too; see here for more info: A better rendition of these data is in the February issue of Sky & Telescope magazine.

Uranus says “Me Too!” Auroras at Jupiter and Saturn have been known for years, including auroral glow at near-infrared wavelengths, caused by an ion of a tri-atomic hydrogen molecule. Recently, astronomers at the Keck Observatory were able to detect near-IR auroras on Uranus in data originally acquired 17 years ago. Uranus’ magnetic field was determined by Voyager 2 to be odd, indeed, off-centered by 1/3 of the planet’s radius and tipped with respect to the rotational axis by 59°. As a result, Uranus undergoes a pole reversal every day, potentially providing information that would inform scientists about the process of geomagnetic reversal on Earth. For a summary of this work, see here, for the Nature Astronomy paper, see here.

Water on 162173 Ryugu: The OSIRIS-REx mission’s return of material from asteroid Bennu has been in the news a lot of late, and rightly so. But let’s not overlook the 5 grams of material returned to Earth from asteroid Ryugu by the Hyabusa 2 spacecraft three years ago. Detailed analysis of the chemistry and isotopic ratios in the Ryugu samples show that the material is similar to carbonaceous chondritic meteorites, and contained water early in the Solar System’s history. Accretion of such material may have been the source of Earth’s water, so understanding how much water was contained in the material from which the Solar System formed gives an important initial condition in the process of planetary formation. For more information on the Ryugu results, see:

Asteroid Ryugu’s Organics: Initial analysis the sample of Ryugu’s surface material returned to Earth in December, 2020, by the Hayabusa 2 spacecraft, showed a “rich complement of organic molecules” (remember, “organic” means “contains carbon compounds,” not “biological!”). “The discovery adds support to the idea that organic material from Space contribute to the inventory of chemical components necessary for life.” The bulk chemistry of the sample is “mostly consistent” with that of carbonaceous chondrite meteors. For a summary of this work, see here; for the abstract of the paper in Science, see here.

Keep Your Eyes on Asteroids! NASA’s newest entry in their wonderful “Eyes On” websites, “Eyes on Asteroids,” is now available here. It’s “a new 3D real-time visualization tool (that allows you to) explore the asteroids and comets that approach Earth’s orbital neighborhood – and the spacecraft that visit these objects.” Find more info here

Eyes on the Solar System: Asteroids are not the only objects in the Solar System to get the “Eyes On” treatments! Exoplanets, the Solar System as a whole, and even the Earth get the Eyes On treatment. For more see:; the Earth version got a recent updating.

NOTE: Be sure to check out the e-book from the Cassini mission, “The Saturn System: Through the Eyes of Cassini,” here:

The Earth Counts in Planetary Studies! Part One: One of the divisions comprising NASA’s Science Mission Directorate is the Earth Sciences Division, tasked with using NASA flight/orbital assets to learn more about the one planet upon which we can live. You have all heard about greenhouse gases and how methane, CO2, and other polluting gases are directly leading to human-induced climate change. Methane is a particularly potent greenhouse gas, so monitoring it is a NASA priority. A recent study of the tundra cover of Alaska’s largest river delta shows that past fires, even those decades old, leave an area of decomposing carbon that creates methane when the permafrost of the delta melts away. Methane “hot spots” are ~30% more likely in areas scorched by wildfires in the last few decades than non-burned areas. For more information, see:

The Earth Counts in Planetary Studies! Part Two: Geologists routinely use seismographic studies of the Earth’s interior to determine subsurface structures that could lead to oil/gas deposits, and other economically-important areas. Seismometry also can reveal deep-seated structures, much like those the InSight lander’s seismometer did for Mars (see immediately below). Decades ago, seismologists found two zones deep within the Earth through which seismic waves moved more slowly than expected. One of these “Large Low-Velocity Provinces” lies deep beneath Africa and the other lies deep beneath the Pacific Basin. A new study published in Nature on November 1 contains the hypothesis that the LLVPs are actually remnants of the Mars-sized impactor (“Theia”) that hit the proto-Earth that resulted in the formation of the Moon! The research team involved was inspired by a 2019 presentation by Mikhail Zolotov of Arizona State University. He presented the giant-impact model of the Moon’s formation, and pointed out that while the Moon was formed from a ring of debris resulting from the mega-impact, no trace of the original impacting body had been found. That statement piqued the interest of Cal Tech’s Qian Yuan, who then assembled a team to investigate further. Their Nature paper was the result, where they show that both the LLVPs and the Moon could be the consequence of that ancient impact. For a summary of their work, see here and here; for the abstract of their Nature paper, see here. [Personal Note: I was a post-Doc at ASU when Misha Zolotov made his first visit there. I had the pleasure of hosting a dinner at my home for Misha, Ruslan Kuzmin of the Vernadsky Institute or the Russian Academy of Science, and Francois Costard, now at the University of Paris. I served a pot roast that Ruslan said was as large as his family’s monthly meat ration, and afterward we enjoyed a hockey game (Ruslan had played both hockey and basketball in his younger days). It was Christmas time, and we visited a local home where the late Bob Rix, the owner, spent six months a year decorating it lavishly to the point where it was a local crowd scene; Phoenix even added a special temporary bus route to take people there. The Russians were impressed by the “collective community effort,” and it was difficult to explain it was rather a one-man affair, to most of his neighbor’s consternation at the traffic. Except for the guy who cleaned up by setting up a taco stand in his driveway! I had the pleasure of exchanging emails with Misha a few months ago, and am glad to see how well he is doing in his career.]

Venusian Plate Tectonics in the Past: Radar observations of the venusian surface have long suggested that Earth-like plate tectonics is not presently happening on Venus; its crust consists of a thick, inflexible single “plate,” rather than a hodgepodge of moving crustal plates “floating” on a plastic mantle. But that may not always have been so. A new study conducted at Brown University, using data from spacecraft observations and computer modeling, concludes that the present venusian atmosphere’s composition and high pressure requires an early form of plate tectonics. Plate tectonics in Venus’ early history raises the possibility that conditions much more conducive to the development of biological activity may have prevailed in the distant past, but Venus evolved in a way the caused the present runaway greenhouse. Such severe changes in surface conditions over time could bode poorly for life on Earth. Food for thought, and a LOT more study! For more info on this topic, see:, and for the paper in Nature Astronomy, see:

Bennu is Shedding; NASA Style; and How “Science” Operates: The line between “asteroid” and “comet” has been blurred significantly by recent discoveries.Decades ago, solar system astronomers discovered that an asteroid (Phaeton), not a comet, was the source of the Geminid meteor shower. As a consequence, some would come to refer to it as a “rock comet” (Somewhere Bill Haley is smiling!). Then, in early 2019, the OSIRIS-REx spacecraft, then in orbit around asteroid Bennu showed that it was shedding considerable material, albeit at a low rate. 

But are asteroids (and comets) the only source of debris in the inner Solar System? 

A few months ago, authors of a paper published in JGR: Planets make the case that the very small particles responsible for the Zodiacal Light (the “False Dawn” of Omar Khayyam) actually come from either Mars or its two tiny moons (or perhaps martian moon(s) no long in existence). The data upon which that conclusion was based came primarily from the analysis of micro-meteoroid impacts on the solar panels of the Juno spacecraft when it was en route to Jupiter!

Longtime A+StW fans know that I frequently cite NASA’s know-how, and how they not only do the extremely difficult, they do it with style. The radio science experiment aboard Mariner 4 was one case in point; the item above is another example. Not only is Juno actively returning data and accomplishing its mission objectives, creative scientists have figured out a way to squeeze very interesting information from an unanticipated source!

Here’s another example of how the process of scientific inquiry works, too. The data from Juno’s micrometeoroid hits very strongly suggest the Mars system is the source of the impactors. However, neither the researchers or other planetary scientists have come up with a mechanism that would remove material from Mars, Phobos, or Deimos and get it into the interplanetary medium to cause the ZL. But the observational data will now drive more investigation, and Science will march on!

We had a similar situation when the first identification of the martian origin of some of the meteorites on Earth was announced. The observational data were overwhelming, but nobody thought impact could remove material from Earth’s gravity field, that is, until the data spurred them to investigate further.

Remember, this thing we call “Science” in not just a body of accumulated knowledge, it’s more importantly the process through which that knowledge was acquired!

For more info, see:

Summary of Bennu activity:

JGR Planets paper:

More on NASA’s Juno Mission - at Io: The Juno Jupiter orbiter is one of NASA’s successes, now in Extended Mission status. Since it is nearing its operational limit, NASA is more willing to take risks to get scientific observations too risky for a mission with a long life ahead. One of the interesting objects of study in the Jupiter system is its innermost large Moon, Io, where tidal heating is so severe that Io has many active volcanoes (predicted a week before their discovery in a “called shot” greater than Babe Ruth’s famous 1932 home run).

The radiation environment in Io’s location is intense, and could damage Juno, but a series of progressively-close fly-bys are planned for the coming months, necessary to observe Io’s ever-changing surface closely. The first such occurred on July 30, and Juno survived getting to within 22,000 km of Io’s surface without damage, and is presently returning interesting data to Earth. Fly-bys planned for December 30 and then February 3 next year will get to within 1,500 km of Io. For more information about the Juno mission, see here and here. For more on the Juno mission, in a style unusual for NASA, see here.

Voyager 2 was an amazing mission. Check out the excitement of its encounters with all four gas giants, conveyed as only Al Hibbs could, see here, the very first Item of the Week in the Archive. And don’t miss my retirement missive about those days, too!

A Primer on Planetary Aeolian Processes: Solar System bodies with an atmosphere and loose particulate material on their surface suffer erosion and deposition processes and develop similar distinctive landforms, such as yardangs, dunes, and ripples. The work is ongoing as we learn more about other environments. A good summary of the studies was published recently in Eos; see here.

Expanding Knowledge, Expanding Nomenclature: We all know about the “demotion” of Pluto from planetary status, even if we do not agree about it. Personally, I believe that making such changes in nomenclature is a necessary and proper reflection of our expanding knowledge of the nature of the Solar System, and I like to use as an analogy the actions taken during a spring cleaning of my garage (as long-time A+StW readers will recall).

Ancient astronomers knew the five major planets quite well, and could predict their locations quite accurately, enough so to forecast eclipses and other astronomical events/movements. But occasionally a strange interloper would make a temporary appearance, causing consternation all around. Most of these objects received the name, “comet,” or “hairy stars,” based on their appearance. And Galileo showed that at least some planets have smaller objects, moons, orbiting them. So the nomenclature had to expand from “stars and planets” in the sky to “stars, planets, moons, asteroids, and comets” in the sky.

The objects we then called “asteroids” reflect another aspect of the nomenclature changes that are a natural attendant of learning more about our Solar System. Thousands of them have been discovered and had their orbits calculated in considerable detail. Most of them are confined to the “Main Belt” between the orbits of Mars and Jupiter; the few outliers were initially considered inconsequential oddballs.

Astronomers also knew that something strange was going on in the Solar System’s outer reaches, even if they at first didn’t know enough to “clean out the garage.” Uranus’ obliquity was unlike any other planet’s, Neptune’s large moon, Triton, has a retrograde orbit that is decaying, and Pluto’s orbit is more elliptical than the orbits of the planets and is inclined to the Plane of the Ecliptic much more than any of the planets.

The discovery of Kuiper Belt objects “muddied the crick” considerably. So did the recognition of “active asteroids” that blur the line between “asteroids” and “comets.” So did the recognition that Jupiter’s gravity has an enormous effect on the evolution of the Solar System. But that’s a good thing, too, because it reflects an increase in our understanding of the nature of the Solar System as a whole.

Astronomers are now considering a more comprehensive classification scheme.

Trans-Neptunian planets are more like Pluto, Charon, Arrokoth, and other distant objects (KBOs). They are rich in volatile materials because they have never been heated by the Sun to any extent. Comet C/2014 UN271 Bernardinelli-Berntein may be another example. Those that do approach the Sun have highly-elliptical orbits, at least at first.

Blame Jupiter. Its gravity can either eject first-timers (as Comet B-B likely will be) or make their orbits much less elliptical, exposing their surfaces to periodic solar heating and devolatilization. Some will eventually lose so much of their volatiles that they are no longer comets, but rather more asteroidal in nature.

Jupiter’s gravity tends to force shorter-period comets more and more toward the Main Belt. By the time that happens, they are comets no more but asteroids, some still capable of shedding meteoroids, some not.

Those bodies in the transition phase often show characteristics of both comet and asteroid. They are rare because the overall time taken in transition is short compared to the age of the Solar System. Now called “Centaurs,” their discovery played an important role in astronomers figuring out this evolutionary process. 

Most meteor showers we see today are the result of comets shedding rocky debris as they devolatilize, a process that could continue over many orbits. Two bodies very near the end of their activity are the parent bodies for two different showers: the Geminids last month are debris from the asteroid 3200 Phaeton, and the Quadrantids appearing now are debris from the near-Earth asteroid 2004 EH.

And the whole Uranus, Triton, Pluto thing will continue to refine our understanding. Science marches on! The January, 2022, issue of Sky and Telescope (pages 14-19) has an excellent description of this whole issue, written by Kat Volk at the University of Arizona’s Lunar and Planetary Laboratory.

Forget the Fountains of TitanJWST Observes the Fountains of Enceladus!  Kurt Vonnegut’s second novel, The Fountains of Titan (1959), was referenced by Al Stewart in 1971’s song of a similar name (see this week’s Didja Know? section). Jupiter’s moon, Europa, and Saturn’s moon, Enceladus, both are covered with a high-albedo fractured surface that looks for all the world like a terrestrial ocean ice pack, and for good reason, that’s what it is. Many of the icy moons in the outer Solar System may have liquid oceans under a heavy cover of ice, kept liquid due to the action of tides, but Europa and Enceladus are the most blatant examples. Enceladus even has geyser-like plumes of dirty water they have been seen spewing above some of its surface fractures, and the Cassini spacecraft was even sent to pass through one such plume, sample it, and relay compositional information back to Earth. Cassini’s gone now, but Enceladus was recently observed by the JWST, and detected a plume of water vapor extending 6,000+ miles above the surface of Enceladus. That’s one energetic geyser! For more on the JWST Enceladus observations, see:

Uranian Moons Harbor Subsurface Oceans: The National Academy’s 2023 Planetary Science and Astrobiology Decadal Survey identified the further exploration of Uranus and its larger moons as a priority goal. NASA has only visited Uranus once before, a fly-by by the Voyager 2 spacecraft in January, 1986 (the excitement the real-time release of the images of the fly-by is related here). The need for information to assist planning the recommended mission led scientists to revisit the 37-year-old data. Computer modeling not possible back then shows that the four largest moons (Ariel, Umbriel, Titania, and Oberon) are large enough to have Uranus’ gravity generate internal tidal heating that could lead to their having a subsurface ocean of liquid, likely water. This is the same mechanism driving internal geologic processes on Jupiter’s large satellites and Saturn’s Titan. For more information on this study, see:

Cassini’s Final Gift: The Cassini mission to Saturn, a joint endeavor by NASA, ESA, and the Italian Space Agency, was an overwhelming success. Its orbiter component returned large amounts of image and other data during its 13 years in orbit, and its Huygens probe that soft-landed on Titan returned a lot of information about the only moon in the Solar System to have an appreciable atmosphere. When the Cassini orbiter was about to out of attitude-control fuel, its was flown on a risky path through plumes of water vapor being spewed from fissures on Saturn’s moon, Enceladus, and then on a daring Grand Finale, flying beneath the great ring system. In its last moments of communications with Earth, Cassini relayed data that showed much more mass than previously thought were falling from the rings into Saturn. That, and other evidence, has led some scientists to propose that Saturn’s ring system is astronomically very young, on the order of 100 million years or so.

Hmmm. All four gas giants have a ring system, with only Saturn’s being a showpiece. Might it be possible that disruption of moons to form short-lived rings are a more ubiquitous planetary process than previously supposed? For more on this hypothesis, see here; for the paper in Icarus, see here.

The Daniel K. Inouye Solar Telescope, located at the Haleakala Observatory site on Maui, will be the most powerful ground-based solar telescope when it comes on line. The NSF recently released eight new images from the IST as a preview, hinting at the “Inouye Solar Telescope's unique ability to capture data in unprecedented detail (which) will help solar scientists better understand the Sun's magnetic field and drivers behind solar storms.” The telescope is in its Operations Commissioning Phase, a gradual work-up to being in full operation mode. For more information on the IST, see here; for a summary of the released images, see here.

Planetary Fleet Chart: NASA’s Planetary Science Division has posted a chart that shows the names, approximate locations, and stages of development of present and upcoming Solar System exploration spacecraft. It’s quite striking, and a great antidote for those who think NASA is doing little since the Shuttle stopped flying. Download your own at:!

See links at the end of this section (in the website version) to all Mars missions presently in operation!

JWST Works Nearer Home, Too: We’ve all seen some amazing pictures of the deepest of deep-space objects acquired by the JWST. Numerous objects now bear (perhaps temporary) labels as the “most distant known.” But the JWST makes important observations much closer to home, too!

Most asteroids in the Solar System lie in the “Main Belt” between Mars and Jupiter. A few have orbits elliptical enough to take them near to the Sun than Mars or farther from the Sun than Jupiter. And a few, collectively called “centaurs,” have orbits that lie entirely between Saturn and Uranus. The largest centaur is asteroid 10199 Chariklo, discovered in 1997 and named for the wife of the centaur Chiron and (perhaps) a daughter of Apollo.

Recall how the rings of Uranus were discovered – it’s a classic case of learning things by looking at them in front of other things. Astronomer James Elliot, aboard the Kuiper Airborne Observatory, was measuring the brightness of a background star as Uranus passed in front of it, hoping to gain information about the uranian atmosphere (a la Mariner 4 at Mars). Just prior to the occultation, Elliot and his team saw the light from the background star dim slightly five times, and then they saw the same thing just after the star was occulted. Elliot knew those dips were caused by Uranus’ hitherto unknown ring system!

Well, the same thing happened in 2013 with Chariklo. Astronomers calculated that Chariklo would pass in front of a minor star, and they wanted to observe that occultation closely from many locations on Earth in order to be able to refine estimates of Chariklo’s size and shape. Those observations went well but were overshadowed (sorry) by a scene straight out of Jim Elliot’s experience.

Seven seconds before the occultation would begin, astronomers saw two small dips in the star’s light, and another two seven seconds after the occultation. Rings!

Finding rings around one of the Sun’s larger planets was a wonderful accomplishment, but rings around an asteroid?!?

Chariklo was in the news again recently. The JWST was able to see it occult star named Gaia DR3 6873519665992128512, the first time it had observed any occultation event and a portent of JWST’s ability to “do science” much closer to home than the very-distant objects it was built to study.

The leading hypothesis so far as to why an asteroid could have rings are that the rings are remnants of a larger debris field created by an impact with another icy body. For more info an Chariklo and the JWST, see here:

Envious Quaoar sez “Hey, I Have Rings, Too! All four gas giants in the Solar System have rings. Asteroid Chariklo has a rudimentary ring. The uranian rings were found when Uranus occulted a background star; Chariklo’s was the same. And now that Kuiper Belt denizen Quaoar also has a ring, found by the same occultation technique. Rings, rings, everywhere! Most such rings have relatively short lifetimes, so the disruption of moons that produce them must happen relatively often if so many rings are presently observable. For more on Quaoar’s ring, see here.

Rounded Rocks and Ventifacts on Mars! Mars rovers have been imaging rocks and sediments on Mars that bear the clear sign of transport by water for two decades now. More were expected to be seen at Jezero, but WOW. Mars has a thin atmosphere, but its winds are still strong enough to lift dust and sand from the surface. Rocks can be abraded by wind-blown material, producing distinctively-shaped forms called “ventifacts.” Perseverance recently returned images from and area called “Yori Pass” that show several such, see:!

Jim Bell and many co-authors have recently posted a paper to Science Advances, “Geological, multispectral, and meteorological images results from the Mars 2020 Perseverance rover in Jezero Crater,” see here.

Chicxulub Tsunami: Researchers recently analyzed the consequences of the Chicxulub impact, using the latest computer modeling code to predict tsunami size and effects. The effects were severe; the impact-caused wave was huge and affected much of the Earth. One hour after impact, the tsunami would have traversed the Gulf of Mexico and headed on into the Atlantic. At the time of the impact, there was a strait between proto- North and South America; four hours after impact, the tsunami would have roared through the strait and into the Pacific. One day after the impact, the tsunamis from the Atlantic and Pacific sides would have been converging on the proto- Indian Ocean. All of the world’s coasts would have felt the effects of the tsunamis before the second post-impact day had passed. For a summary of this latest research, see:; for the paper itself, see:

Was Chicxulub Alone? Planetologists have observed clusters of impact craters on a variety of bodies that suggest that some impact events involve multiple impactors – remember fragments of Comet Shoemaker-Levy 9 hitting Jupiter in July, 1994? The Chicxulub impact off the Yucatan Peninsula 65 million years ago caused enough environmental damage to cause the extinction of many species. But it might have had at least on traveling companions which also hit the Earth.

A research team from the Herlott-Watt University in Edinburgh, Scotland, was examining seismic data from the seafloor off West Africa and found the signature of a crater, approximately 5 miles in size, in sediments that date from the time of Chicxulub. The impacting body would have been about 400 meters across, smaller than the Chicxulub by quite a bit but still packing a strong regional punch. For more on this discovery, see here.

As Long as We’re Considering Mega-Impacts… One of the key findings from the Apollo program was the development of the Origin of the Moon by Impact theory, which holds that the early Earth was struck by a Mars-sized object (“Theia”) during the very final end of the “terminal bombardment” stage of planetary formation. The Earth had already differentiated by that time, with an iron core and rocky mantle. The impact blew much of the mantle away from the Earth. That material, plus the remnants of Theia, then re-accreted to form the Moon.

Recent impact modeling by a team at NASA Ames Research Center supports the basic notion of Theia impacting the early Earth, but that the re-accretion process was quite rapid, a with the bulk of the material coming together in a matter of hours. For a summary of this work, see here:; for a summary and an amazing video simulation of the Earth-Theia impact from NASA Ames, see here:

Elliptical Craters Inform Models: Most impact craters are circular in map view, because impactors coming in vertically, and those coming in at an angle, produce circular craters. However, if the impact angle is low, the resulting crater form is elliptical, with the long axis of the ellipse in the direction of the impactor’s motion. Some ejecta was sent straight downrange, but most is ejected laterally (think of the water moved by a slalom ski).

The first study I know of that focused on elliptical craters was an ingenious paper by Peter Schultz and Ann Lutz-Garihan, published in JGR in November, 1982. They looked at the non-uniform distribution of such craters on Mars, and realized that they were probably due to fragments of moons disrupted by martian gravity (a fate that will be eventually suffered by Phobos). Such moons were likely to be in equatorial orbits, due to tidal forces, so the groups of crater orientations they measured were likely proof of past polar shifts on Mars. The item linked to above also lists some of the other papers that have resulted from the examination of elliptical craters.

The most recent example of how elliptical craters can be useful is study conducted at the Southwest Research Institute, where a team looked at Cassini images of elliptical craters on Saturn’s moons Tethys and Dione, and compared them with the pattern of elliptical craters on Neptune’s moon, Triton, as imaged by Voyager 2. They found all had a group of elliptical craters aligned with the moon’s equators and a group more random in orientation. For a summary of this interesting work, see here; for the abstract of the paper in Earth and Planetary Science Letters, see here.

NASA’s The Invisible Network Podcast: Watch this podcast to find out more about JPL and the origin of NASA’s Deep Space Network, without which Solar System exploration would be impossible. The program features Suzy Dodd, the Director of the DSN at JPL. She knows what she’s talking about; she’s been with JPL since the Voyager 2 encounter with Uranus! Find out more about this vital infrastructure and its history here:

The Deep Space Network is also the topic of Season Five of NASA’s “The Invisible Network” podcast. “’The Invisible Network” first debuted in 2018 with a six-episode season covering a variety of topics related to NASA’s Space Communications and Navigation (SCaN) program office. Since then, the podcast’s 22 episodes have covered burgeoning commercialization effortslaser communications technologiesNASA’s Artemis Moon missions, and so much more.” The Invisible Network’s new six-episode season also will showcase the DSN. For a preview, see the season trailer at:

Good Science on the Cheap: NASA is always exploring new and innovative ways to explore the Solar System economically. The latest example is a science and technology demonstration mission, one of ten small secondary payloads to be carried aloft by the uncrewed test flight of the Artemis system. Called the “Near-Earth Asteroid Scout,” the new spacecraft will be the size of a shoebox and will use an innovative solar sail system to visit the newly-discovered NEA named 2020 GE, which is only about 18 meters across. The Scout will carry a camera with a 4 inch/pixel resolution at closest approach. For more on this mission, see: and:!


Active Volcano on Venus! The fabulously-successful Magellan mission to Venus provided us a good look via radar mapping of the cloud-shrouded surface of Earth’s fraternal twin. It was intentionally de-orbited on October 13, 1994, after sending back a LOT of radar images. Magellan data showed clear evidence of basaltic-style volcanism, including several types of large volcanic constructs and lots of lava flows. Impact crater populations suggest that Venus’ surface has been covered by new rock extensively in the past. But there was no direct evidence that such activity was occurring in the present. Until now. A new look at three-decade-old data shows one volcanic vent, on the side of the large Maat Mons volcano, that changed significantly over the course of the Magellan mission. [The Magellan data are on many CDs and there is no automated way of surveying them, so there are probably a lot more nuggets of important info yet to be uncovered!] The next two missions to Venus, NASA’s VERITAS and ESA’s Envision, will be able to image the surface in more detail. We’ll learn a lot about Venus in the next few years, and that is vitally important, because Venus should be more Earth-like, but isn’t, and since it is basically a twin planet to the only one on which we can live, we probably should know why! For more on this big discovery, see the summaries here and here.

Follow-up on Venus Volcanism: A team at Wahington University (St. Louis) has recently published a surface map of Venus that reveals over 85,000 volcanoes of various sizes and types. For a summary of this survey, see here; for the paper in JGR Planets, see here.

Could Venusian Clouds be an Abode for Life? Venus’ surface conditions are truly hellish, a CO2 atmosphere 90x as dense as Earth’s, with a temperature hot enough to melt lead. Life there, at least as we know it, is very unlikely. But what about far above the venusian surface, high in the clouds that shroud the surface? We know that the chemistry there contains at least some of the building blocks of life, and now the results of a recent study of light levels that might prevail in those clouds would be conducive to photosynthesis. In fact, a form of photosynthesis could go on continuously, even at “night,” using infrared energy being radiated from the surface. For a summary of the study, see:; for the paper itself, see:

Did Venus Ever Have Oceans? Venus’ and Earth’s similarities and differences are important topics of study in understanding Earth’s surface environment and its future ( One of the factors to consider is whether or not the present hellish conditions on Venus are ancient or relatively new. If Venus ever had oceans would be an important part of that, and recent modeling suggests that Venus never did have the atmospheric conditions that would allow oceans to form. For a summary of this research, see:; for the abstract of the paper in Nature, see:

Magellan Data Reveal Young Venusian Activity: A direct visible-light view of Venus’ surface is not possible because of Venus’ heavy cloud deck, but radar can penetrate those clouds easily. Over three decades ago, the Magellan orbiter carried such a radar, and from the data returned planetologists learned a lot about Venus’ surface processes, and some things about its internal processes. One of the odd features revealed in Magellan data are “coronae,” circular features marked by a ring of fractures, and in some cases, what appear to be lava flows. Further, careful analysis of the impact craters seen in Magellan data show that the venusian surface has undergone significant resurfacing, but whether it happened “all at once,” or in a gradual piecemeal fashion is still an open question. Recently, two scientists re-examined the Magellan data for one volcano, not looking for craters but rather how the weight of the volcano had deformed the venusian crust locally (such deflections are known on Earth). From the deflection, the rate of heat flow from Venus’ interior, hence the recentness of its volcanic activity, can be determined. The volcano studied may or may not be active today, but it certainly is very young in a geologic sense. For a summary of this work, see:; for the abstract in their paper in the Journal of Geophysical Research, Planets, see:

The Possible Significance of Venus Surface Fractures: Understanding Venus and its evolutionary history is one of the most important questions in comparative planetology. Earth and Venus are very similar in size, mass, and bulk density (hence, composition). We’d expect it to be somewhat hotter because it is closer to the Sun, but its present surface conditions a much, much hotter than that factor alone could cause. On Earth, carbon dioxide is largely sequestered in biological material in the upper crust; on Venus it’s all in the atmosphere. What causes these drastic differences, and was Venus always this way, or did it suffer a catastrophic climate tipping point in its past?

Venus is a difficult place to study, due to its permanent cloud cover and awful surface conditions. But we have built up a lot of information over the years. We know that Venus does not have large impact basins left over from its formation, and that its surface is not particularly heavily cratered, implying some sort of resurfacing process. Further, we don’t see any features suggestive of Earth-style plate tectonics, so Venus’ interior processes have been thought to be much less than those on Earth.

A recent re-study of older data, however, suggests that Venus’ surface resembles pack ice on Earth, suggesting Venus’ interior might be more active than previously thought. Lavinia Planitia, a lowland area on Venus, shows a number of undeformed surface blocks surrounded by ridges and grooves indicative of deformation. Computer modeling suggests that this “mini-plates” are moving/have moved relative to one another, much like blocks of ice in pack ice on Earth. This type of surface behavior on Earth’s surface is seen on Earth in certain places, not globally; the similarity between them and pack ice was first described by a Dr. Seuss (not that one) in 1875. [A re-read of Suess’ paper is a hoot: “See the cracks in the ice. Such cracks are very nice. Similar cracks are on land, too. Cracking the ground, through and through.”] Pack ice movement is driven by wind above and currents below; perhaps Venus’ surface indicates a mobile interior (“squishy” topology), driven by convective processes in the mantle (the driving force for Earth’s plate tectonics. Oh, the places we’ll go! – To learn more about our home planet!

See a summary of this interesting work at:; see the paper abstract at:


Methane and the Geysers of Enceladus: As the Cassini Saturn mission wound down, mission controls were much more willing to risk the spacecraft to gather important data from potentially-dangerous places. The best example was that the spacecraft was flown into the plume of material actively geysering from fractures in the crust of Enceladus. Analysis of the composition of the geyser chemistry reveals more methane than expected. Some sort of mechanism is creating the methane. The composition resembles that of terrestrial seawater from deep-ocean vent areas. You know, the ones with abundant anaerobic sea life…. For more on this discovery, see:

Methane in Mars’ Atmosphere: Enceladus is not the only place where unexpected traces of methane have been detected. A scientific dispute of sorts has been going on for months about some observations of methane there. The Trace Gas Orbiter on ESA’s ExoMars mission should be able to detect methane but it doesn’t, but the chemistry lab on NASA’s Curiosity rover does. The methane is coming from Mars’ interior, either being actively formed at/near present day or relict from an ancient time. 

As with so many disputes, in final analysis both could be right. It’s all a matter of the time of martian day at which the measurements are made. TGO looks through the atmosphere during daytime, Curiosity has to make its at night (the chem lab requires most of the rover’s power, so chem work is done when none of the other instruments are operating).

For a summary, see:; for the full paper in Astronomy & Astrophysics, see:


Mars Odyssey

Mars Express

Mars Science Laboratory (aka Curiosity)

Robert P. Sharp:

Mars Reconnaissance Orbiter

HiRISE homepage:


Mars Atmosphere and Volatile EvolutionN (MAVEN)

Interior exploration using Seismic investigations, geodesy, and heat transport (InSight)

Emirates Mars Mission (aka “Hope”)

China’s Tianwen-1

Perseverance and the Ingenuity Mars Helicopter

JPL has prepared a Mars 2020 Perseverance Landing Press Kit, see:

NASA’s other Perseverance Press Kit has lots of info about the spacecraft and its mission; see:

 For the Latest Info about Perseverance, see: