SOLAR SYSTEM

SOLAR SYSTEM EXPLORATION INFORMATION

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SOLAR SYSTEM EXPLORATION NEWS

Ryugu Dust Yields Big Science: Japan’s Hayabusa spacecraft visited the asteroid 162173 Ryugu (“Dragon Palace”), arriving in June, 2018. Hayabusa orbited, observed, and then collected a sample of its surface material and returned it to Earth on December 5, 2020. Scientists have been studying the material intensely ever since. One of their discoveries was that the grains returned had condensed from the proto-solar nebula and had a weak magnetic signal from the field that pervaded the space in which they formed. While weak, that magnetic field was strong enough to affect the formation of the Solar System. "We're showing that, everywhere we look now, there was some sort of magnetic field that was responsible for bringing mass to where the sun and planets were forming," says study author Benjamin Weiss, the Robert R. Shrock Professor of Earth and Planetary Sciences at MIT. "That now applies to the outer solar system planets." (source of quote, and details on this advance.: https://www.sciencedaily.com/releases/2024/11/241106132119.htm).

Researchers eagerly await examination of material collected from asteroid 101955 Bennu by NASA’s OSIRIS-REx spacecraft.

Voyager 2 Still Rules! Voyager 2 flew past Uranus on January 24, 1986, and while we have made great strides in telescopic imaging, we haven’t gotten an up-close look in almost 39 years. A more-advanced mission to Uranus was listed as one of the highest priority objectives in the Planetary Science and Astrobiology Decadal Survey, 2023-2032, prepared by the National Academy of Science. Voyager 2 did a great job with the instruments it carried (think what the state of technology was 40 years ago!), finding additional moons and rings, but to everyone’s surprise, it showed that Uranus had radiation belts as intense as those of Jupiter, a very unexpected observation, especially since Voyager 2 no source of energized particles that would make the belts so intense, and that much of Uranus’ magnetic field was devoid of plasma. The only other source of such particles was the Sun. Close examination of the Voyager 2 data has now made scientists realize that there must have been a solar event, like a CME, that contributed temporarily to the radiation belt. Had Voyager 2 come a few weeks earlier or later, the radiation belt would have been more as expected. For more on this new old development, see: https://www.jpl.nasa.gov/news/mining-old-data-from-nasas-voyager-2-solves-several-uranus-mysteries. BTW: NASA is still in contact with both Voyagers. Thank you, Ed Stone!

Meanwhile: Voyager 1 Glitch Partially Resolved: The spacecraft’s fault-protection system was activated when a command was sent to the venerable probe to turn on an onboard heater, causing a shut-down of the spacecraft’s main communications transmitter. NASA was able to connect with a less-powerful secondary transmitter (unused since 1981!) and is presently working to understand the problem, no mean feat given that the spacecraft has been in Space for 47 years and is now 23 light-hours away (15 billion miles)! For more on this situation, see: https://blogs.nasa.gov/voyager/2024/10/28/after-pause-nasas-voyager-1-communicating-with-mission-team.

Bad News for Marvin: The Curiosity rover presently exploring Gale Crater on Mars has encountered a lot of carbonate rocks, which may indicate that conditions in the martian past were more suitable for life. However, Curiosity has instruments that can measure the isotopic composition of the carbonates it has encountered, and the results show that the heavier isotopes are more concentrated than in any carbonate on Earth. David Burtt of NASA Goddard Space Flight Center was the lead author on a paper that states, "Our samples are not consistent with an ancient environment with life (biosphere) on the surface of Mars, although this does not rule out the possibility of an underground biosphere or a surface biosphere that began and ended before these carbonates formed." Some previous analyses lead to the same conclusion, but this is the first study to include measurements of carbon isotopes on Mars. For a summary of this work, see: https://www.sciencedaily.com/releases/2024/10/241007165317.htm; for the paper in the Proceedings of the National Academy of Science, see here: https://www.pnas.org/doi/10.1073/pnas.2321342121. Oh Dear!

ALL IN THE (ASTEROID) FAMILY: FROM WHENCE DO THE AMBASSADORS COME? Meteorites are “ambassadors of knowledge,” giving many clues about the formation of the Solar System, orbital dynamics, and more. Some are left-overs from the formation of the Solar System, some have come from the Moon, Vesta, and even Mars, but until recently, planetary scientists knew the origin of only a small percentage of the meteorites collected and studied to date.

That all recently changed.

Meteoriticists can determine the composition of most asteroids from their reflection spectra, and they have long wondered why most of the meteorites found on Earth, type H and L ordinary chondrites, are types fairly uncommon in the rest of at Belt. Astronomers have known for some time that asteroids in the belt between Mars and Jupiter can be grouped into “families” based out similarities in their orbital parameters, formed by the breakup of parent bodies long ago. Extensive observation of asteroid types and computer simulations of asteroid movement have revealed that there have been three large-scale collisions in the past 40 million years or so, two of which produced families of H ordinary chondrites, and one the produced a family of L ordinary chondrites. Alteration of the orbits of the fragments from those collisions sent some/much of the material Earthward to produce their abundances observed today.

The two collisions that produced the H families were so recent that the computer simulations could reveal the age of the collisions that produced them. One family, with orbits similar to asteroid 158 Koronis, dates to 7.6 million years ago; another event, 5.8 million years ago, was when Koronis fragmented, spinning of asteroid 832 Karin and its family.

The origin of the L ordinary chondrites is older and more complex. They trace back to a collision 466 million years ago, which produced a family of objects along with the larger asteroid 20 Massalia, now considered to be the parent body for the L chondrite family. A more recent collision with Massalia likely produced a branch on its family tree.

For more about this research, see: https://skyandtelescope.org/astronomy-news/weve-found-the-source-of-most-meteorites.

JUNO NEWS

More on NASA’s Juno Mission - at Io: Since Juno 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! And Juno’s extended mission has paid off, because it recently found a …

MARS NEWS

InSight’s Insight into Mars’ Water: Evidence for Mars to have had abundant surface water in its distant past (~3 Ga) can be found in many places, including Gale and Jezero Craters. But there is little water in Mars’ surface environment today. Where could it have gone? Four choices are possible, not mutually exclusive: the water was incorporated into surficial minerals, the water was buried as ice, the water was sequestered in deep aquifers, and/or the water was photo-dissociated and lost to Space. We know that there is at least some ice buried in Mars’ (near) polar regions, and we know some has been lost to Space (part of the ongoing MAVEN orbiter’s mission is to give data on how much water is being lost). Some water is likely hydrating surface minerals, too. But what about deep aquifers?

The now-defunct InSight lander carried a good seismometer to the martian surface, and there recorded a number of marsquakes. Terrestrial geologists can determine a lot about the conditions in Earth’s crust from how earthquake energy propagates through the ground, and Mars is similar. The InSight seismic signals passing through the upper 300 meters or so of the martian surface are consistent with that layer being totally dry, but the seismic waves passing much deeper, 11-20 km down, are consistent with a fragmented igneous rock layer with liquid water in the interstices. That’s too deep for easy exploitation, but it is important scientifically. For a summary of this research, see here; for the paper in the Proceedings of the National Academy of Science, see here.

The InSight seismometer also detected a number of small impact-induced Marsquakes, which, combined with images from orbit, are helping planetary scientists make better estimates of the present impact rate.For a summary of this important InSight insight, see: https://www.sciencedaily.com/releases/2024/06/240628124857.htm ; for the paper in Nature Astronomy, see: https://www.nature.com/articles/s41550-024-02301-z

Percy is Doing Great Work, but Don’t Forget Curiosity; Here’s Four Reasons Why!

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 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 recently returned a 1.8-Billion-Pixel panorama of this interesting place; it’s quite spectacular!

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: https://www.nasa.gov/missions/mars-science-laboratory/nasas-curiosity-searches-for-new-clues-about-mars-ancient-water.

Curiosity at Whitebark Pass: The Curiosity rover at Gale Crater continues to find interesting things as it explores Gediz Vallis. 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: https://science.nasa.gov/blogs/sols-4209-4211-just-out-of-reach.

Mars in the Past: Warm and Wet or Cold and Icy? A new study suggests the latter, based on a comparison of Curiosity data from Gale Crater and terrestrial soils from the Canadian sub-arctic. Curiosity uses X-ray diffraction to identify regolith material, but much of it appears amorphous, lacking crystalline structure. The material is rich in iron and silica, but relatively-poor in aluminum. Soils from three sites in the Canadian sub-arctic show similar amorphous material, but soils produced from similar rocks in warm climates do not, suggesting that Mars was a cold place when the Gale Crater deposits formed. For a summary of the research, see here: https://phys.org/news/2024-07-mars-cold-icy.html, for the paper in Nature Communications, see here: https://www.nature.com/articles/s43247-024-01495-4.

Surprise! On May 30, Curiosity was driving through an area covered with “bright rocks.” Its battered wheels crushed one of them, and rover managers were amazed to see that it was filled with yellow crystals of what proved to be elemental sulfur! Sulfur compounds had been detected in a number of places, a good indicator for the past presence of liquid water that evaporated, but crystalline sulfur was a big surprise. It now looks like Gediz Vallis was formed by a series of flows of liquid water and debris that left a “ridge of boulders and sediments extending 2 miles down the mountainside below the channel.” Since its formation, smaller local landslides have contributed to the deposits on the channel floor. For more on this development, see: https://phys.org/news/2024-07-nasa-curiosity-rover-martian.html. See also: https://go.nasa.gov/3LuYCTf (includes a 3-D view of Gediz Vallis).

Perseverance at Neretva Vallis:Percy’s Jezero Crater landing site was chosen because geological and geomorphic evidence is strong that it once contained a lake, and had a river running into it that made a delta deposit on the crater’s floor. Percy has been examining that delta and is now roving across one of the channels, Neretva Vallis, that fed water into the crater and helped make the delta. The channel is sandy, with many larger rocks that challenge Percy’s auto-navigation system. The sandy material of the channel has been reworked by the martian wind to form a number of dunes, which also pose a hazard to rover drivers. Their goal is work the extra effort; there is a formation of lighter material along the base of the channel wall that may be older material exposed by river erosion. For more about this cool place, see: https://www.nasa.gov/missions/mars-2020-perseverance/perseverance-rover/nasas-perseverance-fords-an-ancient-river-to-reach-science-target!

UPDATE:Perseverance reached the above-mentioned “lighter material” at the edge of the Neretva Vallis last week. Its cameras returned images showing “intriguing surface textures on the light-toned rocks” its drivers had seen from a distance and named “Bright Angel.” Percy’s instruments are being used to make a series of in-depth observations here, with the possibility of acquiring a sample that will be part of the suite of samples for future return to Earth (I hope). The site has been renamed “Walhalla Glades,” after a famous archeological site on the banks of the Colorado River. For more info, see: https://science.nasa.gov/blogs/a-bright-new-abrasion.

The texture of the rocks at Walhalla Glades has been termed “popcorn-like” and may be due to the action of ground water after the sediments comprising the Glades was laid down. The rover team is planning to climb up the whitish material to examine the contact between it and the surrounding sedimentary rocks. The next target for Percy is a place intriguingly called the “Serpentine Rapids.” For more information, see: https://science.nasa.gov/blogs/perseverance-finds-popcorn-on-planet-mars.

Not long before getting to Neretva Vallis, Percy had sent back an image that makes …

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: https://www.universetoday.com/160320/our-best-instruments-couldnt-find-life-on-mars. 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…

More Evidence from Jezero! The Perseverance rover recently completed its 1000^th 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: https://www.jpl.nasa.gov/news/nasas-perseverance-rover-deciphers-ancient-history-of-martian-lake.

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: https://phys.org/news/2024-01-ancient-lake-mars-perseverance-rover.html; for the paper in Science Advances, see: https://www.science.org/doi/10.1126/sciadv.adi8339.

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.

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

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: https://eos.org/editors-vox/up-close-with-an-active-asteroid

JGR Planets paper: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JE006381

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: https://www.sciencedaily.com/releases/2024/02/240207120512.htm and https://www.astronomy.com/science/evidence-grows-for-a-young-ocean-lurking-under-mimas-icy-crust

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 Titan – JWST 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: https://phys.org/news/2023-05-webb-telescope-towering-plume-saturn.html.

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: https://www.jpl.nasa.gov/news/new-study-of-uranus-large-moons-shows-4-may-hold-water.

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: https://science.nasa.gov/science-red/s3fs-public/atoms/files/psd-fleet-03092022b.pdf!

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: https://phys.org/news/2023-01-webb-spies-chariklo-high-precision-technique.html.

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: https://mars.nasa.gov/mars2020/mission/status/419/a-picture-is-worth-a-thousand-words!

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: https://www.sciencedaily.com/releases/2022/10/221004105010.htm; for the paper itself, see: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021AV000627.

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: https://www.sciencedaily.com/releases/2022/10/221004104943.htm; for a summary and an amazing video simulation of the Earth-Theia impact from NASA Ames, see here: https://www.nasa.gov/feature/ames/lunar-origins-simulations.

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: https://www.nasa.gov/mediacast/23-deep-space-network-origins-nasas-the-invisible-network-podcast.

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 efforts, laser communications technologies, NASA’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: https://soundcloud.com/nasa/the-invisible-network-deep-space-network-season-trailer.

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: https://phys.org/news/2022-01-nasa-solar-mission-tiny-asteroid.html and: https://www.nasa.gov/content/nea-scout!

VENUS

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: http://www.sci-news.com/astronomy/venusian-clouds-phototrophy-10123.html; for the paper itself, see: https://www.liebertpub.com/doi/10.1089/ast.2021.0032.

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 (e.g.here). 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: https://www.sciencedaily.com/releases/2021/10/211013114018.htm; for the abstract of the paper in Nature, see: https://www.nature.com/articles/s41586-021-03873-w.

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: https://phys.org/news/2021-08-evidence-geologically-recent-venusian-volcanism.html; for the abstract in their paper in the Journal of Geophysical Research, Planets, see: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JE006783.

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: https://skyandtelescope.org/astronomy-news/venus-surface-is-fragmented-like-pack-ice; see the paper abstract at: https://www.pnas.org/content/118/26/e2025919118.

METHANE

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: https://www.sciencedaily.com/releases/2021/07/210706180905.htm.

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: https://skyandtelescope.org/astronomy-news/solar-system/nasas-curiosity-takes-step-toward-solving-mars-methane-mystery; for the full paper in Astronomy & Astrophysics, see: https://www.aanda.org/articles/aa/pdf/2021/06/aa40030-20.pdf.

MARS EXPLORATION REFERENCES

Mars Odyssey

https://mars.nasa.gov/odyssey

https://mars.nasa.gov/odyssey/files/odyssey/Odyssey0302.pdf

https://themis.asu.edu

Mars Express

https://sci.esa.int/web/mars-express/-/31021-summary

https://sci.esa.int/web/mars-express/-/55263-beagle-2-lander-found-on-mars

Mars Science Laboratory (aka Curiosity)

https://mars.nasa.gov/msl/home

https://www.jpl.nasa.gov/missions/mars-science-laboratory-curiosity-rover-msl