SOLAR SYSTEM

SOLAR SYSTEM NEWS

NASA Says Percy discovered potential biosignatures in 2026: “A sample collected by NASA’s Perseverance Mars rover from an ancient dry riverbed in Jezero Crater could preserve evidence of ancient microbial life. Taken from a rock named “Cheyava Falls” last year, the sample, called “Sapphire Canyon,” contains potential biosignatures, according to a paper published Wednesday in the journal Nature.“ For more information, see: https://www.nasa.gov/news-release/nasa-says-mars-rover-discovered-potential-biosignature-last-year.

NASA Marsquake Data Reveals (sic.) Lumpy Nature of Red Planet’s Interior: “What appear to be fragments from the aftermath of massive impacts on Mars that occurred 4.5 billion years ago have been detected deep below the planet’s surface. The discovery was made thanks to NASA’s now-retired InSight lander, which recorded the findings before the mission’s end in 2022. The ancient impacts released enough energy to melt continent-size swaths of the early crust and mantle into vast magma oceans, simultaneously injecting the impactor fragments and Martian debris deep into the planet’s interior.” For more info, see: https://www.nasa.gov/missions/insight/nasa-marsquake-data-reveals-lumpy-nature-of-red-planets-interior.

Ceres May Have Had Long-Standing Energy to Fuel Habitability: “New NASA research has found that Ceres may have had a lasting source of chemical energy: the right types of molecules needed to fuel some microbial metabolisms. Although there is no evidence that microorganisms ever existed on Ceres, the finding supports theories that this intriguing dwarf planet, which is the largest body in the main asteroid belt between Mars and Jupiter, may have once had conditions suitable to support single-celled lifeforms.” For more information, see: https://www.nasa.gov/missions/dawn/nasa-ceres-may-have-had-long-standing-energy-to-fuel-habitability.

SOLAR SYSTEM FYI

The Plumes of Enceladus: Saturn’s small moon, Enceladus, has fascinated planetary scientists with its plumes of water and other material being ejected from fractures on its surface. The Cassini spacecraft, late in its orbital mission, was sent through one such plume, finding that its chemistry contained a number of organic molecules akin to those in biologically-rich deep-water hydrothermal vents on Earth, suggesting the intriguing possibility of life arising there! So much material is being spewed that it forms a faint ring around Saturn. But how much is “so much?” New supercomputer modeling suggests that less water is being emitted than previously thought. The new model also provides insight into the temperature and speed of the material emitted. For more in the new model, see: https://www.sciencedaily.com/releases/2025/11/251117095650.htm.

HOW SCIENCE OPERATES: 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.

2060 Chiron is a Unique Hybrid: Chiron is a member of a class of bodies called “Centaurs.” Just as a centaur is a man/horse hybrid in mythology, Centaurs have characteristics of both asteroids and comets in reality, and their orbits are confined to the belt between Jupiter and Neptune. Detailed observations from the JWST show the presence of CO2 and CO ice on Chiron’s surface and CO2 and CH4 in its comet-like coma, a shroud of gas and dust released from Chiron. CO2 and CH4 ices have also been detected on some Trans-Neptunian Objects. Chiron was discovered in 1977, and has been observed in more detail than the other Centaurs. Trans-Neptunian Objects tend not to have a coma, because they are so far from the Sun that their surface ice cannot sublimate. Classical asteroids have no surface ices. Centaurs do have surface ices, but sublimation is limited to those times when they are closer to the Sun. The details of the chemistry of ices and gases has implications for the evolution of the Solar System. For a summary of this work and its implications, see: https://www.sciencedaily.com/releases/2024/12/241218131526.htm; for the paper in Nature Geoscience, see: https://www.nature.com/articles/s41561-024-01612-0.

Chiron isn’t the only Centaur of Note! 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!

Chiron is the oddest Centaur (see news above), but the largest Centaur asteroid is 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.

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

OCEANS ON (UNDER) MOONS

Callisto is an Ocean World (?): We are confident that some of the icy bodies in the Solar System have a thick liquid ocean surface, overlain by a thick cover of ice. Jupiter’s Europa and Saturn’s Enceladus are prime candidates, but some of the other moons and perhaps Pluto may have enough interior tidal heating that they differentiated enough to have a thick, iced-over surface, too. Jupiter’s Callisto is the latest to be found to have evidence of a sub-surface liquid ocean, based on repeated observations of its magnetic field and ionosphere acquired during eight close passes by the Galileo spacecraft. For more info in this intriguing possibility, see: https://eos.org/research-spotlights/jupiters-moon-callisto-is-very-likely-an-ocean-world.

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

Uranian Moons Harbor Subsurface Oceans: Mimas, Europa, and Enceladus aren’t the only outer planet moons with a subsurface ocean! 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.