Posted by Most answers to what’s new on Mars turn into a list of landings. That list is the least interesting part. Over roughly the past decade the planet itself changed shape in our heads: it acquired a measured interior, a mapped inventory of buried ice, a lake that may not be a lake, an organic chemistry that is genuinely odd, and a methane problem two spacecraft still cannot reconcile. Almost none of that was settled in 2015.
And most of it arrived not from photographs but from instruments that listen, ping and sniff.
The planet finally got an inside
Before 2018, everything anyone said about the Martian interior came from gravity fields, orbital tracking and models built on assumptions. InSight landed on Elysium Planitia on 26 November 2018 and set its seismometer, SEIS, straight onto the ground a few weeks later. The first confirmed marsquake came on 6 April 2019. It was faint enough that a truck driving past would have drowned it out. By the time the lander went quiet under a coat of dust, with final contact on 15 December 2022, the team had logged well over a thousand seismic events on a world where nobody knew whether there would be any.
Three papers in Science in July 2021 turned those wiggles into architecture. The crust under the lander is thin and layered, on the order of 20 to 40 kilometres depending on which layering model you accept. The mantle is stiffer than Earth’s. And the core, with a radius near 1,830 kilometres, is liquid, and too light to be plain iron and sulphur, which forces a helping of lighter elements into the mix.
Then it got revised, publicly and fast. In October 2023 two Nature papers argued that part of what had been read as core was really a molten silicate layer draped over the top of it, pulling the core radius back toward roughly 1,650 kilometres and making it denser. Mars still has a liquid core. It is probably smaller than the 2021 headlines said.
The biggest quake InSight caught, S1222a at magnitude 4.7 on 4 May 2022, released more energy than everything else the mission recorded put together. The lander also heard rocks arrive. A meteoroid strike on 24 December 2021 in Amazonis Planitia dug out blocks of water ice at about 35 degrees north latitude, well nearer the equator than shallow ice was supposed to survive.
Ice you can map, and ice you can argue about
Two radars have been quietly rewriting the water budget: SHARAD, working from Mars Reconnaissance Orbiter since 2006, and MARSIS on Mars Express, whose antenna was unfurled in 2005. Both send pulses into the ground and read what bounces back from buried boundaries.
The most persuasive ice result of the decade needed no radar at all. In January 2018, a team publishing in Science reported eight steep scarps in the mid-latitudes, near 55 to 58 degrees, where erosion had sliced open thick deposits of nearly pure water ice sitting under a metre or two of dry material. Not inferred. Visible in cross-section, like a cliff face in a quarry. If what’s new on Mars had to be boiled down to one practically usable fact, it would be that one: mid-latitude ice stopped being a modelling argument and became something a future crew could, in principle, chip at.
Radar keeps producing bigger and shakier numbers. A reanalysis of MARSIS data presented in January 2024 found that the Medusae Fossae Formation, a strange soft deposit near the equator, may hold layered material up to about 3.7 kilometres thick that looks ice-rich in its dielectric properties. If it really is ice, melting it would spread water a couple of metres deep across the whole planet. If it is dry dust with the right porosity, the same echoes appear. Radar cannot tell you which without help, and that ambiguity is the running theme of the past ten years.
The lake that keeps failing to be a lake
In July 2018 an Italian-led team announced in Science that MARSIS had found an unusually bright reflection about 1.5 kilometres beneath the south polar layered deposits at Ultimi Scopuli, roughly 20 kilometres across, and read it as liquid water. In September 2020 a follow-up in Nature Astronomy extended the claim to several smaller patches around it.
The pushback has been thorough. Work published from 2021 onward showed that ordinary smectite clays can produce equally bright basal echoes at Martian temperatures, that saline ice can do it too, and that thin alternating layers of ice and dust can create constructive interference indistinguishable from a lake at MARSIS resolution. There is also a heat problem: keeping brine liquid down there needs either a salt content near saturation or a local heat source nobody has found.
Nobody has drilled. This is what an unresolved question actually looks like, as opposed to how it gets reported.
Carbon in the mudstone
Curiosity has been baking Martian rock since 2012, and the organic results have grown steadily less deniable. Chlorobenzene came first, in 2015. In June 2018 came thiophenes and aromatic and aliphatic fragments out of roughly three-billion-year-old lake mudstone at Pahrump Hills. In January 2022 a PNAS paper reported that several samples were oddly enriched in carbon-12, which can be a biological fingerprint on Earth but is equally consistent with sunlight breaking down atmospheric methane, or with the solar system drifting through a cold interstellar cloud.
The most striking one arrived in March 2025. Analysis of the Cumberland sample, drilled back in May 2013 and revisited with a different laboratory protocol, produced decane, undecane and dodecane: the longest carbon chains yet found on Mars, plausibly broken-off pieces of fatty acids. On Earth, fatty acids are made overwhelmingly by cells. On Mars they can also be built without any biology at all.
Perseverance added its own ambiguity at Cheyava Falls in Jezero, where a July 2024 sample showed millimetre-scale spots with iron-phosphate and iron-sulphide rims of the kind microbial metabolism produces in terrestrial sediments. A formal description in Nature in September 2025 called it a potential biosignature, which is a technical phrase meaning nobody can yet rule biology out. It is not a discovery of life, and the researchers said so first and loudest.
The methane two spacecraft cannot agree on
Curiosity’s tunable laser spectrometer has measured a background of roughly 0.4 parts per billion in Gale crater, rising and falling with the seasons to a peak near 0.65 in northern summer, as reported in 2018, plus occasional spikes around ten times that. Mars Express saw 15.5 parts per billion in June 2013.
Then the ExoMars Trace Gas Orbiter arrived, built specifically to hunt trace gases, and starting with its first results in 2019 it found nothing. Upper limits around 0.05 parts per billion, later tightened further. Both instruments work. Both teams are careful.
The leading reconciliation, developed from about 2019 onward, is unglamorous and probably right: methane seeps slowly out of the ground at night, pools under a stagnant near-surface layer where Curiosity is sitting, and gets churned away and destroyed by day before it ever mixes up to the altitudes the orbiter samples. Salt-crusted regolith may act as a valve, sealing and burping with temperature. The upshot is that Martian methane became a question about near-surface transport rather than a question about life, which is a demotion, and also an answer. A good deal of what’s new on Mars works that way: a loud claim quietly turning into a better-posed question.
The water that did not happen
Recurring slope lineae were the decade’s most photogenic disappointment. Dark streaks that lengthen down warm slopes in Martian summer and fade in winter, first described in 2011, they were tied in 2015 to hydrated perchlorate salts detected from orbit, and the news cycle turned that into flowing water. In 2017 the same imaging team showed the streaks stop exactly where slopes reach the angle of repose for loose sand, behaving like dry granular avalanches. A machine-learning survey published in May 2025 catalogued around half a million slope streaks and found their distribution tracks dust and wind, not water, frost or humidity.
The brine story survived, but smaller. Phoenix confirmed perchlorate in the soil in 2008, which lets salty films stay liquid far below zero. Modelling published in 2020 found that brines can be thermodynamically stable over much of Mars, for a few percent of the year, at temperatures near minus 48 degrees Celsius. That is liquid, technically. It is also colder than anything known to metabolise on Earth.
Which is the quiet result underneath all of this. What’s new on Mars, taken together over ten years, is a planet described far more precisely and judged far less generously. The wet, borderline-habitable present that people argued about in the early 2010s has mostly evaporated, while the ancient, genuinely habitable past has become harder to dismiss. That trade is worth having, because a well-characterised dead planet next door is the calibration we need before claiming anything about an atmosphere seventy light years away.
SETIworld follows these arguments while they are still arguments, not after they harden into textbook lines. If you would rather watch the evidence move than read the press release, come read along with us.
