This Week in Astronomy: Martian Ice From Nothing, Heavy Alcohol and a Planet With Two Births
A quiet week for big announcements, but an unusually good one for new physics. A cloud on Mars turns out to be made by a process never before seen in any planetary atmosphere, ALMA finds the heaviest form of alcohol yet detected in space, a dead star appears to be feeding on a planet that may have formed after its host died, and a first year undergraduate publishes a solo paper on three galaxies that should not exist where they do.
A Martian cloud that freezes out of nothing
If you have followed Mars Express you will have met the Arsia Mons Elongated Cloud. Every southern spring and summer a ribbon of water ice forms over Arsia Mons, the 20 km high volcano just south of the Martian equator. It grows westwards through the early morning, reaches as much as 1,800 km in length, detaches, drifts off on high altitude winds and evaporates before lunchtime. Then it does the whole thing again the next day, for months.
Astronomers have known the broad shape of that cycle since the Visual Monitoring Camera began tracking it in 2018. What nobody could do was reproduce it. Standard models of mountain clouds assume water vapour needs a seed, usually a dust grain, to condense onto, and they would not build anything resembling the cloud Mars Express keeps photographing.
A team led by Jorge Hernández-Bernal of Sorbonne Université and CNRS has now found what was missing, in Nature Geoscience on 7 October. Their simulations matched the observations only once they allowed homogeneous nucleation: water vapour freezing straight into ice crystals with no seed particle at all. Hernández-Bernal describes needing to include "some exotic physics" in the modelling.
Getting there requires extraordinary conditions. Wind climbing the volcano's flanks sets up an atmospheric wave that lifts moist air several kilometres in minutes and cools it by roughly 30 degrees, driving it far past saturation. At that point vapour can skip the middle step entirely.
Be clear about what is measured and what is inferred: the extreme humidity is a model result, and the paper's own title says "suggested" rather than demonstrated. Homogeneous nucleation has long been proposed for the upper atmospheres of Earth and Venus and never confirmed there either. If it holds up, Mars is the first place we have caught it happening.
Heavy alcohol in the planet building zone
Methanol matters in star formation because it is the gateway to the larger organic chemistry that ends up in comets and, presumably, on planets. This week NRAO announced results from COMPASS, an ALMA Large Program that pointed up to 66 antennas at eleven nearby, Sun-like infant stars for more than a hundred hours, yielding seven papers in Astronomy & Astrophysics.
Two stand out. Arnaud Belloche of the Max Planck Institute for Radio Astronomy and colleagues report the first interstellar detection of fully deuterated methanol, CD3OD, around the protostar IRAS 4A2 in the Perseus molecular cloud about 1,000 light years away. Every hydrogen atom has been swapped for deuterium, which is demanding to assemble and an exquisitely sensitive record of the cold, dark conditions it formed in. Deuteration ratios are one of the few tools we have for working out where a molecule was built, so the fully substituted version gives chemists a hard anchor point.
Separately, Jae-Hong Jeong, a graduate student at Seoul National University, found methanol masers in more than half the sample. Masers switch on only in narrow ranges of density and temperature, which makes them pinpoint probes of regions otherwise hopelessly blended together. Finding them so often hints that they are routine in early stellar evolution rather than a curiosity, though with eleven targets that remains a hint.
Principal investigator Jes Jørgensen, of the Niels Bohr Institute in Copenhagen, frames the collection as a chemical starter kit that may one day enrich planets. That part is firmly speculative; the detections are not. The full survey should settle whether the chemistry a young system inherits comes from its birth cloud or from what happens afterwards.
Reference: Cosmic Cocktail: Exotic Methanol Discovered in Planet-Building Zones, NRAO, 7 October 2026
A planet that may have been born after its star died
HS 0209+0832, also catalogued as Feige 20, is a hot white dwarf roughly 270 light years away in Cetus, only about five million years into its life as a stellar remnant. Something is falling onto it.
Jamie Williams of the University of Warwick and colleagues, writing in Nature Astronomy on 5 October, pulled apart an archival Hubble STIS far ultraviolet spectrum taken in 1999, supported by FUSE and VLT/UVES data and Gaia and Pan-STARRS photometry. Around a hundred lines defied identification, and the ones they could pin down are strange. Niobium is enhanced by more than three orders of magnitude relative to the Sun, and was absent in all 33 other polluted white dwarfs they checked. Nickel outweighs iron by at least a factor of two, unlike the Sun, Earth or primitive meteorites.
That is not what a shredded asteroid gives you. It is close to what models of nucleosynthesis in dying giant stars predict: niobium, nickel, copper and zinc enhanced, oxygen, silicon, calcium and iron largely untouched. The suggestion is that the star's own late life winds built a disc enriched in carbon and heavy elements, and that a giant planet grew inside it. A 4.4 day periodicity in the TESS light curve, well away from the 1.25 days typical of white dwarf rotation, could belong to such a planet orbiting at about 0.04 AU.
The accretion and the abundances are measured. The planet is only a candidate, and the second generation origin is a hypothesis, but one that fits unusually well. If it is right, we are watching planet formation that began after a star had finished dying.
Three quiet dwarf galaxies, found in old data
Our last story is a reminder that the data already sitting in public archives is nowhere near exhausted. Julian Shapiro, now in his first semester as an astrophysics undergraduate at UC Berkeley, is the sole author of a paper published in The Astrophysical Journal on 6 October, begun while he was still at school.
Combing through imaging from the Sloan Digital Sky Survey, the Hyper Suprime-Cam Legacy Archive and the Canada France Hawaii Telescope, he found three faint dwarf galaxies near M101, the Pinwheel, now named Shapiro I, II and III. All three are isolated, and all three have essentially stopped forming stars. That combination is the problem: dwarf galaxies normally have their gas stripped by a larger neighbour, so a quenched dwarf is expected to sit close to one. These do not.
His answer is that they are backsplash galaxies: they fell through M101's halo in the past, lost their gas to the passage, and were slung back out into apparent isolation. Simulations support the idea that something external shut them down. The caveats are honest ones. These are candidates, Shapiro II might simply be a satellite of the nearby spiral NGC 5585, and confirmation needs higher resolution follow up. Shapiro expects the Vera C. Rubin Observatory to turn up many more.
M101 is one of the most frequently requested targets on the Telescope Live network, which makes this a pleasing result to read: the faint smudges near the edge of a familiar field are not always noise. As Shapiro puts it, "public archival telescope data is a critical tool for new discoveries".
Reference: A UC Berkeley undergraduate's research leads to an astronomical first, Berkeley News, 6 October 2026
Clear skies, and we will see you next week.