Mars Gullies Aren't Made by Water: The Surprising Dry Ice Answer

Perseverance drove to the edge of an ancient Martian lake expecting a beach and found the inside of a volcano — rock that water has been through at least three separate times. Europe's Jupiter probe comes home on Monday night and crosses Australia in a fully dark sky. Two teams, using two completely different techniques, both find something hiding inside the most famous planetary system we have ever photographed — and an Australian instrument is in the middle of one of them. Plus: heavy water in an interstellar comet, and what it says about the star that made it. In this episode · LEAD — Three floods at the crater's edge. Candice Bedford (Purdue) and colleagues publish in Communications Earth & Environment: the Margin Unit at Jezero is igneous, not sedimentary, and records at least three distinct episodes of water — CO₂-rich groundwater making carbonate ridges, then silica associated with the lake, then a later hot-water event leaving fluorite veins. Habitability context, not a biosignature. · Juice returns. ESA confirms the third Earth gravity assist for 28 September — closest approach 11:45 UTC over the Indian Ocean, bending the trajectory ~20° and adding ~3.5 km/s. The spacecraft crosses Australia north-east to north-west 15–30 minutes earlier, in full darkness. · HR 8799. Two preprints in two weeks point at a fifth, inner planet — one from archival JWST aperture-masking data (~7 au, a few Jupiter masses), one from Gaia astrometry (2–3 au, 10–14 Jupiter masses). They do not obviously describe the same object. Neither is peer-reviewed. · 3I/ATLAS. A modelling paper explains the high deuterium-to-hydrogen ratio measured in March as consistent with formation around a low-metallicity — meaning old — star. · Quick hit: Starship Flight 14 still targeting 28 September; Crew-13 still 'no earlier than early October' on NASA's own page; Albania signs the Artemis Accords as the 73rd country. · Skywatch: the equinox as an instant rather than a date, the Juice pass over Australia, Venus and Mercury for the south, Mars and Jupiter before dawn for the north, and Saturn heading into opposition. Sources and further reading · Bedford, C. C. et al., 'Lake- and groundwater-associated alteration of the olivine-rich Margin unit in Jezero crater, Mars', Communications Earth & Environment (2026). DOI 10.1038/s43247-026-03997-9 · NASA/JPL, 'NASA Discovery Reveals Complex Water Systems on Early Mars', 21 September 2026. · ESA, 'Juice to fly past Earth for third gravity assist', 21 September 2026. · Nguyen, J. S. et al., 'A Candidate Innermost Fifth Planet In the HR 8799 System Revealed By JWST NIRISS Aperture Masking Interferometry', arXiv:2609.10507. · Lagrange, A.-M. et al., 'A fifth companion in the HR 8799 system revealed by Gaia', arXiv:2609.20996 (submitted to Nature Astronomy). · Furuya, K., Cordiner, M., Bockelée-Morvan, D. et al., arXiv:2609.12370. · NASA OIIR, 'NASA Welcomes Albania as Newest Artemis Accords Signatory', 21 September 2026. Skywatch figures computed in-session with PyEphem 4.2.1 for Sydney, Los Angeles, New York and London. Times are local unless marked UTC.

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