Show Notes
Today's episode — The Weekend Wrap, Saturday 12 September 2026: OUR LEAD: A SMALLER MERCURY Mercury has been contracting for four and a half billion years as its huge iron core cools, and it writes the record on its own surface — in long lobe-fronted cliffs called lobate scarps, where one slab of crust has ridden up over another. Add up all that shortening and you get the total contraction. The trouble was that the surface record always gave a smaller number than thermal models predicted. New work led by Gaku Nishiyama at the German Aerospace Center in Berlin, published in Geophysical Research Letters and released by the American Geophysical Union on 10 September, explains the gap — and the explanation is beautifully simple. Impact debris buries the cliffs. Using MESSENGER imagery reworked with stereophotogrammetry, the team showed that the rougher the terrain, the fewer shortening structures you can find per unit area. Since faults don't know what the surface above them looks like, that correlation isn't geology — it's a detection limit. Correct for it and Mercury's total loss of diameter rises by 10–30%, from a range topping out near 16 km to as much as 23 km. That points to a larger metal core, fewer light elements in it, or a hotter start — and it closes the long-standing mismatch with the physics. BepiColombo is about ten weeks from gravity capture at Mercury, carrying a far better laser altimeter and a much less eccentric orbit. If Nishiyama is right, it should find the missing small scarps in exactly the rough ground where today's maps look suspiciously empty. Some of that data will come home through ESA's New Norcia station in Western Australia, run in partnership with CSIRO. THE WEEK THAT WAS · Monday — Isar Aerospace's Spectrum reached orbit from Andøya Spaceport in Norway on 5 September, the first vehicle ever to do it from Western European soil, carrying five university cubesats. · Tuesday — giant-impact simulations including temperature-dependent rock strength can produce an intact Moon in about five hours rather than a slowly accreting debris disc. A sensitivity result, not a new origin story. · Wednesday — Hubble and Webb together found 27 previously unknown trans-Neptunian objects down to about 5 km, and the small ones keep the colours of their birth population rather than looking like collision fragments. · Thursday — 109 localised fast radio bursts were used to measure how far galactic feedback has smoothed the clumpiness of matter, finding more cool gas in big haloes than X-ray surveys see. · Friday — population synthesis suggests magnetars are roughly half of all neutron stars at birth, not one in a hundred, which doubles the Galactic supernova rate and makes magnetar central engines affordable. ALSO IN THIS EPISODE · The Sun's superflare potential — new work from the Max Planck Institute for Solar System Research with the University of Colorado, released 10 September. Scaling the 300 strongest modern solar flares against the size of their active regions, then applying that relation to the giant sunspot group of 1947 — the largest in four centuries of observation — gives a region with enough stored magnetic energy to power a superflare. Potential, not prediction: the caveats are covered properly on air. · Rocket Lab has filed a protest with the US Government Accountability Office over NASA's ~$700M Mars Telecommunications Network award to Blue Origin, on eligibility and technical-evaluation grounds. A GAO decision is due around mid-December. · Starship Flight 14 has slipped to no earlier than 18 September — and the tower catch of the ship is deferred to a later flight, which corrects how we framed it earlier this month. SKYWATCH — BOTH HEMISPHERES · The Moon and Venus about half a degree apart in front of Spica on the evenings of 13–14 September — Southern Hemisphere observers get the better geometry. · Venus reaches greatest brilliancy on 18 September at magnitude −4.8. · SN 2026aaiv, a Type Ia supernova i
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Show notes Last November the Sun produced its strongest radiation storm in almost twenty years, and this time scientists were ready: neutron monitors from Cornwall to Shetland, sensors on transatlantic airliners, and weather balloons launched within the hour. A new Space Weather paper shows just how patchy the storm was, with one Shetland balloon passing aviation warning thresholds while others saw nothing. Also: a marsquake proves Valles Marineris is still tectonically active, a near-synchronised binary powers the Kepler field's most violent superflares, suspected Chinese rocket debris lands in a Borneo plantation, a correction on NASA's Artemis briefing, Hera's second braking burn, and a both-hemispheres skywatch with Venus at inferior conjunction, Mercury for the south, and the Moon with Saturn. Sources · Baird et al., Space Weather (DOI) — https://doi.org/10.1029/2026SW005279 · University of Surrey release, 20 Oct 2026 — https://www.surrey.ac.uk/news/rare-solar-radiation-storm-gives-scientists-clearest-picture-yet-flight-risks · NICT — ICAO space weather centres (ACFJ) — https://swc.nict.go.jp/en/knowledge/icao.html · Song et al., Nature Communications — https://www.nature.com/articles/s41467-026-78193-6 · Columbia/phys.org — Valles Marineris — https://phys.org/news/2026-10-giant-canyon-mars-tectonically-today.html · Kővári et al., arXiv 2610.11799 — https://arxiv.org/abs/2610.11799 · Konkoly Observatory release via phys.org — https://phys.org/news/2026-10-astronomers-uncover-powerful-stellar-flares.html · AFP via phys.org — Indonesia debris — https://phys.org/news/2026-10-indonesia-probes-chinese-rocket-fragment.html · CGTN — Zhuque-2E launch 14 Oct — https://news.cgtn.com/news/2026-10-14/China-s-Zhuque-2E-rocket-launches-10-satellites-into-space-1ReYXyOhz5C/share_amp.html · ESA — Hera braking manoeuvres — https://www.esa.int/Space_Safety/Hera/Brake!_Time_for_ESA_s_Hera_asteroid_mission_to_go_slow · NASA — Artemis update advisory — https://nasa.gov/news-release/nasa-to-discuss-artemis-acceleration-status-of-upcoming-moon-missions
Show notes The Milky Way's disc settled in two stages; metal-rich gas around Sgr A*; two mirror-image simulated universes; shadows in the Orion Bar; quick hits on Hera, Uzbekistan and Artemis; Orionid-night skywatch. Sources · IAC — Milky Way's disc formed in two very distinct stages — https://www.iac.es/en/outreach/news/research-iac-reveals-milky-ways-disc-formed-two-very-distinct-stages · Mirabal et al. — ApJL 1010 L38 — https://doi.org/10.3847/2041-8213/aeb0a3 · McGill — Gas around Milky Way's central black hole is rich in metals — https://www.mcgill.ca/newsroom/channels/news/gas-around-milky-ways-central-black-hole-rich-metals-study-finds-375101 · Ford et al. — AJ (DOI) — http://doi.org/10.3847/1538-3881/ae994d · Ford et al. — arXiv 2605.13995 — https://arxiv.org/abs/2605.13995 · Argonne — Aurora powers two of the largest cosmological simulations — https://www.anl.gov/article/argonnes-aurora-supercomputer-powers-two-of-the-largest-cosmological-simulations-to-date · UDE — New 3D model reveals hidden chemistry of stellar nurseries — https://www.uni-due.de/2026-10-16-publication-aa-brandt-gaches-3d-model-en · Gaches et al. — A&A 714 A295 — https://doi.org/10.1051/0004-6361/202660769 · ESA — Finding Hera's way: Flight Dynamics team in action — https://www.esa.int/Space_Safety/Hera/Finding_Hera_s_way_Flight_Dynamics_team_in_action · Kun.uz — Uzbekistan joins Artemis Accords — https://kun.uz/en/news/2026/10/19/uzbekistan-joins-artemis-accords-on-peaceful-space-exploration · NASA — To discuss Artemis acceleration, status of upcoming Moon missions — https://nasa.gov/news-release/nasa-to-discuss-artemis-acceleration-status-of-upcoming-moon-missions · The Planetary Society — Night sky, October 2026 — https://www.planetary.org/night-sky/night-sky-what-to-see-this-month
Show notes The Moon Is Still Shrinking Watters, Banks, Nypaver and Robinson (Planetary Science Journal, 14 Oct 2026) map more than 10,000 young thrust faults — ~8,900 lobate scarps and 2,000+ small mare ridges — with LRO's camera. Together they record about 42–46 m of radial contraction over the last ~400–800 million years, at most ~11 cm per million years. That's less than thermal models predict, pointing to a thick, porous, insulating megaregolith (or a strong elastic lithosphere) that delayed faulting. The ~4 MPa stress matches Apollo shallow-moonquake stress drops, so faults may still be growing today — relevant to siting lunar bases. A Soil Map for Mars University of Sydney PhD student Daniel Irving and Prof. Alex McBratney (Catena 275) classify almost 800 million Martian locations into 10 realms, 100 assemblages and 2,000 forms of 'areths', mapping 92% of the planet. Top candidate for plant growth, Nohibareth (score 0.93; ~72% clay, pH 6.8), covers 0.14% of the surface around Tharsis, Arabia Terra and Elysium. Candidates for study, not greenhouse sites; perchlorate and nitrogen not yet included. Euclid Finds Its First Comet ESA's Euclid discovered C/2026 S1 (Euclid) in Deep Field North images from 16–24 September, flagged by Mikko Pöntinen's moving-object software and confirmed by the Minor Planet Center on 8 October. ~1.3 billion km away on a steep, thousands-of-years orbit. Uranus and Neptune: Cousins, Not Twins Briand, Hue, Mousis, Cavalié et al. (A&A 714, A364) use upper-tropospheric carbon monoxide, including ALMA data, to infer deep oxygen: Uranus ~47–177× protosolar, Neptune ~182–342×. Contrasting C/O ratios suggest Neptune's building blocks formed closer to the Sun. Accepted version online since late August. Quick hits MMX launched 04:41:03 JST 20 Oct on H3 F10; separation ~71 min 13 s; JAXA confirms the spacecraft is operating normally. Roman's Wide Field Instrument focused to 63 nm RMS against ~90 nm required. Artemis II heat shield: 9 char-loss spots vs 103 on Artemis I. Hera's BRM-2 burn Thursday 22 October. Skywatch Orionids peak 21–22 Oct — watch between moonset and dawn (moonset Thu morning: 03:38 Sydney, 03:22 LA, 03:12 NY, 02:49 London). Mercury 16.5° up at civil dusk from Sydney. Venus at inferior conjunction ~24 Oct. Moon ~6° from Saturn 24 Oct. Full Moon 26 Oct 04:11 UTC. UK clocks go back 25 Oct, US on 1 Nov. Always use ISO 12312-2 certified filters for any solar viewing. Sources · Watters et al. — Thrust Faulting and the Late-stage Contraction of the Moon (PSJ, 14 Oct 2026) — https://doi.org/10.3847/PSJ/ae9eae · Smithsonian NASM — New Study Reveals How Much the Moon Is Shrinking — https://airandspace.si.edu/newsroom/press-releases/new-study-reveals-how-much-moon-shrinking · University of Sydney — Sydney student creates first map of Martian soils — https://www.sydney.edu.au/news-opinion/news/2026/10/16/sydney-student-creates-first-map-of-martian-soils.html · McBratney, Irving et al. — Areths and PPACS (Catena 275) — https://doi.org/10.1016/j.catena.2026.110649 · ESA — Euclid discovers new comet — https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_discovers_new_comet · SwRI — New ideas about origins of Uranus, Neptune — https://www.swri.org/newsroom/press-releases/swri-staff-contribute-new-ideas-about-origins-of-uranus-neptune · Briand et al. — Contrasting C/O ratios in Uranus and Neptune (A&A 714, A364) — https://doi.org/10.1051/0004-6361/202660770 · JAXA — Launch result of MMX aboard H3 F10 — https://global.jaxa.jp/press/2026/10/20261020-1_e.html · NASA — Roman team checks out main instrument, sharpens focus — https://science.nasa.gov/missions/roman-space-telescope/ · NASA — Rigorous analysis confirms Artemis II heat shield performance — https://www.nasa.gov/missions/artemis/artemis-2/rigorous-analysis-confirms-nasas-artemis-ii-heat-shield-performance/
MMX: A Round Trip to Phobos JAXA's Martian Moons eXploration mission launched on schedule on H3 Flight No. 10 at 04:41:03 JST on 20 October 2026 (19:41 UTC 19 Oct; 06:41 AEDT Tue; 15:41 EDT / 12:41 PDT / 20:41 BST Mon). Mars orbit August 2027, Phobos quasi-satellite orbit from September 2027, Idefix rover (CNES/DLR) release early 2029, landing and sampling 2030, and at least 10 g of Phobos returned in 2031 to South Australia. Eleven science instruments including NASA's MEGANE. The aim: settle whether Phobos and Deimos are captured asteroids or debris from a giant impact on Mars. Half a Giant Mirror ESO reports that nearly 500 of the ELT's primary-mirror segments are now at Paranal — more than half of the 931 being made (798 plus 133 spares for continual recoating). Safran Reosc is finishing a segment a day and the last one is in production. The ELT is more than 75% complete, with first observations with scientific instruments planned for late 2030. The Window That Closes Carr, Cen and colleagues (Nature Astronomy, 15 Oct 2026) used Hubble/COS spectra of six matched local starbursts to show ionising light escapes most in the first few million years, before supernova-driven winds load the outflow with neutral gas and shut it down. Escape fractions fall from ~21% (mean age ~2.7 Myr) to under 0.4% (~5.4 Myr). Preprint first posted October 2025. The Treble Clef Rises Again Botteon et al. (A&A; NASA/Chandra release 14 Oct) show VLSS J0318.9+5755, behind the Milky Way's plane, is a radio phoenix in a merging cluster at z ≈ 0.117: an old black-hole outburst re-lit by a cluster collision a few hundred million years ago. Spectral index above 4 between 400 and 650 MHz; electrons ~190–200 Myr old. Preprint from July. Quick hits Hera's 93-minute BRM-1 confirmed within parameters; BRM-2 on Thursday 22 October. Sentinel-3C's first images and altimetry. Swift: no NASA re-entry date yet. Skywatch Full Moon 26 Oct 04:11 UTC. Orionids peak 21–22 Oct: go after moonset (03:38 Sydney, 03:22 LA, 03:12 NY, 02:49 London on the 22nd). Mercury 17° up at civil dusk from Sydney (21 Oct). Venus inferior conjunction ~24 Oct. Moon ~6° from Saturn ~24 Oct. Mars–Jupiter 10.8° → 8.0° pre-dawn. Always use ISO 12312-2 certified filters for any solar viewing. Sources · JAXA — MMX launch on H3 F10 — https://mmx-news.isas.jaxa.jp/?p=2753 · ESA — Mars moon lander set to launch on 19 October — https://www.esa.int/Science_Exploration/Space_Science/Mars_moon_lander_set_to_launch_on_19_October · Australian Space Agency — MMX sample return — https://www.space.gov.au/node/950 · ESO ann26009 — More than half of the ELT's giant mirror is now in Chile — https://www.eso.org/public/announcements/ann26009/ · Carr et al. — arXiv 2510.21197 (Nature Astronomy, 15 Oct 2026) — https://arxiv.org/abs/2510.21197 · NASA — Chandra breaks down Treble Clef's galaxy cluster collision — https://science.nasa.gov/missions/chandra/nasas-chandra-breaks-down-treble-clefs-galaxy-cluster-collision/ · Botteon et al. — arXiv 2607.06659 — https://arxiv.org/abs/2607.06659 · ESA — Sentinel-3C returns its first views of Earth — https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-3/Sentinel-3C_returns_its_first_views_of_Earth · ESA Hera on X — BRM-1 confirmed — https://x.com/ESA_Hera · NASA — Lessons learned from the Swift boost mission — https://science.nasa.gov/missions/swift/nasa-highlights-lessons-learned-from-swift-boost-mission/
Show notes Time Lets Go of the Sky On 15 October 2026 the 28th General Conference on Weights and Measures in Versailles adopted Resolution 5: UTC becomes continuous on 20 May 2027, ending leap seconds, with the UTC–UT1 gap allowed to reach one hour. The driver: a growing chance (about 30% by 2035) of a first-ever negative leap second. Resolution 6 starts work on an international lunar reference time scale traceable to UTC; Resolution 4 prepares an optical-clock redefinition of the second for 2030. Earth's rotation (UT1) is still measured — by VLBI, with Australia's AuScope dishes part of the network. The Week That Was WISE 0855's changing water clouds (JWST); Hera's 93-minute braking burn; Artemis II's five lunar impact flashes; UCL questions the chemical evidence for hypernovae; the Arsia Mons cloud needs ice from nothing; the first green star. Also: ZTF J0440+2325, Meteor 2-7, Juno's crumpled magnetodisk, WASP-17 b, two planetary families, and new Magellanic Cloud pulsars from the Parkes archive. Skywatch First quarter Mon 19 Oct 03:12 AEDT (16:12 UTC Sun). Mercury 24° up at sunset from Sydney vs 10° LA, 7° NY, 3° London. Venus gone from northern evening skies; inferior conjunction ~03:00 UTC Sat 24 Oct. Saturn all evening, rings ~7° open. Orionids peak 21–22 Oct; Moon sets ~03:00–03:40 local, radiant 39–70° up at 04:30. Mars–Jupiter 11.5° apart, 1.2° on 16 Nov. AR4551 beta-gamma-delta. Solar safety: ISO 12312-2 filters only. Sources · BIPM — Resolutions adopted at the 28th CGPM: https://www.bipm.org/en/-/cgpm-2026-resolutions-adopted · BIPM — Resolution 5 (2026): https://www.bipm.org/en/cgpm-2026/resolution-5 · BIPM — Statement by the CCTF President, 15 Oct 2026: https://www.bipm.org/documents/d/guest/statement-cctf-president-cgpm-2026 · AuScope VLBI array (Lovell et al.): https://arxiv.org/abs/1304.3213 · ESA — Braking news! Hera: https://www.esa.int/Space_Safety/Hera/Braking_news!_Time_for_ESA_s_Hera_asteroid_mission_to_go_slow · JAXA — MMX launch schedule: https://global.jaxa.jp/press/2026/08/20260820-1_e.html · EarthSky — Sun news, AR4551 (16 Oct): https://earthsky.org/sun/sun-news-activity-solar-flare-cme-aurora-updates/ · Week That Was sources: see S05E202–S05E206 show notes.