The Orbital Index

• Based on tantalizing evidence returned from the Moon nearside by Chang'e 5, volcanic activity may have occurred there far more recently than previously thought: 120 million years ago vs 2 billion years ago.
• Meanwhile, initial analysis of Chang’e-6’s lunar farside samples provides its own data, via isotope ratios, on lunar volcanism stretching over billions of years in the Moon’s past, with grains found dating from erupted lavas during a period ranging from 2.83 to 4.2 billion years ago (paper, paper).
• Modeling of how impact craters on Titan appear to quickly relax and become shallow after impact led researchers to suggest a 10 km thick crust composed of solid methane clathrate, a compound of methane trapped in a water ice lattice (paper). Hopefully, Dragonfly will teach us more.
• Considering the orbits of more than 35,000 near-Earth asteroids, researchers found some that made close approaches to both Earth and either Mars or Venus. They suggest that astronauts could use these objects as vehicles (and their materials as shielding) during an interplanetary transfer (paper). Perhaps one could be converted into an Earth-Mars cycler?
• Much of Mars’s ancient atmosphere may be locked up in smectite clay, a porous mineral formed by the weathering of volcanic rocks, that can trap gasses. One paper suggests that as much as 80% of Mars’s ancient atmosphere is now trapped in this clay, which could also contain methane and carbon dioxide.
• The giant heart-shaped feature on Pluto composed of nitrogen ice, which was observed by New Horizons in 2015, appears (via simulation) to be the result of a slow but massive oblique-angle collision early in Pluto’s life. The same simulational work also suggests that there is likely no subsurface ocean on Pluto (paper) after all.

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NG-1, ready for launch. New Glenn is now fully stacked and stands at KSC’s LC-36 pad ahead of its maiden launch, potentially before the end of the year. The mission, NG-1 or So You’re Telling Me There’s A Chance, will fly a fixed demonstrator of the Blue Ring OTV after NASA pulled ESCAPADE from the mission due to launch window concerns. "The [Blue Ring] demonstrator includes a communications array, power systems, and a flight computer affixed to a secondary payload adapter ring. The pathfinder will validate Blue Ring’s communications capabilities from orbit to ground. […] The pathfinder will remain onboard New Glenn’s second stage for the duration of an expected six-hour mission."  The first stage may also attempt a landing, although success is definitely not expected. Blue static-fired the GS2 second stage in September and cryo-tested GS1 earlier this month. The 98-meter rocket is now “ready for launch this year,” but the company has yet to provide a launch date, so the timeline is looking tight—they’re currently awaiting regulatory approval for the final hot fire and then launch.

Starship Block 2 rolls out, and static fires. The first Block 2 version of Starship, Ship 33, recently rolled out for testing and completed its first static fire test. It will be stacked on Booster 14 before it is targeted to complete the first flight of the Block 2 reusable upper stage in January (currently NET January 11, but could slip to later in the month or early February). This upgraded Ship adds catch hardware for potential use on Flight 8 and an additional ring, making it 1.8 m taller and now totaling 124.4 m when eventually stacked on top of Booster 14. The added height will allow it to pack 300 tons more propellant. Block 2 shrinks the payload section height of the stage but makes up for it with better use of internal space in the nose cone, meaning there will only be a small reduction in usable volume—in fact, Block 2 should increase the number of carryable Starlink V3 sats from ~40 to 54 per launch. The upgrade also moves the forward flaps to 140° apart (vs 180° on previous vehicles), putting them out of the main plasma stream during reentry and significantly reducing the number of required glued-on tiles (which are less reliable and were previously used around section and dome welds).

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• What we thought we knew about type Ia supernovae may be wrong. White dwarfs accreting mass from a companion until crossing the Chandrasekhar limit is out; surface novas resulting in compression waves that trigger core detonation are in (paper). This could explain why type Ia supernovae have varying brightness, their high observed occurrence even with few white dwarfs thought to be close to the Chandrasekhar mass limit, and even explain an origin for some hypervelocity stars.
• “Einstein and his peers were 'irrationally resistant' to black holes. This illustrated story explores why.”
• Here’s a cozy video for your TV over the holidays from NASA: 8 hours of four RS-25 engines firing away cheerily.
• We’ve linked to them before, but all of chemist Derek Lowe’s Things I Won't Work With articles are fantastic. See, for example, his article on the higher states of bromine, or the one on mild-mannered chlorine trifluoride, which will happily set sand on fire. Or, this article on dioxygen difluoride, with the telling chemical formula of FOOF, which is made by heating elemental fluorine, where “at seven hundred freaking degrees, fluorine starts to dissociate into monoatomic radicals, thereby losing its gentle and forgiving nature. But that’s how you get it to react with oxygen to make a product that’s worse in pretty much every way.”