Comments on: August 11, 2025 Quick space links

By: Michael McNeil

Michael McNeil — Tue, 12 Aug 2025 22:15:30 +0000

On the contrary, Venus' atmosphere—like Earth's—thick though the former is compared with the latter, would nonetheless provide essentially no protection against the scale of impacts of the Late Heavy Bombardment (and occasionally after), such as one sees on the Moon in its maria and great craters like Tycho and Copernicus. Beyond that, it's the thick, unbroken (unfragmented into “plates”) crust of a “stagnant-lid” world that holds in the mantle and core's heat—leading to eventual crustal overturn—not the relatively mild heat and temperature of the present venusian surface, which is wholly insufficient to cause such a geological cataclysm. (It might happen on Mars too someday, whose present core and mantle—contrary to myth—is considerably more molten than Earth's, which pace people's intuition is why Mars lacks a planetary magnetic field.)

By: Jeff Wright

Jeff Wright — Tue, 12 Aug 2025 14:14:46 +0000

To Michael,

I wonder if Venus had CO2 that far back –which held heat in to help cause that overturn.

No life, no carbonate rock-no chance.

A dense, early atmosphere would also prevent all but the largest craters anyway.

By: Richard M

Richard M — Tue, 12 Aug 2025 13:58:27 +0000

Shocking news from Russia: Luna 27 has run into delays.

The launch of the Luna 27A spacecraft has been moved from 2028 to 2029, while Luna 27B is due to be launched in 2030, academic supervisor of the Russian Academy of Sciences’ Space Research Institute, scientific director of the Russian lunar program’s first stage, Russian Academy of Sciences member Lev Zelyony told Interfax.

“These launches are always moved. This time to 2029, that’s the real date,” Zelyony said in reply to when Luna 27A might be launched.

https://interfax.com/newsroom/top-stories/113182/

By: Questioner

Questioner — Tue, 12 Aug 2025 06:55:46 +0000

Preliminary indications of the scarcity of ancient impact craters on Venus actually came before NASA’s Magellan mission, from the Soviet orbiters Venera 15 and Venera 16, launched in 1983. Operating in near-polar orbits, these spacecraft used synthetic aperture radar to map roughly 25% of the Venusian surface, mainly in the high northern latitudes (north of about 30°). With a spatial resolution of about 1–2 km, their data were far less detailed than Magellan’s later 120–300 m resolution, but they were sufficient to reveal large-scale geological features, extensive volcanic plains, and an apparent absence of heavily cratered ancient terrain.

However, it was Magellan (1990–1994) that provided the global confirmation and temporal context for this observation. By mapping about 98% of the surface at much higher resolution, Magellan demonstrated that the paucity of old craters was a planet-wide phenomenon and not confined to the regions imaged by the Soviet orbiters, thus strengthening the hypothesis of a global resurfacing event about 500 million years ago.

By: Michael McNeil

Michael McNeil — Tue, 12 Aug 2025 01:06:27 +0000

Magellan also revealed a dearth of antique craters on Venus. But it, as with all the other terrestrial rocky worlds of the inner solar system (including the moon), must have been pummeled by many gigantic not to speak of lesser impacts during (e.g.) the solar system's “Late Heavy Bombardment” era of about 4 billion years ago. The lack of any such old craters (and only a relatively few new) on the venusian surface shows that—apparently as a result of internal heat buildup due to Venus' geological so-called “stagnant lid” tectonics—the planet's surface got thoroughly resurfaced around half a billion years back, in a stupendously catastrophic event whereby the planet's entire crust basically turned over and melted, thereafter resolidifying again with the (since lightly cratered) surface that we see. This wholly geological cataclysm—not a mythical, climatological, “runaway greenhouse effect”—appears to be what propelled Venus' entire sequestered stock of crustal carbon (if any was still in the ground at that point—as these planet-wide disasters may have occurred [up to 6-8 times] before) into the atmosphere as CO2. Thus the dangers of “stagnant-lid” tectonics for worlds (not just planets) in our universe.