first_imgAsteroids should not be so active. This one was, and is.The Dawn spacecraft is winding down its mission. It orbited the two largest asteroids (or dwarf planets, depending on which astronomer you ask), Vesta and Ceres. Both turned out to be surprisingly dynamic for small bodies that should have lost their internal heat long ago. Short-lived radionuclides and gravitational potential energy can heat a body for some time, but not for billions of years. Tidal flexing can pump energy into a body, but when it runs out of volatiles, it can only melt and re-erupt the same material over and over. The Dawn targets, especially Ceres, defy the old ages assumed for them.Dawn Finds Possible Ancient Ocean Remnants at Ceres (NASA Jet Propulsion Laboratory). This press release states what should be very surprising to long-age believers. It’s not that they are unable to explain it away within their belief system, but “recent geologic activity” points to a problem with that belief:The Dawn team found that Ceres’ crust is a mixture of ice, salts and hydrated materials that were subjected to past and possibly recent geologic activity, and that this crust represents most of that ancient ocean. The second study builds off the first and suggests there is a softer, easily deformable layer beneath Ceres’ rigid surface crust, which could be the signature of residual liquid left over from the ocean, too.Giant Ice Volcanoes Once Covered Dwarf Planet Ceres ( Amidst the bluffing about long ages, Charles Q. Choi mentions in passing that an ice volcano on Ceres is much younger than the age of the solar system—like 5% as old. What happened to keep this relatively tiny world active enough to erupt volatiles for 95% of its assumed age?Based on the number and size of meteor craters that Ahuna Mons has engulfed and the estimated rate of meteor strikes that Ceres has experienced, prior work suggested that Ahuna Mons is at most 240 million years old. (Like the rest of the solar system, Ceres itself formed about 4.56 billion years ago.)Synthesis of the special issue: The formation and evolution of Ceres’ Occator crater (Icarus). The eminent planetary science journal Icarus devoted a special issue to a crater on Ceres that early on caught scientists’ eyes: a large crater named Occator with bright spots in its center. One of the highlights: “Ceres is an active world where brines have been mobile in the recent geologic past.” The features are “geologically young,” the Abstract points out.Ceres bright spots (faculae) in Occator CraterPost-Impact Thermal Structure and Cooling Timescales of Occator Crater on Asteroid 1 Ceres (Icarus). Impacts to the rescue! This paper explains some hydrothermal structures in the crater as short-lived responses to impacts that exposed bright material. Old-age planetary scientists love to use impacts to cover for young surface features, but after awhile, that story seems too improbably convenient. The authors consider impacts a “viable mechanism” to explain faculae (irregular bright patches) around the Occator crater, “with the proviso that the faculae formed within a relatively short time window after the crater itself formed.” But the story presumes “a deep subsurface volatile reservoir.” Why is that there after billions of years? If the impacts happened early in its history, the faculae should have dimmed by space weathering long ago.Ice volcano activity on dwarf planet Ceres (Science Daily). This press release from the University of Arizona puts the facts into easily understandable form. UA planetary scientist Michael Sori uses pithy analogies:“We found that one volcano forms every 50 million years,” Sori said.This amounts to an average of more than 13,000 cubic yards of cryovolcanic material each year — enough to fill a movie theater or four Olympic-sized swimming pools.The eruptions are tamer and not as voluminous as those on Earth, Sori points out, but Ceres is much smaller than the Earth. That a small body like this should be active now at all is the issue. Sori is the lead author of a paper in Nature Astronomy about this. It says, “Ceres has experienced cryovolcanism throughout its geologic history.” For 4.5 billion years at this average eruption rate, simple math (4,500,000,000 years x 13,000 cubic yards per year) would force them believe that Ceres has barfed almost 60 trillion cubic yards of material over its lifetime. Is that reasonable? That equals 11,000 cubic miles on a body much smaller than our moon.Ring‐Mold Craters on Ceres: Evidence for Shallow Subsurface Water Ice Sources (Geophysical Research Letters). Ring-mold craters are a special kind of impact crater that implies shallow ice under the impact site. They have been postulated at Mars, and now are seen within the Occator Crater as well. The authors conclude that these craters are “a sign of water ice reservoirs in the subsurface,” another indication of abundant volatile materials that are still present under a shallow crust. Should these ices be there after billions of years?Water ice! Ceres might be habitable! Thus the authors of that last paper, with their hydrobioscopy reflex kicking into action, change the subject. Instead of fretting over how this body stayed so warm to be “geologically young,” they leap into speculation that ring-mold craters might be a sign of habitable planets. Why? Water must be there! Life can’t be far behind!Perceptive readers must be alert to such tactics, just like they look for tricks of misdirection magicians use to make you believe in miracles. (Visited 472 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

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