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For the first time, scientists have spotted large patches of water ice on the surface of a comet, thanks to instruments aboard the European Space Agency's Rosetta orbiter.
The finding, published Wednesday in Nature, solves a long-standing mystery about water ice in comets. Scientists already knew that the coma - the expansive cloud of gas surrounding the comet's nucleus - is dominated by water molecules. They also knew that water ice is one of the main components of the nucleus. But until now, traces of water ice on the surface of the comet had been difficult to detect.
"First, not finding ice was a surprise; now, finding it is a surprise," said Murthy Gudipati a planetary scientist at the Jet Propulsion Laboratory in La Canada Flintridge, Calif., and an author on the paper. "It is exciting because now we are starting to understand the upper dynamic layers of the comet and how they evolved."
The surface of comet 67P, like most comets, is primarily covered by dark organic materials that appear almost black. That's because as comets fly toward the sun, they are exposed to warm temperatures that cause volatiles like water ice on their surface to sublimate - or go directly from solid to gas.
What remains on the crust are what are known as refractory materials. These include silicates similar to rocks, sand and dirt on Earth and carbonaceous materials. Because these materials do not sublimate, the comet's surface becomes increasingly organic and silicate rich over time, said Michael Combi, who studies comets at the University of Michigan and co-authored the paper.
The surface water ice on comet 67P Churyumov-Gerasimenko was discovered in two places several tens of feet across in a region known as Imhotep, on the bottom part of the main lobe of the comet. It was found using the VIRTIS infrared instrument, which scanned the area looking for water ice spectra signals not long after the Rosetta orbiter caught up with 67P in the fall of 2014.
In both cases the ice appeared on cliff walls and debris falls, and appeared as noticeably bright patches in visible light.
"It looked like there was a breakage, or something fell down on the surface of the comet, and a large, new inside area that had water ice was exposed," Gudipati said. "Although we knew water ice had to be in the nucleus, this was our first direct detection of that interior ice."
Further analysis of the VIRTIS data revealed the water ice grains in the newly exposed areas came in two different sizes.
The small grains that are in the micrometer range are likely associated with a thin layer of frost that forms as a function of the comet's rotation. As this region of the comet turns away from the sun, water ice condenses out of the coma and onto the nucleus, the authors wrote. During the "day" the water goes back into the coma.
The larger ice grains, which are a few millimeters across, probably have a more complex origin story, the authors said. One possibility is that water ice in the shallow subsurface of the comet might vaporize as the comet flies closer to the sun, and then move downward into the cooler lower surface lawyers where it condenses again in the voids.
"Keep in mind that comets are very porous, like cotton candy," Gudipati said. "Seventy percent of this comet is a void, and because of that, the heat from the surface does not go that deep."
It should be noted that water ice made up just a small percentage of the material scanned by VIRTIS, suggesting that it is mixed in with the refractory materials in the upper layers of the comet.
The research team, lead by Gianrico Filacchione of the Institute for Space Astrophysics and Planetology in Rome, is now analyzing data captured by the same instrument later in the mission to see how the amount of ice exposed on the surface changed as the comet zoomed closer to the sun.
In the meantime, Gudipati said the new findings have already given comet scientists a lot to work with.
"We knew water ice made up the majority of the comet, but we didn't know how deep or in what condition it was," he said. "This shows that it not very deep at all - perhaps just a few feet beneath the surface." [Reply]
Paleontologists searching far and wide in Tunisia made a discovery of massive proportions: the world's largest sea-dwelling crocodile, previously unknown to science.
This prehistoric crocodile is believed to have measured more than 30 feet long and weighed three tons. The skull alone is more than five feet long. Researchers named the new species the Machimosaurus rex and described their findings this week in the journal Cretaceous Research.
"Massive" is how lead author Federico Fanti of the University of Bologna described the crocodile. "It's just big. It's almost the size of a bus."
[Fossils might reveal the colors of ancient critters]
He added: "It definitely was at the top of the food chain at the time, at least in this particular locality."
Fanti and his team, supported by National Geographic Society Committee for Research and Exploration, found the fossils buried below just a few inches of sediment on the edge of the Sahara Desert in Tunisia, a country rich with fossils.
"This one was a big surprise, not because we found fossils, but we found beautiful ones," Fanti said. The skull took two days to uncover, and the "rest of the body was just lying there."
[125 million-year-old fossil shows remarkably preserved organs and hair]
This particular site was likely home to a lagoon that faced the ocean. Researchers also found the remains of fish and turtles that they still need to identify.
The M. rex was "absolutely capable" of hunting in the water and could have been an ambush predator or a scavenger, Fanti said. Comparing M. rex to other crocodiles that also have big heads and short teeth suggests the M. rex had "a very incredibly powerful bite force" that would let it crush its food, Fanti said. Turtles, for instance, would have been an ideal meal.
This discovery is groundbreaking for reasons other than girth; Fanti said this finding undermines previous theories about prehistoric life. The group of crocodiles that M. rex belongs to was considered to have gone extinct about 150 million years ago at the end of the Jurassic Period, but this particular M. rex lived about 130 million years ago.
Previous studies pointed to "a big global extinction between the Jurassic and Cretaceous periods that wiped out a number of marine reptiles, including this group of reptiles," Fanti said. M. rex lived way after this "hypothesized mass extinction."
"That's leading us to consider the mass extinction theory is wrong and that we should better understand what's going on at the end of the Jurassic period," Fanti said. [Reply]
It's definitely larger than a modern salt water croc, but it's not really that much larger. Well, it is, but it's not stupendously larger. 50 percent longer than the largest modern ones and 2 to 3 times the weight.
Originally Posted by Fish:
So we have nuclear powered robots buzzing millions of miles away from earth taking HD photos of water and ice spewing from comets.
For the first time, scientists have spotted large patches of water ice on the surface of a comet, thanks to instruments aboard the European Space Agency's Rosetta orbiter.
The finding, published Wednesday in Nature, solves a long-standing mystery about water ice in comets. Scientists already knew that the coma - the expansive cloud of gas surrounding the comet's nucleus - is dominated by water molecules. They also knew that water ice is one of the main components of the nucleus. But until now, traces of water ice on the surface of the comet had been difficult to detect.
"First, not finding ice was a surprise; now, finding it is a surprise," said Murthy Gudipati a planetary scientist at the Jet Propulsion Laboratory in La Canada Flintridge, Calif., and an author on the paper. "It is exciting because now we are starting to understand the upper dynamic layers of the comet and how they evolved."
The surface of comet 67P, like most comets, is primarily covered by dark organic materials that appear almost black. That's because as comets fly toward the sun, they are exposed to warm temperatures that cause volatiles like water ice on their surface to sublimate - or go directly from solid to gas.
What remains on the crust are what are known as refractory materials. These include silicates similar to rocks, sand and dirt on Earth and carbonaceous materials. Because these materials do not sublimate, the comet's surface becomes increasingly organic and silicate rich over time, said Michael Combi, who studies comets at the University of Michigan and co-authored the paper.
The surface water ice on comet 67P Churyumov-Gerasimenko was discovered in two places several tens of feet across in a region known as Imhotep, on the bottom part of the main lobe of the comet. It was found using the VIRTIS infrared instrument, which scanned the area looking for water ice spectra signals not long after the Rosetta orbiter caught up with 67P in the fall of 2014.
In both cases the ice appeared on cliff walls and debris falls, and appeared as noticeably bright patches in visible light.
"It looked like there was a breakage, or something fell down on the surface of the comet, and a large, new inside area that had water ice was exposed," Gudipati said. "Although we knew water ice had to be in the nucleus, this was our first direct detection of that interior ice."
Further analysis of the VIRTIS data revealed the water ice grains in the newly exposed areas came in two different sizes.
The small grains that are in the micrometer range are likely associated with a thin layer of frost that forms as a function of the comet's rotation. As this region of the comet turns away from the sun, water ice condenses out of the coma and onto the nucleus, the authors wrote. During the "day" the water goes back into the coma.
The larger ice grains, which are a few millimeters across, probably have a more complex origin story, the authors said. One possibility is that water ice in the shallow subsurface of the comet might vaporize as the comet flies closer to the sun, and then move downward into the cooler lower surface lawyers where it condenses again in the voids.
"Keep in mind that comets are very porous, like cotton candy," Gudipati said. "Seventy percent of this comet is a void, and because of that, the heat from the surface does not go that deep."
It should be noted that water ice made up just a small percentage of the material scanned by VIRTIS, suggesting that it is mixed in with the refractory materials in the upper layers of the comet.
The research team, lead by Gianrico Filacchione of the Institute for Space Astrophysics and Planetology in Rome, is now analyzing data captured by the same instrument later in the mission to see how the amount of ice exposed on the surface changed as the comet zoomed closer to the sun.
In the meantime, Gudipati said the new findings have already given comet scientists a lot to work with.
"We knew water ice made up the majority of the comet, but we didn't know how deep or in what condition it was," he said. "This shows that it not very deep at all - perhaps just a few feet beneath the surface."
I'm too high to read this right now, but when i'm not, i'm going to totally fucking read the shit out of this. [Reply]
Originally Posted by Rain Man:
It's definitely larger than a modern salt water croc, but it's not really that much larger. Well, it is, but it's not stupendously larger. 50 percent longer than the largest modern ones and 2 to 3 times the weight.
