A recent study suggests that deposits Ice cube In the pits of CeriseHe Asteroid Very large The Solar SystemMust have accumulated in the last 6,000 years or less.
Deposits Ice cube en craters de observed CeriseHe Asteroid Very large The Solar SystemThe most recent: less than 6,000 years old in a 4-billion-year-old body.
This is a decision A new study published in The Planetary Science JournalIt looked at these permanently dark craters and their deposits in 2016 based on data collected by NASA's Dawn mission. Ice cube Some of them are bright.
“The 2016 discovery raised a puzzle: many craters in the polar regions Cerise They remain in the shade throughout the year (in which Cerise lasting 4.6 Earth years) and therefore very cold, but only a few of them have deposits. Ice cubePlanetary Science Institute (PSI) scientist and lead author of the study, Norbert Schorhofer, said in a statement.
“Soon, another discovery provided a clue as to why: the axis of rotation Cerise It oscillates back and forth every 24,000 years due to the tides of the Sun and Jupiter. When the axial gradient is high and the seasons are strong, only a few craters remain in shade throughout the year, and these are craters. Ice cube brilliant”.
To determine the size of the thousands of shadows cast within craters years ago, scientists create digital elevation maps and then perform ray tracing calculations on them to theoretically reconstruct the shadows cast on the crater floor. Results are only reliable based on digital format samples. It must be taken into account that the bases of these ditches are always in the shade, so it is not easy to measure their depth.
The Dawn spacecraft had a highly sensitive camera that could detect features at the bottom of the shadow crater. Stereo images of sunlit areas are often used to create digital elevation maps of sunlit areas, but creating an elevation map of shaded terrain is a rarely taken up challenge.
Improved elevation maps
As part of the new study, PSI scientist Robert Gaskell developed a new technique to reconstruct heights even in the shadow areas of a pair of stereo images. These enhanced elevation maps are then used to trace rays to predict the extent of cooler, permanently shaded areas.
These precise maps yielded a surprising result: when Cerise It reaches its maximum axial tilt, which last occurred about 14,000 years ago, without cratering Cerise Perpetually in the shadows Ice cube In them it must have been quickly sublimated into space.
“That leaves only one plausible explanation: deposits Ice cube They must have been created very recently. The results suggest that all these deposits Ice cube They must have accumulated in the last 6,000 years or less. With that in mind Cerise “Over 4 billion years old, that's a remarkably young age,” Schorkofer said.
A map of the north polar region of Ceres. Colored areas are areas that are constantly in shade during the Ceres year and are therefore very cold.Fuente: Europa Press
“Cerise It is a rich material Ice cubeBut almost none of these exist Ice cube exposed to the surface. Only the so-called polar craters and some small areas outside the polar regions are exposed Ice cube. However, the Ice cube As PSI scientist Tom Prettyman and his team discovered in 2017, it's ubiquitous at shallow depths, so even a small dry impact can evaporate some of it. Ice cube” Schorkofer explained.
“An asteroid may have collided Cerise About 6,000 years ago, it created a temporary watery atmosphere. Once the water atmosphere is formed, the Ice cube It condensed in the cold polar craters, forming the bright deposits we still see today. Alternatively, deposits Ice cube Probably formed by material-laden avalanches Ice cube. This is Ice cube Then it survives only in cool, shady ditches. “In any case, these events are very recent on an astronomical time scale.”
Other types of ice
The study also explored the possibilities of other categories Ice cubeBesides Ice cube Water can get trapped in these unusual pits Cerise. On our moon, some parts of the polar craters are very cold Ice cube CO2 and some other chemical species persist in them for billions of years. Cerise It's far from the Sun, so you'd expect its polar craters to be cooler than those on the Moon.
Schorghofer calculated the temperature inside the polar trenches Cerise, something that has never been done before. The answer was surprising: these craters are cold enough to hold water ice, but too hot to hold other common types of ice. Ice cube.
Two circumstances contribute to this. First, the tilt of the axis Cerise, currently 4 degrees, is greater than the Moon's 1.5 degree inclination, so more of the crater rims are illuminated by the Sun and more light is scattered on the crater floor. In second place, Cerise Unlike the Moon, there are no permanently shadowed craters very close to the North Pole, where there is a crater almost at the South Pole. For these reasons, the temperature is not low Cerise Like parts of the lunar surface.
(with information from Europa Press)
