The dwarf planet Ceres has permanently shadowed regions in its polar regions, and these regions are interesting, similar to Mercury and the Moon. Ceres’ permanently shadowed regions were mapped by NASA’s Dawn spacecraft, and thanks to scattered sunlight, bright deposits were discovered in parts of the permanently shadowed regions. To understand more clearly the nature of Ceres’ cold-trapped ice deposits, researchers from the Planetary Science Institute and NASA’s Goddard Space Flight Center are investigating the nature of the crater, which forms a permanently shadowed region. An improved shape model was constructed.
A permanently shadowed region in the arctic region of Ceres. The color indicates the maximum inclination at which the position will be shaded throughout the trajectory. Image credit: Schorghofer other., doi: 10.3847/PSJ/ad3639.
“For Ceres, the story began in 2016, when the Dawn spacecraft, then orbiting around Ceres, glimpsed these permanently dark craters and saw bright ice deposits in some of them. “, said lead author and researcher Dr. Norbert Schorhofer. At the Planetary Science Institute.
“The 2016 discovery raised a mystery: many of the polar craters on Ceres are in shadow all year round, which lasts 4.6 Earth years on Ceres, so it remains extremely cold, but the ice Only a few of these craters hold deposits.”
“Soon, another discovery provided a clue as to why: Tides from the Sun and Jupiter cause Ceres’ axis of rotation to oscillate back and forth every 24,000 years.”
“When the Earth’s axial tilt is high and the seasons are strong, only a few craters remain in shadow throughout the year, and these craters contain bright ice deposits.”
To determine how big a shadow was inside the crater thousands of years ago, scientists created a digital elevation map and used it to perform ray-tracing calculations to cast images onto the crater’s floor. Theoretically reconstructs the shadows created by shadows.
The results are only as reliable as the digital shape model on which they are based. Note that the bottoms of these craters are always in shadow, so it is not easy to measure their depth.
NASA’s Dawn spacecraft has a very sensitive camera on board that was able to identify features on the shadowed crater floor.
Stereo images of sunny areas are often used to create digital elevation maps of sunny regions, but creating elevation maps of shaded terrain is a challenge that has rarely been addressed to date.
As part of their research, the authors developed a new technique to reconstruct heights even in shadowed parts of stereo image pairs.
These improved elevation maps can be used for ray tracing to predict the extent of cold, permanently shaded areas.
These more accurate maps yielded surprising results. The last time, about 14,000 years ago, when Ceres’ axial tilt reached its maximum, the crater on Ceres did not remain in shadow forever, and the ice within the crater quickly entered space. It must have sublimated.
“Then there is only one plausible explanation left: the ice deposits must have formed more recently,” Scholghofer said.
“The results suggest that all of these ice deposits were accumulated within the past 6,000 years.”
“That’s a surprisingly young age considering Ceres’ age is well over 4 billion years.”
“Ceres is an ice-rich body, but very little of this ice is exposed on the surface. The only exposed ice is in the aforementioned polar craters and a few small patches outside the polar regions. However, Ice is everywhere at shallow depths, so even small dry impactors can cause some of that ice to evaporate.”
“About 6,000 years ago, an asteroid fragment may have impacted Ceres, creating a temporary water atmosphere.”
“Once a water atmosphere was created, the ice would condense in the frigid crater, forming the bright deposits we still see today.”
“Alternatively, the ice deposits could have formed by an avalanche of ice-rich material. This ice would survive only within the cold, shaded crater.”
“In any case, these events are very recent on an astronomical time scale.”
The researchers also investigated the possibility that other types of ice besides water ice were trapped in these unusual craters on Ceres.
On our moon, some of the polar craters are so cold that even carbon dioxide ice and some other chemical species can remain inside them for billions of years.
Because Ceres is farther from the Sun, its polar craters are expected to be even colder than those on the Moon.
Scientists have calculated the temperature inside Ceres’ polar crater, something that has never been done before.
The answer was surprising. These craters are cold enough to hold water ice, but too warm to hold other common types of ice. Two circumstances contribute to this.
First, Ceres’s axial tilt is currently 4 degrees, higher than the Moon’s 1.5 degrees, allowing sunlight to hit more of the crater rim and scattering more light onto the crater floor.
Second, Ceres has no permanently shadowed craters in the immediate vicinity of its north pole, unlike the moon, which has one crater almost exactly at its south pole.
For these reasons, temperatures on Ceres are not as cold as on parts of the moon’s surface.
“Whatever the history of ice accumulation, it does not result from events much older than human civilization,” Dr. Scholghofer said.
of findings will appear in Planetary Science Journal.
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Norbert Schorghofer other. 2024. History of Ceres cold traps based on sophisticated geometric models. planet. Science. J 5(99); doi: 10.3847/PSJ/ad3639
Source: www.sci.news
