NASA’s rover has spotted a phenomenon that scientists have lost hope of seeing on Mars.
On Earth, when conditions are just right, ice crystals in the atmosphere can distort sunlight to create the appearance of a bright spot on either side. the sun, or an aura you ring. Scientists have long believed that a similar optical illusion could occur on other planets, too. But despite decades of robotic explorers on the surface Mars Taking countless thousands of photos of the sky, scientists have seen no sign of the sun’s corona.
Until December 15, 2021, that is.
“perseverance It really surprised us with some of the images we got in December,” Mark Lemon, a planetary scientist at the Space Science Institute, a nonprofit research institute in Boulder, told Space.com.
“I’ve been involved in this for a long time, and we’ve been looking for halos everywhere and in a lot of pictures,” he added. “I looked at that and thought, ‘I’m going to have a hard time finding an explanation for that. “Because it was all a false alarm, and it’s so much like corona that I thought it would be a lot of work to figure out what was really going on.”
ice in the sky
even so a landThe appearance of a corona around the sun requires special conditions.
The sunlight should encounter the pencil-like ice crystals flowing through it Earth’s atmosphere, usually in the form of very high soft inferior clouds. The hexagonal structure of the water ice crystals determines the size of the corona, at 22 degrees from the sun, or about the width of two fists held along the arms.
If the crystals are too small or the clouds are too dense or too warm, then the Sun is alone – without a halo. Crystals of other chemicals in the atmosphere can have a similar effect, but the crystal structure of each chemical will create a halo of distinct size. “It’s like a fingerprint that tells you what the element was, the shape of the particle, and then a little bit about the size,” Lemon said.
Carbon dioxide is more abundant in Mars atmosphere of water, so the team examined how much dry ice halo crystals could form, but that calculation didn’t match what it saw as perseverance.
Nor did Lemon and his colleagues examine anything else.
They investigated whether the camera itself created the bright ring, but the feature did not match these artifacts in other images. Moreover, the strange image was part of a series of five images taken by Perseverance across the sky; The sun and the corona both appeared in three, each time in a different place in the frame.
It certainly wasn’t dust. “We have a lot of images that show you what kind of features you get from dust in the sky, and we know for sure you’re not going to get an aura from that,” Lemon, now lead author on the paper describing the work, said. “There were really no other candidates.”
Strange Atmosphere Study
Scientists have spent decades studying the atmosphere of Mars, both as a way to understand Mars and also as a way to understand the atmosphere in general.
“Every planet with an atmosphere is a laboratory for how the atmosphere works,” Lemon said. “We can’t fully understand something by looking at one example of it and then trying to figure out what it would be like if things were a little different.”
And while the fleet of orbiters that has orbited the Red Planet for decades has excelled at collecting atmospheric data, scientists need more: a view from the surface. “Everything we can know about the atmosphere anywhere on Mars — looking at clouds, looking at dust storms, looking at dust devils — we have to check how it looks there on the surface, where the weather is important,” Lemon said. .
This is why Perseverance, like the Mars landing missions and the rover that preceded it, is equipped with small weather stationWhy don’t scientists keep the rover’s cameras pointed at Earth firmly? Perseverance also carries a SkyCam, a camera that just looks and takes pictures on every Mars or Sol day. Several images from the rover’s navigation camera also show a patch of sky. (NavCam took the photo where Lemmon identified the aura.)
And the presence of a halo around the sun informs scientists about the Martian atmosphere, especially since ice crystals can grow larger than any ice crystals that scientists have measured directly. But with only one example at hand, Lemon is reluctant to draw any exhaustive conclusions.
“I think the most important thing for us is that we’ve learned that it’s something that can happen,” he said. “We need to look more seriously at that in perseverance, in that location.”
In particular, Lemmon is eager for the next time Mars enters the same season of December 2021 observations, what scientists call the Ogian cloud belt season, which will then roll when the Northern Hemisphere is in the summer of next year. “When it comes back up again, we’ll spend the whole season looking for that and getting ready to follow up and trying to investigate in more detail if we see anything,” Lemon said.
The search is described in paper (Opens in a new tab) Published September 3 in Geophysical Research Letters.
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