Pluto is one of the smallest planets in the solar system, and it's located very far away from the Sun, beyond the orbit of Neptune. It's one of the dwarf celestial bodies, having a diameter of only one fifth that of the Earth. But, unlike our planet, it's made almost entirely out of rock and ice, and features a surface temperature of minus 220 degrees Celsius, which means that it's very close to the temperature of deep space. Now, astronomers from the European Southern Observatory (ESO) have managed to get the first glances of how the atmosphere on the dwarf planet have come to be, as well as of what elements compose it.
Pluto completes one revolution around the Sun in roughly 248 years, during which time it travels a very long distance. At the point in its orbit when it's farthest from it, the atmosphere of the celestial body, made primarily of nitrogen, some methane and, probably, carbon monoxide, freezes over and falls to the ground. Once the planet enters a portion of its orbit that brings it closer to the Sun, the frozen matter on its surface sublimates and the atmosphere is restored again.
Thus far, scientists have only managed to assess the condition of the upper atmosphere on Pluto, through a process called stellar occultation, which involved looking at the planet while it passed in front of a background star. This has revealed the fact that the upper parts of the halo of gases that surround Pluto is about 50 degrees Celsius warmer than the surface, or minus 170 degrees Celsius.
But now, using ESO's CRyogenic InfraRed Echelle Spectrograph (CRIRES) instrument, on the Very Large Telescope Array, astronomers have succeeded in concluding that the lower atmosphere is also warmer than the surface, though admittedly a bit colder than the upper portion. Thus, the mean temperature of the entire gas cloud around the dwarf planet is of about minus 180 degrees Celsius.
“It is fascinating to think that with CRIRES we are able to precisely measure traces of a gas in an atmosphere 100 000 times more tenuous than the Earth's, on an object five times smaller than our planet and located at the edge of the Solar System. The combination of CRIRES and the VLT is almost like having an advanced atmospheric research satellite orbiting Pluto,” Hans-Ulrich Käufl, one of the co-authors of the new paper, says.
The analysis has also shown that methane is the second-most prevalent gas on the planet, after nitrogen. “We were able to show that these quantities of methane play a crucial role in the heating processes in the atmosphere and can explain the elevated atmospheric temperature,” the lead author of the new study, Emmanuel Lellouch, an astronomer at the Observatoire de Paris, in France, adds.
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