Astronomers have confirmed, for the first time, a trans-Neptunian object with a thin atmosphere, something previously thought to be unique to Pluto among similar objects.
Trans-Neptunian objects (TNOs) are small icy bodies that orbit the Sun beyond Neptune. in a Nature Astronomy article published today, researchers led by Ko Arimatsu from the National Astronomical Observatory of Japan describe (612533) 2002 XV93, a TNO with a very thin atmosphere. Arimatsu explained that trans-Neptunian objects are so cold and distant that scientists have long assumed they are largely immutable and inactive, which made Pluto stand out among them.
“Our result shows that even a much smaller object, only about 500 kilometers (311 miles) in diameter, can have an atmosphere, at least temporarily,” Arimatsu told Gizmodo. “Discoveries like this show that the outer Solar System may be more dynamic than we expected.” 2002
An unfortunate discovery
According to Arimatsu, the team did not directly image the atmosphere surrounding 2002 XV93. The discovery came from ground-based campaigns with contributions from professional and amateur astronomers at four different observatories in Japan. Specifically, the team captured a stellar occultationwhich is when a cosmic object in the solar system passes in front of a background star.
“If the object has no atmosphere, the starlight should disappear and reappear abruptly,” Arimatsu explained. “If it has an atmosphere, starlight can bend by refraction and change more gradually.”
When the team saw signs of the latter phenomenon, they set about analyzing the resulting light curves, testing three simplified models of atmospheric composition against previous research, according to the paper. As a result, the researchers concluded that atmospheric refraction better reflected the data.
Improbable worlds of ice and rocks
The findings challenge the conventional explanation of TNOs, which were generally thought to be too small to “retain an observable atmosphere” for long periods of time, Arimatsu said. In fact, according to the paper, “despite specific searches using stellar occultations,” no major TNO other than Pluto appeared to have a measurable atmosphere.
Planetary scientists are interested in finding these types of atmospheres because “they control how heat is transported, how surface ice evaporates or freezes, how material escapes into space, and how the surface evolves over time,” Arimatsu explained. Even if a TNO’s atmosphere is nowhere near Earth’s, understanding its presence allows scientists to better understand how volatile materials such as methane, nitrogen or carbon monoxide enter and exit the cosmic object, he added.
A solar system in motion
It is still unclear whether the object’s atmosphere is a temporary or permanent feature. This could be the subject of follow-up research into the origins of the atmosphere, he told Gizmodo. Does it come from cryovolcanic activity inside the TNO? Or did another small icy body collide with the object?
“If the atmosphere were produced by an impact, it could fade in the next few years,” he speculated. “If it persists or varies seasonally, that would favor domestic gas supply.”
It’s fascinating how small changes in starlight can reveal such significant features of small, distant worlds, he added. In the future, the team plans to conduct similar occultation campaigns at multiple sites to see if Pluto might have even more relatives.
“The outer Solar System is not simply a collection of frozen, unchanging worlds,” he concluded. “There is still a frontier in astronomy where creativity, time and collaboration can make an important discovery.”
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