Pluto is a world of surprises. The dwarf planet is not a dead rock at the edge of the Solar System, but a geologically active object with a thin atmosphere, seen in all its glory in 2015 with NASA’s New Horizons flyby. Pluto's atmosphere, in particular, has fascinated astronomers.
Researchers are puzzled as to whether the atmosphere is permanent or if it changes with the seasons as the planet orbits the Sun. For a long time, it was assumed that when Pluto moved closer to the Sun, the dwarf planet’s ice turned to gas. When it moved further away, it condensed and froze once again. However, a new study, published in Icarus, suggests this is not quite the case.
Using the Stratospheric Observatory for Infrared Astronomy, or SOFIA, researchers studied the atmosphere during a stellar occultation. When Pluto passed in front of a star, SOFIA used the light of the star to study the atmosphere. The observations from SOFIA were conducted just a couple of weeks before New Horizons' incredible flyby of Pluto, which when combined together provide great insight into the dwarf planet's atmosphere.
Pluto’s orbit is a lot more egg-shaped than Earth's. In its 248-year trek around the Sun, it spends 20 years closer to the Sun than Neptune. This last happened between 1979 and 1999, so it is now going into the colder, more distant remit of its orbit. So far, its atmosphere appears to be unaffected, at least for now.
The data showed haziness in the atmosphere and no changes between observations in 2015 and those from 2011 to 2013.
“Pluto is a mysterious object that is constantly surprising us,” said lead author Michael Person, the director of Massachusetts Institute of Technology’s Wallace Astrophysical Observatory, in a statement. “There had been hints in earlier remote observations that there might be haze, but there wasn’t strong evidence to confirm it really existed until the data came from SOFIA. Now we’re questioning if Pluto’s atmosphere is going to collapse in the coming years – it may be more resilient than we thought.”
“There’s still a lot we don’t understand, but we’re forced now to reconsider earlier predictions,” said Person. “Pluto’s atmosphere may collapse more slowly than previously predicted, or perhaps not at all. We have to keep monitoring it to find out.”
The atmospheric haze is made of small particles roughly 0.06-0.10 microns thick, about 1,000 times smaller than a human hair. These are extremely good at scattering blue light, giving Pluto’s atmosphere a poetic blue hue.