Pluto's Atmosphere Is Slowly Vanishing, Scientists Discover

It's not easy to hang on to your atmosphere as a celestial body. Just ask Mars. A new study has shown that the gases surrounding Pluto are disappearing and turning back into ice, as the dwarf planet moves further from the Sun.
Pluto's atmosphere is already thin and consists mainly of nitrogen, with some methane, carbon monoxide, and a few other elements. It seems that as temperatures drop, nitrogen freezes up, which causes the atmosphere to fade.

This assessment was done using what is known as occultation, which involves using a distant star to act as a backlight for telescopes located on Earth in order to see what's going on on Pluto. This is a well-known observation technique that has been used extensively in astronomy.

New Horizons observes Pluto and its atmosphere. (NASA/JHU–APL/SwRI).

Eliot Young, a planetary scientist at the Southwest Research Institute (SwRI), Texas says that scientists have been using occultations since 1988 to monitor changes in Pluto’s atmosphere.

"The New Horizons mission received an excellent density profile during its 2015 flyby. This is consistent with Pluto's bulk atmospheric doubling every decade. However, our 2018 observations don't show this trend continuing since 2015.

Pluto's atmosphere is made from the vaporized surface ice. Small changes in temperature can lead to large changes in the bulk density. Sputnik Planitia is the largest known nitrogen glacier. It can be seen on Pluto's surface in the western portion of the Tombaugh Regio, which has a heart-shaped shape.

It takes the dwarf planet 248 Earthyears to orbit the Sun. At one point, it can get as close as 30 Astrological Units (AUs) from Sun. This is 30 times the distance between Earth & the Sun.

This distance is increasing, however, and Pluto has less sunlight and lower temperatures. Most likely, the 2015 increase in atmosphere density is due to thermal inertia residual warmth trapped in nitrogen glaciers. This delayed reaction to increasing distance between Pluto (and the Sun) causes the increased atmospheric density.

Leslie Young, a SwRI planetary scientist, says that this analogy is how the Sun heats up sand at a beach. "Sunlight is strongest at high noon, but the sun continues to soak up heat throughout the afternoon so it is hot in the late afternoon."


Above: Telescopes located near the middle of shadow's path noticed a "central flash" caused by Pluto's atmosphere reflecting light into the region at the shadow's center.

Although Pluto may not be considered a planet anymore, it is still an area of controversy for experts. However, it remains a planetary body that is of interest to astronomers. Every day, we learn more about this distant rock.

Astronomers have discovered that Pluto has snowcapped mountains and that it has liquid oceans beneath its surface. These discoveries can help us understand the functioning of Pluto's atmosphere. Both were made by the 2015 New Horizons flyby.

The 2018 observations were aided by a "central flash", which indicated that the telescopes were directly looking at Pluto, while atmospheric measurements were taken, further increasing their credibility.

Young says that the 2018 central flash was "by far the strongest ever seen in a Pluto Occultation." "The central flash provides us with very precise knowledge about Pluto's shadow path on Earth," Young says.

These findings were shared at the American Astronomical Society Division for Planetary Sciences Annual Meeting.