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Pluto, what used to be the 9th planet of our solar system, lying 3 billion miles from Earth, has recently caught the attention of astronomers and scientists as it passed by in front of a star in 2018. This unique occurrence allowed scientists to come to an unsettling discovery---Pluto's atmosphere is disappearing.

What is Pluto?

Pluto in True Color - High-Res
(Photo : NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker / WikiCommons)
Pluto's image taken by New Horizons on July 14, 2015, from a range of 22,025 miles (35,445) kilometers. The striking features on Pluto are clearly visible, including the bright expanse of Pluto's icy, nitrogen-and-methane rich "heart," Sputnik Planitia.

Pluto, according to NASA, is a dwarf planet that travels around the sun just like other planets. However, it is significantly smaller. It was initially discovered in 1930 by Clyde Tombaugh and was named Pluto in the same year by Venetia Burney. 

It takes Pluto roughly 248 years to complete a full orbit around the sun, where a day on the icy dwarf planet is 6 ½ days on Earth.

Pluto is significantly colder than the other planets. It is cold enough to freeze Earth's air into the snow. Additionally, it also has much less gravity than what we have on Earth.

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Pluto's Disappearing Atmosphere

In 2018, Pluto passed by in front of a star that allowed researchers to peer into the happenings of the icy dwarf planet. As the star backlit Pluto, a team of researchers drew observations on the planet and its atmosphere. This unique view paved the way for a surprising conclusion that was shared by researchers at the Division for Planetary Sciences of the American Astronomical SocietyAstronomers observed that Pluto's atmosphere was beginning to disappear. 

The researchers used telescopes across multiple states in both Mexico and the U.S. and noticed Pluto's already thin atmosphere. Much like Earth, the icy dwarf planet's thin atmosphere consisted of Nitrogen, supported by the vapor pressure of ices on its surface. Hence, if the ice warms up on the surface, it will dramatically alter the density of Pluto's atmosphere, as per a statement from the Southwest Research Institute.

For the past 25 years or more, Pluto has steadily been moving further and further away from the Sun. Hence, its surface temperature has steadily decreased. In light of recent observations, researchers found conclusive evidence that showed the dwarf planet's atmosphere refreezing back onto its surface as Pluto gets colder.

Because of a phenomenon known as thermal inertia, the dwarf planet's surface pressure and atmospheric density have continued to rise up until 2018. Essentially, the planet had residual heat from when it orbited closer to the sun. On the other hand, the inertia has begun to wear off, and Pluto is getting colder; more of its atmosphere will freeze back onto its surface and eventually disappear. 

Elliot Young, a senior program manager at SwRI, said in the statement that the New Horizon missions had obtained a detailed density profile from its flyby in 2015 consistent with the dwarf planet's bulk atmosphere doubling every decade. However, observations in 2018 were not able to show the continuing trend of 2015.

As the team observed Pluto as it wheezed past in front of the star, they noticed a "central flash" caused by the dwarf planet's atmosphere refracting light into the center of the shadow, changed, and the curvature of light Space reports.

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