Low atmospheric density confirmed on Pluto

Madrid, 4 (European Press)

As it moves away from the Sun, Pluto’s atmosphere begins to “freeze” on its surface, which at the same time causes a decrease in atmospheric density.

When Pluto passed the star on the night of August 15 2018, a team of astronomers led by the Southwest Research Institute (SwRI) deployed telescopes at several locations in the United States and Mexico to observe Pluto’s atmosphere. Meanwhile it is briefly illuminated by the exact location of the star. Scientists used this invisible event to measure the overall abundance of Pluto’s thin atmosphere and found strong evidence that it began to fade, freezing again on its surface as it faded from the sun.

The occultation lasted about two minutes, during which time the star disappeared from view as Pluto’s atmosphere and solid bodies passed in front of it. The speed at which stars disappear and reappear determines the density profile of Pluto’s atmosphere.

“Scientists have been using obscurity to observe changes in Pluto’s atmosphere since 1988,” said Dr. Eliot Young, senior program director in SwRI’s Department of Aerospace Science and Engineering, said in a statement. “The New Horizons mission obtained an excellent density profile from the 2015 flyby, consistent with Pluto’s atmosphere doubling every decade, but our 2018 observations show no continuation of this trend since 2015.”

Several telescopes scattered near the center of the shadow path have observed a phenomenon called “central flare,” which is caused by the refraction of light from Pluto’s atmosphere into the region at the center of the shadow. When measuring the occultation around an object with the atmosphere, the light dims as it passes through the atmosphere and then gradually returns. This results in moderate steepness at each end of the U-shaped light curve. In 2018, refraction from Pluto’s atmosphere caused the central glow to be near the center of its shadow, turning it into a W-shaped curve.

“The central flash seen in 2018 was the most powerful anyone has ever seen in Pluto’s cloud,” Young said. “The central flare gives us very accurate knowledge of the path of Pluto’s shadow on Earth.”

Like Earth, Pluto’s atmosphere is mostly nitrogen. Unlike Earth’s, Pluto’s atmosphere is powered by the vapor pressure of surface ice, which means that a small change in the temperature of the surface ice will cause a large change in the mass density of the atmosphere. Pluto takes 248 Earth years to complete one full revolution around the Sun, and its distance varies from its closest point, about 30 AU from the Sun (1 AU is the distance from Earth to the Sun), to 50 AU from the Sun.

Over the past quarter century, Pluto has received less sunlight as it moves away from the Sun, but as of 2018, its surface pressure and atmospheric density have continued to increase. Scientists attribute this to a phenomenon known as thermal inertia.

“The analogy for this is the way the sun warms the beach sand,” said SwRI scientist Dr. Leslie Young, who specializes in modeling interactions between the surface and atmosphere of icy bodies outside the solar system. “The sun’s rays are strongest during the day, but the sand continues to absorb heat throughout the afternoon, making it even hotter in the afternoon. The persistence of Pluto’s atmosphere suggests that the nitrogen deposits of ice on Pluto’s surface are kept warm by the heat stored beneath the surface. Pluto. Surface. New data shows it’s starting to cool off.”

The largest known nitrogen reservoir is Sputnik Planitia, a glossy glacier that forms the heart-shaped western lobe of the Tombaugh Region. The data will help atmospheric designers improve their understanding of Pluto’s aquifer, particularly regarding its composition consistent with the observed heat transfer limits.

Eliot Young presented the findings on October 4 at the 53rd annual meeting of the Division of Planetary Sciences of the American Astronomical Society.

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