JAKARTA – When Pluto passed in front of a star on the night of August 15, 2018, a team of astronomers led by the Southwest Research Institute deployed telescopes at various locations in the US and Mexico to observe Pluto’s atmosphere illuminated by the star’s light.
Scientists used this occult event to measure the overall abundance of Pluto’s weak atmosphere and found strong evidence that it began to disappear, re-frozen to its surface as it moved further away from the Sun.
The occultation took about two minutes, during which time the star faded from view as Pluto’s atmosphere and solid bodies passed in front of it. The rate at which stars disappear and reappear determines the density profile of Pluto’s atmosphere.
“Scientists have been using occultation to monitor changes in Pluto’s atmosphere since 1988,” said Dr. Eliot Young, senior program manager in SwRI’s Division of Aerospace Science and Engineering.
“The New Horizons mission obtained an excellent density profile from the 2015 flyby, consistent with Pluto’s mass atmosphere doubling every decade, but our 2018 observations do not show that the trend has continued since 2015,” he explained. (6/10/2021).
Several telescopes placed near the center of the shadow path observed a phenomenon called “central flash,” which is caused by Pluto’s atmosphere refracting light 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 a moderate tilt at either end of the U-shaped light curve. In 2018, refraction of Pluto’s atmosphere created a central flash near the center of its shadow, turning it into a W-shaped curve. “The central flash seen in 2018 is by far the strongest anyone has seen. in Pluto’s occultation,” Young said. “The central flash gives us very accurate knowledge of the path of Pluto’s shadow on Earth.”
Like Earth, Pluto’s atmosphere is predominantly nitrogen. Unlike Earth’s, Pluto’s atmosphere is supported by the vapor pressure of the ice on its surface, which means that a small change in the temperature of the surface ice will result in a large change in the mass density of its atmosphere. Pluto takes 248 Earth years to complete one full orbit around the Sun, and its distance varies from its closest point, about 30 astronomical units 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 and less sunlight as it moves further away from the Sun, but, as of 2018, its surface pressure and atmospheric density continued to increase. Scientists attribute this to a phenomenon known as thermal inertia.
“The analogy for this is the way the Sun heats the sand on the beach,” said SwRI Staff Scientist Dr. Leslie Young, who specializes in modeling interactions between the surface and atmosphere of icy bodies outside the solar system. “The sun is most intense during the day, but the sand then continues to absorb heat throughout the afternoon, so it’s hottest in the afternoon.
The persistence of Pluto’s atmosphere suggests that the nitrogen ice reservoirs on Pluto’s surface are kept warm by heat stores beneath its surface. New data shows that they are starting to cool off.”
The largest known reservoir of nitrogen is Sputnik Planitia, a bright glacier that forms the heart-shaped western lobe of the Tombaugh Region. The data will help atmospheric modelers improve their understanding of Pluto’s subsurface layer, particularly regarding compositions compatible with the observed limits on heat transfer. (E-4)
News Source: RRI.
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