Pluto atmosphere is going through a weird conversion, scientists are finding.
The icy dwarf-planet which lies over 3 billion miles (4.8 billion kilometers) far away from Earth in Kuiper Belt, caught astronomers’ attention as it passed in front of a star back in 2018.
With star backlighting Pluto, team of researchers was able to make compliances of the dwarf globe & its atmosphere. With this unique view, they came to a surprising conclusion that they describe in a new study.
The astronomers found evidence that Pluto’s atmosphere is starting to vanish.
Using telescopes at different locations in both U.S. & Mexico, team observed Pluto & its thin atmosphere, which is primarily made up of nitrogen, like that of Earth. Pluto’s atmosphere is supported-by the vapour pressure of ices on the dwarf planet’s surface. So, if ice warms up on Pluto, it can dramatically alter density of its atmosphere, consistent with a statement from Southwest Research Institute (SwRI), home institution of multiple members of the research team.
For nearly 25 years, Pluto has been moving farther & farther away from sun, so its surface temperature has been going-down. With these recent observations, researchers found evidence showing that Pluto’s atmosphere is really refreezing back onto its surface as the dwarf planet gets colder & colder. Pluto is so-far from sun that, as time goes on, it’ll get distinctly farther away (& colder) before getting closer to the sun in other areas of its immense orbit.
Thanks to a phenomenon called thermal inertia, Pluto’s surface pressure & atmospheric density continued to increase until 2018. Essentially, Pluto had residual heat from when it was nearer to the sun. However, inertia starting to wear-off and as Pluto gets colder, more & more of its atmosphere will freeze-back onto its surface & “disappear.”
“An analogy to this is the way sun heats-up sand on a beach, “SwRI staff scientist Leslie Young, who studies interaction between icy solar system bodies & their surfaces & atmospheres, said in the same statement.
“Sunlight is most-intense at high noon, but sand then continues soaking-up the heat over the course of the afternoon, so it’s hottest in the late afternoon. The continued-persistence of Pluto’s atmosphere suggests that nitrogen ice reservoirs on Pluto’s surface were kept warm-by stored heat under the surface. The new data suggests they’re starting to cool,” Young said.
So how did they figure out just by watching Pluto move in front of a star?
The researchers watched star fade as Pluto moved in front of it, then come back into view once the dwarf-planet had passed. Using rate that star came in & out of view, a transition that lasted about two minutes, they were able to determine the density of dwarf planet’s atmosphere, consistent with the statement.
This method relies on what’s known as an “occultation,” an event that happens when one cosmic object is hidden-by another passing in front of it. Studying occultations is an old & well- worn technique in the world of astronomy and researchers used it to study Pluto’s atmosphere since 1988, Eliot Young, a SwRI senior program manager, said in statement.
“The New Horizons mission obtained a great density profile from its 2015 flyby, consistent with Pluto’s bulk atmosphere doubling each decade, but our 2018 observances don’t show that trend continuing from 2015,”Young added, referring to pioneering NASA mission that gave the world its first close look at Pluto.
In observing Pluto as it passed in front of star, team noticed a “central flash” in the middle of path of dwarf planet’s shadow. The flash, caused by Pluto’s atmosphere refracting light into the middle of the shadow, changed the light curve that normally happens during occultation from a “u-shape” into a “w- shape.”
“The central flash that seen in 2018 was by far the strongest that anyone has ever seen in a Pluto occultation,” Young said. “The central flash gives us very accurate information of Pluto’s shadow path on the Earth.”
Young discussed the results of this study October 4 at 53rd American Astronomical Society Division for Planetary Sciences Annual Meeting.