Pluto’s atmosphere backlit by the Sun, photographed by New Horizons as it departed the Pluto system. Credit: NASA/JHU-APL/SwRI
Three years after the New Horizons spacecraft’s historic flyby, Pluto’s atmosphere appears to be starting to condense and refreeze, according to scientists who observed the dwarf planet occult or pass in front of a star on Aug. 15, 2018.
Pluto reached perihelion, the closest point to the Sun in its elliptical orbit, in 1989, one year after scientists first discovered its atmosphere as it passed in front of a different star.
In its 248-year orbit, Pluto’s distance from the Sun ranges from 30 AU (astronomical units, with one AU equal to the average Earth-Sun distance, or 93 million miles) at perihelion, to 50 AU at aphelion, its furthest point from the Sun.
During an occultation, scientists can study a foreground object’s atmosphere by measuring the amount of time that the background star dims as the object passes in front of it and the amount of time the light takes to re-emerge.
Since the discovery of Pluto’s atmosphere in 1988, researchers have been using stellar occultations to monitor atmospheric changes. Some scientists feared that delays in getting a spacecraft to Pluto might ...