EXPECT a sharp frost on Pluto for the next 100 years. That is the forecast from an analysis suggesting the dwarf planet鈥檚 atmosphere has reached maximum pressure and will begin freezing nitrogen onto the surface.
Pluto鈥檚 tenuous atmosphere was first spotted in 1985 as astronomers watched the world pass in front of a distant star, an event known as an occultation. Since then, about a dozen occultations have been used to study its gassy layer, which has gradually grown in size over the past 30 years.
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The cause of this increase is the slowly changing seasons on Pluto during its elliptical orbit that lasts 248 Earth years. After reaching its closest point to the sun in 1989, its northern hemisphere gradually tilted towards our star. This raised the temperature of Sputnik Planitia, a vast reservoir of nitrogen ice spotted by NASA鈥檚 New Horizons spacecraft during its 2015 fly-by of Pluto. The ice warmed and turned into gas, increasing the atmospheric pressure.
From 1988 to 2016, the surface pressure increased by a factor of three, from 0.4 to 1.2 pascals. But Sputnik Planitia is now moving into a century-long period of twilight, suggesting the atmosphere will begin to condense and freeze on the surface of Pluto, almost vanishing in the next 100 years ().
鈥淚t will not disappear, but more than 95 per cent of the atmosphere will collapse onto the surface,鈥� says Bruno Sicardy at Sorbonne University in Paris, who has been tracking the atmosphere as part of the analysis. 鈥淚t will 鈥榮now鈥�, it will freeze on the surface and create a frost.鈥�
The results let us get a glimpse of Pluto on a longer timescale than a spacecraft鈥檚 brief fly-by, says Leslie Young of the New Horizons team. 鈥淚t really highlights the importance of both ground-based observations and space observations,鈥� she says.
