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Astronomers Discover Something Strange and Beguiling on Pluto's Largest Moon

When the New Horizons space probe flew by Pluto in 2015, it picked up something strange: a big red spot on the north pole of Charon, Pluto's largest moon. By modeling the temperatures of Pluto and Charon over time, scientists discovered that the red spot was caused by gasses in Pluto's atmosphere getting frozen at Charon's poles.