Pluto and Charon targeted by James Webb Telescope
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September 18, 2022


This week James Webb Telescope spent hours observing Pluto and its moon Charon. On September 14, 2022, James Webb Telescope used NIRSpec IFU Spectroscopy to gather data on Pluto and its largest moon Charon. The largest of Pluto's five moons, Charon, was discovered on June 22, 1978, by James Christy and Robert Harrington at the U.S. Naval Observatory in Flagstaff, Arizona.

As Charon is almost half the size of Pluto, the two are also referred to as a double dwarf planet system and have a distance of 12,200 miles (19,640 km) between them. Charon takes 6.4 earth days to orbit around Pluto. Charon and Pluto are in tidal locking which means that Charon neither rises nor sets, but appears at the same spot on Pluto's surface with its same side facing always facing Pluto.

Like earth's moon, Charon doesn't have an atmosphere, while the planet it orbits, Pluto, does. Albeit, there has been speculation about a minuscule atmosphere surrounding Charon but nothing has been proven yet. With the James Webb Telescope gathering data on Pluto and Charon, we hope to get more information about their atmospheres. As Charon is believed to be formed in a collision, it would also mean that there was no cooling stage which would have allowed surrounding gases to condense into a solid atmosphere.

Hubble Space Telescope/Faint Object Camera image of Pluto and Charon taken in 1994. Credit: Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA

The Hubble observations found that Charon is bluer than Pluto which means that both worlds have different surface composition and structure. Further observations on Pluto suggest it has a smoothly reflecting surface layer. A detailed analysis of the Hubble image also suggests there is a bright area parallel to the equator on Pluto. Though Pluto was discovered in 1930, Charon wasn't detected until 1978 because the moon is so close to Pluto that the two objects appea as one when viewed through ground-based telescopes. At a comparable distance, Earth's moon would appear as big in the night sky as an apple held at arm's length.

As James Webb Telescope discovers new information about Pluto and Charon with these observations, we will have new pictures and data released to the public soon. Data and images are typically released within a few months of the observation after the peer review has been completed. In addition to Pluto and Charon, James Webb Telescope is observing, high redshift galaxies, Asteroid Sedna and NCG 104 amongst other objects this week. The entire schedule of weekly James Webb Telescope observations can be found here.