Secrets of Pluto’s Largest Moon
16 June 2014

This artist rendition shows Pluto and its largest moon, Charon, as they appear in the sky of one of the dwarf planet’s small moons.
Credit: NASA, ESA and G. Bacon (STScI)

Pluto (2,300 km across) is a mysterious distant icy world. It never comes closer to the Sun than 4.4 billion km, nearly 30 times the average Earth-Sun distance. It has a family of five moons, which is a big number of satellites for a dwarf planet. Intriguingly, a new, NASA-sponsored study has revealed that Pluto’s largest moon, Charon (1,200 km across), may have had an ocean of liquid water beneath its crust.

According to the recently published study, if the icy surface of Charon is cracked, analysis of the fractures could reveal if its interior was warm, probably even warm enough to have sustained a subterranean layer of liquid water.

Interestingly, some moons around the outer gas giant planets, such as Jupiter's moon Europa and Saturn's moon Enceladus, have cracked surfaces, hinting for underground oceans.

In Charon's case, this study finds that a past highly eccentric orbit of Charon around Pluto could have heated the moon’s interior, and caused fractures on its surface, due to the influence of Pluto’s gravity on Charon. Charon is a relatively massive moon, about one-eighth the mass of Pluto. This is unusual among the planetary moons. For instance, the Earth (12,756 km across) is 81 times more massive than the Moon (3,476 km across), and Jupiter (143,000 km across), the largest planet, is thousands of times more massive than Ganymede (5,250 km across), its largest moon.

Because of its remoteness and small size, observing Pluto from Earth is very difficult. However, planetary scientists eagerly await the arrival of NASA’s New Horizons spacecraft at Pluto, due in July 2015. New Horizons will be the first probe ever to visit the Pluto system. It is expected to provide detailed images of Pluto and Charon. 

Aymen Mohamed Ibrahem
Senior Astronomy Specialist
News Center

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