Space and Physics
PUBLISHED
Charon and Pluto are locked in a celestial dance. The dwarf planet and its largest moon are not that dissimilar in size, and in fact, Charon doesn’t orbit around Pluto. They both move around a point just above the surface of Pluto. This peculiar interaction has led to a major change on Charon: it has slowed down the moon massively.
Tidal forces between close bodies can massively change the spin rate of bodies. This is what happened to the Earth and the Moon. The same has been suspected to have happened to Charon too.
Researchers believed that they could find evidence for this in the geological features of Charon. The moon was visited briefly by NASA’s New Horizons, together with Pluto, 11 years ago today. The features on Charon are named after fictional and mythological places, vessels, or explorers; so the red spot at the north pole is the Mordor Macula, but for this work we need to go to Oz Terra.
Charon’s surface has not changed much in the last 4 billion years, so it keeps a trace of what the moon was like at its formation. Mountain ranges in the Oz Terra stretch for over 200 kilometers (120 miles) and show asymmetric slopes, which suggests that they have been compressed.
The researchers were able to use a model to work out that an ice shell of at least 30 to 36 kilometers (19-22 miles) was present when Charon formed. During the early days of the moon, the crust at the equator shortened by about 1 percent due to the moon’s spin. This shortening is responsible for the ridges seen in Oz Terra.
“Charon's geological past was proposed to have undergone global extension. In this study, besides extensional features, we identified potential compressive landforms. These compressional features are distributed in the equatorial region and generally extend in a north-south direction,” lead author Hanzhang Chen from the University of California, Los Angeles, told IFLScience.
Though Charon is not as 'active' and 'bright' as Pluto, it records information about the early Solar System.
Hanzhang Chen
“We relate this observation to the reverse process of rotational flattening, which suggests Charon is a despun planetary body. This interpretation is further strengthened by the east-west orientations of extensional features, especially those in the polar region.”
The model suggests that Charon started with a spin on its axis of about 14.3 hours. That’s over 10 times faster than the current state, which is around 153.3 hours. The evidence of its original fast rotation remains trapped in its unchanged surface.
“We know that Charon is currently tidally locked with Pluto, as confirmed by NASA's New Horizons mission. From despinning, we are able to estimate its rotational state soon after its formation. This study provides a new approach to infer the initial states of icy satellites from their geologic records,” Chen told IFLScience.
This approach could be employed to understand the rotational history of other objects in the Solar System. Their surfaces might be hiding a lot more insights, as long as they are not too active. What’s being gleaned from Charon might be a really exciting view into the formative years of the outer edges of the Solar System.
“Though Charon is not as 'active' and 'bright' as Pluto, it records information about the early Solar System,” Chen told IFLScience.
The study is published in the journal Nature Communications.
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