New Delhi: Pluto’s largest moon, Charon, may have had a much shorter day billions of years ago than it does today. A new study has found geological evidence
suggesting the icy moon gradually slowed its rotation over time due to Pluto’s powerful gravitational pull. The results provide a unique insight into the formation of one of the solar system’s most distant worlds.
It is based on images taken by NASA’s New Horizons spacecraft when it made its historic flyby of Pluto in 2015, as detailed in a new article published in the journal Nature Communications. Scientists are able to reconstruct the history of how the moon’s rotation has changed over time because Charon’s surface is virtually unchanged and frozen, according to the researchers.
Ancient ridges point to a slower spin
Hanzhang Chen from the University of California, Los Angeles (UCLA) led the study in the northern hemisphere of Charon’s territory of Oz Terra. The team mapped out long mountain ranges, compressional ridges and large fault systems that prominently trace a pattern over the surface.
The researchers say that these features are similar to what scientists would expect to see if a planetary body slowly “despins”. Tidal forces from Pluto caused Charon’s rotation rate to decrease, changing its shape. The moon’s icy crust was compressed, buckled and cracked over time as the moon became less flattened around the equator.
The results have a profound impact on scientists’ new views of the geology of Charon, Chen told Gizmodo. The team’s models indicated that the moon may have rotated once in about 14.3 hours at one time. Today the moon Charon is tidally locked to Pluto, orbiting around the planet in the same time that it takes to spin around itself.
A frozen time capsule from the early solar system
Charon has no atmosphere and is likely to have undergone very little resurfacing due to geological activity, compared to icy moons like Europa and Enceladus. This makes it one of the very best preserved accounts of ancient events. Its impact craters and tectonic features have remained more or less intact over the past few billion years.
The researchers believe that the despinning occurred earlier in the geologic history, prior to additional geological events such as global crustal extension or even perhaps cryovolcanism. This sequence also favours a relatively cold interior for Charon, as opposed to a warm and geologically active one.
The work is a new element in the puzzle of the evolution of icy worlds over time. Charon seems to be placid today, but its old surface remains to show signs of major events that occurred soon after the planet’s creation. The dwarf planet system continues to tell new tales over a decade after New Horizons’ flyby, and scientists are still investigating data from the mission.
