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Saturn's moon Titan is rapidly migrating away from the planet

Posted June 10, 2020 4:00 a.m. EDT

— Titan, Saturn's largest moon, is moving away from its planet a hundred times faster than previously established, according to a new study.

The giant moon isn't alone in this behavior; other moons among the 150 known moons in our solar system are also slowly distancing themselves from the planets they orbit, including our own moon. Earth's moon moves about 1.5 inches away each year, according to NASA.

This is caused by the moon's gravity tugging on the planet, which creates a temporary bulge in the planet. That energy pushes the moon further away.

Data collected during NASA's Cassini-Huygens mission to study Saturn and some of its moons has revealed that Titan's migration rate equals about 4 inches per year.

The study published Monday in the journal Nature Astronomy.

Saturn, the second-largest planet in our solar system, likely formed during the infancy of our solar system 4.6 billion years ago. But scientists are less certain about when the planet's signature rings and many moons formed. Currently, the planet has 82 moons.

Titan, which is larger than the planet Mercury, orbits Saturn at a distance of 759,000 miles away. And if it's been moving away from the planet at a rapid rate each year, Titan was likely much closer to Saturn in the beginning billions of years ago before migrating.

This implies that Saturn's entire planetary system also expanded quickly.

"This result brings an important new piece of the puzzle for the highly debated question of the age of the Saturn system and how its moons formed," said Valery Lainey, lead study author and scientist at Paris Observatory at Université Paris Sciences et Lettres, in a statement.

Lainey worked on the study as a scientist at NASA's Jet Propulsion Laboratory.

Background stars in images captured by Cassini helped the researchers track Titan. This was also compared with radio data gathered by Cassini over the course of 10 flybys of Saturn between 2006 and 2016. Together, these showed the shift in Titan's orbit as it moves outward.

"By using two completely different datasets, we obtained results that are in full agreement, and also in agreement with Jim Fuller's theory, which predicted a much faster migration of Titan," said Paolo Tortora, study coauthor and professor of aerospace systems and member of the Cassini Radio Science Team at the University of Bologna in Italy, in a statement.

Fuller, a theoretical astrophysicist and assistant professor at the California Institute of Technology, has a theory that both inner and outer moons of planets migrate away at similar rates. Both types of moons get stuck in orbits related to the planet's wobble, which pushes them away.

Fuller's theory, which he published as a research study around four years ago, changed the long-prevailing view that outer moons migrated more slowly than inner moons. This idea was based on the fact that the outer moons are more distant from the gravity of their planet.

He is also a coauthor on the new study.

"The new measurements imply that these kind of planet-moon interactions can be more prominent than prior expectations and that they can apply to many systems, such as other planetary moon systems, exoplanets — those outside our solar system -— and even binary star systems, where stars orbit each other," Fuller said in a statement.

Titan is unique in our solar system. It's the only known moon with a considerable atmosphere and the only planetary body in addition to Earth with liquid rivers and lakes on its surface.

In 2026, NASA will send the Dragonfly mission to further investigate Titan. It will arrive at the moon by 2034. The Mars rover-size drone will be able to fly through Titan's thick atmosphere for about two and a half years.

The ultimate goal is for Dragonfly to visit an impact crater, where they believe that important ingredients for life mixed together when something hit Titan in the past, possibly tens of thousands of years ago.

"Titan has the key ingredients for life," said Lori Glaze, director of NASA's Planetary Science Division, when the mission was announced in 2019.

"It has complex organic molecules and the energy required for life. We will have the opportunity to observe processes similar to what happened on early Earth when life formed and potentially conditions that could harbor life today."

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