After decades of studying Saturn’s moon Titan, scientists have discovered it is drifting away from the ringed planet 100 times faster than previously believed. Titan currently resides 759,000 miles from Saturn, but the new data proposes it was initially far closer 4.5 billion years ago.
This means the entire system expanded much faster than scientists originally theorised.
This implies that the Saturnian moon system, and potentially its rings, have formed and evolved more dynamically than previously believed
Professor Jim Fuller
The findings also confirm outer moons migrate at a rate similar to inner moons because they enter an orbit pattern connected to the wobble of a planet, slinging them outward.
Titan is the largest of Saturn’s 62 known moons and sits 886 million miles from the sun.
This distance means Titan’s surface temperature is approximately minus 179C.
The surface pressure on the moon is also roughly 50 percent higher than Earth’s.
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The recent discovery was made using data from NASA’s Cassini spacecraft, which has been observing Saturn since 2004.
A team analysed measurements and calculations from the probe and discovered Titan’s orbit around Saturn is expanding.
This means Titan is drifting 100 times faster from Saturn, which is estimated to be four inches per year.
The scientists now also understand when the moon first formed it was much closer to Saturn.
The moon then drifted out to its current distance of about 759,000 miles over the course of 4.5 billion years.
To better understand the basics of orbital migration, astronomers can use Earth’s Moon for comparison.
Earth’s Moon exerts a small gravitational pull on the planet as it orbits, with this rhythmic tug responsible for tides.
Frictional processes inside the Earth convert some of this energy into heat, distorting the Earth’s gravitational field so that it pulls the Moon forward in its orbit.
This allows the Moon to gain energy and gradually drift farther away from the planet, at an annual rate of about 1.49 inches (3.8cm).
The rate of this lunar retreat has varied over millions of years, with the Moon drifting away at times as fast as 8.2 inches (20.8cm) per year.
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This process is, however, extremely gradual and Earth is not expected to lose its Moon until the Sun expands into a red giant some six billion years from now.
Jim Fuller, an assistant professor of theoretical astrophysics at the California Institute of Technology (Caltech) and co-author on the new paper, said: “Most prior work had predicted that moons like Titan or Jupiter’s moon Callisto were formed at an orbital distance similar to where we see them now.
“This implies that the Saturnian moon system, and potentially its rings, have formed and evolved more dynamically than previously believed.”
Along with this discovery, scientists can now confirm a theory proposed by Professor Fuller four years ago.
This theory predicted outer moons can migrate outward at a similar rate to inner moons because they become locked in a different kind of orbit pattern that links to the particular wobble of a planet and slings them outward.
Professor Fuller said: “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.”
The researchers mapped stars around Titan shown in photographs shot by Cassini and tracked the moon’s position.
They then compared the research with radio science data collected by the NASA space probe during 10 flybys between 2006 through 2016.
Scientists studied how the signal’s frequency was changed by their interactions with their surroundings to estimate how Titan’s orbit evolved.
Co-author Paolo Tortora, of Italy’s University of Bologna, said: “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.”
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