Cute satellite spies hot Jupiters on faraway stars

A spacecraft slightly bigger than an A4 sheet of paper has been measuring huge, gassy exoplanets – called hot Jupiters – spinning around stars hundreds of light-years away.

The Colorado Ultraviolet Transition Experiment (or CUTE), a satellite just 35cm (14 inches) in length, has just released its first observations.

CUTE was launched in September 2021, fitted with just one telescope designed to see ultraviolet light. It uses this telescope to record planetary transitions: a planet passing in front of its star, causing the star to dim slightly. When starlight dims by as little as 1%, CUTE can spot it.

The spacecraft is orbiting Earth at an altitude of 525 kilometres, and is due to return by 2027.

“CUTE is still working and collecting data today,” says Dr Kevin France, principal investigator for the mission and an associate professor at the University of Colorado Boulder.

“When we got our first real science results, it was really exciting.”

CUTE has been observing a variety of “hot Jupiters,” so-called because they’re gas giants that orbit very close to their stars, making them very high in temperature. Some of these planets are losing their atmosphere to their stars, while others are stable.

“We want to understand how our solar system fits into the family of solar systems in the universe,” says France.

“That means understanding the big planets, the small planets, the ones that have life and the ones that definitely don’t – and all of the important physical processes that are operating on these planets.”

France provided an update on CUTE’s observations at the 2023 Meeting of the American Geophysical Union.

These observations include an exoplanet called WASP-189b, which is orbiting a star 300 light-years away in the constellation of Libra.

Aside from its temperature, which is more than 8,000°C, WASP-189b is of interest because of the speed that it’s losing mass to its sun. A paper published by France and colleagues in the Astrophysical Journal has shown that the exoplanet is shedding about 400 million kilograms of gas each second.

It’s not entirely clear why some planets get stripped so quickly while others don’t, but these processes could be precursors to other types of planets – like super-Earths, which are rocky planets notably larger than Earth.

“There’s a lot of evidence that suggests that super Earths begin as planets the size of Neptune with large, puffy atmospheres, which then lose so much mass that all that is left is the rocky core and possibly a thin atmosphere,” says France.

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