Astronomers discover planet in the process of becoming a hot jupiter

In the unfathomable expanse of our galaxy, planets come in a variety of sizes, compositions and orbits. Among these, 'hot Jupiters' stand out as a particular enigma thanks to their extreme ways.

These massive, scorching planets orbit very close to their stars, completing their circuits in mere days compared to the leisurely 4,000-day orbit of Jupiter around our sun.

Recent research from MIT, Penn State University, along with a few other institutions, has identified a planet that appears to be in the midst of transforming into one of these hot Jupiters. What's more, the discovery could provide crucial insights into how such large, hot planets evolve.

The newly discovered planet, named TIC 241249530 b, orbits a star about 1,100 light-years from Earth in a highly eccentric orbit. This means it swings extremely close to its star before slinging far out, then doubling back. If placed in our solar system, it would come ten times closer to the sun than Mercury, before moving out past Earth’s orbit.

Simulations of orbital dynamics conducted by the astronomers also indicate that TIC 241249530 b is likely evolving into a hot Jupiter. The planet currently orbits its primary star, which in turn orbits a secondary star in a binary system. The gravitational interactions between these bodies cause the planet to migrate closer to its star over time. In approximately one billion years, it is predicted to settle into a tighter, circular orbit, fully becoming a hot Jupiter.

"This new planet supports the theory that high eccentricity migration should account for some fraction of hot Jupiters," says Sarah Millholland, assistant professor of physics in MIT’s Kavli Institute for Astrophysics and Space Research.

"We think that when this planet formed, it would have been a frigid world. And because of the dramatic orbital dynamics, it will become a hot Jupiter in about a billion years, with temperatures of several thousand kelvin. So it’s a huge shift from where it started."

The discovery was made using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), which monitors the brightness of nearby stars for transits or brief dips in starlight caused by planets passing in front of their stars. On January 12, 2020, TESS detected a possible transit of the star TIC 241249530. Further measurements confirmed the presence of a Jupiter-sized planet with a highly eccentric orbit.

"This new planet experiences really dramatic changes in starlight throughout its orbit," Millholland says. "There must be really radical seasons and an absolutely scorched atmosphere every time it passes close to the star."

'A big dance'

To understand how the planet fell into such an extreme orbit and how it might evolve, the team ran simulations of "planetary orbital dynamics". These simulations revealed that the planet likely formed as a cold Jupiter, far from its star, before gravitational interactions with a secondary star in the binary system caused its orbit to stretch and become eccentric.

“It’s a pretty extreme process in that the changes to the planet’s orbit are massive,” Millholland explained. “It’s a big dance of orbits that’s happening over billions of years, and the planet’s just going along for the ride.”

In another billion years, researchers believe that the planet’s orbit will stabilise into a close-in, circular path around its star, fully transforming it into a hot Jupiter. This discovery not only supports the theory of high eccentricity migration but also highlights the incredible diversity and complexity of exoplanetary systems.

"It’s clear not only from this, but other statistical studies too, that high eccentricity migration should account for some fraction of hot Jupiters" added Millholland.

"This system highlights how incredibly diverse exoplanets can be. They are mysterious other worlds that can have wild orbits that tell a story of how they got that way and where they’re going. For this planet, it’s not quite finished its journey yet."