Astronomers have recently discovered a planet that’s in the process of becoming one of the most extreme types of planets in our galaxy—a hot Jupiter.
These giant planets are similar in size to Jupiter but have scorching temperatures because they orbit very close to their stars, completing their orbits in just a few days.
Unlike our Jupiter, which takes about 4,000 days to circle the sun, hot Jupiters swing incredibly close to their stars.
Scientists believe hot Jupiters didn’t start out so hot. They likely formed as “cold Jupiters” in distant, icy regions of their solar systems.
The big mystery has been how these cold Jupiters transformed into the sizzling hot Jupiters we see today.
A team of astronomers from MIT, Penn State University, and other institutions has found a planet that could provide some answers. Their findings were published in the journal Nature.
This new planet, named TIC 241249530 b, orbits a star about 1,100 light years from Earth. The planet has a very unusual orbit—it comes extremely close to its star before swinging far out again, tracing a narrow, elliptical path.
If this planet were in our solar system, it would come ten times closer to the sun than Mercury before hurtling out past Earth’s orbit and then back again. The planet’s orbit is so stretched out that it has the highest eccentricity of any planet discovered so far.
Even more interesting, this planet orbits in the opposite direction of its star’s rotation, a “retrograde” orbit, unlike the Earth and other planets in our solar system.
To understand how TIC 241249530 b ended up with such a wild orbit, the team ran simulations of its orbital dynamics.
They found that the planet’s eccentric and retrograde orbit suggests it is undergoing “high-eccentricity migration.” This is a process where a planet’s orbit wobbles and shrinks over time due to gravitational interactions with another star or planet.
In this case, TIC 241249530 b orbits a primary star that is part of a binary system with a second star. The gravitational pull between these two stars and the planet has gradually drawn the planet closer to its star.
Currently, the planet’s orbit is elliptical, taking about 167 days to complete one lap around its star. The researchers predict that in about 1 billion years, the planet’s orbit will become more circular, turning it into a hot Jupiter with a much shorter orbit of just a few days.
Sarah Millholland, an assistant professor of physics at MIT, explained that this discovery supports the theory that high eccentricity migration is one way hot Jupiters form. “When this planet formed, it would have been a frigid world,” she said.
“Due to the dramatic changes in its orbit, it will become a hot Jupiter in about a billion years, with temperatures of several thousand kelvin. It’s a huge shift from where it started.”
The planet was first spotted using data from NASA’s Transiting Exoplanet Survey Satellite (TESS). TESS looks for dips in starlight that could indicate a planet passing in front of a star. On January 12, 2020, TESS detected a possible transit by the star TIC 241249530.
Arvind Gupta and his team at Penn State confirmed that the transit was caused by a Jupiter-sized planet. Further measurements showed that the planet’s orbit was highly eccentric.
Before this discovery, only one other planet, HD 80606 b, was thought to be an early-stage hot Jupiter. That planet, discovered in 2001, held the record for the highest eccentricity until now.
“This new planet experiences dramatic changes in starlight throughout its orbit,” Millholland said. “There must be radical seasons and a scorched atmosphere every time it passes close to the star.”
Millholland and MIT undergraduate Haedam Im ran simulations to model how the planet’s orbit has evolved and will continue to evolve over billions of years. Their models show that TIC 241249530 b started as a cold Jupiter far from its star and gradually moved closer due to gravitational forces from the binary star system. In another billion years, the planet’s orbit will stabilize into a circular path around its star, fully becoming a hot Jupiter.
“This system shows how incredibly diverse exoplanets can be,” Millholland noted. “They have wild orbits that tell a story of how they got that way and where they’re going. For this planet, its journey isn’t quite finished yet.”
