Astronomers have found a planet with the most unusual orbit ever seen among planets outside our solar system, known as exoplanets.
This planet’s extreme path looks more like a stretched-out cucumber than a circle.
Even more fascinating, this exoplanet, named TIC 241249530, is orbiting its star in the opposite direction of the star’s rotation.
This backward orbit provides new insights into how massive gas planets, known as hot Jupiters, form and evolve over time.
The research, led by scientists from Penn State, was published in the journal Nature.
“We caught this massive planet making a sharp, hairpin turn during its close passage to its star,” said Suvrath Mahadevan, a professor of astronomy at Penn State.
“Such highly eccentric transiting planets are incredibly rare—and it’s really amazing that we were able to discover the most eccentric one.”
The term “eccentric” refers to the shape of a planet’s orbit, which is measured on a scale from zero to one, with zero being perfectly circular. TIC 241249530 has an orbital eccentricity of 0.94, making it more eccentric than any other known transiting exoplanet. For comparison, Pluto’s orbit around the sun has an eccentricity of 0.25, and Earth’s is 0.02. This extreme orbit would cause temperatures on the planet to vary dramatically, from mild to extremely hot.
Adding to its uniqueness, TIC 241249530 orbits backward, unlike most exoplanets and planets in our solar system. This rare trait helps scientists understand the planet’s formation history.
“While we can’t exactly rewind and watch the process of planetary migration in real-time, this exoplanet serves as a snapshot of the migration process,” said Arvind Gupta, the lead author of the study and a researcher at NOIRLab. “Planets like this are hard to find, and we hope it can help us unravel the hot Jupiter formation story.”
There are over 5,600 confirmed exoplanets in more than 4,000 star systems. About 300 to 500 of these are hot Jupiters—large, Jupiter-like planets that orbit very close to their star. The formation of hot Jupiters remains a mystery, but astronomers suspect they start in distant orbits and gradually move closer to their star. The discovery of TIC 241249530, with its unusual orbit, brings scientists closer to understanding this process.
The team used several advanced instruments built at Penn State to study the exoplanet. They first detected the planet using NASA’s Transiting Exoplanet Survey Satellite (TESS) in January 2020, which noticed a dip in a star’s brightness, indicating a planet passing in front of it. To confirm the planet’s nature, astronomers used instruments on the WIYN 3.5-meter Telescope at the U.S. National Science Foundation’s Kitt Peak National Observatory.
They used a technique called speckle imaging to ensure there were no other nearby stars confusing the TESS measurements. Then, they observed the planet’s spectrum using the HPF and NEID spectrographs, confirming its eccentric orbit and backward motion.
The detailed analysis showed that TIC 241249530 is about five times more massive than Jupiter and follows an extremely eccentric path. “This is the most eccentric transiting planet known and will be as important as the previous record holder, HD80606b,” said Jason Wright, a professor of astronomy at Penn State.
These discoveries suggest that high-mass gas giants evolve to become hot Jupiters as they migrate from eccentric orbits to tighter, more circular ones. The team’s findings open up new possibilities for studying the dynamics of exoplanet atmospheres, especially during their close passages to their stars.
With future observations using telescopes like NASA’s James Webb Space Telescope, scientists hope to learn more about TIC 241249530’s atmosphere as it undergoes rapid heating. There is still much more to discover about this fascinating exoplanet.
