Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific advances and more.
Astronomers have detected an exoplanet with an extremely elongated orbit and drastic temperature changes that could be evolving into another kind of world.
The exoplanet, named TIC 241249530 b, orbits a star about 1,100 light-years from Earth. The star is part of a binary pair, so the planet orbits the primary star, while the primary star orbits a secondary star.
In a study published Wednesday in the journal Nature, researchers report that interactions between two stars with misaligned orbits may be responsible for putting this planet on the path to becoming a “hot Jupiter.”
Astronomers have found more than 5,600 confirmed exoplanets, 300 to 500 of which are “hot Jupiters.” These planets are large Jupiter-like bodies of gas that orbit their parent stars, heating them to scorching temperatures.
While Jupiter takes 4,000 Earth days to complete one orbit around the Sun, hot Jupiters complete their orbit in a few days.
Scientists believe that large planets initially orbited their stars from afar but migrated closer over time. But they have long questioned how the massive worlds ended up in such tight orbits, much closer to their stars than Mercury is to our sun.
First captured by NASA’s planet-hunting TESS satellite in January 2020, observations of TIC 241249530 b provide rare and revealing insights into a planet on its way to becoming a hot Jupiter.
“Astronomers have been searching for exoplanets that are possible precursors or intermediate products of the migration process of hot Jupiters for more than two decades, so I was very surprised and excited to find one,” lead study author Arvind Gupta, a postdoctoral fellow at NOIRLab who discovered the planet while a doctoral student at Penn State, said in a statement.
Noticing a changing world
On January 12, 2020, the Transiting Planet Survey Satellite collected data that suggested something had passed in front of its host star, TIC 241249530. TESS monitors the brightness of nearby stars, looking for dips in starlight that could indicate the presence of exoplanets.
Gupta and his colleagues followed the data and determined that a Jupiter-sized planet had passed in front of the star. They then used instruments on the WIYN 3.5-meter Telescope at Kitt Peak National Observatory in Arizona to measure the star’s radial velocity, or how much the star wobbles back and forth as the planet’s gravity pulls on it.
Radial velocity data also confirmed the existence of the same planet, helping researchers clarify that the planet is about five times more massive than Jupiter and has “a very eccentric orbit,” astronomers say.
Astronomers use the term “eccentric” to describe the shape of a planet’s orbit on a scale of zero to 1. Zero equals a perfectly circular orbit. In our solar system, Earth’s eccentricity is 0.02, while Pluto’s rather oval-shaped orbit around the sun is considered to be 0.25.
The newly discovered exoplanet has an eccentricity of 0.94, which is longer than any other transiting exoplanet astronomers have found so far, according to the researchers. The strange world takes about six months to complete an orbit around its parent star, coming in extremely close, then shooting wide, then dropping back down to a narrow, oval orbit that resembles a cucumber.
“We caught this massive planet making a sharp, sharp turn during its close passage around its star,” study co-author Suvrath Mahadevan, the Verne M. Willaman Professor of Astronomy at Penn State, said in a statement. “Such highly eccentric transiting planets are incredibly rare, and it’s truly surprising that we were able to discover the most eccentric one.”
The planet is just 3 million miles away from its star, 10 times closer than Mercury is to the sun. For reference, Mercury is an average of 36 million miles (58 million kilometers) from the sun, according to NASA.
The extreme orbit causes “tremendous temperature variations” throughout the planet’s year, said Jason Wright, co-author of the study and professor of astronomy and astrophysics at Penn State University.
“The cloud top temperatures get hot enough to melt titanium during the few days when the star is screaming from its close gravity,” Wright said via email. “It is farther away for most of its orbit, and at its farthest point the daytime cloud top temperature is like a hot summer day on Earth.”
The team also discovered that the planet orbits in a backward, or opposite, direction compared to the rotation of its star — a rare phenomenon not seen in most exoplanets and not seen in our Solar System either.
All the oddities observed in TIC 241249530 b are helping astronomers understand how the planet formed.
“While we can’t press rewind and watch the planetary migration process in real time, this serves as a kind of snapshot of the exoplanet migration process,” Gupta said. “Planets like this are hard to find, and we hope it helps us unravel the story of hot Jupiter formation.”
Dance of orbits
The team ran simulations to determine how the planet might have ended up in such an unusual orbit and how it might evolve over time. The simulations included modeling the gravitational interactions between TIC 241249530 b and its parent star and secondary star.
The team estimated that the planet likely formed far from the parent star and started out in a wide, circular orbit similar to Jupiter. However, the researchers said the parent star had an orbit that was out of alignment with the secondary star, which exerted gravitational forces on the planet and elongated its orbit.
“Over many orbits, the gravitational influence of that outer star changed the orbit of TIC 241249530 b, making it progressively more elongated,” Wright said.
The planet’s orbit loses energy with each passage of its host star, so astronomers predict that over hundreds of millions of years the orbit will narrow, and the current 167-day orbit will last only a few days.
The planet would then likely evolve into a true hot Jupiter, said Sarah Millholland, an assistant professor of physics at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research and a co-author of the study.
“This is a pretty extreme process in that the changes in the planet’s orbit are so big,” Millholland said. “This is a big orbital dance that’s happening over billions of years, and the planet is along for the ride.”
Twin hot Jupiters
The only known early hot Jupiter before TIC 241249530 b was an exoplanet called HD 80606 b, discovered in 2001. HD 80606 b was considered the planet with the most eccentric orbit until its recent discovery.
HD 80606 b has an eccentricity of 0.93 and an orbit of 111 days, orbiting in the same direction as its star. But otherwise the planets are practically twins, Wright said. Finding two planets at such a short stage of planetary orbital evolution is “like finding a butterfly at the moment its chrysalis opens,” he said.
The discovery of a second hot Jupiter progenitor helps astronomers confirm the idea that high-mass gas giants transform into hot Jupiters as they migrate from eccentric to circular orbits, the researchers said.
The team hopes to observe TIC 241249530 b with the James Webb Space Telescope to uncover the dynamics of its atmosphere and see how it responds to such rapid heating. And the search is on for such planets to evolve into hot Jupiters.
“This system shows how incredibly diverse exoplanets can be,” Millholland said. “These are mysterious otherworlds that can have wild orbits that tell a story about how they got here and where they’re going. For this planet, its journey is not yet complete.”
For more CNN news and bulletins, create an account at CNN.com