Astronomers Find a Blazing Hot Planet That Orbits Its Star in Just 16 Hours!

Mercury is the speed champion in our Solar System. It orbits the Sun every 88 days, and its average speed is 47 km/s. Its average distance from the Sun is 58 million km (36 million miles), and it’s so fast it’s named after Mercury, the wing-footed God.

But what if instead of Mercury, JupiterJupiter is the largest planet in the solar system and the fifth planet from the sun. It is a gas giant with a mass greater then all of the other planets combined. Its name comes from the Roman god Jupiter.”>Jupiter was closest to the Sun? And what if Jupiter was even closer to the Sun than Mercury and far hotter?

In a remote solar system about 855 light-years away, there’s a planet that makes Mercury seem like a slow, chilled, distant neighbor of the Sun. This planet orbits its star in only 16 hours, giving it one of the shortest orbits ever measured. At that distance and speed, and with the planet’s extremely high surface temperatures, it’s one of the most exotic planets ever found.

The planet’s name is TOI-2109b, and it’s what astronomers call an “Ultrahot Jupiter.” Hot Jupiters are gas giants that orbit extraordinarily close to their stars and have extremely high surface temperatures. Ultrahot Jupiters are even more extreme. Their surface temperatures are greater than 2200 Kelvin (1900 C, 3500 F). Astronomers estimate that TOI-2109 b’s dayside temperature is greater than 3500 K (3225 C, 5840 F), as hot as some small stars.

A new paper published in The Astronomical Journal presented the discovery. The paper’s title is “TOI-2109: An Ultrahot Gas Giant on a 16 hr Orbit.” The lead author is Ian Wong, currently at NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. It’s vision is “To discover and expand knowledge for the benefit of humanity.””>NASA’s Goddard Space Flight Center, but a postdoc at MITMIT is an acronym for the Massachusetts Institute of Technology. It is a prestigious private research university in Cambridge, Massachusetts that was founded in 1861. It is organized into five Schools: architecture and planning; engineering; humanities, arts, and social sciences; management; and science. MIT’s impact includes many scientific breakthroughs and technological advances.”>MIT during this research.

NASA’s TESSLaunched on April 18, 2018, aboard a SpaceX Falcon 9 rocket, NASA’s Transiting Exoplanet Survey Satellite (TESS) is a mission to search nearby stars for undiscovered worlds with a gold of discovering thousands of exoplanets around nearby bright stars.”>TESS (Transiting Exoplanet Survey Satellite) found the planet in May 2020. TESS started observing it on May 13th and kept watching for almost a month. Over the next year, multiple ground-based observatories performed follow-up observations in different wavelengths. All those observations confirmed that TOI-2109b is a rare and unusual planet.

“Everything was consistent with it being a planet, and we realized we had something very interesting and relatively rare,” said study co-author Avi Shporer from MIT’s Kavli Institute for Astrophysics and Space Research.

TOI-2109 b’s 16-hour orbital period is the shortest ever measured for a gas giant. (The previous record-holder has an 18-hour orbit.) The planet is about five times more massive than our own Jupiter, and it orbits an F-type star about 1.5 times more massive than our Sun. It’s difficult to imagine what this arrangement would look like to any observer in the same system.

Artist’s rendering of a Jupiter-sized exoplanet and its host, a star slightly more massive than our sun. Credit: ESO

The planet is so hot because it’s an average of only 2.4 million km (1.5 million mi) from its star. It’s probably tidally locked to its star like other Hot Jupiters and Ultrahot Jupiters. The extremely high dayside temperature can tear molecules apart into their constituent atoms. Theoretical modeling shows that this can happen to molecular hydrogen. If the night side is significantly cooler, the hydrogen can combine into molecules again.

A month of TESS observations meant that the team could observe the planet as it orbited its star. They watched the secondary eclipse—when a planet passes behind its star—in multiple wavelengths. That helped them determine that the daytime temperature likely exceeds 3500 K. But the researchers aren’t sure what happens on the nightside because TESS isn’t sensitive enough. If it’s true that molecular hydrogen is torn apart on the dayside and recombines on the nightside, then that could contribute to more efficient temperature mixing in the atmosphere and could mean the temperature isn’t as extreme.

“Meanwhile, the planet’s night side brightness is below the sensitivity of the TESS data, which raises questions about what is really happening there,” said Shporer. “Is the temperature there very cold, or does the planet somehow take heat on the day side and transfer it to the night side? We’re at the beginning of trying to answer this question for these ultrahot Jupiters.”

The researchers found that TOI-2109b is slowly spiraling into the star at about 10 to 750 milliseconds per year. Astronomers have found other Hot Jupiters whose orbital decay draws them into their stars, but nothing as fast as this.

Artist’s concept of Jupiter-sized exoplanet that orbits relatively close to its star (aka. a “hot Jupiter”). Credit: NASA/JPL-Caltech

TOI-210 b’s extreme nature helps confirm the status of Ultrahot and Hot Jupiters as one of the most extreme types of exoplanets. More powerful telescopes will reveal more of the planet’s nature, and the team hopes that the Hubble will be able to study it, along with the soon-to-be-launched James Webb Space TelescopeThe James Webb Space Telescope (JWST or Webb) is an orbiting infrared observatory that will complement and extend the discoveries of the Hubble Space Telescope. It covers longer wavelengths of light, with greatly improved sensitivity, allowing it to see inside dust clouds where stars and planetary systems are forming today as well as looking further back in time to observe the first galaxies that formed in the early universe.”>James Webb Space Telescope. Watching what happens as the planet gets closer and closer to the star is especially interesting to astronomers.

“Ultrahot Jupiters such as TOI-2109b constitute the most extreme subclass of exoplanetAn exoplanet (or extrasolar planet) is a planet that is outside the Solar System, orbiting around a star other than the Sun. The first suspected scientific detection of an exoplanet occurred in 1988, with the first confirmation of detection coming in 1992.”>exoplanet,” Wong says. “We have only just started to understand some of the unique physical and chemical processes that occur in their atmospheres — processes that have no analogs in our own solar system.”

Future observations of TOI-2109b may also reveal clues to how such dizzying systems come to be in the first place. “From the beginning of exoplanetary science, hot Jupiters have been seen as oddball,” Shporer says. “How does a planet as massive and large as Jupiter reach an orbit that is only a few days long? We don’t have anything like this in our Solar System, and we see this as an opportunity to study them and help explain their existence.”

In the distant past, Jupiter may have migrated to within 1.5 AU of the Sun before reversing course to the orbital path it follows now. That’s called the Grand Tack Hypothesis. That would’ve been something for human eyes to behold.

Shortly after forming, Jupiter migrated toward the Sun. Saturn did too, and eventually, their fates became linked. When Jupiter was about where Mars is now, the pair turned and moved away from the Sun. Scientists have referred to this as the “Grand Tack,” a reference to the sailing maneuver. Credit: NASA/GSFC

Finding extreme and unusual exoplanets teaches us a lot about the range of planet types out there. Exoplanet surveys find lots of Hot Jupiters and Ultrahot Jupiters because they’re huge and close to their stars. But they’re actually scarce.

The authors point out that only about 0.5% of Sun-like stars host these extreme planets. But even though their numbers are few, they make a massive contribution to our understanding of exoplanets overall. “Their large size in relation to their host stars and high temperatures enable a broad range of intensive studies that extend far beyond the rudimentary measurements of planet mass and radius,” the authors explain.

“Over the past two decades, a wide arsenal of observational techniques has been leveraged to probe the atmospheric properties of hot Jupiters in ever-increasing detail,” they write in their paper. Things like temperature distribution, chemical composition, condensate clouds, photochemical hazes, and heat transport mechanisms are becoming easier to study.

Astronomers are learning that Ultrahot Jupiters are “… characterized by a number of distinct physical and dynamical properties that set them apart from the rest of the hot gas-giant population.”

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No article on exoplanets can be complete without looking ahead to the James Webb Space Telescope. The JWST will have the power to probe exoplanet atmospheres more rigorously than any other tool currently at astronomers’ disposal.

Part of the search for and study of exoplanets is centred around finding Earth-like planets in habitable zones. But Ultrahot Jupiters like TOI-2109b can teach us a lot about planets at their most extreme and about planet-star interactions that we can’t study in our Solar System. And the JWST will make a considerable contribution to our knowledge.

“While future advances in telescope capabilities will allow for comparably in-depth explorations of smaller and cooler exoplanets, ultrahot Jupiters will continue to be among the most fruitful candidates for impactful efforts at characterization, providing crucial insights into the nature of planets at their most extreme,” the authors write.

Originally published on Universe Today.

For more on this discovery, read Newly Discovered Extreme “Ultrahot Jupiter” Blitzes Around Its Star – One Year Is Just 16 Hours Long.

Reference: “TOI-2109: An Ultrahot Gas Giant on a 16 hr Orbit” by Ian Wong, Avi Shporer, George Zhou, Daniel Kitzmann, Thaddeus D. Komacek, Xianyu Tan, René Tronsgaard, Lars A. Buchhave, Shreyas Vissapragada, Michael Greklek-McKeon, Joseph E. Rodriguez, John P. Ahlers, Samuel N. Quinn, Elise Furlan, Steve B. Howell, Allyson Bieryla, Kevin Heng, Heather A. Knutson, Karen A. Collins, Kim K. McLeod, Perry Berlind, Peyton Brown, Michael L. Calkins, Jerome P. de Leon, Emma Esparza-Borges, Gilbert A. Esquerdo, Akihiko Fukui, Tianjun Gan, Eric Girardin, Crystal L. Gnilka, Masahiro Ikoma, Eric L. N. Jensen, John Kielkopf, Takanori Kodama, Seiya Kurita, Kathryn V. Lester, Pablo Lewin, Giuseppe Marino, Felipe Murgas, Norio Narita, Enric Pallé, Richard P. Schwarz, Keivan G. Stassun, Motohide Tamura, Noriharu Watanabe, Björn Benneke, George R. Ricker, David W. Latham, Roland Vanderspek, Sara Seager, Joshua N. Winn, Jon M. Jenkins, Douglas A. Caldwell, William Fong, Chelsea X. Huang, Ismael Mireles, Joshua E. Schlieder, Bernie Shiao and Jesus Noel Villaseñor, 23 November 2021, Astronomical Journal.
DOI: 10.3847/1538-3881/ac26bd