On This 'Ultrahot' Planet, One Year Is Just 16 Hours Long

The newly discovered exoplanet, designated TOI-2109b, has an orbital period of 16 hours, and has an orbit which is the shortest of any known gas giant.

The newly discovered exoplanet is 1.5 million miles away from its host star | Photo: NASA/ESA

New Delhi: A team of astronomers from the Massachusetts Institute of Technology (MIT) has recently discovered one of the most extreme ultrahot Jupiters. It is the second hottest planet to have been detected in the universe, according to a study published in the Astronomical Journal. 

Ultrahot Jupiter is a gas giant with a mass around five times that of Jupiter, and are an extreme version of hot Jupiters, which are massive gas giants about the size of Jupiter, but are different only in terms of orbital period. They revolve around their host stars in less than 10 days. 

The newly discovered exoplanet, designated TOI-2109b, has an orbital period of 16 hours. The planet's orbit is the shortest of any known gas giant, the study states.

Since the planet has an extremely tight orbit, and has a close proximity to its host star, the temperature on the planet's day side is around 3,500 Kelvin. This makes the planet about as hot as a small star. Also, TOI-2109b is the second hottest planet detected so far, says the study.

TOI-2109b In The Process Of 'Orbital Decay'

The researchers analysed the planet's properties, and observed it to be in the process of "orbital decay". This means the planet is spiralling into its star, in a fashion similar to bathwater circling a drain, the study states. Orbital decay is a process that leads to a gradual decrease of the distance between two orbiting bodies at their closest approach. The planet is spiralling towards its star faster than other hot Jupiters due its extremely short orbit. The planet's discovery was initially made by NASA's Transiting Exoplanet Survey Satellite, mentions the study.

The study will help astronomers understand how planets behave as they are drawn in and swallowed by their star. 

Ian Wong, the lead author of the study, said astronomers may be able to detect how the planet moves closer to its star in one or two years, and that the planet may fall into its star in another 10 million years, according to a statement by MIT.

A Star In Hercules Constellation Hosts The Newly Discovered Planet

NASA's TESS satellite began observing a star named TOI-2109 on May 13, 2020. The star is located in the southern portion of the Hercules constellation, and is about 855 light years from Earth. It was called the 2,109th "TESS Object of Interest" because scientists believed it could possibly host an orbiting planet. 

TESS collected measurements of the star's light for almost a month. Scientists searched for transits, which are periodic dips in starlight that may indicate a planet passing in front of a star, and analysis of the data confirmed that TOI-2109 hosts an object that transits the star about every 16 hours.

Follow-up studies involved the use of ground-based telescopes to observe the star more closely. The initial detection of TESS, together with the follow-up observations, confirmed the fact that the object transiting the star was an orbiting planet, the study states.

Avi Shporer, a co-author of the study, said they observed something "very interesting and relatively rare".

Properties Of The Planet

The MIT astronomers analysed data using optical and infrared wavelengths, and determined the mass of the planet to be five times that of Jupiter, or about 35 per cent larger than the gas giant. Also, TOI-2109b is extremely close to its star, at a distance of about 1.5 million miles, the study states. This distance is much less than the distance between Mercury and the Sun, which is 36 million miles. 

The planet's host star is almost 50 per cent larger in size and mass than the Sun. TOI-2109b is spiralling into its star at a rate of 10 to 750 milliseconds per year, which is faster than any hot Jupiter observed till date, according to the study. 

The planet has a perpetual day and night side, similar to the Moon with respect to Earth. Shporer said the astronomers were trying to seek answers to some questions, mentions the statement. It is not known whether the temperature on the planet is very cold, or the planet take heat on the day side and transfers it to the night side. 

The researchers hope they can make further observations of TOI-2109b using the Hubble Space Telescope, and the soon-to-launch James Webb Space Telescope.

Wong said ultrahot Jupiters such as TOI-2109b constitute the most extreme subclass of exoplanets. He added that astronomers have just started to understand some of the unique physical and chemical processes that occur in the atmosphere of such planets, and that these processes have no analogs in our solar system.

Shporer said future observations will search for answers to some questions. For instance, what leads to the formation of such large planets with small orbits, and why such systems are not a part of our solar system, are some of the questions.