SANTA CRUZ DE TENERIFE, 17 Jul. (EUROPA PRESS) –
An international team of scientists, including the Instituto de Astrofísica de Canarias (IAC), has identified the extremely peculiar orbit of a giant gas exoplanet, providing insights into the formation of hot Jupiters.
This planet, known as TIC 241249530 b, not only follows one of the most elongated orbits among all transiting exoplanets known, but it also does so in the opposite direction to the rotation of its parent star. This discovery sheds light on the enigma of how these massive gas giants transition into hot Jupiters, with very close and circular orbits. The findings are published in the journal ‘Nature’.
Among the myriad exoplanets identified, there exist a group known as hot Jupiters: large exoplanets similar to Jupiter that orbit extremely close to their star, some even closer than Mercury is to the Sun. The process through which hot Jupiters end up in such close orbits is a mystery, as they cannot form there. Astronomers hypothesize that they initially form in distant orbits from their stars and gradually migrate inwards over time.
The initial stages of this migration process have seldom been observed. However, a recent analysis of the exoplanet TIC 241249530 b, discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS) in 2020, has indicated that its orbit is highly eccentric, tracing an ellipse with one axis significantly larger than the other. This unique trajectory suggests that the planet is in the phase just before migration to becoming a hot Jupiter. Data also confirms that the exoplanet possesses a mass approximately five times that of Jupiter.
TIC 241249530 b is the second exoplanet discovered to be in a stage of development prior to shifting to tighter orbits. Detecting such exoplanets observationally supports the notion that gas giants with higher masses transform into hot Jupiters as they progress from highly eccentric orbits to closer, more circular paths. This transformation occurs due to tidal forces from the star extracting energy from the orbit, causing it to shrink and become more rounded.
“Whilst we are unable to witness the planetary migration process unfolding in real time, this exoplanet offers a glimpse into this phenomenon,” expressed Arvind Gupta, a postdoctoral researcher at NOIRLab and the lead author of the study published in Nature. “Planets like this are exceedingly rare and challenging to detect, and we anticipate that it can aid in unravelling the history of hot Jupiter formation.”
THE MOST UNUSUAL PLANET YET DISCOVERED
The orbital eccentricity of a planet is rated on a scale from 0 to 1, with 0 indicating a perfectly circular orbit and 1 representing a highly elliptical orbit. This exoplanet possesses an orbital eccentricity of 0.94, making it the most eccentric planet identified using the transit method. For comparison, Pluto’s highly elliptical orbit around the Sun has an eccentricity of 0.25, while Earth’s eccentricity is 0.02.
If this planet were part of our Solar System, its orbit would span from its closest approach, ten times nearer to the Sun than Mercury, to its farthest distance, at the same distance as Earth. This unusual orbit would result in temperature fluctuations on the planet, ranging from scorching heat akin to a summer day to temperatures so extreme that they could liquefy titanium during its closest approach to the star.
Moreover, the team also noted that TIC 241249530 b orbits in a retrograde manner compared to the usual orbit, meaning it moves in the opposite direction to the rotation of its host star. This phenomenon is uncommon among most exoplanets, including those in our Solar System, and it aids the team in interpreting the distinct evolution of the exoplanet.
The team utilised the 3.5-meter WIYN telescope at the U.S. National Science Foundation’s (NSF) Kitt Peak National Observatory for their research. In future endeavours, the team aims to enhance their understanding of TIC 241249530 b’s atmosphere through observations with advanced telescopes like the James Webb Space Telescope (JWST).
“We are particularly intrigued by what we can uncover about the dynamics of this planet’s atmosphere after it experiences one of its searingly close encounters with its star,” remarked Enric Pallé, a researcher at the IAC and a co-author of the study. “Telescopes such as JWST have the capability to analyse variations in the atmosphere of the newly detected exoplanet as it undergoes rapid heating, indicating that the team still has much to learn about the exoplanet,” he added.
“Astronomers have been scouring the skies for exoplanets that could potentially serve as precursors to hot Jupiters or intermediary products of the migration process for over twenty years, hence I was extremely taken aback – and exhilarated – to find one. It’s precisely what I had been anticipating discovering,” Gupta concluded.
