Exoplanets are planets located outside our solar system. This exoplanet, called TOI-1231 b, performs a full orbit around its star every 24 Earth days.
It orbits a red, or M-type, dwarf star known as NLTT 24399, which is smaller and darker than stars like our sun.
The discovery of the planet has been detailed in a new study to be published in an upcoming issue of The Astronomical Journal.
“Even though TOI 1231 b is eight times closer to its star than the Earth is to the Sun, its temperature is similar to that of the Earth, thanks to its colder and less bright host star,” said Diana Dragomir , co-author of the study, assistant professor. in the Department of Physics and Astronomy at the University of New Mexico, in a statement.
“However, the planet itself is actually larger than Earth and a bit smaller than Neptune – we could call it a sub-Neptune.”
Why this exoplanet could have clouds
The researchers were able to determine the radius and mass of the planet, which helped them calculate its density and deduce its composition.
The exoplanet has a low density, which suggests that it is a gaseous rather than a rocky planet like Earth, but scientists do not yet know for sure the makeup of the planet or its atmosphere.
“TOI-1231b is quite similar in size and density to Neptune, so we believe it has an equally large gaseous atmosphere,” said lead author of the study Jennifer Burt, postdoctoral fellow at the Jet Propulsion Laboratory. from NASA in Pasadena, California.
“TOI1231b could have a large hydrogen or hydrogen-helium atmosphere, or a denser water vapor atmosphere,” Dragomir said. “Each of them would indicate a different origin, allowing astronomers to understand if and how planets form differently around M dwarfs compared to planets around our Sun, for example.”
Researchers believe TOI-1231 has an average temperature of 140 degrees Fahrenheit (60 degrees Celsius), making it one of the coolest small exoplanets available for future study of its atmosphere.
“Compared to most of the transit planets detected so far, which often have scorching temperatures of several hundred or thousand degrees, TOI-1231b is positively freezing,” said Burt.
The colder the exoplanet, the more likely it is to have clouds in its atmosphere.
The equally small exoplanet K2-18 b, discovered in 2015, was recently observed in more detail, and researchers have found evidence of water in its atmosphere.
“TOI-1231b is one of the only other planets we know of in a similar size and temperature range, so future observations of this new planet will allow us to determine how common (or rare) it is for clouds of water form around these temperate worlds, ”Burt said in a statement.
This makes TOI-1231b the ideal candidate for observations of the Hubble Space Telescope – or the James Webb Space Telescope, which is scheduled to launch in October. Webb will have the ability to scan the atmosphere of exoplanets and help determine their composition. And Hubble is expected to observe the exoplanet later this month.
The search for exoplanets
Burt, Dragomir, and their colleagues discovered the planet using data from NASA’s Transiting Exoplanet Survey Satellite, or TESS. The planet-hunting satellite, launched in 2018, observes different areas of the sky for 28 days at a time. So far, TESS has helped scientists find large and small exoplanets orbiting stars like our sun as well as smaller M dwarf stars. These tiny stars are common in the Milky Way galaxy.
When a planet passes in front of its orbiting star, it blocks a certain amount of light. It’s called a transit, and it’s a way for astronomers to search for exoplanets using missions like TESS.
Since M dwarf stars are smaller, the amount of light blocked by an orbiting planet is greater, making the transit more detectable. Scientists are looking for at least two transits before determining whether they have found a candidate exoplanet. Follow-up observations were made using the Planet Finder spectrograph on the Magellan Clay Telescope at the Las Campanas Observatory in Chile.
“One of the most intriguing findings from the past two decades of exoplanet science is that, so far, none of the new planetary systems we’ve discovered resemble our own solar system,” Burt said.
“This new planet that we have discovered is still strange – but it is one more step in resembling our neighboring planets a bit.”