Exoplanets are planets located outside our solar system. This exoplanet, called TOI-1231 b, completes 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 was described in detail in a new study that will be published in a future issue of The Astronomical Journal.
“Although TOI 1231 b is eight times closer to its star than Earth to the Sun, its temperature is similar to that of Earth, thanks to its cooler and less bright host star,” said the study’s co-author. Diana Dragomir, Assistant Professor of Physics and Astronomy at the University of New Mexico.
“However, the planet itself is actually larger than Earth and slightly smaller than Neptune ̵
Why this exoplanet may have clouds
The researchers were able to determine the radius and mass of the planet, which helped them calculate its density and draw conclusions about its composition.
The exoplanet has a low density, suggesting that it is a gaseous planet, not a rocky one like Earth, but scientists still do not know for sure the composition of the planet or its atmosphere.
“TOI-1231 b is quite similar in size and density to Neptune, so we think it has an equally large, gaseous atmosphere,” said study lead author Jennifer Burt, a doctoral student at NASA’s Jet Propulsion Laboratory in Pasadena, California.
“TOI1231b could have a large atmosphere of hydrogen or hydrogen-helium or a denser atmosphere of water vapor,” Dragomir said. “Each of them would point to a different origin, allowing astronomers to understand whether and how planets form differently around M dwarfs than planets around our Sun, for example.”
The researchers believe that TOI-1231 b has an average temperature of 140 degrees Fahrenheit (60 degrees Celsius), making it one of the coolest of the small exoplanets available for future exploration of its atmosphere.
“Compared to most transit planets discovered so far, which often have burning temperatures in the hundreds or thousands of degrees, the TOI-1231 b is positively cool,” Burt said.
The cooler the exoplanet, the more likely it is to have clouds in its atmosphere.
Like the small exoplanet K2-18 b, discovered in 2015, it was recently observed in more detail and researchers found evidence of water in its atmosphere.
“TOI-1231 b is one of the only other planets we know in a similar size and temperature range, so future observations of this new planet will allow us to determine how often (or rarely) water clouds form moderate worlds around them. “Burt said in a statement.
This makes the TOI-1231 b the ideal candidate for observations by the Hubble Space Telescope – or the James Webb Space Telescope, which is due to launch in October. The web will have the ability to peek into the atmosphere of exoplanets and help determine their composition. And Hubble is due to observe the exoplanet later this month.
The search for exoplanets
Bert, Dragomir and their colleagues discovered the planet using data from NASA’s or TESS’s exoplanet transit satellite. The planet hunting satellite, launched in 2018, observed different areas of the sky for 28 days. So far, TESS has helped scientists find large and small exoplanets orbiting stars like our sun, as well as smaller dwarf stars. These diminutive stars are common in the Milky Way galaxy.
When a planet crosses in front of its star during orbit, it blocks a certain amount of light. This is called transit, and it’s one of the ways astronomers search for exoplanets using missions like TESS.
Given that the M dwarfs are smaller, the amount of light blocked by the planet orbiting them is greater, making transit more detectable. Scientists are looking for at least two transits before determining if they have found a candidate for an exoplanet. Subsequent 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 results of the last two decades of exoplanet science is that so far none of the new planetary systems we’ve discovered look like our own solar system,” Burt said.
“This new planet we’ve discovered is still weird, but it’s one step closer to being somewhat like our neighboring planets.”