TESS (Transiting Exoplanet Survey Satellite) has found a new planet, and the discovery of this sub-Neptune exoplanet has scientists excited about atmospheres. The combination of the planet’s size, its thick atmosphere, and its orbit around a small M-class star close to Earth provides researchers with an opportunity to learn more about exoplanet atmospheres. We’re getting better and better at finding exoplanets, and studying their atmospheres is the next step in understanding them as a whole.

All of our exoplanet-detection strategies have an observation bias. It seems impossible to avoid. Even TESS (Transiting Exoplanet Survey Satellite), probably our most adept planet-finder, has an observation bias. Its predecessor Kepler was biased towards larger planets, and TESS doesn’t share that bias. But TESS still has a sort of blind spot due to how it operates.

No telescope can look everywhere at once, and TESS is no exception. It observes the sky mostly in 28-day chunks. So for one of those chunks, it focuses on one area for 28 days. To be confirmed as an exoplanet, an object must pass in front of its star twice in that 28 days. The end result of all this is that most of the planets TESS finds have orbital periods of less than 14 days.

Most of TESS’s observing is done in 28 day chunk, as the image shows. Image Credit: NASA/JPL

But this new planet, named TOI-1231 b, has a 24-day orbital period. This makes it a great target for the study of exoplanet atmospheres because it’s in front of its star longer and can be more easily studied. Universe Today readers know that studying light as it interacts with things is how we gain most of our knowledge about space. TESS itself won’t study the planet. Other missions like the James Webb Space Telescope (JWST) will take care of that by watching the starlight as it passes through the planet’s atmosphere.

“This new planet we’ve discovered is still weird – but it’s one step closer to being somewhat like our neighborhood planets.”

Jennifer Burt, Paper Lead Author, NASA-JPL.

Since TOI-1231 b spends so much time in front of its star relative to other TESS planets, missions like the JWST will get a much better look at it.

But it’s not only the planet’s orbital period that makes it an ideal target. Its size relative to its star also helps. Since the star is so small, the planet blocks out more of its light than if the planet and star were more similar to Earth and the Sun. “In a sense, this creates a larger shadow on the surface of the star, making planets around M dwarfs more easily detectable and easier to study,” the press release says.

The paper outlining TOI 1321-b’s discovery is titled “TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399.” The lead author is NASA JPL scientist Jennifer Burt. The paper will be published in The Astrophysical Journal but is up now on the pre-press site arxiv.org.

“Working with a group of excellent astronomers spread across the globe, we were able to assemble the data necessary to characterize the host star and measure both the radius and mass of the planet,” said Burt in a press release. “Those values in turn allowed us to calculate the planet’s bulk density and hypothesize about what the planet is made out of. TOI-1231 b is pretty similar in size and density to Neptune, so we think it has a similarly large, gaseous atmosphere.”

The team that found TOI-1321 b says the planet is similar to Neptune and likely has a similar gaseous atmosphere. Image Credit: NASA/JPL
The team that found TOI-1321 b says the planet is similar to Neptune and likely has a similar gaseous atmosphere. Image Credit: NASA/JPL

The new planet has a radius of about 3.65 times that of Earth. It has an orbital period of 24.26 days and mass of about 15.5 Earth masses. The star it orbits is an M-dwarf star about 90 light years away in the constellation Vela.

The planet is a lot closer to its star
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