TESS (Transiting Exoplanet Survey Satellite) has found a new planet, and the discovery of this sub-Neptune exoplanet is exciting scientists to atmospheres. The combination of the planet’s size, its thick atmosphere, and its orbit around a small M-class star near Earth offers researchers an opportunity to learn more about the atmospheres of exoplanets. 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. Even TESS (Transiting Exoplanet Survey Satellite), probably our most adept planet finder, has a tendency to observe. Its predecessor, Kepler, was geared towards larger planets, and TESS does not share that bias. But TESS still has a kind of blind spot because of the way it works.
No telescope can look everywhere at the same time, and TESS is no exception. It mostly observes the sky in 28-day blocks. For one of those chunks, it focuses on one area for 28 days. To be confirmed as an exoplanet, an object must pass its star twice in 28 days. The bottom line of all of this is that most of the planets TESS finds have orbital times of less than 14 days.
Most of the observations from TESS are done in 28-day chunks as the picture shows. Image source: NASA / JPL
But this new planet, named TOI-1231b, has an orbital period of 24 days. This makes it a great target for studying exoplanet atmospheres because it is longer in front of its star and easier to study. Universe Today readers know that by studying light and how it interacts with things, we gain most of our knowledge of space. TESS itself will not study the planet. Other missions like the James Webb Space Telescope (JWST) will make sure of this by watching the starlight as it pours through the planet’s atmosphere.
“This new planet we discovered is still strange – but it is one step closer to being like our neighboring planets.”
Jennifer Burt, lead author of the paper, NASA-JPL.
Since TOI-1231b spends so much time in front of its star compared to other TESS planets, missions like the JWST will get a much better look at it.
But it’s not just the planet’s orbital period that makes it an ideal destination. Its size in relation to its star also helps. Because the star is so small, the planet blocks more of its light than if the planet and star were more similar to the earth and the sun. “In a way, this creates a larger shadow on the star’s surface, making planets around M-dwarfs easier to see and easier to study,” the press release said.
The paper describing the discovery of TOI 1321-b is entitled “TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Near M3 Dwarf NLTT 24399”. The lead author is NASA JPL scientist Jennifer Burt. The paper will be published in the Astrophysical Journal but is now available on the prepress site arxiv.org.
“Working with a group of excellent astronomers around the world, we were able to compile the data necessary to characterize the host star and measure both the radius and mass of the planet,” Burt said in a press release. “These values, in turn, enabled us to calculate the planet’s bulk density and hypothesize what the planet is made of. TOI-1231b is quite similar in size and density to Neptune, so we think it has a similarly sized gaseous atmosphere. “
The team that found TOI-1321b says the planet is similar to Neptune and likely has a similar gas atmosphere. Image source: NASA / JPL
The new planet has a radius about 3.65 times the radius of the earth. It has an orbital period of 24.26 days and a mass of about 15.5 Earth masses. The star it orbits is an M dwarf star in the constellation Vela, about 90 light-years away.
The planet is much closer to its star than the earth is to the sun. But 1321 b is roughly the same temperature because its star is so much cooler than the sun. This lower temperature also makes it a desirable object for further studies with the JWST and other telescopes. Its equilibrium temperature is only about 330 Kelvin, making it one of the coolest little planets available for atmospheric studies. For comparison: the average temperature of the earth is around 288 Kelvin, and an ultra-hot Jupiter can have a daytime temperature of up to 2700 K, hotter than many stars.
“TOI-1231b is one of the few other planets we know of a similar size and temperature range, so through future observations of this new planet we will be able to determine how often (or rarely) water clouds form around it.” Temperate worlds “Said Burt.
This picture from the study shows the Transmission Spectroscopy Metric (TSM) values for some small exoplanets with a temperature of less than 1000 Kelvin. The four filled in planets with black circles and lettering were subjected to a follow-up examination with the Hubble. TOI-1231b is next, giving scientists another opportunity to study the atmosphere of smaller, cooler planets. The horizontal axis shows the J size of the stars orbiting the planets. Image source: Burt et al. 2021.
In addition to being a target destination, it has a high systemic radial velocity. Astronomers are particularly fond of this because it could allow them to observe low-velocity hydrogen atoms emerging from the atmosphere. TOI-1231b’s properties and relationship with its star are similar to those of another star called GJ-436 and its planet GJ-436b. GJ-436b is known for its atmospheric escape, so astronomers believe the newly discovered exoplanet will also experience atmospheric escape, albeit at a much slower rate than GJ-436b. Hydrogen is the most likely reason to flee, but difficult to see because of the interstellar gas. But TOI-1232 b is moving away from Earth very quickly, which makes the hydrogen more visible.
Diana Dragomir is one of the co-authors of the paper. In the same press release, she said, “The low density of TOI-1231b suggests that it is surrounded by a sizeable atmosphere and is not a rocky planet. But the composition and extent of this atmosphere are unknown! ”Said Dragomir. “TOI-1231b could have a large hydrogen or hydrogen-helium atmosphere, or a denser water vapor atmosphere. Each of them would point to a different origin, which enables astronomers to understand whether and how planets around M-dwarfs, for example, form differently than the planets around our sun. Our upcoming HST observations will answer these questions, and the JWST promises to provide an even deeper insight into the planet’s atmosphere. “
It will be a while before the JWST can train its sensors on the newly discovered exoplanet, although the space telescope is about to launch (™). But the Hubble is ready to go. In fact, one of the many authors on the paper plans to monitor TOI-1231b later this month.
The James Webb Space Telescope in June 2020. We have been told it will launch soon. Image source: NASA / JPL
All of these exoplanet discoveries show us the great diversity that exists in other solar systems. There are some downright strange planets out there, at least compared to Earth. But this one is more like Earth than any hot Jupiter we’ve found, and while it’s still different, it could at least teach us something about our own solar system and the planets that live there.
“One of the most fascinating results of the last two decades of exoplanet research is that none of the new planetary systems we have discovered looks like our own solar system,” said Burt. “They are full of planets between the size of Earth and Neptune in orbits much shorter than Mercury’s, so we have no local examples to compare them to. This new planet we discovered is still weird – but it’s one step closer to being like our neighboring planets. Compared to most of the transit planets discovered so far, which often have scorching temperatures of many hundreds or thousands of degrees, TOI-1231 b is downright cold. “