An international group of collaborators, including scientists from NASA’s Jet Propulsion Laboratory and the University of New Mexico, have discovered a new, temperate sub-Neptune-sized exoplanet with a 24-day orbit orbiting a nearby M dwarf star. The recent discovery provides exciting research opportunities thanks to the planet’s large atmosphere, small star, and how fast the system is moving away from Earth.
The research entitled TOI-1231 b: A temperate, Neptune-sized planet that passes the nearby M3 dwarf NLTT 24399 will be published in a future issue of The Astronomical Journal. The exoplanet, TOI-1231 b, was detected using photometric data from the Transiting Exoplanet Survey Satellite (TESS) and followed up with observations using the Planet Finder Spectrograph (PFS) on the Magellan Clay Telescope at Las Campanas Observatory in Chile. PFS is a sophisticated instrument that registers exoplanets through their gravity on their host stars. As the planets orbit their hosts, the measured star velocities vary periodically, revealing the planetary presence and information about their mass and orbit.
The observation strategy adopted by NASA’s TESS, which divides each hemisphere into 13 sectors studied for approximately 28 days, produces the most comprehensive search for transiting planets. This approach has already proven its ability to detect both large and small planets around stars ranging from sun-like down to M-dwarf stars with low mass. M dwarf stars, also known as a red dwarf, are the most common type of star in the Milky Way, making up approx. 70 percent of all stars in the galaxy.
M-dwarfs are smaller and have a fraction of the mass of the sun and have low brightness. Because an M dwarf is smaller when a planet of a given size passes the star, the amount of light blocked by the planet is larger, making transit more easily detectable. Imagine an Earth-like planet passing in front of a star the size of the sun, it will block a little bit of light; but if it passes in front of a star that is much smaller, the proportion of light that is blocked will be greater. In a way, this creates a larger shadow on the star’s surface, making planets around M-dwarfs easier to detect and easier to study.
Although it enables the detection of exoplanets across the sky, TESS’s exploration strategy also produces significant observational perturbations based on orbital time. Exoplanets must transit their host stars at least twice within TESS’s range to be detected with the correct period by the Science Processing Operations Center (SPOC) pipeline and the Quick Look Pipeline (QLP) searching for 2-minute and 30-minute cadence TESS data , respectively. Since 74 percent of TESS’s total cloud cover is only observed for 28 days, the majority of the discovered TESS exoplanets have periods below 14 days. The TOI-1231bs 24-day period therefore makes the discovery even more valuable.
NASA JPL scientist Jennifer Burt, lead author of the paper along with her collaborators, including Diana Dragomir, an assistant professor at UNM’s Department of Physics and Astronomy, measured both the planet’s radius and mass.
“Working with a group of excellent astronomers spread across the globe, we were able to gather the data needed to characterize the host star and measure both the radius and mass of the planet,” Burt said. “These values again allowed us to calculate the planet’s density and hypotheses about what the planet is made of. TOI-1231 b is largely similar in size and density to Neptune, so we think it has a similarly large, gaseous atmosphere.”
“Another advantage of exoplanets orbiting M dwarf hosts is that we can more easily measure their masses because the ratio of planetary mass to star mass is also greater. When the star is smaller and less massive, it makes detection methods work better. because the planet suddenly plays a bigger role as it more easily stands out in relation to the star, “Dragomir explained.” Like the shadow cast on the star. The smaller the star, the less massive the star, the more the effect of the planet can be detected.
“Although the TOI 1231b 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 cooler and brighter host star,” says Dragomir. “However, the planet itself is actually larger than Earth and slightly smaller than Neptune – we could call it a sub-Neptune.”
Burt and Dragomir, who actually started this research while fellows at MIT’s Kavli Institute, worked with scientists who specialize in observing and characterizing atmospheres on small planets to find out what current and future space-based missions might be. could look into the outer layers of TOI-1231 b to inform scientists exactly what kind of gases are spinning around the planet. With a temperature of about 330 Kelvin or 140 degrees Fahrenheit, the TOI-1231b is one of the coolest, small exoplanets available for atmospheric studies so far discovered.
Previous studies suggest that planets like this cool may have clouds high in their atmosphere, making it difficult to determine what types of gases surround them. But new observations of another small, cool planet called K2-18 b broke this trend and showed signs of water in its atmosphere, surprising many astronomers.
“TOI-1231 b 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 let us determine how common (or rare) it is to form. water clouds around these temperate worlds, “Burt said.
In addition, with its host star’s high near-infrared (NIR) brightness, it is an exciting target for future missions with the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST). The first set of these observations, led by one of the newspaper’s co-authors, was to take place later this month using the Hubble Space Telescope.
“The low density of TOI 1231b indicates that it is surrounded by a significant atmosphere rather than being a rocky planet. But the composition and extent of this atmosphere is unknown!” said Dragomir. “TOI1231b could have a large hydrogen or hydrogen helium atmosphere or a denser water vapor atmosphere. Each of these would point to a different origin so astronomers could understand if and how planets form differently around M dwarfs compared to the planets around our Sun, for example. Our upcoming HST observations are beginning to answer these questions, and JWST promises an even more in-depth look at the planet’s atmosphere. “
Another way to study the planet’s atmosphere is to investigate whether gas is blown away by looking for evidence of atoms such as hydrogen and helium surrounding the planet as it passes over the face of the host star. In general, hydrogen atoms are almost impossible to detect because their presence is hidden by interstellar gas. But this planetary star system provides a unique opportunity to apply this method because of how fast it moves away from Earth.
“One of the most exciting results of the last two decades of exoplanet science is that so far none of the new planetary systems we have discovered resemble anything like our own solar system,” Burt said. “They are full of planets between the size of Earth and Neptune on orbits that are much shorter than Mercury, so we have no local examples to compare them with. This new planet we have discovered is still strange – but it is a step closer to being something like our neighborhood planets. Compared to most transiting planets discovered so far, which often have burning temperatures in the hundreds or thousands of degrees, the TOI-1231 b is positively frigid. “
Finally, Dragomir reflects that “this planet joins the ranks of only two or three other nearby small exoplanets that will be explored with every chance we get, and using a wide range of telescopes in the coming years, so keep an eye on the new TOI1231b development! “
This article is in the press The Astronomical Journal.
New sub-Neptune exoplanet discovered by astronomers
TOI-1231 b: A temperate, Neptune-sized planet that passes the nearby M3 dwarf NLTT 24399, arXiv: 2105.08077 [astro-ph.EP] arxiv.org/abs/2105.08077
Provided by the University of New Mexico
Citation: Scientists discover new exoplanet with a mature atmosphere for study (2021, June 9) retrieved June 9, 2021 from https://phys.org/news/2021-06-scientists-exoplanet-atmosphere-ripe.html
This document is subject to copyright. Except for any fair trade for the purpose of private investigation or research, no parts may be reproduced without written permission. The content is provided for informational purposes only.