![]() ![]() Past research suggests planets this cool may have clouds high in their atmospheres, which makes it hard to determine what types of gases surround them. With a temperature around 330 Kelvin or 140 degrees Fahrenheit, TOI-1231b is one of the coolest, small exoplanets accessible for atmospheric studies discovered thus far. "However, the planet itself is actually larger than earth and a little bit smaller than Neptune - we could call it a sub-Neptune."īurt and Dragomir, who actually initiated this research while they were Fellows at MIT's Kavli Institute, worked with scientists specializing in observing and characterizing the atmospheres of small planets to figure out which current and future space-based missions might be able to peer into TOI-1231 b's outer layers to inform researchers exactly what kinds of gases are swirling around the planet. "Even though TOI 1231b is eight times closer to its star than the Earth is to the Sun, its temperature is similar to that of Earth, thanks to its cooler and less bright host star," says Dragomir. The smaller the star, the less massive the star, the more the effect of the planet can be detected. When the star is smaller and less massive, it makes detection methods work better because the planet suddenly plays a bigger role as it stands out more easily in relation to the star," explained Dragomir. ![]() "Another advantage of exoplanets orbiting M dwarf hosts is that we can measure their masses easier because the ratio of the planet mass to the stellar mass is also larger. TOI-1231 b is pretty similar in size and density to Neptune, so we think it has a similarly large, gaseous atmosphere." "Those values in turn allowed us to calculate the planet's bulk density and hypothesize about what the planet is made out of. "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. NASA JPL scientist Jennifer Burt, the lead author of the paper, along with her collaborators including Diana Dragomir, an assistant professor in UNM's Department of Physics and Astronomy, measured both the radius and mass of the planet. TOI-1231b's 24-day period, therefore, makes its discovery even more valuable. Because 74 percent of TESS' total sky coverage is only observed for 28 days, the majority of TESS exoplanets detected have periods less than 14 days. Exoplanets must transit their host stars at least twice within TESS 's observing span to be detected with the correct period by the Science Processing Operations Center (SPOC) pipeline and the Quick Look Pipeline (QLP), which search the 2-minute and 30-minute cadence TESS data, respectively. 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.Īlthough it enables the detection of exoplanets across the sky, TESS's survey strategy also produces significant observational biases based on orbital period. Imagine an Earth-like planet passing in front of a star the size of the sun, it's going to block out a tiny bit of light but if it's passing in front of a star that's a lot smaller, the proportion of light that's blocked out will be larger. Because an M dwarf is smaller, when a planet of a given size transits the star, the amount of light that is blocked out by the planet is larger, making the transit more easily detectable. M dwarfs are smaller and possess a fraction of the sun's mass and have low luminosity. M dwarf stars, also known as a red dwarf, are the most common type of star in the Milky Way making up some 70 percent of all stars in the galaxy. This approach has already proven its capability to detect both large and small planets around stars ranging from sun-like down to low-mass M dwarf stars. The observing strategy adopted by NASA's TESS, which divides each hemisphere into 13 sectors that are surveyed for roughly 28 days, is producing the most comprehensive all-sky search for transiting planets. As the planets orbit their hosts, the measured stellar velocities vary periodically, revealing the planetary presence and information about their mass and orbit. The PFS is a sophisticated instrument that detects exoplanets through their gravitational influence on their host stars. 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. The research, titled TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399, will be published in a future issue of The Astronomical Journal. ![]()
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