An international team of collaborators, including scientists from NASA’s Jet Propulsion Laboratory and the University of New Mexico, have discovered a new, moderate exoplanet the size of Neptune with a 24-day orbit around a nearby dwarf star. The recent discovery offers exciting exploration opportunities thanks to the planet’s considerable atmosphere, the small star, and how fast the system is moving away from Earth.
The study, entitled TOI-1231 b: A temperate, Neptune-sized planet passing through 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 Exoplanet Transit Satellite (TESS) and followed by observations using the Planet Finder (PFS) spectrograph on the Magellan Clay telescope at the Las Campanas Observatory in Chile. PFS is a complex instrument that detects exoplanets through their gravitational influence on their host stars. As the planets orbit their hosts, the measured stellar velocities change periodically, revealing the planetary presence and information about their mass and orbit.
The monitoring strategy adopted by NASA’s TESS, which divides each hemisphere into 13 sectors that are studied in about 28 days, leads to the most comprehensive search for planets in transit. This approach has already proven its ability to detect both large and small planets around stars ranging from sun-like down to low-weight stars M. Dwarf stars, also known as red dwarfs, are the most common type of star in the Milky Way. making up about 70 percent of all stars in the galaxy.
M dwarfs are smaller and have part of the solar mass and have low luminosity. Because the M dwarf is smaller when a planet of a certain size passes through the star, the amount of light that is blocked by the planet is greater, making transit easier to detect. Imagine an Earth-like planet passing in front of a star the size of the sun that will block some 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 sense, this creates more shadow on the star’s surface, making the planets around the M dwarfs easier to detect and easier to study.
Although it makes it possible to detect exoplanets in the sky, TESS’s research strategy also produces significant biased observations based on the orbital period. Exoplanets must pass through their receiving stars at least twice as part of TESS observation to be detected with the correct period from the Science Center (SPOC) pipeline and the QLP pipeline, which search for 2-minute and 30 TESS data per minute per clock, respectively. Because 74 percent of the total TESS sky cover is observed in just 28 days, most of the TESS exoplanets discovered have periods of less than 14 days. Therefore, the 24-day period of TOI-1231b makes its discovery even more valuable.
NASA JPL scientist Jennifer Burt, the lead author of the article, along with her collaborators, including Diana Dragomir, an assistant professor at the Department of Physics and Astronomy at UNM, measured the radius and mass of the planet.
“Working with a group of excellent astronomers around the world, we were able to gather the data needed to characterize the receiving star and measure both the radius and mass of the planet,” Burt said. “These values, in turn, allowed us to calculate the total density of the planet and guess what the planet is made of. TOI-1231 b is quite similar in size and density to Neptune, so we think it has such a large gaseous atmosphere.”
“Another advantage of exoplanets orbiting M-dwarfs is that we can measure their masses more easily, as the ratio of planetary mass to stellar mass is also greater. When the star is smaller and smaller massive, this makes detection methods work better, because the planet suddenly plays a bigger role, as it stands out more easily 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 planet’s effect can be detected.
“Although TOI 1231b is eight times closer to its star than Earth to the Sun, its temperature is similar to that of Earth, thanks to a cooler and less bright host star,” says Dragomir. “However, the planet itself is actually larger than Earth and slightly smaller than Neptune – we could call it sub-Neptune.”
Bert and Dragomir, who actually initiated this study while collaborating at MIT’s Kavli Institute, worked with scientists specializing in observing and characterizing the atmosphere of small planets to find out which current and future space missions could look into. in TOI- The outer layers of 1231 b to inform researchers exactly what gases revolve around the planet. With a temperature of about 330 Kelvin or 140 degrees Fahrenheit, TOI-1231b is one of the coolest, smallest exoplanets available for atmospheric research ever discovered.
Past research has shown that planets that are so cool may have clouds high in their atmosphere, making it difficult to determine the types of gases that surround them. But new observations on another small, cool planet called K2-18 b have disrupted this trend and shown evidence of water in its atmosphere, surprising many astronomers.
“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 addition, with the high near-infrared (NIR) brightness of the receiving star, it makes it 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 co-authors of the article, is to be conducted later this month with the help of the Hubble Space Telescope.
“The low density of TOI 1231b indicates that it is surrounded by a significant atmosphere instead of a rocky planet. But the composition and extent of this atmosphere are unknown!” said Dragomir. “TOI1231b could have a large atmosphere of hydrogen or hydrogen-helium or a denser atmosphere of water vapor. Each would indicate a different origin, allowing astronomers to understand if and how planets formed differently around M dwarfs compared to the planets around our Sun, for example. Our upcoming HST observations will begin to answer these questions, and JWST promises an even deeper look at the planet’s atmosphere. “
Another way to study the planet’s atmosphere is to study whether the gas is blowing out, looking for evidence of atoms such as hydrogen and helium surrounding the planet as it passes through the face of its receiving star. In general, hydrogen atoms are almost impossible to detect because their presence is masked by interstellar gas. But this star-planet system offers a unique opportunity to apply this method because of how fast it is moving away from Earth.
“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 something like our own solar system,” Burt said. “They are full of planets between the size of Earth and Neptune in orbits much shorter than those of Mercury, so we have no local examples to compare them with. This new planet we found is still strange, but this is one step closer to being somewhat like our neighboring planets. Compared to most transit planets discovered so far, which often have scorching temperatures of many hundreds or thousands of degrees, the TOI-1231 b is positively cool. “
In conclusion, Dragomir reflects that “this planet joins the ranks of only two or three nearby small exoplanets that will be explored at any chance and with the help of a wide range of telescopes for years to come, so stay tuned for new TOI1231b developments! “
This article is in the press The Astronomical Journal.
A new exoplanet under Neptune, discovered by astronomers
TOI-1231 b: Moderate, Neptune-sized planet passing through the nearby M3 dwarf NLTT 24399, arXiv: 2105.08077 [astro-ph.EP] arxiv.org/abs/2105.08077
Provided by the University of New Mexico
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