2021-06-09

Astronomers newly discovered a Neptune-sized exoplanet with a dense atmosphere

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Astronomers newly discovered a Neptune-sized exoplanet with a dense atmosphere

The topic of this study is TOI-1231 b: A temperate, Neptune-sized planet orbits nearby The M3 dwarf star NLTT 24399 operates and will be published in a future issue of Astronomy Magazine. This exoplanet named TOI-1231 b was detected by the photometric data of the Transiting Exoplanet Exploration Satellite (TESS) and passed through the planetary detection spectrometer on the Magellan Clay telescope at the Las Campanas Observatory in Chile ( PFS) for tracking and observation. PFS is a complex instrument that uses their gravitational influence on their host stars to detect exoplanets. As planets orbit their hosts, the measured star speeds periodically change, revealing the existence of planets and information about their mass and orbit.

The observation strategy adopted by NASA’s TESS divides each hemisphere into 13 regions and conducts approximately 28 days of investigation. The most comprehensive all-sky search for transiting planets is being produced. This method has proven its ability to detect large and small planets ranging from sun-like stars to low-mass M-type dwarfs. M-type dwarfs, also known as red dwarfs, are the most common type of stars in the Milky Way, accounting for about 70% of all stars in the Milky Way.

M-type dwarfs are small, possessing only a small part of the mass of our sun, and low luminosity. Because M-type dwarfs are relatively small, when a planet of a certain size passes by the star, the amount of light blocked by the planet is relatively large, making it easier to detect the transit of the planet. Imagine that a planet similar to the Earth passes in front of a sun-sized star, it will block a small part of the light; but if it passes in front of a much smaller star, the proportion of blocked light will be Will be bigger. In a sense, this creates a larger shadow on the surface of the star, making the planets around the M-type dwarf easier to detect and easier to study.

Although it can detect exoplanets in the entire sky, TESS’s survey strategy will also produce significant observational deviations based on the orbital period. An exoplanet must pass through its host star at least twice within the observation range of TESS before the correct period can be detected by the Scientific Processing Operations Center (SPOC) pipeline and the Quick Observation Pipeline (QLP). These two pipelines search TESS’s 2 Minute and 30-minute rhythm data. Since 74% of the total sky coverage of TESS has been observed for only 28 days, most of the exoplanets detected by TESS have periods less than 14 days. Therefore, the 24-day cycle of TOI-1231b makes its discovery more valuable.

NASA JPL scientist Jennifer Burt (Bert) is the lead author of this paper. Her collaborators include UNM Assistant Professor Diana Dragomir in the Department of Physics and Astronomy. They The radius and mass of the planet were measured. Burt said: “In collaboration with a group of excellent astronomers scattered around the world, we can collect the necessary data to describe the characteristics of the host star and measure the radius and mass of the planet. These values ​​in turn allow us to calculate the planet. The volume density of the planet and assume what the planet is made of. The size and density of TOI-1231 b are quite similar to that of Neptune, so we think it has a similar large gaseous atmosphere. “Exoplanets orbiting M-type dwarf hosts Another advantage is that we can measure their masses more easily, because the ratio of planetary mass to star mass is also larger. When the star is smaller and the mass is smaller, the existing detection methods can work better, because the planet is easier to protrude from the star. It’s like a shadow cast on a star. The smaller the star, the lower the mass of the star, the more the influence of the planet can be detected. 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 the Earth, thanks to its host star being colder and less bright. However, the planet itself is actually larger than the Earth. A little smaller than Neptune-we can call it sub-Neptune. ”

Bert and Dragomir started this research when they were researchers at the Cavley Institute at MIT. They collaborated with scientists who specialize in observing and describing the atmosphere of asteroids to get Find out which current and future space-based missions may be able to peek into the outer layer of TOI-1231 b to tell researchers what gases are orbiting the planet. The temperature of TOI-1231b is about 330 Kelvin or 140 degrees Fahrenheit. It is one of the coldest small exoplanets found so far that can be used for atmospheric research.

Past research has shown that such an icy planet may have clouds in the upper part of its atmosphere, which makes it very It is difficult to determine what type of gas is around them. But new observations of another small icy planet named K2-18 b broke this trend and showed evidence of the presence of water in its atmosphere, making many astronomers feel that Surprised. Bert said: “TOI-1231 b is one of the only other planets of similar size and temperature range that we know of, so future observations of this new planet will allow us to determine whether water clouds are forming around these temperate worlds. How common (or rare). ”

In addition, due to the high near-infrared (NIR) brightness of its host star, it will be an exciting opportunity for future missions of the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST). Exciting goal. The first set of these observations, led by one of the paper’s co-authors, should be performed using the Hubble Space Telescope later this month.

“TOI 1231b’s low density suggests that it is being Surrounded by a large amount of atmosphere, not a rocky planet. But the composition and extent of this atmosphere is unknown,” Dragomir said. “TOI1231b may have a large atmosphere of hydrogen or hydrogen helium, or a denser atmosphere of water vapor. Each one points to a different origin, allowing astronomers to understand whether and how planets around M-type dwarfs form different planets compared to planets around our sun, for example. Our upcoming HST observations will begin to answer these questions, and JWST is expected to conduct a more thorough observation of the planet’s atmosphere. ”

Another way to study the planet’s atmosphere is to investigate whether the gas has been blown away by looking for evidence of atoms such as hydrogen and helium around the planet because it passes through the surface of its host star. Generally speaking , Hydrogen atoms are almost impossible to be discovered because their existence is obscured by interstellar gas. But this planet-star system provides a unique opportunity to apply this method because it moves away from the Earth very fast.

Bert said: “One of the most interesting results of exoplanet science in the past 20 years is that none of the new planetary systems we have discovered so far looks like our solar system. They are full of planets between the size of Earth and Neptune, and their orbits are much shorter than those of Mercury, so we don’t have any local examples to compare with. The new planet we discovered is still weird–but it’s a step closer to being a bit like a planet near us. Compared with most transiting planets detected so far, their temperature is usually between hundreds or thousands of degrees, and TOI-1231 b is very cold. This planet has joined the ranks of two or three other nearby small exoplanets. In the next few years, we will use various telescopes to carefully examine it, so please pay close attention to the new development of TOI1231b! “