素晴らしい赤い矮星を回す巨大なふわふわの惑星

Kitt Peak National Observatory望遠鏡は、以下を決定するのに役立ちます。[{” attribute=””>Jupiter-like Planet is the lowest-density gas giant ever detected around a red dwarf.

A gas giant exoplanet with the density of a marshmallow has been detected in orbit around a cool red dwarf star. A suite of astronomical instruments was used to make the observations, including the NASA-funded NEID radial-velocity instrument on the WIYN 3.5-meter Telescope at Kitt Peak National Observatory, a Program of NSF’s NOIRLab. Named TOI-3757 b, the exoplanet is the fluffiest gas giant planet ever discovered around this type of star.

Using the WIYN 3.5-meter Telescope at Kitt Peak National Observatory in Arizona, astronomers have observed an unusual Jupiter-like planet in orbit around a cool red dwarf star. Located in the constellation of Auriga the Charioteer around 580 light-years from Earth, this planet, identified as TOI-3757 b, is the lowest-density planet ever detected around a red dwarf star and is estimated to have an average density akin to that of a marshmallow.

Red dwarf stars are the smallest and dimmest members of so-called main-sequence stars — stars that convert hydrogen into helium in their cores at a steady rate. Although they are “cool” compared to stars like our Sun, red dwarf stars can be extremely active and erupt with powerful flares. This can strip orbiting planets of their atmospheres, making this star system a seemingly inhospitable location to form such a gossamer planet.

「赤い矮星の周りの巨大な惑星は伝統的に形成するのが難しいと考えられてきました」とカーネギー科学研究所地区と惑星研究所の研究者 天文学ジャーナルエル。 「これまで、これは通常、これらの赤い矮星から遠く離れた巨大な惑星を発見したドップラー照射の小さなサンプルとしてのみ調査されています。 」

TOI-3757bを取り巻くまだ説明されていない謎があります。最大の問題は、ガス巨大惑星が赤い矮星、特にそのような低密度惑星の周りにどのように形成されるかということです。 しかし、Kanodiaのチームは、その謎の解決策があるかもしれないと思います。

NSFのNOIRLabプログラムであるKitt Peak National Observatory（KPNO）の地上から、Wisconsin-Indiana-Yale-NOIRLab（WIYN）3.5メートルの望遠鏡が地平線から降り注ぐ天の川を眺めるようです。 自然現象である赤い気光も地平線を彩ります。 KPNOはTohono O’odham NationのArizona-Sonoran砂漠に位置し、私たちの銀河の銀河の平面の一部のこの明確なビューは、薄暗い天体を見るために必要なこの環境の有利な条件を示しています。 低レベルの光公害、震度20よりも暗い空、乾燥した大気条件を含むこれらの条件により、WIYNコンソーシアムの研究者は、銀河、星雲、地球外惑星だけでなく、他の多くの天文標的の観測を追求することができました。 WIYN 3.5メートル望遠鏡とその兄弟望遠鏡であるWIYN 0.9メートル望遠鏡。 ソース：KPNO / NOIRLab / NSF / AURA / R。 火花

彼らは、TOI-3757bの超低密度が2つの要因の結果である可能性があることを示唆している。 最初は惑星の岩の核に関連しています。 ガス巨人は地球の質量の約10倍に達する巨大な岩石コアから始まると考えられています。 TOI-3757bの星は、ガス巨人を持つ他のM型矮星に比べて中元素の量が少なく、岩石核がゆっくりと形成され、ガス沈着の開始が遅れ、惑星の全体密度に影響を及ぼす可能性があります。

第２の要因は、暫定的にやや楕円形と考えられる惑星の軌道であり得る。 他の時より星に近づく場合があり、その結果、過度の加熱により惑星の大気が膨張することがあります。

NASAのエイリアン惑星探査衛星 （[{” attribute=””>TESS) initially spotted the planet. Kanodia’s team then made follow-up observations using ground-based instruments, including NEID and NESSI (NN-EXPLORE Exoplanet Stellar Speckle Imager), both housed at the WIYN 3.5-meter Telescope; the Habitable-zone Planet Finder (HPF) on the Hobby-Eberly Telescope; and the Red Buttes Observatory (RBO) in Wyoming.

TESS surveyed the crossing of this planet TOI-3757 b in front of its star, which allowed astronomers to calculate the planet’s diameter to be about 150,000 kilometers (100,000 miles) or about just slightly larger than that of Jupiter. The planet finishes one complete orbit around its host star in just 3.5 days, 25 times less than the closest planet in our Solar System — Mercury — which takes about 88 days to do so.

The astronomers then used NEID and HPF to measure the star’s apparent motion along the line of sight, also known as its radial velocity. These measurements provided the planet’s mass, which was calculated to be about one-quarter that of Jupiter, or about 85 times the mass of the Earth. Knowing the size and the mass allowed Kanodia’s team to calculate TOI-3757 b’s average density as being 0.27 grams per cubic centimeter (about 17 grams per cubic feet), which would make it less than half the density of Saturn (the lowest-density planet in the Solar System), about one quarter the density of water (meaning it would float if placed in a giant bathtub filled with water), or in fact, similar in density to a marshmallow.

“Potential future observations of the atmosphere of this planet using NASA’s new James Webb Space Telescope could help shed light on its puffy nature,” says Jessica Libby-Roberts, a postdoctoral researcher at Pennsylvania State University and the second author on this paper.

“Finding more such systems with giant planets — which were once theorized to be extremely rare around red dwarfs — is part of our goal to understand how planets form,” says Kanodia.

The discovery highlights the importance of NEID in its ability to confirm some of the candidate exoplanets currently being discovered by NASA’s TESS mission, providing important targets for the new James Webb Space Telescope (JWST) to follow up on and begin characterizing their atmospheres. This will in turn inform astronomers what the planets are made of and how they formed and, for potentially habitable rocky worlds, whether they might be able to support life.

Reference: “TOI-3757 b: A low-density gas giant orbiting a solar-metallicity M dwarf” by Shubham Kanodia, Jessica Libby-Roberts, Caleb I. Cañas, Joe P. Ninan, Suvrath Mahadevan, Gudmundur Stefansson, Andrea S. J. Lin, Sinclaire Jones, Andrew Monson, Brock A. Parker, Henry A. Kobulnicky, Tera N. Swaby, Luke Powers, Corey Beard, Chad F. Bender, Cullen H. Blake, William D. Cochran, Jiayin Dong, Scott A. Diddams, Connor Fredrick, Arvind F. Gupta, Samuel Halverson, Fred Hearty, Sarah E. Logsdon, Andrew J. Metcalf, Michael W. McElwain, Caroline Morley, Jayadev Rajagopal, Lawrence W. Ramsey, Paul Robertson, Arpita Roy, Christian Schwab, Ryan C. Terrien, John Wisniewski and Jason T. Wright, 5 August 2022, The Astronomical Journal.
DOI: 10.3847/1538-3881/ac7c20