天文学者は、2つの地球サイズの惑星を持つ近くの多惑星系を発見します

地球からわずか33光年の場所にあるこのシステムは、地球サイズの2つの岩石惑星をホストしているように見えます。

新しい多惑星系が、私たちの隣接する銀河内で、天文学者によって発見されました。[{” attribute=””>MIT and elsewhere. It lies just 10 parsecs, or about 33 light-years, from Earth, making it one of the closest known multiplanet systems to our own.

At the heart of the system lies a small and cool M-dwarf star, named HD 260655, and astronomers have found that it hosts at least two terrestrial, Earth-sized planets. The rocky worlds have relatively tight orbits, exposing the planets to temperatures that are too high to sustain liquid surface water. Therefore, they are unlikely to be habitable.

Nevertheless, scientists are excited about this system because the proximity and brightness of its star will give them a closer look at the properties of the planets and signs of any atmosphere they might hold.

“Both planets in this system are each considered among the best targets for atmospheric study because of the brightness of their star,” says Michelle Kunimoto, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research and one of the discovery’s lead scientists. “Is there a volatile-rich atmosphere around these planets? And are there signs of water or carbon-based species? These planets are fantastic test beds for those explorations.”

The team will present its discovery on June 15, 2022, at the meeting of the American Astronomical Society in Pasadena, California. Team members at MIT include Katharine Hesse, George Ricker, Sara Seager, Avi Shporer, Roland Vanderspek, and Joel Villaseñor, along with collaborators from institutions around the world.

Illustration of NASA’s Transiting Exoplanet Survey Satellite (TESS) at work. Credit: NASA’s Goddard Space Flight Center

Data power

The new planetary system was initially identified by NASA’s Transiting Exoplanet Survey Satellite (TESS), an MIT-led mission that is designed to observe the nearest and brightest stars, and detect periodic dips in light that could signal a passing planet.

In October 2021, Kunimoto, a member of MIT’s TESS science team, was monitoring the satellite’s incoming data when she noticed a pair of periodic dips in starlight, or transits, from the star HD 260655.

She ran the detections through the mission’s science inspection pipeline, and the signals were soon classified as two TESS Objects of Interest, or TOIs — objects that are flagged as potential planets. The same signals were also found independently by the Science Processing Operations Center (SPOC), the official TESS planet search pipeline based at NASA Ames. Scientists typically plan to follow up with other telescopes to confirm that the objects are indeed planets.

The process of classifying and subsequently confirming new planets can often take several years. For HD 260655, that process was shortened significantly with the help of archival data.

The Keck observatory domes atop Mauna Kea. Credit: T. Wynne / JPL

Soon after Kunimoto identified the two potential planets around HD 260655, Shporer looked to see whether the star was observed previously by other telescopes. As luck would have it, HD 260655 was listed in a survey of stars taken by the High Resolution Echelle Spectrometer (HIRES), an instrument that operates as part of the Keck Observatory in Hawaii. HIRES had been monitoring the star, along with a host of other stars, since 1998, and the researchers were able to access the survey’s publicly available data.

HD 260655 was also listed as part of another independent survey by CARMENES, an instrument that operates as part of the Calar Alto Observatory in Spain. As these data were private, the team reached out to members of both HIRES and CARMENES with the goal of combining their data power.

“These negotiations are sometimes quite delicate,” Shporer notes. “Luckily, the teams agreed to work together. This human interaction is almost as important in getting the data [as the actual observations]。 「」

プラネタリープル

最終的に、この共同作業により、約6か月でHD260655の周りに2つの惑星が存在することがすぐに確認されました。

TESSからの信号が実際に2つの軌道を回る惑星からのものであることを確認するために、研究者は星のHIRESとCARMENESの両方からのデータを調べました。 どちらの調査も、視線速度としても知られる星の重力振動を測定します。

「星を周回するすべての惑星は、その星に小さな重力をかけます」と国本は説明します。 「私たちが探しているのは、その星のわずかな動きであり、惑星の質量の物体がそれを引き込んでいることを示している可能性があります。」

両方のアーカイブデータのセットから、研究者は、TESSによって検出された信号が実際に2つの軌道を回る惑星であるという統計的に有意な兆候を発見しました。

「それから、私たちは非常にエキサイティングなものがあることを知りました」とSporerは言います。

次に、チームはTESSデータを詳しく調べて、公転周期やサイズなど、両方の惑星の特性を決定しました。 彼らは、HD 260655bと呼ばれる内側の惑星が2.8日ごとに星を周回し、地球の約1.2倍の大きさであると判断しました。 2番目の太陽系外惑星HD260655cは、5.7日ごとに回転し、地球の1.5倍の大きさです。

HIRESとCARMENESの視線速度データから、研究者は惑星の質量を計算することができました。これは、各惑星がその星を引きずる振幅に直接関係しています。 彼らは、内側の惑星の質量が地球の2倍であるのに対し、外側の惑星の質量は約3つの地球質量であることを発見しました。 そのサイズと質量から、チームは各惑星の密度を推定しました。 小さい方の外惑星は地球よりわずかに密度が高く、大きい方の外惑星はわずかに密度が低くなっています。 両方の惑星は、それらの密度に応じて、構成が地上または岩石である可能性があります。

研究者たちはまた、彼らの短い軌道に基づいて、惑星の内面が710 K（818度）の焙煎であると推定しています。[{” attribute=””>Fahrenheit), while the outer planet is around 560 °K (548 °F).

“We consider that range outside the habitable zone, too hot for liquid water to exist on the surface,” Kunimoto says.

“But there might be more planets in the system,” Shporer adds. “There are many multiplanet systems hosting five or six planets, especially around small stars like this one. Hopefully, we will find more, and one might be in the habitable zone. That’s optimistic thinking.”

This research was supported, in part, by NASA, the Max-Planck-Gesellschaft, the Consejo Superior de Investigaciones Científicas, the Ministerio de Economía y Competitividad, and the European Regional Development Fund.