天文学者は、海の深さで完全に覆われる可能性のある太陽系外の世界を発見します

太陽系外惑星 TOI-1452 b の技術翻訳。深海に完全に覆われている小惑星。 クレジット: Benoit Gougeon、モントリオール大学

カナダで部分的に設計された機器の助けを借りて、天文学者のチームが発見した[{” attribute=””>exoplanet that could be completely covered in water.

An international team of scientists has announced the discovery of TOI-1452 b, an exoplanet orbiting one of two small stars in a binary system located in the Draco constellation about 100 light-years from Earth. The researchers were led by Charles Cadieux, a Ph.D. student at the Université de Montréal and member of the Institute for Research on Exoplanets (iREx).

With a size and mass slightly greater than that of Earth, the exoplanet is located at a distance from its star where its temperature would be neither too hot nor too cold for liquid water to exist on its surface. The astronomers believe it could be an “ocean planet,” a planet completely covered by a thick layer of water. This would make it similar to some of the moons of Jupiter and Saturn.

Cadieux and his team describe the observations that elucidated the nature and characteristics of this unique exoplanet in an article published on August 12 in The Astronomical Journal.

Artistic representation of the surface of TOI-1452 b, which could be an “ocean planet”, i.e. a planet entirely covered by a thick layer of liquid water. Credit: Benoit Gougeon, Université de Montréal

“I’m extremely proud of this discovery because it shows the high calibre of our researchers and instrumentation,” said René Doyon, Université de Montréal Professor and Director of iREx and of the Observatoire du Mont-Mégantic (OMM). “It is thanks to the OMM, a special instrument designed in our labs called SPIRou, and an innovative analytic method developed by our research team that we were able to detect this one-of-a-kind exoplanet.”

It was NASA’s space telescope TESS, which surveys the entire sky in search of planetary systems close to our own, that put the astronomers on the trail of this exoplanet. Based on the TESS signal, which showed a slight decrease in brightness every 11 days, scientists predicted a planet about 70% larger than Earth.

Charles Cadieux belongs to a group of astronomers that does ground follow-up observations of candidates identified by TESS in order to confirm their planet type and characteristics. He uses PESTO, a camera installed on the OMM’s telescope that was developed by Université de Montréal Professor David Lafrenière and his Ph.D. student François-René Lachapelle.

天文学者の国際チームが、完全に水で覆われている可能性のある太陽系外惑星を発見しました。 クレジット: Benoit Gougeon、モントリオール大学

「OMM は、この信号の性質を確認し、惑星の半径を推定する上で重要な役割を果たしました」と Cadeaux 氏は説明しました。 「これは定期的なチェックではありませんでした。TESS によって検出された信号が、連星系の 2 つの最大の星である TOI-1452 を周回する太陽系外惑星によって実際に引き起こされたことを確認する必要がありました。」

ホスト スター TOI-1452 は、太陽よりもはるかに小さく、連星系で同じようなサイズの 2 つの星のうちの 1 つです。 2 つの星は互いの軌道を周回し、短い距離 (97 天文単位)、または太陽と天体の間の距離の約 2.5 倍の距離で離れています。[{” attribute=””>Pluto — that the TESS telescope sees them as a single point of light. But PESTO’s resolution is high enough to distinguish the two objects, and the images showed that the exoplanet does orbit TOI-1452, which was confirmed through subsequent observations by a Japanese team.

Ingenuity at work

To determine the planet’s mass, the astronomers then observed the system with SPIRou, an instrument installed on the Canada-France-Hawaii Telescope in Hawai’i. Designed in large part in Canada, SPIRou is ideal for studying low-mass stars such as TOI-1452 because it operates in the infrared spectrum, where these stars are brightest. Even then, it took more than 50 hours of observation to estimate the planet’s mass, which is believed to be nearly five times that of Earth.

Étienne Artigau and Neil Cook, researchers also with iREx at the Université de Montréal, played a key role in analyzing the data. They developed a powerful analytic method capable of detecting the planet in the data collected with SPIRou. “The LBL method [for line-by-line] これにより、SPIRou で得られたデータを寄生虫の多くの信号から消去し、私たちのチームが発見したような惑星の弱い特徴を明らかにすることができます」と Artigau は説明します。

チームには、ケベック州の研究者であるファーボッド・ジャハンダーとトーマス・ヴァンダルも含まれています。 モントリオール大学の学生。 Jahandarは惑星の内部構造を拘束するのに役立つ主星の組成を分析し、VandalはSPIRouで収集されたデータの分析に参加しました。

水の世界

太陽系外惑星 TOI-1452 b は地球と同じくらい岩が多いかもしれませんが、その半径、質量、および密度は、私たちの世界とは非常に異なる世界を示唆しています。 地球は基本的に非常に乾燥した惑星です。 表面の約 70% が海に覆われているため、青い惑星と呼ばれることもありますが、実際には水はその質量のわずかな割合 (1% 未満) しか占めていません。

一部の太陽系外惑星では、水がより豊富に存在する可能性があります。 近年、天文学者は、地球から 100 メートルまでのサイズに及ぶ多くの太陽系外惑星の半径と質量を決定し、決定しました。[{” attribute=””>Neptune (about 3.8 times larger than Earth). Some of these planets have a density that can only be explained if a large fraction of their mass is made up of lighter materials than those that make up the internal structure of the Earth such as water. These hypothetical worlds have been dubbed “ocean planets.”

“TOI-1452 b is one of the best candidates for an ocean planet that we have found to date,” said Cadieux. “Its radius and mass suggest a much lower density than what one would expect for a planet that is basically made up of metal and rock, like Earth.”

The University of Toronto’s Mykhaylo Plotnykov and Diana Valencia are specialists in exoplanet interior modeling. Their analysis of TOI-1452 b shows that water may make up as much as 30% of its mass, a proportion similar to that of some natural satellites in our Solar System, such as Jupiter’s moons Ganymede and Callisto, and Saturn’s moons Titan and Enceladus.

To be continued…

An exoplanet such as TOI-1452 b is a perfect candidate for further observation with the James Webb Space Telescope, or Webb for short. It is one of the few known temperate planets that exhibit characteristics consistent with an ocean planet. It is close enough to Earth that scientists can hope to study its atmosphere and test this hypothesis. And, in a stroke of good fortune, it is located in a region of the sky that the telescope can observe year-round.

“Our observations with the Webb Telescope will be essential to better understanding TOI-1452 b,” said Doyon who overviewed the conception of James Webb’s component Near Infrared Imager and Slitless Spectrograph (NIRISS). “As soon as we can, we will book time on Webb to observe this strange and wonderful world.”

Reference: “TOI-1452 b: SPIRou and TESS reveal a super-Earth in a temperate orbit transiting an M4 dwarf” by Charles Cadieuxg, René Doyon, Mykhaylo Plotnykov, Guillaume Hébrard, Farbod Jahandar, Étienne Artigau, Diana Valencia, Neil J. Cook, Eder Martioli, Thomas Vandal, Jean-François Donati, Ryan Cloutier, Norio Narita, Akihiko Fukui, Teruyuki Hirano, François Bouchy, Nicolas B. Cowan, Erica J. Gonzales, David R. Ciardi, Keivan G. Stassun, Luc Arnold, Björn Benneke, Isabelle Boisse, Xavier Bonfils, Andrés Carmona, Pía Cortés-Zuleta, Xavier Delfosse, Thierry Forveille, Pascal Fouqué, João Gomes da Silva, Jon M. Jenkins, Flavien Kiefer, Ágnes Kóspál, David Lafrenière, Jorge H. C. Martins, Claire Moutou, J.-D. do Nascimento Jr., Merwan Ould-Elhkim, Stefan Pelletier, Joseph D. Twicken, Luke G. Bouma, Scott Cartwright, Antoine Darveau-Bernier, Konstantin Grankin, Masahiro Ikoma, Taiki Kagetani, Kiyoe Kawauchi, Takanori Kodama, Takayuki Kotani, David W. Latham, Kristen Menou, George Ricker, Sara Seager, Motohide Tamura, Roland Vanderspek and Noriharu Watanabe, 12 August 2022, The Astronomical Journal.
DOI: 10.3847/1538-3881/ac7cea

The article was published on August 12, 2022, in The Astronomical Journal. In addition to Charles Cadieux, René Doyon, Étienne Artigau, Neil Cook, Farbod Jahandar and Thomas Vandal at the Université de Montréal’s iREx, the research team includes Nicolas B. Cowan (iREx, MSI, McGill, Canada); Björn Benneke, Stefan Pelletier and Antoine Darveau-Bernier (iREx, UdeM, Canada); Ryan Cloutier, former member of iREx (Harvard, U.S.); and co-authors from University of Toronto, France, Brazil, the United States, Japan, Spain, Switzerland, Portugal, Hungary, Germany, and Crimea.