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With the help of instruments partially designed in Canada, a team of Université de Montréal astronomers has discovered an exoplanet that could be completely covered in water, a target they hope to soon observe with the Webb telescope. Artist’s rendering of the exoplanet TOI-1452 b, a small planet that may be entirely covered in a deep ocean. Credit: Benoit Gougeon, Université de Montréal. Charles Cadieux, the Ph.D. who led the discovery of the exoplanet TOI-1452 b. Photo provided by Cadieux. An international team of researchers led by Charles Cadieux, Ph.D. student at the Université de Montréal and member of the Institute for Research on Exoplanets (iREx), announced the discovery of an exoplanet orbiting TOI-1452, one of two small stars in a binary system located in the constellation Draco about 100 light years away from the earth. The exoplanet, known as TOI-1452 b, is slightly larger in size and mass than Earth and 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 . Astronomers believe it could be an “ocean planet,” a planet completely covered by a thick layer of water, similar to some of the moons of Jupiter and Saturn. In an article published on August 12 at The Astronomical JournalCadieux and his team describe the observations that clarified the nature and characteristics of this unique exoplanet. “I am extremely proud of this discovery because it shows the high caliber of our researchers and instruments,” said René Doyon, a professor at the University of Montreal and director of iREx and the Observatoire du Mont-Mégantic (OMM). “Thanks to the OMM, a special instrument designed in our laboratories called SPIRou and an innovative analytical method developed by our research team, we were able to detect this one-of-a-kind exoplanet.” Key role of the Mont-Mégantic Observatory The Observatoire du Mont-Mégantic located in the eastern cities of Quebec houses a 1.6 meter telescope that was instrumental in confirming this discovery. Credit: Emir Chouchane, University of Montreal. It was NASA’s TESS space telescope, which surveys the entire sky in search of planetary systems similar to our own, that put researchers on the trail of TOI-1452 b. Based on the TESS signal, which showed a slight decrease in brightness every 11 days, the astronomers predicted a planet that is about 70% larger in diameter than Earth. Charles Cadieux is part of a team of astronomers making ground-based observations of candidates identified by TESS in order to confirm their planet type and characteristics. It uses PESTO, a camera installed on the OMM telescope developed by Université de Montréal Professor David Lafrenière and his Ph.D. pupil of François-René Lachapelle. “OMM played a critical role in confirming the nature of this signal and estimating the planet’s radius,” Cadieux explained. “It was not a routine check. We had to make sure that the signal detected by TESS was really caused by an exoplanet orbiting TOI-1452, the larger of the two stars in this binary system.” The host star TOI-1452 is much smaller than our Sun and is one of two similarly sized stars in a binary system. The two stars orbit each other and are separated by such a short distance — 97 AU, or about two and a half times the distance between the Sun and 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 is orbiting TOI-1452, which was confirmed through later observations by a Japanese team. Quebec ingenuity at work The SPIRou instrument, designed in part by a Canadian team, made it possible to determine the mass of the exoplanet and, therefore, determine its nature. Credit: S.Chastanet – CNRS/OMP. To determine the planet’s mass, the researchers then observed the system with SPIRou, an instrument installed on the Canada-France-Hawaii Telescope in Hawaii. Designed largely in Canada, SPIRou is ideal for studying low-mass stars like TOI-1452 because it operates in the infrared spectrum, where these stars are the brightest. Even then, it took more than 50 hours of observation to calculate the mass of the planet, which is believed to be nearly five times that of Earth. Researchers Étienne Artigau and Neil Cook, also with iREx at the Université de Montréal, were instrumental in analyzing the data. They developed a powerful analytical method capable of detecting the planet in the data collected with SPIRou. “The LBL method [for line-by-line] ]allows us to clean the data obtained with SPIRou of many spurious signals and reveal the weak signature of planets like the one our team discovered,” explained Artigau. The team also includes Quebec researchers Farbod Jahandar and Thomas Vandal, two Ph.D. students at the Université de Montréal. Jahandar analyzed the composition of the host star, which is useful for constraining the internal structure of the planet, while Vandal participated in the analysis of the data collected with SPIRou. A water world TOI-1452 b is probably rocky like Earth, but its radius, mass and density suggest a world very different from our own. Earth is essentially a very dry planet. although we sometimes call it the Blue Planet because about 70% of its surface is covered by ocean, water actually makes up only a negligible fraction of its mass – less than 1%. Water may be much more abundant on some exoplanets. In recent years, astronomers have detected and determined the radius and mass of several exoplanets between the size of Earth and Neptune (about 3.8 times the size of Earth). Some of these planets have a density that can only be explained if a large fraction of their mass consists of volatiles such as water. These hypothetical worlds have been called “oceanic planets”. “TOI-1452 b is one of the best candidates for an ocean planet we’ve found to date,” Cadieux said. “Its radius and mass suggest a much lower density than would be expected for a planet composed primarily of metal and rock like Earth.” Artist’s rendering of the surface of TOI-1452 b, which could be an “ocean planet,” meaning a planet entirely covered by a thick layer of liquid water. Credit: Benoit Gougeon, Université de Montréal. Mykhaylo Plotnykov and Diana Valencia of the University of Toronto are experts in modeling exoplanet interiors. Their analysis of TOI-1452 b shows that water may make up as much as 30% of its mass, a ratio similar to that of some natural moons in our Solar System, such as Jupiter’s moons Ganymede and Callisto and Saturn’s moons Titan and England. To be continued… An exoplanet like 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 researchers can hope to study its atmosphere and test this hypothesis. And, in a stroke of luck, it’s in a region of the sky that the telescope can observe year-round. “Our Webb observations will be essential to better understanding TOI-1452 b,” said Doyon, who is also the principal investigator of NIRISS, one of the four science instruments on the James Webb Space Telescope. “As soon as we can, we will book time on Webb to observe this strange and wonderful world.” To learn more The article “TOI-1452 b: SPIRou and TESS reveal a temperate-orbiting super-Earth transiting an M4 dwarf” was published in The Astronomical Journal on August 12. In addition to Charles Cadieux, René Doyon, Étienne Artigau, Neil Cook, Farbod Jahandar and Thomas Vandal at Université de Montréal iREx and Mykhaylo Plotnykov and Diana Valencia from the University of Toronto, the research team includes Nicolas B. Cowan (iREx , MSI, , Canada); Björn Benneke, Stefan Pelletier and Antoine Darveau-Bernier (iREx, UdeM, Canada); Ryan Cloutier, former member of iREx (Harvard, USA). and 43 co-authors from Ontario, France, Brazil, the United States, Japan, Spain, Switzerland, Portugal, Hungary, Germany, and Crimea.

Media contacts Marie-Eve NaudEducation and Public Outreach Coordinator Institute for Extraterrestrial ResearchUniversity of Montreal514-279-3222, [email protected] Nathalie OuelletteCoordinatorInstitute for ExoplanetsUniversité de Montré[email protected]

Scientific contacts Charles CadieuxPh.D. Student University of Montreal514-503-0176, [email protected] Rene DoyonProfessor, University of MontrealDirector, Institute for Research on ExoplanetsDirector, Mont-Mégantic Observatory514-349-5779, [email protected]

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