Astronomers discover an extrasolar world that could be entirely covered by a deep ocean

Using instruments designed in part in Canada, a team of astronomers discovered a[{” 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.

“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 " data-gt-translate-attributes="[{" attribute="">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.

An international team of astronomers has discovered an exoplanet that could be completely covered in water. Credit: Benoit Gougeon, University of Montreal

“WMO played a crucial role in confirming the nature of this signal and in estimating the radius of the planet,” explains Cadieux. “It was not a routine check. We had to make sure that the signal detected by TESS was indeed caused by an exoplanet circling 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 stars of similar size in the binary system. The two stars revolve around each other and are separated by such a small distance – 97 astronomical units, or about two and a half times the distance between the Sun and[{” 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] allows to clean the data obtained with SPIRou from many parasitic signals and to reveal the weak signature of planets like the one discovered by our team”, explains Artigau.

The team also includes Quebec researchers Farbod Jahandar and Thomas Vandal, two Ph.D. students from the University of Montreal. Jahandar analyzed the composition of the host star, useful for constraining the internal structure of the planet, while Vandal helped analyze data collected with SPIRou.

An aquatic world

Although exoplanet TOI-1452 b is likely rocky like Earth, its radius, mass, and density suggest a world very different from our own. Earth is essentially a very dry planet. Even though 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 can be much more abundant on some exoplanets. In recent years, astronomers have identified and determined the radius and mass of many exoplanets that range in size from Earth to Earth. Neptune (about 3.8 times larger than Earth). Some of these planets have a density that can only be explained if a large part of their mass is made up of materials that are lighter 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 we’ve found to date,” Cadieux said. “Its radius and mass suggest a much lower density than would be expected for a planet composed mostly of metal and rock, like Earth.”

Mykhaylo Plotnykov and Diana Valencia of the University of Toronto are specialists in modeling the interiors of exoplanets. Their analysis of TOI-1452b shows that up to 30% of its mass can be water, a proportion similar to that of some natural satellites in our solar system, such as Jupiter’s moons Ganymede and Callisto, and the moons of Saturn Titan and Enceladus. .

To be continued…

An exoplanet such as TOI-1452 b is a perfect candidate for closer 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 oceanic planet. It is close enough to Earth that scientists could hope to study its atmosphere and test this hypothesis. And, fortunately, it is located in a region of the sky that the telescope can observe all year round.

“Our observations with the Webb telescope will be essential to better understand TOI-1452 b,” said Doyon who presented James Webb’s Near Infrared Imager and Slitless Spectrograph (NIRISS) component design. “As soon as we can, we’ll set aside time on Webb to observe this weird and wonderful world.”

Reference: “TOI-1452 b: SPIRou and TESS reveal a super-Earth in temperate orbit passing through 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 HC Martins, Claire Moutou, J.-D. by 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, August 12, 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 of the iREx at Université de Montréal, 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, USA); and co-authors from the University of Toronto, France, Brazil, USA, Japan, Spain, Switzerland, Portugal, Hungary, Germany and Crimea.