Exoplanet orbiting twin suns 100 lightyears from Earth could be a water world

A potentially ocean-covered exoplanet has been discovered orbiting binary stars in the Draco constellation about 100 lightyears from Earth.

The planet was given the catchy name TOI-1452 b and its discovery was announced in an article published in the Astronomical Journal.

Slightly larger and heavier than Earth, the planet sits in the binary star system’s “Goldilocks zone” – where it is neither too hot nor too cold for liquid water to exist on its surface. The astronomers believe that, like some of Jupiter and Saturn’s moons, the planet could be covered in a deep ocean.

The study of the exoplanet was conducted by an international team led by PhD student Charles Cadieux from the Université de Montréal Institute for Research on Exoplanets (iREx).

“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,” says René Doyon, professor at University of Montreal and director of iREx and of the Mont Mégantic Observatory (OMM).

The planet was first observed by NASA’s Transiting Exoplanet Survey Satellite (TESS) space telescope.

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Conducting follow-up observations using ground telescopes, Cadieux and the team sought to determine the planet’s characteristics.

“This was no routine check. We had to make sure the signal detected by TESS was really caused by an exoplanet circling the largest of the two stars in that binary system.”

Both stars are of a similar size with the larger roughly a quarter the mass of our Sun. They orbit each other at a distance around 97 times the orbital distance of the Earth from the Sun. So close together are the two stars that TESS sees them as a single point of light. But OMM’s PESTO camera was able to resolve the two objects and determined that the exoplanet is orbiting the larger of the two stars.

Using SPIRou, an infrared instrument installed on the Canada-France-Hawaii Telescope in Hawaii, the team compiled data from 50 hours of observations to determine that the planet likely has five times the mass of Earth.

Earth is often called the “Blue Planet” because its surface is 70% covered by water. But that water makes up a negligible fraction of Earth’s total mass – less than one percent.

TOI-1452 b is probably much more deserving of that moniker. Though probably rocky like Earth, the planet’s radius, mass and density suggest a world very different.

A number of exoplanets discovered in recent years have densities which suggest a large fraction of their mass is made up of lighter materials than those that make up the internal structure of rockier planets like Earth. Many of these worlds have been dubbed “ocean planets.”

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

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.

In fact, modelling done by University of Toronto scientists suggests that water may make up as much as 30% of the planet’s mass – similar to Jupiter’s moons Ganymede and Callisto, and Saturn’s moons Titan and Enceladus.

The researchers say TOI-1452 b is a good candidate for further observation with the James Webb Space Telescope which can analyse its atmosphere.

“Our observations with the Webb Telescope will be essential to better understanding TOI-1452 b,” says Doyon. “As soon as we can, we will book time on Webb to observe this strange and wonderful world.”

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