Astronomers discover a Waterworld planet with deep oceans in the habitable zone

In the search for extrasolar planets, astronomers and astrobiologists generally pursue a “follow the water” policy. It’s like looking for planets orbiting a star’s circumsolar habitable zone (HZ), where conditions are warm enough for liquid water to flow across its surface. The reason is simple: water is the only known solvent capable of sustaining life and is necessary for all life on Earth. However, since the 1970s, scientists have speculated that there might be a class of rocky planets in our universe that are completely covered in water.

With the explosion of exoplanets confirmed, scientists are eager to find examples of this type of planet, so they are studying them more closely. Thanks to an international team of researchers led by the Institute for Research on Exoplanets (iREx) of the University of Montreal, an exoplanet orbiting inside the HZ of its system has recently been discovered and could be completely covered. in the deep oceans. This “ocean world” (aka “Waterworld”) could reveal things about the nature of habitability when tracked using the James Webb Space Telescope (JWST).

The international team was led by Charles Cadieux, Ph.D. student at the University of Montreal and member of IREX. He was joined by a team of fifty-five astronomers and astrophysicists from Canada, France, the United States, Japan, Brazil, Hungary, Spain, Switzerland, Portugal, Germany and Russia. The team represents institutions such as the Harvard & Smithsonian Center for Astrophysics, the Canada-France-Hawaii Telescope, the Max Planck Institute for Astronomy, the NASA Ames Research Center, the NASA Exoplanet Science Institute (NExScI) and numerous universities and institutes.

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Artist’s rendering of the Transiting Exoplanet Survey Satellite (TESS). Credit: NASA Goddard Space Flight Center

As they explain in their article published on August 12 in The Astrophysical Journal, the exoplanet (TOI-1452 b) orbits in a binary system located in the constellation Draco about 100 light-years from Earth. The system is made up of two M-type stars (red dwarfs) that orbit very close to each other, 97 astronomical units (AU), or about two and a half times the distance between the Sun and Pluto. The possibility of an exoplanet orbiting one of these stars was initially considered based on data obtained by the Transiting exoplanet study satellite (TESS).

Based on the TESS data, the astronomers noted that the exoplanet experienced a slight dip in brightness every 11 days, from which they estimated it was about 70% larger in diameter than Earth. Cadieux and his colleagues then carried out follow-up observations (a function commonly performed by the iREx) using the Extrasolar Planets in Transition and Occultation (PESTO) camera on the Observatory’s 1.6-meter telescope. du Mont-Mégantic (OMM) – part of the University of Montreal.

Due to their dimness and close proximity, the two stars of TOI-1452 appeared as a single bright spot when observed by TESS. However, the resolution of PESTO is high enough to distinguish the two objects, and the images obtained confirmed that an exoplanet orbits around TOI-1452. Later observations were made by a team from the National Astronomical Observatory of Japan (NAOJ) using the Subaru 8.2-meter Infrared Optical Telescope at Maunakea, Hawaii. As co-author René Doyon, professor at the University of Montreal and director of iREx and OMM explained in an IREX press release:

“I am extremely proud of this discovery as it shows the high caliber of our researchers and our instrumentation. It is thanks to the OMM, a special instrument designed in our laboratories called SPIRou and an innovative analysis method developed by our research team that we were able to detect this unique exoplanet.

The SPIRou instrument, partly designed by a Canadian team, made it possible to determine the mass of TOI-1452 b. Credit: S. Chastanet – CNRS/OMP

“WMO played a crucial role in confirming the nature of this signal and in estimating the radius of the planet,” Cadieux added. “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.

After confirming the presence of an exoplanet and obtaining estimates of its size, the team turned to the instrument a SpectroPolarimètre Infra-Red (SPIRou), a near-infrared spectropolarimeter installed on the Canada-France-Hawaii Telescope . Designed largely in Canada, SPIRou is ideally suited for studying low-mass stars like the binary components of TOI-1452, as they are brightest in the infrared wavelength. Despite this, it still took more than 50 hours of observation to produce estimates of the mass of the planet (nearly five times that of Earth).

The next big challenge was data analysis, which was performed using the line-by-line (LBL) analysis method developed by researchers Étienne Artigau and Neil Cook (also with iREx). This allowed the team to identify the weak signal produced by the exoplanet in the SPIRou data. Finally, a doctorate. University of Montreal students Farbod Jahandar and Thomas Vandal analyzed the SPIRou data to learn more about the composition of the host star, which is useful for constraining the internal structure of the planet. Based on their estimates of its radius, mass, and density measurements, astronomers theorize that TOI 1452 b is likely a rocky planet.

However, these same estimates led them to conclude that TOI 1452 b could be covered by a thick layer of water, similar to the larger moons of Jupiter, Saturn and other icy bodies in the outer solar system. This is supported by interior modeling conducted by Mykhaylo Plotnykov and Diana Valencia of the University of Toronto, which suggests that water may make up to 30% of the mass of TOI 1452 b, which is also similar to satellites like the Jupiter’s moons Europea, Ganymede and Callisto, and Saturn’s moons Titan, Dione and Enceladus.

In recent years, astronomers have detected hundreds of similar exoplanets with radii and masses between Earth and Neptune but much lower densities. This suggests that much of the mass of these exoplanets is made up of volatiles such as water, earning them the nickname “ocean planets”. As Cadieux explained, this latest discovery may be the first such planet discovered:

“TOI-1452 b is one of the best candidates for an ocean planet we have found to date. Its radius and mass suggest a much lower density than would be expected for a planet composed mostly of metal and rock, like Earth.

Since TOI-1452 b orbits in the HZ of its host star, it is unlikely to have an icy surface, which means it could have oceans several kilometers deep. This makes TOI-1452 a perfect candidate for further observations using the JWST, as it is one of the few known temperate planets that also exhibits characteristics of an oceanic planet. Its proximity to Earth also makes it a good candidate for atmospheric characterization, which Webb is very competent at – as demonstrated by the spectra he obtained twice from WASP-59 (confirming the presence of water and carbon dioxide).

To make things even better, TOI-1452 is located in a region of the sky that Webb can observe all year round, making it perfectly positioned for follow-up observations. “Our observations with the Webb telescope will be essential to better understand TOI-1452 b,” said Doyon, who is also the principal investigator of the Near Infrared Imager and Slitless Spectrograph (NIRISS), the Canadian Space Agency’s contribution to JWST. “As soon as we can, we will set aside time on the Webb to observe this weird and wonderful world.”

Further reading: IREX

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