A Waltz of Six Planets Discovered Around a Star – Radio-Canada.ca

There are at least six exoplanets orbiting the star HD 110067 in the Berenice Hair constellation, according to work by astrophysicist Rafael Luque of the University of Chicago in the US and Swiss colleagues, published in the journal Nature (New Window). has been published.

All of these planets are located about 100 million light-years from Earth and have a radius between that of Earth and Neptune.

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HD 110067 is an orange dwarf star whose luminosity varies between that of yellow stars like the Sun and that of red dwarfs like its neighbor Proxima Centauri (around which the closest exoplanet to Earth is located). Previous discovery).

These orange dwarfs are much older stars [que le Soleil] around which exoplanets had time to evolve and stabilize, explains astrophysicist Olivier Hernandez, director of the Montreal Planetarium.

HD 110067 therefore represents a research object of great interest to astronomers, as it shows us the virgin configuration of a planetary system that developed without major upheavals.

Sightseeing features

  • No fewer than 5,539 exoplanets have been officially discovered in more than 4,128 planetary systems. (NASA/November 2023)
  • More than 10,009 additional exoplanets are currently awaiting confirmation.
  • According to the latest estimates, there are up to 700 million billion rocky planets in the observable universe.
  • Almost two thirds of the exoplanets known to date, Earths and super-Earths, are located in the habitable zone of their star.

From one telescope to another

The system’s first two exoplanets were discovered in 2020 and 2022 using NASA’s TESS telescope. The data collected by TESS showed irregularities and several dips in brightness in front of the star, suggesting the presence of other exoplanets.

ESA's CHEOPS telescope.  (Artistic illustration)

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ESA’s CHEOPS telescope. (Artistic illustration)

Photo: ESA

For these reasons, astrophysicist Rafael Luque and his colleagues at the University of Chicago decided to use the European Space Agency’s CHEOPS telescope to study the HD 110067 system.

The data collected by CHEOPS made it possible to quickly discover a third planet but also to find the key to deciphering the entire system, notes Rafael Luque. Result: There are at least six planets around the star.

Artistic illustration showing the orbits of the planets.

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Due to the precision of the six planets’ resonant orbits, each planet’s orbits are closely related to each other. (Artistic illustration)

Photo: University of Bern/Hugh Osborn

A system in resonance

The reason why scientists found the other three so quickly is because they occupy resonant orbits in which the planets exert regular forces on each other.

When we are near several planets that are sufficiently close to each other orbiting a star, we experience a kind of dynamic anchoring between them. A bit like what happens when the moon orbits the earth. This means that, for example, the Moon’s rotation period around the Earth and its rotation period around itself are synchronized.

The rotation periods of the planets around the star are generally in the resonance ratio of 3 to 2, that is, while there is one that makes three revolutions, the other makes two revolutions, the astrophysicist adds.

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By studying the three innermost planets, the authors of this work were able to calculate the orbits of the six planets, which range from about 9 days for the innermost planet to about 21 days for the outermost planet.

For example, if the planet closest to the star makes three complete revolutions around it, the second closest planet makes exactly two revolutions in the same amount of time.

If the closest planet completes six orbits, the farthest planet only completes one orbit.

Astronomers estimate that only about 1% of all planetary systems remain in resonance as they evolve. According to them, the discovery of this type of orbital system represents a unique opportunity to study the formation and evolution of a planetary system.

The authors of the work assume that the six exoplanets of HD 110067 are not small rocky super-Earths, but rather gaseous mini-Neptunes.

They say the system would have remained virtually unchanged since its formation at least 4 billion years ago, providing an opportunity to learn more about sub-Neptunes and the formation of systems of this configuration. Train, notes Rafael Luque.

None of these planets are in the habitable zone around the star, which would contain liquid water, a necessary condition for life to exist.

HD 110067 is the brightest star yet discovered to host more than four transiting exoplanets. It could contain other planets that could exist inside or outside the temperate zone, although such observations have not yet been made.

The authors calculated the masses of three of the planets in the system. This work shows that they have low density, suggesting the presence of dense atmospheres dominated by hydrogen.

Because these planets are all smaller than Neptune and likely have extensive atmospheres, they are ideal candidates for studying the composition of their atmospheres with ESA’s James Webb Space Telescope and future Ariel and Plato telescopes.

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The desert of the hot Neptunes

To date, we have discovered very few hot Neptunes among exoplanets near their star, compared to hot Jupiters on the one hand and super-Earths on the other, notes Olivier Hernandez.

A plausible explanation is that they would lose their atmosphere fairly quickly and become chthonic planets, which are in some ways planetary remnants of a gas planet.

The interest of this type of study is to understand whether we can find hot Neptunes in these regions.

Do hot Neptunes turn into super-Earths just because they are too close to their star and their atmosphere disappears completely? Or do they tend to migrate outside the planetary system and cool like those in our solar system?

HD 110067 is the second planetary system in orbital resonance discovered by CHEOPS. The first is called TOI 178 and is located about 200 light-years from Earth.

Artist's impression of the TOI-178 system from the most distant planet.

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This artist’s impression represents the view of the TOI-178 system from the most distant planet.

Photo: ESO/L. Calçada/spaceengine.org