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A star just 35 light years away has been found to harbor a number of rocky exoplanets, and one that has a good chance of habitability.
Around the red dwarf L 98-59 orbit at least four planets, and the system seems fascinating. New observations confirm what previous research had already suggested – the existence of an earthly world with half the mass of Venus.
But the new observations also reveal new worlds in the same system, including an ocean planet, and what appears to be a super-Earth bang in the middle of the star’s habitable zone.
“The planet in the habitable zone may have an atmosphere that could protect and support life,” said astrophysicist María Rosa Zapatero Osorio of the Center for Astrobiology in Spain.
The discoveries mark a pretty big milestone, not only in our search for potentially habitable worlds, but also in our search for rocky exoplanets like Earth, Mars, and Venus, as the tiny half-Venus represents a technical breakthrough.
It is the least massive exoplanet ever measured by examining its gravitational effect on the position of the star.
While there are potentially many more exoplanets in the Milky Way than there are stars, to date we have only found and conclusively identified a few thousand.
This is because they are much smaller and darker and harder to see. Our most prolific methods therefore work best on more massive exoplanets relatively close to their stars.
Most exoplanets are discovered using the transit method. This is where a telescope such as Kepler or TESS (or, in the case of L 98-95’s initial research, the Carnegie Planet Finder Spectrograph) looks at a patch of sky and looks for repeated and steady drops of light from the stars during the transits of an orbiting exoplanet. between us and the host star.
The radial velocity method, on the other hand, looks for changes in a star’s position. This is because the planets exert a very weak gravitational pull on their stars, causing them to move a bit in mutual orbit (the Sun does too). The more massive the exoplanet, the more pronounced the signal.
The L 98-59 system was discovered in 2019, with three planets orbiting the star, using the TESS exoplanet-hunting space telescope, which relies on the transit method. This can provide information about the exoplanets themselves, such as a rough estimate of size based on the amount of attenuation of starlight.
Radial velocity measurements can add more information. Based on how much the star moves, astronomers can calculate the mass of the exoplanet. Once they know the mass and size of a planet, they can calculate its density, which means we can determine its makeup: the densest exoplanets are probably rocky, while the fluffier ones are probably gaseous.
“If we want to know what a planet is made of, the minimum we need is its mass and radius,” said astronomer Olivier Demangeon from the University of Porto in Portugal.
A team of astronomers led by Demangeon used the European Southern Observatory’s Very Large Telescope to take measurements of the radial speed of the star L 98-59. They confirmed that the innermost exoplanet, L 98-59 b, was about half the mass of Venus, and probably rocky.
The second-innermost exoplanet, 1.4 times the size of Earth, is also likely rocky.
The third exoplanet is about 1.5 times the size and double the mass of Earth, with a density profile, the researchers said, that suggests high water content. Up to 30 percent of the mass of the exoplanet could be water, making it an ocean world.
Surprisingly, the team’s radial velocity measurements recorded two periodic signals that did not match any of the known exoplanets. These suggested two other exoplanets in the system that don’t orbit in the same plane as the others, so they don’t actually transit.
The former has a mass of about three times that of Earth and an orbital period of about 12.8 days. The second detection, more provisional, is however really interesting.
“We have clues to the presence of a terrestrial planet in the habitable zone of this system,” said Demangeon.
Comparison of the temperatures of L 98-59 and the solar system. (ESO / L. Calçada / M. Kornmesser)
The fifth exoplanet, if it can be confirmed, appears to point at 2.46 times the mass of Earth, with an orbital period of about 23 days. It might seem too close for comfort, but because red dwarf stars are much cooler than the Sun, it means the exoplanet would be a temperate distance from the star – not too hot (not too cold) to support life as we know it. .
Unfortunately, we would need a transit to be able to see if the exoplanet has an atmosphere, which means it’s not a good candidate for a follow-up study in habitability research.
But it shows that planetary systems can hide a lot of tricks up their sleeves – and we could take a closer look at inner exoplanets to study the diversity of planetary systems.
“This system heralds what’s to come,” Demangeon said.
“We as a society have been hunting terrestrial planets since the birth of astronomy and now we are finally getting closer and closer to detecting a terrestrial planet in the habitable zone of its star, which we could study. ‘atmosphere.”
The research was published in Astronomy & Astrophysics.
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