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Astronomers find three new planets including one that ‘could protect and support life’ and an ‘ocean world’

Astronomers have found three new exoplanets around a nearby star that are very similar to those in our own solar system - including one that could support life.

The star, L 98-59, is only 35 light-years away from Earth; its orbiting planets may also contain water in their interiors or atmosphere. Two of the planets nearest to the star are likely dry, but one “ocean world” could have as much as one third of its mass made up of liquid.

“The planet in the habitable zone may have an atmosphere that could protect and support life,” María Rosa Zapatero Osorio, an astronomer at the Centre for Astrobiology in Spain, said.

The innermost planet in the system has a mass just half that of Venus. This makes it the lightest exoplanet ever measured, if the radial-velocity method used to detect this world is accurate.

This method relies on the fact that stars wobble, every so slightly, when gravity from their host star pulls them in their orbit. Using sensitive spectrographs (which split light into the different wavelengths that make it up), astronomers can detect whether a star has been shifted towards the blue end or the red end of the colour spectrum.

If the shifts repeat regularly, it is likely a body orbiting a star, and although it is difficult to distinguish mass through this method there can be a directly proportional relationship between the suspected planet and the star’s wobble.

“Without the precision and stability provided by ESPRESSO [the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations on the European Space Agency’s ‘Very Large Telescope’] this measurement would have not been possible,” says Zapatero Osorio. “This is a step forward in our ability to measure the masses of the smallest planets beyond the Solar System.”

These three planets may not be the only ones orbiting the star. The team found “hidden” exoplanets that had not previously spotted, discovering a fourth world and suspect there is a fifth that could also have water. It is also likely that these planets are close enough to the star to be warm.

The astronomers first spotted three of L 98-59’s planets in 2019, using Nasa’s Transiting Exoplanet Survey Satellite (TESS) by detecting when light from their nearby star dipped when the planets passed in front of it. It was, however, only with the addition of radial velocity data from ESPRESSO that the extra planets were able to be discovered, and the first three planets were able to have their masses and radii measured - which could provide insights into what the planets are made of.

“We have hints of the presence of a terrestrial planet in the habitable zone of this system,” said Olivier Demangeon, of the University of Porto in Portugal.

“This system announces what is to come. We, as a society, have been chasing terrestrial planets since the birth of astronomy and now we are finally getting closer and closer to the detection of a terrestrial planet in the habitable zone of its star, of which we could study the atmosphere.” 

Reference: Independent: Adam Smith