rocky planet like venus

Rocky planet discovered half the size of Venus, with potential for life

Image credit: PA

The lightest ever exoplanet – an ocean world that is possibly in the habitable zone of its star – has been discovered by a team of astronomers using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile.

The VLT, which was updated in 2017 to better detect potentially habitable planets, is comprised of four telescopes that operate at visible and infrared wavelengths.

It has shed new light on planets around a nearby star, L 98-59, that resemble those in the inner Solar System, including this new ocean-based exoplanet.

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

The results are deemed to be an important step in the quest to find life on Earth-sized planets outside the Solar System.

The detection of biosignatures on an exoplanet depends on the ability to study its atmosphere, but current telescopes are not large enough to achieve the resolution needed to do this for small, rocky planets.

The newly studied planetary system, named L 98-59 after the star, is an attractive target for future observations of exoplanet atmospheres. Its orbits a star only 35 light years away and has now been found to host rocky planets, like Earth or Venus, which are close enough to the star to be warm.

The team was able to infer that three of the planets may contain water in their interiors or atmospheres. The two planets closest to the star in the L 98-59 system are probably dry, but might have small amounts of water, while up to 30 per cent of the third planet’s mass could be water, making it an ocean world.

Furthermore, the team found “hidden” exoplanets that had not previously been spotted in this planetary system. They discovered a fourth planet and suspect there is a fifth, in a zone at the right distance from the star for liquid water to exist on its surface.

“We have hints of the presence of a terrestrial planet in the habitable zone of this system,” said Olivier Demangeon, lead author of the new study.

The study represents a technical breakthrough, as astronomers were able to determine - using the radial velocity method - that the innermost planet in the system has just half the mass of Venus.

This makes it the lightest exoplanet ever measured using this technique, which calculates the wobble of the star caused by the tiny gravitational tug of its orbiting planets.

The astronomers first spotted three of L 98-59’s planets in 2019, using Nasa’s Transiting Exoplanet Survey Satellite (TESS). This satellite relies on a technique called the transit method, where the dip in the light coming from the star caused by a planet passing in front of it is used to infer the properties of the planet and measure their sizes.

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