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EI2GYB > ASTRO 30.08.21 10:31l 110 Lines 5877 Bytes #999 (0) @ WW
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Subj: Ocean world: Rocky exoplanet has just half the mass of Venu
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Ocean world: Rocky exoplanet has just half the mass of Venus
A team of astronomers have shed new light on planets around a
nearby star, L 98-59, that resemble those in the inner Solar System.
Amongst the findings are a planet with half the mass of Venus --
the lightest exoplanet ever to be measured using the radial velocity
technique -- an ocean world, and a possible planet in the habitable zone.
A team of astronomers have used the European Southern Observatory's
Very Large Telescope (ESO's VLT) in Chile to shed new light on planets
around a nearby star, L 98-59, that resemble those in the inner Solar System.
Amongst the findings are a planet with half the mass of Venus --
the lightest exoplanet ever to be measured using the radial velocity
technique -- an ocean world, and a possible planet in the habitable zone.
"The planet in the habitable zone may have an atmosphere that could
protect and support life," says Mar¡a Rosa Zapatero Osorio, an
astronomer at the Centre for Astrobiology in Madrid, Spain, and one
of the authors of the study published today in Astronomy & Astrophysics.
The results are 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, called L 98-59 after its 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.
With the contribution of ESO's VLT, 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% 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," explains Olivier Demangeon, a
researcher at the Instituto de Astrof¡sica e Ciˆncias do Espa‡o,
University of Porto in Portugal and 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 team used the Echelle SPectrograph for Rocky Exoplanets and Stable
Spectroscopic Observations (ESPRESSO) instrument on ESO's VLT to study
L 98-59. "Without the precision and stability provided by ESPRESSO 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."
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 -- to find the planets and measure their sizes.
However, it was only with the addition of radial velocity
measurements made with ESPRESSO and its predecessor, the High
Accuracy Radial velocity Planet Searcher (HARPS) at the ESO La
Silla 3.6-metre telescope, that Demangeon and his team were able to
find extra planets and measure the masses and radii of the first three.
"If we want to know what a planet is made of, the minimum that we
need is its mass and its radius," Demangeon explains.
The team hopes to continue to study the system with the forthcoming
NASA/ESA/CSA James Webb Space Telescope (JWST) , while ESO's Extremely
Large Telescope (ELT), under construction in the Chilean Atacama Desert
and set to start observations in 2027, will also be ideal for studying
these planets.
"The HIRES instrument on the ELT may have the power to study the
atmospheres of some of the planets in the L 98-59 system, thus
complementing the JWST from the ground," says Zapatero Osorio.
"This system announces what is to come," adds Demangeon. "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."
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