Free Astronomy Magazine September-October 2021

SEPTEMBER-OCTOBER 2021 T his infographic shows a compari- son between the L 98-59 exoplan- et system (top) with part of the inner Solar System (Mercury, Venus and Earth), highlighting the similarities between the two. [ESO/L. Calçada/M. Kornmesser (Ack.: O. Demangeon)] 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 mini- mum 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 Ex- tremely Large Telescope (ELT), under construction in the Chilean Atacama Desert and set to start observations in 2027, will also be ideal for study- ing these planets. “The HIRES instru- ment on the ELT may have the power to study the atmos- pheres of some of the planets in the L 98-59 system, thus complement- ing the JWST from the ground,” says Zapatero Osorio. “This system an- nounces what is to come,” adds Demangeon. “We, as a society, have been chas- ing terrestrial planets since the birth of astronomy and now we are finally getting closer and closer to the detection of a ter- restrial planet in the hab- itable zone of its star, of which we could study the atmosphere.” planet in the system has just half the mass of Venus. This makes it the lightest exoplanet ever measured using this technique, which calcu- lates the wobble of the star caused by the tiny gravitational tug of its orbiting planets. The team used the Echelle SPectro- graph for Rocky Exo- planets and Stable Spectroscopic Observa- tions (ESPRESSO) instru- ment on ESO’s VLT to study L 98-59. “With- out the precision and stability provided by ESPRESSO this measure- ment would have not been possible,” says Za- patero Osorio. “This is a step forward in our ability to measure the masses of the smallest planets beyond the So- lar System.” The astronomers first spotted three of L 98- A team of astronomers have used ESO’s Very Large Telescope in Chile to shed new light on planets around a nearby star that resemble those in the inner Solar System. This video summarises what they found about the planetary system, called L 98-59. [ESO] 59’s planets in 2019, using NASA’s Transiting Exoplanet Survey Satellite (TESS). This satellite relies on a tech- nique 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 measure- ments made with ESPRESSO and its predecessor, the High Accuracy Ra- dial velocity Planet Searcher (HARPS) at the ESO La Silla 3.6-metre tele- scope, that Demangeon and his team !