Gaia Discovers Her First Planet (Planetary Science)

It is the first exoplanet discovered entirely thanks to the data collected by the ESA space telescope for astrometry. Identified with the transit method, it has a mass similar to that of Jupiter and makes one revolution every three days. The confirmation came thanks to follow-up observations conducted with the Large Binocular Telescope

Born to compile the largest ever census of the stars of the Milky Way, measuring the properties of over a billion sources on several occasions, the Gaia ESA Space Telescope has now managed to discover its first exoplanet. Shadows of the passage of exoplanets in front of their stars, to tell the truth, Gaia had already caught many others in the past, but this announced yesterday by the Cu7 team – the unit of the Data Processing and Analysis Consortium of Gaia that deals with phenomena variables – is the first previously unknown, therefore identified for the first time by the ESA telescope.

The photometric measurements of the star, made by Gaia (here arranged in temporal order, at the top, and by phase, at the bottom), which made it possible to discover the presence of the exoplanet.  Credits: Esa / Gaia / Dpac / Cu7 / Tau + Inaf, Aviad Panahi, Shay Zucker, Avaraham Binnenfeld, Tsevi Mazeh (Tel Aviv University), Gisella Clementini (Inaf Oas Bologna), Laurent Eyer (University Of Geneva), Krzysztof Nienartowicz ( Sednai Sàrl) and the whole Cu7 / Dpcg Team, and Cu5 Team

The star around which it orbits has a name that looks like the digits of pi, a sequence of letters and numbers that alone is enough to give an idea of ​​the quantity of sources observed by Gaia: it is a solar-type star cataloged as Edr3 3026325426682637824 , where the first part of the impossible acronym stands for early data release 3and the 19 digits that follow are the code that uniquely identifies the star itself. But how did Gaia realize that there is a planet around Edr3 3026325426682637824? To betray its presence were four slight dimming of the apparent brightness of the star. Very slight, completely imperceptible to the human eye: we are talking about just 1.5 percent. Inaudible but systematic, and repeated at regular intervals. Extremely regular: they recur every 3.0525 +/- 0.0001 days. Let’s add that there in deep space – one and a half million kilometers from Earth, where Gaia is– there are no clouds, no passing planes and no atmospheric variations, and here it becomes inevitable to interpret these variations of luminosity as periodic partial eclipses: in other words, the passage of a body between the very sensitive eye of Gaia and the disc of the star observed. The transit , as astronomers say.

Yeah, but which body? There are not only the planets, to transit regularly in front of the stars. Although more unlikely, in principle it could be – in a binary system, for example – also another star, a brown dwarf, opaque and with dimensions comparable to that of a planet. To establish with certainty the planetary nature of the body that obscures the light of Edr3 3026325426682637824 it was therefore necessary to resort to a second observational method, able this time to allow the estimation not so much of the dimensions of the obscuring object – as happens with the transit method, since the dimming of the brightness is proportional to the area of the body that passes in front of the star – how much of its mass.

The radial velocities measured by Lbt’s Pepsi instrument (in temporal order and re-phased based on the estimated orbital period of the planet).  Credits: Felice Cusano, Andrea Rossi (Inaf Oas Bologna) and Ilya Ilyin (Aip, Potsdam) / Pepsi / Lbt

This is what the radial velocity method allows to do . Starting from the principle that it is not only the planet that orbits the star but also, albeit to a much lesser extent, the star that orbits the planet, it is in fact possible to calculate the mass of the planet by measuring – through the periodic displacement of the spectral lines caused by the Doppler effect – the slight movements of the star induced by the planet itself. It is a bit like trying to estimate the mass of the Earth by measuring the movements that its revolution induces on the Sun. However, it is a type of measurement that Gaia is unable to perform, at least not with the required accuracy. You need a very high resolution spectrograph mounted on a large telescope. A tool like Pepsi, the spectropolarimeter installed on Lbt , the Large Binocular Telescope, in Arizona. A telescope with two 8.4-meter mirrors and partly Italian, being INAF member of the international collaboration of the Lbt Observatory . And it is precisely by exploiting the so-called Italian Director’s Discretionary Time of Lbt – the time at the telescope made available at the discretion of the director of the Observatory – that it was possible to carry out the required observation. It was conducted by two astronomers of the INAF OAS of Bologna, Felice Cusano and Andrea Rossi , together with Ilya Ilyinof the Leibniz Institute for Astrophysics in Potsdam. Result: the object passing in front of the star has a mass equal to 1.1 times that of Jupiter. So yes, there is confirmation: it is indeed a planet. The first exoplanet discovered by Gaia.

“It was just a matter of time, but we knew that Gaia would eventually demonstrated its potential to reveal even planetary transits”, he tells Media Inaf Gisella Clementini , Oas astrophysics INAF Bologna and member unit CU7 Gaia who signed the discovery. “That the confirmation of this first planet in transit discovered by Gaia has been obtained thanks to the spectra acquired with an Inaf partnership telescope such as Lbt fills us even more with satisfaction”.

Provided by ESA

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