Utilizing tools for purposes they weren’t initially intended for is a strength of the astronomical community. Scrounging through data collected for one purpose and looking for hints of another seems to be a favorite pastime of many a professional astronomer. That tradition is alive and well, with a team reanalyzing the first few data sets from Gaia, ESA’s star cataloging explorer. They found hints of exoplanets, and it turns out the probe launched in 2013 is a much better planet hunter than initially thought.
Gaia’s original mission was to track stars very carefully. Initially, it aimed to create a catalog of over 1 billion astronomical objects, including everything from quasars to asteroids. So far, it has far exceeded expectations by cataloging 1.8 billion stars alone. It does so using three main instruments. Astro is an astrometry instrument that measures the angular position of many of the stars it is observing. Photometry is covered by the BP/RP instrument, which measures the luminosity of its subjects. Finally, the RVS instrument measures the speed at which the objects are musing using the radial-velocity technique.
Combining data from these three instruments allows Gaia to sense how far away hundreds of millions of astronomical objects are and how fast they are moving. And it has delivered spectacularly on its original promise, with its data underpinning dozens of papers ranging from observations of globular cluster mergers to the dimmest galaxy ever discovered.
But that’s not all; the international team of researchers involved in analyzing and releasing Gaia’s data sets thought they might be able to find other ghosts hiding in the star cataloger’s data. Thousands of exoplanets have been found thus far, many of them using the radial-velocity method of watching a star move back and forth as the orbiting planet’s gravity makes it jiggle slightly in the sky. They believed that Gaia could do just that.
With Gaia’s super precise instruments, it was well placed to detect the minute changes in a star’s position when it was disturbed by a planet. In fact, the team utilized photometric data sets from all three primary instruments on the craft. They then fed that data into a training algorithm that used TESS’s exoplanet survey results to help train the algorithm on what to look for as a positive exoplanet finding.
What they did find were at least two new planets. Now known as Gaia-1 and Gaia-2, these two planets are both “hot Jupiters” – giant planets that have an orbital period so fast that they are tidally locked to their star. However, despite first having shown up in the Gaia data, the existence of the planets was confirmed by observations from TESS, an observatory much more focused on exoplanet hunting.
TESS has an entirely different underlying observational strategy than Gaia. It focuses on repeated, high-accuracy measurements of a star that might host a planet. In contrast, Gaia takes much less frequent images of its target as part of its whole sky observational requirements. That didn’t stop the researchers from trying, though. They managed to find that even with Gaia’s sparse data points, they were able to detect not only the two confirmed new planets but also 41 other exoplanet candidates that still need further validation before officially being accepted into the ranks of known exoplanets.
Overall that is an excellent record for Gaia searching for things it was not designed for. But there is more yet to come, with the next release of Gaia data, known as DR3, expected for release in June this year. There is undoubtedly evidence of even more exoplanets just waiting to be found in Gaia’s new data with this newly trained algorithm.
Panahi et al – The Detection of Transiting Exoplanets by Gaia
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Artist’s concept of Gaia in space.
Credit – ESA / D. Ducros