The power of GAIA
In an attempt to answer one of the fundamental questions of mankind “Are we alone in the universe?” The planets and stars nearest to us, within a hundred light years from the Sun, are the most obvious and immediate sample to be analyzed. The interdisciplinary field of extrasolar planets with increasingly rapid expansion has recently recorded an increase of interest in the study of low-mass stars, commonly called dwarf M stars, besides looking for stars similar to the Sun. Dwarf M stars are main sequence stars, i.e. they are objects that are in the developmental phase longer and more stable, burning hydrogen safely in their central regions, with lower surface temperatures than those of the Sun.
The search for planets around these “cold” stars is extremely interesting because they are the most common in our Galaxy, and are also the most frequent around the Sun. Determining the frequency of planets around these stars has deep implications for theories of formation and evolution of planetary systems.
It was during these days that was accepted by the Monthly Notices of the Royal Astronomical Society – MNRAS for publishing an article which involves several researchers INAF on results of a detailed numerical experiment to estimate the potential of the Gaia mission, departing on 20 November, to detect and characterize giant planets around M dwarf stars that are within 100 light years from the Sun. Gaia space mission of the European Space Agency (ESA) will position measures high (astrometric) accuracy (100 times better than those obtained from the Hipparcos satellite). Thanks to these measures, it can reveal small periodic deviations in stellar motion caused by the gravitational perturbation induced by the presence of planets around the star mother.
Extrapolations made on M dwarfs stars count within 300 light years from the Sun to make the hypothesis that Gaia could detect more than 2000 new giant planets around low-mass stars and get accurate values of the mass and orbital parameters for about 500 planetary systems with orbital period between 0.2 and 6 years. The sample size will put strict limits on the planetary frequencies around M dwarf stars.
We asked Alessandro Sozzetti of INAF Observatory of Astrophysics from Torino, first author of the article, already engaged in other projects concerning the characterization of planetary systems, what will be the added value of Gaia in this field: “the astronomical results derived from Gaia will be complementary to those obtained with the HARPS spectrograph-N installed on the National Telescope Galileo (TNG) in the Canary Islands, given that its comments on the same sample of stars. In the context, for example, of the INAF GAPS project (Global Architecture of Planetary Systems) comments that HARPS-N @ TNG will be a fundamental element of the proposal with the next future Gaia data for a global understanding of the architecture of these planetary systems “.
Sozzetti adds that Gaia will look for five years the outer regions of the planetary systems looking for giant planets (300x Earth masses) with orbits within 5 AU (or up to 10 year period), then objects away from the parent star, with orbital periods of up to double the duration of the mission. The program GAPS with HARPS-N will produce information about low-mass planets (Neptune and Super-Earths with 10-20 Earth masses) within 1 AU (the orbital periods of less than 1 year).
“The radial velocity technique of HARPS-N @ TNG and the astrometrics of Gaia are extremely complementary,” continues Sozzetti. “From this point of view the sample of M dwarfs stars in common between the two programs will be featured with an unprecedented accuracy: Gaia will identify all the Jovian planets on long-period orbits (where is maximum sensitivity), and HARPS-no low-mass planets located inland (maximum sensitivity). In this way it will be able to identify systems with similar architecture to that of our solar system “.
In short, high hopes are expected for this mission and much work to be done for astronomers engaged in this young and charming branch of Astrophysics. Find other lands? Our solar system is a rule or an exception?