The Gaia Data Release 3 (DR3) reported on June 13th transforms our knowledge of the Solar System and the Milky Way and its satellite galaxies.
According to a study by the University of Helsinki, the European Gaia space mission has produced an extraordinary amount of new, improved, and detailed data for almost two billion objects in the Milky Way galaxy and the surrounding cosmos.
The Gaia space mission of the European Space Agency (ESA) is constructing an ultraprecise three-dimensional map of our Milky Way galaxy. The map observes almost two billion stars (approx. one percent of all). Gaia was launched in December 2013 and started collecting science data in July 2014. ESA released Gaia data in DR3 on Monday, June 13. Finnish researchers were strongly involved in the release.
The Gaia data helps unveil the origin and future evolution of the Solar System and the Milky Way. It helps us understand stellar and planetary-system evolution and our place in the cosmos. For instance, it allows for the derivation of asteroid and exoplanet orbits and physical properties.
Gaia revolves slowly about its axis in a time period of about six hours. It is composed of two optical space telescopes. Three science instruments allow for the accurate determination of stellar positions and velocities, along with spectral properties. Gaia resides about 1.5 million kilometers from the Earth in the anti-Sun direction. Here it orbits the Sun together with the Earth in the proximity of the so-called Sun-Earth Lagrange L2-point.
Gaia DR3 was significant across astronomy. Several scientific articles are being published with DR3. Of those, nine articles have been devoted to underscoring the exceptionally significant potential of DR3 for future research.
The new DR3 data comprises chemical compositions, temperatures, colors, masses, brightnesses, ages, and radial velocities of stars, among others. It includes the largest ever binary star catalog for the Milky Way; more than 150,000 Solar System objects, largely asteroids but also planetary satellites, along with millions of galaxies and quasars beyond the Milky Way.
Gaia DR3 will help change the conception of asteroids in our Solar System, exoplanets and stars in our Milky Way galaxy, and even the galaxies themselves, be it the Milky Way or its surrounding satellite galaxies. After returning, Gaia will produce an ultraprecise reference frame for navigation and positioning.
Gaia detected asteroids
The ten-fold increase in the number of asteroids reported in Gaia DR3 when compared to DR2 implies that there is a significant increase in the number of close encounters between Gaia-detected asteroids. These encounters can be used for asteroid mass estimation. When Gaia DR3 astrometry is combined with astrometry from other telescopes, the number of asteroid masses that can be found should go up by a large amount.
In the standard computation of an asteroid’s orbit, the asteroid is assumed to be a point-like object. Its size, shape, rotation, and surface light scattering properties are not taken into account. However, the Gaia DR3 astrometry is so accurate that the angular offset between the asteroid’s center of mass and the center of the area illuminated by the Sun and visible to Gaia must be accounted for.
Based on Gaia DR3, the offset has been certified for asteroid (21) Lutetia. The ESA Rosetta space mission imaged Lutetia during the flyby on July 10, 2010. With the help of that imagery and ground-based astronomical observations, a rotation period, rotational pole orientation, and a detailed shape model were derived.
When the physical modeling is incorporated into orbit the calculation, the systematic errors are removed, and, contrary to the usual computation, all observations can be incorporated into the orbit solution. Consequently, Gaia astrometry provides information about the physical properties of asteroids. These properties need to be taken into account using physical models or empirical error models for astrometry.
For the first time, Gaia DR3 includes spectral observations. The spectrum measures the color of the target, meaning the brightness at different wavelengths. One especially interesting feature is that the new release contains about 60,000 spectra of asteroids in our Solar System. The asteroid spectrum contains information on their composition and, therefore, about their origin and the evolution of the whole Solar System. Before Gaia DR3, there had been only a few thousand asteroid spectra available. Gaia will multiply the amount of data by more than an order of magnitude.
Gaia detected exoplanets
Gaia is predicted to produce detections of up to 20,000 giant exoplanets. This will be done by measuring their gravitational effect on the movements of their host stars. This will enable us to find all the Jupiter-like exoplanets in our Solar neighborhood over the coming years and determine how common are Solar Systems. The first such astrometric Gaia detection was of a giant exoplanet around epsilon Indi A. This corresponds to the nearest Jupiter-like exoplanet, only 12 light years away. The first such detections are possible because acceleration observed in radial velocity surveys can be combined with movement data from Gaia to determine the orbits and planetary masses.
Gaia and galaxies
The microarcsecond resolution of Gaia DR3 provides precise measurements of the motions of stars. This works not only within our own Milky Way galaxy but also for the many satellite galaxies that surround it. From the motion of stars within the Milky Way itself, we can accurately measure their mass, together with the proper motion of satellites. Thus, we can now accurately determine their orbits.
This lets us look both into the past and into the future of the Milky Way galaxy system. For instance, we can find out which of the galaxies that surround the Milky Way are true satellites and which are just passing by. We can also investigate if the evolution of the Milky Way conforms to cosmological models. Specifically, whether the satellite orbits fit the standard dark matter model.
Gaia and reference frames
The International Celestial Reference Frame (ICRF3) is based on the position of a few thousand quasars determined by Very Long Baseline Interferometry (VLBI) at radio wavelengths. ICRF3 is used to obtain the coordinates of celestial objects and to determine the orbits of satellites. Quasars of ICRF3 are also fixed points in the sky that can be used to determine the accurate orientation of the Earth in space at any time. Without this information, satellite positioning would not work.
Gaia’s data contains about 1.6 million quasars, which can be used to create a more precise Celestial Reference Frame in visible light, replacing the current one. Eventually, this will have an impact on the accuracy of both satellite positioning and measurements of Earth-exploring satellites.
