The European Space Agency’s Gaia mission is building an ultra-accurate three-dimensional map of our Milky Way galaxy, observing nearly two billion stars, or about one percent of all the stars in our galaxy. Gaia was launched in December 2013 and has collected scientific data as of July 2014. On Monday 13 June, ESA released Gaia data in Data Release 3 (DR3). Finnish investigators were heavily involved in the release.
For example, Gaia data makes it possible to infer the orbits of asteroids and exoplanets and physical properties. The data helps reveal the origin and future evolution of the solar system and the galaxy, and helps to understand the evolution of stars and planetary systems and our place in the cosmos.
Gaia slowly rotates on its axis in about six hours and is composed of two optical space telescopes. Three scientific instruments provide accurate determination of stellar positions and velocities, as well as spectral properties. Gaia is located about 1.5 million kilometers from Earth in the anti-sun direction, where it orbits the sun with the Earth near the so-called Sun-Earth Lagrange L2 point.
Gaia DR3 on June 13, 2022 was significant in astronomy. Approximately 50 scientific papers are published with DR3, nine of which are devoted to highlighting the exceptionally important potential of DR3 for future research.
For example, the new DR3 data includes the chemical composition, temperatures, colors, masses, luminosity, ages and radial velocities of stars. DR3 contains the largest catalog of binary stars ever for the Milky Way, more than 150,000 objects in the Solar System, mostly asteroids but also planetary satellites, as well as millions of galaxies and quasars outside the Milky Way.
There are so many revolutionary advances that it is difficult to pinpoint a single most significant advance. Based on Gaia DR3, Finnish researchers will change the concept of asteroids in our solar system, exoplanets and stars in our Milky Way galaxy, as well as galaxies themselves, including the Milky Way and surrounding satellite galaxies. Returning to our home planet, Gaia will produce an ultra-precise reference frame for navigation and positioning, says Academy Professor Karri Muinonen from the University of Helsinki.
Gaia and asteroids
The ten-fold increase in the number of asteroids reported in Gaia DR3 compared to DR2 means there is a significant increase in the number of direct encounters between Gaia-detected asteroids. These close encounters can be used for estimating asteroid masses and we expect a significant increase in the number of asteroid masses that can be inferred using Gaia DR3 astrometry, especially in combination with astrometry obtained by other telescopes.
The conventional calculation of an asteroid’s orbit assumes the asteroid to be a point-like object and does not take into account the size, shape, rotation, and light scattering properties of its surface. However, the Gaia DR3 astrometry is so accurate that the angular deviation between the center of mass of the asteroid and the center of the sunlit region visible to Gaia must be taken into account. Based on Gaia DR3, the offset is certified for asteroid (21) Lutetia (Figure 2).
The ESA Rosetta space mission imaged Lutetia during the flyby on July 10, 2010. Using the Rosetta Lutetia images and ground-based astronomical observations, a rotation period, the orientation of the rotation pole and a detailed shape model were derived. When the physical modeling is included in the orbit calculation, the systematic errors are removed and, unlike conventional calculations, all observations can be included in the orbit solution. Consequently, Gaia astrometry provides information about the physical properties of asteroids. These properties must be taken into account by using physical models or empirical error models for astrometry.
The Gaia DR3 contains spectral observations for the first time. The spectrum measures the color of the target, i.e. the brightness at different wavelengths. One particularly interesting feature is that the new release contains approximately 60,000 spectra of asteroids in our solar system (Figure 3). The asteroid spectrum contains information about their composition and thus about their origin and the evolution of the entire solar system. Before the Gaia DR3, only a few thousand asteroid spectra were available, so Gaia will multiply the amount of data by more than an order of magnitude.
Gaia and exoplanets
Gaia is expected to produce detections of as many as 20,000 giant exoplanets by measuring their gravitational effect on the motion of their host stars. This will make it possible to find virtually all Jupiter-like exoplanets in the Solar neighborhood in the coming years and determine the frequency of solar system-like architectures. The first such astrometric Gaia detection was a giant exoplanet around epsilon Indi A, which corresponds to the nearest Jupiter-like exoplanet just 12 light-years away. The first such detections are possible because the acceleration observed in radial velocity studies can be combined with motion data from Gaia to determine the orbits and planet masses.
Gaia and galaxies
Gaia DR3’s microarcsecond resolution provides accurate measurements of the motions of stars not only within our own Milky Way galaxy, but also for the many satellite galaxies that surround it. The motion of stars in the Milky Way itself allows us to accurately measure masses, and together with the motion of satellites, we can now accurately determine their orbits. This allows us to see both the past and the future of the Milky Way Galaxy. For example, 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 examine whether the Milky Way’s evolution corresponds to cosmological models, and in particular whether the satellite orbits fit the Standard Model of dark matter.
Gaia and reference frames
The International Celestial Reference Frame, ICRF3, is based on the position of several thousand quasars determined by Very Long Baseline Interferometry (VLBI) at radio wavelengths. ICRF3 is used to obtain the coordinates of celestial bodies and to determine the orbits of satellites. ICRF3 quasars are also fixed points in the sky that can be used to determine the exact orientation of the Earth in space at any time. For example, 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 accurate visible-light celestial reference frame that replaces the current one. In the future, this will affect the accuracy of both satellite positioning and measurements from Earth-exploring satellites.
-The importance of DR3 and future data releases is in the improved accuracy due to more data, summarizes Professor Markku Poutanen of the National Land Survey of Finland.
Academy Professor Karri Muinonen
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