Gaia space telescope rocks asteroid science

The European space mission Gaia has produced an unprecedented amount of new, improved and detailed data for nearly two billion objects in the Milky Way galaxy and the surrounding cosmos. Monday’s Gaia Data Release 3 revolutionizes our knowledge of the Solar System and the Milky Way and its satellite galaxies.

The European Space Agency ESA’s Gaia space mission is building an ultra-precise three-dimensional map of our galaxy, the Milky Way, by observing nearly two billion stars, or about one percent of all stars in our galaxy. Gaia was launched in December 2013 and collected scientific data from July 2014. On Monday June 13, ESA published the Gaia data in Data Release 3 (DR3). Finnish researchers were heavily involved in the release.

Data from Gaia allow, for example, to derive the orbits and physical properties of asteroids and exoplanets. The data helps unravel the origin and future evolution of the Solar System and the Milky Way and helps to understand the evolution of the star and planetary system and our place in the cosmos.

Gaia slowly spins around its axis in about six hours and is made up of two optical space telescopes. Three scientific instruments allow precise determination of stellar positions and velocities as well as spectral properties. Gaia resides approximately 1.5 million kilometers from Earth in the anti-Sun direction, where it orbits the Sun with Earth near the so-called Sun-Earth Lagrange point L2.

Gaia DR3 on June 13, 2022 was significant throughout astronomy. Around 50 scientific papers are published with DR3, of which nine papers have been devoted to highlighting the exceptionally great potential of DR3 for future research.

The new DR3 data includes, for example, the chemical compositions, temperatures, colors, masses, luminosities, ages and radial velocities of stars. DR3 includes the largest catalog of binary stars ever created for the Milky Way, over 150,000 solar system objects, mostly asteroids but also planetary satellites, and millions of galaxies and quasars beyond the Way milky.

“There are so many groundbreaking advances that it is difficult to identify a single most significant breakthrough. Based on Gaia DR3, Finnish researchers will change the design of our solar system’s asteroids, exoplanets and stars of our Milky Way galaxy, as well as the galaxies themselves, including the Milky Way and its surrounding satellite galaxies. Back on our planet, Gaia will produce an ultra-precise reference frame for navigation and positioning,” said said Academy professor Karri Muinonen of the University of Helsinki.

Gaia and the asteroids

The tenfold increase in the number of asteroids reported in Gaia DR3 compared to DR2 means that there is a significant increase in the number of close encounters between asteroids detected by Gaia. These close encounters can be used for asteroid mass estimation and we expect a significant increase in the number of asteroid masses to be derived using Gaia DR3 astrometry, especially when combined with astrometry obtained by other telescopes.

In the conventional calculation of an asteroid’s orbit, the asteroid is assumed to be a point-like object and its size, shape, rotation, and surface light scattering properties are not taken into account. Gaia DR3 astrometry is so accurate, however, that the angular offset between the center of mass of the asteroid and the center of the sunlit area visible to Gaia must be taken into account. Based on Gaia DR3, the offset was certified for asteroid (21) Lutetia (Figure 2). ESA’s Rosetta space mission imaged Lutetia during the July 10, 2010 flyby. With the help of Rosetta Lutetia imagery and ground-based astronomical observations, a rotation period, rotation pole orientation and model of detailed shape have been derived. When physical modeling is integrated into the orbit calculation, systematic errors are removed and, unlike conventional calculation, all observations can be integrated into the orbit solution. Therefore, Gaia astrometry provides information about the physical properties of asteroids. These properties must be taken into account using physical models or empirical error models for astrometry.

The Gaia DR3 includes, for the first time, spectral observations. The spectrum measures the color of the target, i.e. the brightness at different wavelengths. A particularly interesting feature is that the new version contains around 60,000 spectra of asteroids in our solar system (Figure 3). The spectrum of asteroids contains information on their composition and therefore on their origin and the evolution of the entire solar system. Prior to Gaia DR3, there were only a few thousand asteroid spectra available, so Gaia will multiply the amount of data by more than an order of magnitude.

Gaia and the exoplanets

Gaia is expected to detect up to 20,000 giant exoplanets by measuring their gravitational effect on the motion of their host stars. This will find virtually all Jupiter-like exoplanets in the solar neighborhood over the next few years and determine the frequency of solar system-like architectures. The first astrometric detection of Gaia was a giant exoplanet around epsilon Indi A, which is the closest Jupiter-like exoplanet just 12 light-years away. The first such detections are possible because the acceleration seen in radial velocity surveys can be combined with motion data from Gaia to determine planetary orbits and masses.

Gaia and the galaxies

Gaia DR3’s microarcsecond resolution provides precise measurements of star motions, not only in our own galaxy, the Milky Way, but also for the many satellite galaxies that surround it. From the motion of stars in the Milky Way itself, we can accurately measure its mass, and with the proper motion of satellites, we can now accurately determine their orbits. This allows us to look both into the past and into the future of the Milky Way galactic system. For example, we can know which of the galaxies surrounding the Milky Way are true satellites and which are just passing through. We can also study whether the evolution of the Milky Way conforms to cosmological models, and in particular, whether the orbits of the satellites correspond to the standard model of dark matter.

Gaia and frames of reference

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. ICRF3 quasars are also fixed points on the sky that can be used to determine the precise orientation of the Earth in space at any time. Without this information, for example, satellite positioning would not work.

Gaia’s data contains approximately 1.6 million quasars, which can be used to create a more accurate visible-light celestial reference frame to replace the current one. In the future, this will impact the accuracy of satellite positioning and Earth exploration satellite measurements.

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