Gaia Space Telescope shakes the science of asteroids

Gaia Space Telescope shakes the science of asteroids

Figure 1.

image: Mass estimate for the main belt asteroid (445) Edna based on ground-based astrometry (blue), Gaia DR2 astrometry (red) and their combination (green). The combination of ground-based and Gaia data provides the most accurate estimate of Edna’s mass and the low density indicates that its carbonaceous interior has not been fully compressed.
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Credit: Reference and image credit: Siltala, L. & Granvik, M. 2022, Astronomy & Astrophysics 658, A65.

The European space mission Gaia has produced an unrivaled amount of new, improved and detailed data for almost two billion objects in the Milky Way galaxy and the surrounding cosmos. Gaia Data Release 3 on Monday revolutionizes our knowledge of the solar system and the Milky Way and its satellite galaxies.

The Gaia space mission from the European Space Agency ESA constructs an ultra-exact three-dimensional map of our galaxy, the Milky Way, and observes nearly two billion stars, or about one percent of all stars in our galaxy. Gaia was launched in December 2013 and has been collecting science data from July 2014. On Monday 13 June, ESA released Gaia data in Data Release 3 (DR3). Finnish researchers were strongly involved in the publication.

Gaia data allow, for example, the derivation of asteroids and exoplanet orbits and physical properties. The information helps to reveal the origin and future development of the solar system and the Milky Way and helps to understand the evolution of star and planetary systems and our place in the cosmos.

Gaia rotates slowly around its axis in about six hours and consists of two optical space telescopes. Three scientific instruments enable accurate determination of the stars’ positions and velocities as well as spectral properties. Gaia lives about 1.5 million kilometers from Earth in the direction of the anti-sun, where it orbits the sun along with the earth near the so-called Sun-Earth Lagrange L2 point.

Gaia DR3 on June 13, 2022 was significant in astronomy. About 50 scientific articles are published with DR3, of which nine articles have been devoted to emphasizing the exceptionally significant potential of DR3 for future research.

The new DR3 data includes, for example, the stars’ chemical composition, temperatures, colors, masses, brightness, ages and radial velocities. DR3 includes the largest binary star directory ever for the Milky Way, more than 150,000 solar system objects, largely asteroids but also planetary satellites, as well as millions of galaxies and quasars beyond 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 scientists will change the perception of asteroids in our solar system, exoplanets and stars in our Milky Way galaxy, as well as the galaxies themselves, including the Milky Way and its surrounding satellite galaxies. Returning to our home planet, Gaia will produce an ultra-precise frame of reference 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 that there is a significant increase in the number of close hits between Gaia-detected asteroids. These close hits 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. However, the Gaia DR3 astrometry is so precise that the angular displacement between the asteroid’s center of mass and the center of the area illuminated by the sun and visible to Gaia must be taken into account. Based on Gaia DR3, offset has been certified for the asteroid (21) Lutetia (Figure 2). The ESA Rosetta space mission depicted Lutetia during the bypass on July 10, 2010. Using the Rosetta Lutetia images and ground-based astronomical observations, a rotation period, rotation pole orientation and a detailed shape model were derived. When the physical modeling is incorporated into the orbital calculation, the systematic errors are removed and, in contrast to the conventional calculation, all observations can be incorporated into the orbital solution. Consequently, 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.

Gaia DR3 includes spectral observations for the first time. Spectrum measures the color of the target, which means the brightness at different wavelengths. A particularly interesting feature is that the new version contains about 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 development of the entire solar system. Before Gaia DR3, there were only a few thousand asteroid spectra available, so Gaia will multiply the amount of data by more than one order of magnitude.

Gaia and exoplanets

Gaia is expected to produce detections of up to 20,000 giant exoplanets by measuring their gravitational effect on the movements of the host stars. This will make it possible to find virtually all Jupiter-like exoplanets in the solar region in the coming years and determine how common solar system-like architectures are. The first such astrometric Gaia detection was a giant exoplanet around the epsilon Indi A, which corresponds to the nearest Jupiter-like exoplanet just 12 light-years away. The first such detections are possible because acceleration observed in radial velocity studies can be combined with motion data from Gaia to determine the orbits and planetary masses.

Gaia and galaxies

The microsecond resolution of Gaia DR3 provides accurate measurements of the stars’ movements, not only within our own Milky Way galaxy, 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 together with the correct motion of the satellites, we can now accurately determine their orbits. This allows us to see both into the past and into the future of the Milky Way galaxy system. For example, we can find out which of the galaxies surrounding the Milky Way are true satellites, and which ones just pass by. We can also investigate whether the Milky Way’s development is in line with cosmological models, and in particular whether the satellite orbits fit the standard model for 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. Quasars of ICRF3 are also fixed points in the sky that can be used to determine the exact 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 celestial frame of reference in visible light that replaces the current one. In the future, this will affect the accuracy of both satellite positioning and measurements of Earth exploring satellites.

-The importance of DR3 and future data releases lies in the improved accuracy due to increased data, the professor concludes Markku Poutanen from Lantmäteriet.

More information:

Academy Professor Karri MuinonenUniversity of Helsinki, keri.muinonen@helsinki.fi+358 50 415 5474, Asteroids

Professor Markku Poutanen, National Land Survey, Finnish Geospatial Research Institute FGI, markku.poutanen@nls.fi+358 40 7182152, Reference frames

Teacher Mikael GranvikUniversity of Helsinki and Luleå University of Technology, mikael.granvik@helsinki.fi+358 50 521 7209, Asteroids

Associate professor, university researcher Antti PenttiläUniversity of Helsinki, antti.i.penttila@helsinki.fi+358 50 524 0968, Asteroids

University researcher Mikko Tuomi, University of Helsinki, mikko.tuomi@helsinki.fi+358 40 500 7454, Exoplanets and variable stars

Associate Professor, Academy Researcher To Sawala, University of Helsinki, till.sawala@helsinki.fi+358 440 418000, Galaxies and cosmology

University of Helsinki Gaia DR3 press event, 13 June 2022

  • 10.30 Inauguration, Gaia space mission, Karri Muinonen
  • 10.35 Small solar system bodies, Mikael Granvik
  • 10.45 Discussion
  • 11.00 ESA Central Event
  • 12.00 Lunch
  • 13.00 Gaia Data Release 3 highlights, Asteroid characterization from photometry, Karri Muinonen
  • 13.20 Asteroid masses from astrometry, Mikael Granvik
  • 13.30 Asteroid classifications from spectroscopy, Antti Penttilä
  • 13.40 Exoplanets and variable stars, Mikko Tuomi
  • 13.50 Galaxies, To Sawala
  • 14.00 Reference frames, Markku Poutanen
  • 14.10 Questions and answers, discussion, Anne Virkki (chair)
  • 15.00 Closing, Karri Muinonen

Recordings from the University of Helsinki press event Gaia DR3:

https://www2.helsinki.fi/unitube/video/c47098cf-c15e-4569-a407-0c1c0865198b

Links:

Complete overview of the contents of Gaia DR3: https://www.cosmos.esa.int/web/gaia/dr3

Media Kit for Gaia DR3: https://www.esa.int/Science_Exploration/Space_Science/Gaia/Gaia_data_release_3_media_kit


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