The European Space Agency (ESA) has taken a "galactic census" of the Milky Way, unveiling the second major data release from the Gaia mission. Along with some stars further afield, the data release provides the most detailed map of our home galaxy, which includes position, distance and motion data of nearly 1.7 billion stars, as well as the orbits and positions of thousands of asteroids.
The Gaia spacecraft began scanning the sky in 2014, and in September 2016 the first data release was published based on 14 months of observations. It contained position and brightness data of 1.1 billion stars, as well as the distance and motion data of two million of those stars.
This second data release has expanded the scope dramatically. Using half a million bright, distant quasars as a kind of celestial reference frame, Gaia was able to determine the coordinates of close to 1.7 billion stars, and catalogued the motion of 1.3 billion stars. The latter group includes the velocity and parallax motion – the apparent shift of the stars in the sky caused by the Earth's orbit – and allows researchers to separate their actual movements from those caused by our moving vantage point.
Other information gathered includes brightness data on all 1.7 billion surveyed stars, color measurements of almost all of them, and for about 500,000 stars, how the brightness and color change over time. Surface temperatures have been measured for about 100 million of them, and the effect that interstellar dust plays has been measured for 87 million. Closer to home, Gaia has pinpointed the positions of over 14,000 asteroids in our solar system.
The data was precise enough to observe the motions of 75 globular clusters, which are groups of stars bound together by gravity. Zooming out further, the mission helped identify the orbits of 12 dwarf galaxies, including the Small and Large Magellanic Clouds that orbit around the Milky Way.
"Gaia is astronomy at its finest," says Fred Jansen, Gaia mission manager at ESA. "Scientists will be busy with this data for many years, and we are ready to be surprised by the avalanche of discoveries that will unlock the secrets of our galaxy."
A series of papers describing the finds is published in the journal Astronomy & Astrophysics. The team describes the data in the video below.
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