On December 19, 2013, the European Space Agency began the Gaia mission, an astrometric space probe with an ambitious goal: to create a three-dimensional stellar map more complete and precise than any before, covering a total of one billion stars. Such a map will be a thousand times more complete than the best data astronomers currently have. Yesterday, the agency presented the first major batch of data, featuring more than two million stars, including their positions, temperatures, chemical compositions, and much more.
Mapping the Milky Way
According to experts, the Milky Way has about 100 billion stars, though that is often described as the most 'conservative' number in the specialized press. Other sources suggest our home galaxy may hold four times that amount, but even the lower estimate is enough to show how little we really know about it. The very idea of making a map seems almost impossible—until you remember the Gaia mission. Launched in December 2013, the probe has spent nearly three years collecting data, identifying stars, and calculating positions and basic properties. Gaia is expected to work for five years, and an extension would hardly be surprising. After all, its goal is unique: to shape a 3D map with a billion stars.
Certainly, one billion stars represents barely one percent of the Milky Way's population, but it still stands as a map a thousand times better than the most recent version available to astronomers. Another crucial aspect of Gaia is that its data will help confirm or correct previous observations, because the process is not merely "a simple look"—each object is examined about seventy times on average. The 'primary' dataset, released to the public yesterday, contains 2,057,050 stars with their locations, distances, temperatures, and proper motions, while the billion stars form the general secondary catalog. According to French astronomer Francois Mignard, a member of the Gaia team, those two million stars represent "20 times more content" than they had before.
What Lies Ahead
As if that were not enough, Gaia is expected to detect tens of thousands of Jupiter-like exoplanets, at least half a million quasars, and thousands of comets and asteroids within our Solar System—some of which may eventually "take a shot" at Earth. The long-awaited milestone of one billion stars with all their details should be crossed by the end of 2017. When that happens, certain rules of astronomy will change completely, and others will have to be written from scratch. Welcome be they.
