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Gaia: Mapping a Billion Stars

Milky Way from Gaia
The Milky Way as captured by the Gaia spacecraft. (Image credit: euronews)

Gaia is a European Space Agency space telescope that maps the positions of more than 1 billion stars to the highest precision yet of any mission. Its extended mission is expected to last until at least December 2020, and Gaia has already generated several data releases of information since its mission began in 2013.

The latest data release in April 2018 plotted the positions of more than 1.7 billion stars, which was released in a 3D color map at the ILA Berlin Air Show. The data not only plots the positions of stars, but also helps astronomers understand stellar evolution and history.

[Photos: Gaia Spacecraft to Map Milky Way Galaxy]

Development, operations and science goals

The Gaia concept was approved in 2000 after two years of study. It was modified in 2002 to fit it on a Soyuz-Fregat launch vehicle (a smaller rocket than originally imagined), which caused "a modest loss in astrometric accuracy," according to ESA. Originally expected to launch in 2011, Gaia left Earth two years later on Dec. 19, 2013. This delay was in large part due to technical difficulties with the mirrors and focal cameras.

Artist's concept of the European Space Agency's Gaia spacecraft mapping stars in the Milky Way galaxy. Gaia may discover 70,000 exoplanets if its mission continues for 10 years, researchers have found. (Image credit: ESA/ATG medialab/ESO/S. Brunier)

The mission's name was originally an acronym for Global Astrometric Interferometer for Astrophysics, but interferometry is no longer the method by which the mission does its work. "Although the acronym is no longer applicable, the name Gaia remains to provide continuity with the project," ESA said.

Gaia is located at a Lagrange point, a gravitationally stable spot in the sun-Earth system, called L2, which is located about 930,000 miles (1.5 million kilometers) from Earth in the opposite direction from the sun. Spacecraft here can use a minimum of fuel to maintain the same location in space. Gaia is also far enough from Earth that the light emanating from, and size of, our planet will not interfere with observations.

The spacecraft carries three major instruments — Astro (two identical telescopes and an imaging system), blue and red photometers to measure light photons, and a radial-velocity spectrometer to examine star composition. 

The major objectives of the Gaia mission, according to ESA, are:

  • To learn more about the origins and the evolution of the Milky Way, specifically by creating a 3D map of 1 billion stars.
  • Detecting Jupiter-sized planets through observing the movements of stars — stars that might be affected by the tug of an orbiting planet — to within 150 light-years.
  • Detecting brown dwarfs, or "failed stars" that were not quite large enough to begin nuclear fusion.
  • Searching for asteroids all over the solar system, ranging from near the Earth, to the asteroid belt between Mars and Jupiter, to the icy region of objects beyond Neptune (which is called the Kuiper Belt.)
  • Seeking out exploding stars (supernovas) before they reach maximum brightness.
  • Testing Einstein's theory of general relativity, for example by looking at how the gravity of massive objects distorts light.

Mission highlights

After Gaia's launch in December 2013, the spacecraft took its first image in February 2014. It examined a cluster of stars in the Large Magellenic Cloud. While the mission was still in its early days, a study released in November 2014 suggested that Gaia could find 70,000 new planets. But the final figure may take years to be revealed, since it takes time to analyze Gaia's data releases.

Gaia's first data release in September 2016 encompassed 14 months of observations, and plotted the positions and brightness of about 1,114,200,000 stars. There were also distances and motions found of more than 2 million stars, ESA said at the time. This first data release spurred a series of studies based on Gaia's work, which began churning out in the following months.

For example, in 2017, data from this Gaia release uncovered a couple of interesting astronomical phenomena. The spacecraft revealed a previously unseen star cluster, which scientists dubbed Gaia 1. The cluster is large (30 light-years wide) and bright, but was hidden behind a bright star called Sirius that was located only half a degree away in our sky. 

That year, Gaia tracked half a dozen hypervelocity stars, whose movements might be affected by a substance called dark matter, which makes up most of the universe's mass. It also assisted in observations of MU69, the next target of the New Horizons mission that flew by Pluto in 2015. (New Horizons will fly by MU69 on Jan. 1, 2019.) Also in late 2017, Gaia data showed how in the distant future, a star called Gliese 710 might disturb the paths of objects in the Oort Cloud, or comets far out in our solar system.

In early 2018, astronomers said Gaia's precise observations of star movements would help with the study of a tiny ringed object beyond the orbit of Saturn, called Chariklo. From time to time, objects such as Chariklo pass in front of a star, from Earth's perspective. Studying the pattern of winks and blinks as the object occults the light of the star helps scientists better understand the structure of the rings. But to do so, scientists need to know exactly where the stars are — a matter in which Gaia will assist. (Also, in data from March 2018, Gaia assisted in Earth observations of Neptune's largest moon, Triton.)

Then in May 2018, Gaia's next data release encompassed nearly 1.7 billion stars in full color. While the results of that dataset are still being parsed as of mid-2018, one early result showed how a pair of stars influenced some strange dimmings and brightenings of a star called Epsilon Aurigae.

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Elizabeth Howell
Elizabeth Howell

Elizabeth Howell, Ph.D., is a contributing writer for since 2012. As a proud Trekkie and Canadian, she tackles topics like spaceflight, diversity, science fiction, astronomy and gaming to help others explore the universe. Elizabeth's on-site reporting includes two human spaceflight launches from Kazakhstan, and embedded reporting from a simulated Mars mission in Utah. She holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, and a Bachelor of Journalism from Canada's Carleton University. Her latest book, NASA Leadership Moments, is co-written with astronaut Dave Williams. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.