The Gaia mission's second data set has finally been published and it significantly improves the already impressive original data released in 2016. The mission's goal for the first data release was to measure the position of 1 billion stars and the velocity of a small fraction of that. In this new release, Gaia has gone beyond those targets, jumping closer to the final five years' objective.  

The new data contains about 1.69 billion light sources and their brightness. Gaia, a European Space Agency space observatory launched in 2013, has measured the position, distance, and motion of 1.3 billion stars. It also measured their colors, which will be extremely useful for working out their properties. A hi-res map can be seen here.

The mission was also capable of measuring the radial velocity of about 7 million stars, which tells us if the star is moving towards or away from us. This can be used to construct maps of stellar motion within the Milky Way. And combined with the rest of the information, it is key to creating an animated 3D map of our galaxy.

“It might look like a small number compared to other large ones but it represents the biggest radial velocity survey ever carried out over the whole sky," Anthony Brown, from the Gaia Data Processing and Analysis Consortium, said during a press conference. "This is a fantastic new addition.” 

There is no doubt of the technical capabilities of the probe. In about one minute Gaia measures roughly 100,000 stars. It takes Gaia about two months to image the entire sky and this is done over and over again to increase precision, and each star is imaged about 70 times. The multiple takes are key to improvement.  

“We are actually achieving a spatial resolution all over the sky which is very comparable to the one of the Hubble Space Telescope,” Brown stated.

The extra data and more refined analysis meant the astronomers could produce a more comprehensive view of our galaxy than they did two years ago. Among the particularly intriguing new features is the clear distribution, below the center of the Milky Way of the Sagittarius dwarf, a companion galaxy to our own that's being cannibalized by the Milky Way.

The other clear improvement is that the map is now in color. The main image is not a photograph. It was reconstructed using the new color measurements and positions of all the stars. The color also allowed the astronomers to build a map of the distribution of gas and dust throughout the Milky Way. But Gaia doesn't just focus on stars.

The mission is sensitive to all moving objects in the sky and has allowed for some deep analysis of our immediate neighborhood. The new data release from Gaia also includes 14,000 objects that belong to the Solar System.

“It represents the most accurate survey ever of asteroids in the Solar System. In some cases these two years of data can compete with hundreds of years of data collected,” Brown explained.  

The team hopes to collect more data on the nearby asteroids, like colors, for example. That will allow astronomers to characterize these space rocks more accurately and maybe help to unlock new information about the formation of the Solar System.

  

Gaia sports an incredible 1-billion-pixel camera. The camera is so precise that it can work out the size of a coin on the Moon and is so sensitive that it can detect objects 500,000 times fainter than the human eye’s limit. Two further data releases are planned for Gaia, an intermediate one in late 2020, and then a final one in 2022.

The ambitious final goal hopes to achieve a record of the position and motion of 2 billion stars as well as additional information, like stellar type. The team hopes to prepare an extensive list of variable stars and exoplanet-hosting stars, along with radial velocity measurements for more than 150 million stars.