monomethylhydrazine (MMH) for the chemical propulsion subsystem on board might be enough to stabilize the spacecraft at L2 for several decades. Without the cold gas the space craft can no longer be pointed on a microarcsecond scale. On 12 September 2014, Gaia discovered its first supernova in another galaxy. On 3 July 2015, a map of the Milky Way by star density was released, based on data from the spacecraft. As of August 2016, "more than 50 billion focal plane transits, 110 billion photometric observations and 9.4 billion spectroscopic observations have been successfully processed." Data releases Several Gaia catalogues are released over the years each time with increasing amounts of information and better astrometry; the early releases also miss some stars, especially fainter stars located in dense star fields and members of close binary pairs. The first data release, Gaia DR1, based on 14 months of observation was on 14 September 2016. The data release includes "positions and ... magnitudes for 1.1 billion stars using only Gaia data; positions, parallaxes and proper motions for more than 2 million stars" based on a combination of Gaia and Tycho-2 data for those objects in both catalogues; "light curves and characteristics for about 3,000 variable stars; and positions and magnitudes for more than 2000 ... extragalactic sources used to define the celestial reference frame". The second data release (DR2), which occurred on 25 April 2018, is based on 22 months of observations made between 25 July 2014 and 23 May 2016. It includes positions, parallaxes and proper motions for about 1.3 billion stars and positions of an additional 300 million stars in the magnitude range g = 3–20, red and blue photometric data for about 1.1 billion stars and single colour photometry for an additional 400 million stars, and median radial velocities for about 7 million stars between magnitude 4 and 13. It also contains data for over 14,000 selected Solar System objects. Due to uncertainties in the data pipeline, the third data release, based on 34 months of observations, has been split into two parts so that data that was ready first, was released first. The first part, EDR3 ("Early Data Release 3"), consisting of improved positions, parallaxes and proper motions, was released on 3 December 2020. The coordinates in EDR3 use a new version of the Gaia celestial reference frame (Gaia–CRF3), based on observations of 1,614,173 extragalactic sources, 2,269 of which