Gaia is a European Space Agency (ESA) cornerstone mission. It is special in so many aspects that I find it difficult to highlight just one of them. The core technique used by the mission is astrometry, the branch of astronomy that deals with the positions, distances and movements of the celestial objects. Despite being one of the ancient branches of astronomy, performing accurate astrometric measurements is very tricky, and astrometric studies were scarce in the past.

Gaia is revolutionising astronomy because it is compiling very accurate astrometric measurements for nearly two billion objects. Just to put this figure in context: if you have good eyes and are lucky enough to observe the starry night in a privileged spot (like an astronomical observatory) on a moonless sky, you may see around 2,000 stars. Gaia is producing data for almost one million times that number of stars.

But Gaia is not only doing astrometry; it is also performing photometry and spectroscopy. These complementary techniques measure the intensity of the light that is emitted by a body, and the composition of its radiation. When combined, the measurements collected by Gaia allow us to infer the distance, velocity, age, temperature, mass, chemical composition and even more parameters for a really huge number of stars. 

The way Gaia observes the Universe is unique. The spacecraft, which is equipped with the largest digital camera ever flown in space, is continuously scanning the sky while it rotates around its vertical axis at a rate of four revolutions per day. It is what we call an all-sky survey mission. This means that while collecting data for stars, Gaia is also observing nearby asteroids, gravitational lenses and galaxies. In fact, the Gaia measurements of a selected sample of distant galaxies are being used to construct a celestial reference frame that will allow us to determine the location of our Solar System as never done before at optical wavelengths. 

In short, the products generated by Gaia have an impact in virtually every branch of astrophysics. From now on, most astronomical publications are using the data collected by this mission in one way or another.

The full astrometric, photometric and radial-velocity catalogues generated by Gaia will only be released in the next years, and they will be the result of combining the observations collected during 66 months of operations. DPAC – the scientific consortium composed by hundreds of scientists spread across Europe that is behind the Gaia mission – will need several years to analyse them.

While accomplishing this very complex and long task, DPAC is creating intermediate products that are generated by processing smaller datasets of observations. However, even these early products are of great interest to the astronomy community as they contain extremely valuable information that only Gaia can offer. Because of this, DPAC decided to share growing portions of the analysed data through the various Gaia Data Releases. The first of them, Gaia Data Release 1, happened in 2016. Gaia DR2 and DR3 happened in 2018 and 2022, respectively. Each one of them supersedes its predecessor, as it includes more products and higher quality data. It is also fair to say that for the astronomical community, each of them has been a game changer. ¬¬

Traditionally, astronomers must team up to submit a winning proposal in an open competition to be awarded with precious telescope time. Once their observations have been acquired, the data only becomes public to the entire community after (usually) one year of proprietary data and it usually requires a careful post-processing.

The way Gaia is presenting the data is radically different, as firstly all the catalogues that are part of a data release are fully processed, and secondly this gold mine of astronomical data is freely accessible at the Gaia ESA Archive and its associated partner data centres.

This approach facilitates the scientific exploitation by the community, as it allows every astronomer to have seamless access to a huge (and ready to be used) dataset with information about various astrophysical objects like nearby asteroids, distant galaxies and all types of stars (including binary stars). Thanks to Gaia, we are really entering in a new era of research, where you only need a chair and a computer with internet to do cutting-edge astronomy.

Telespazio is directly involved in different aspects of the Gaia mission. We provide support at the scientific operations, data processing software and data management of the Astrometric Global Iterative Solution (AGIS). AGIS computes the astrometry of all Gaia observations in cycle batches, is therefore the main source of the final catalogue providing with the positions, parallaxes, proper motions (and their associated astrometric uncertainties).

Prior to each Gaia data release, there is always an AGIS production campaign that is a challenge from the science data processing perspective; not only because of the amount of data that is processed (order of Teras), but also because the processing needs to be highly efficient to ensure that AGIS products are delivered on time for the correct integration into the Main Gaia Database.

Telespazio also supports the Project Coordinator (responsible for the short-and-long-term planning of the DPAC activities) in the coordination of the processing and validation of the Gaia data products and their counterpart in the Gaia Data Releases. Furthermore, Telespazio contributes to the analysis of different types of observations, to the development of the Gaia ESA Archive (the main entry point to all the products generated by the mission), and Telespazio provides support to the Gaia Archive scientist (who aims to enhance the scientific use of the Gaia products).

The Gaia Archive at ESA is one of the most popular astronomical data archives. My main task is to support the work of the Gaia Archive Scientist. I tend to see my role as an interface between the scientific community and the team behind the Archive.

My previous experience as an astronomer who used Gaia products to do research helps me to understand the needs of the community. Among other tasks, I try to facilitate the experience of the astronomers when accessing to the vast content of the Gaia catalogues. This involves helping design, develop and implement new functionalities (or updating the existing ones), as well as coordinating the ingestion of the new products and curating some of the external catalogues that are offered in the Archive.

I also contribute to the creation of the road map that allow us to plan the short, mid and long-term tasks that are needed to manage this huge Archive. To do so, I work daily with the Archive Scientist and with a team of expert engineers who have a deep knowledge in relational databases, software development and hardware management.

I also create tutorials and watch very carefully for any potential issue that could affect the access to this invaluable dataset. But I am also in close contact with the astronomy community by actively participating in workshops and conferences where I show how to use the Archive. This also allows me to collect any useful feedback provided by the scientists and eventually help to implement their suggestions. It is a really fun and rewarding job that is well recognised by the community, but at the same time it can be exhausting, especially during the last months before a Data Release.

Sure. The measurements used in this release have been collected during a significantly larger period (34 months, versus 22 months for Gaia Data Release 2 and 14 months for Data Release 1). As a result, the data has higher quality (smaller error bars) when compared to what was included in the previous releases.

In addition, and thanks to this bigger dataset, there is a considerable number of new products in this release. To begin with, there are high- and low-resolution spectra for roughly 220 million objects (most of them stars, but also Solar System asteroids). A spectrum is like a fingerprint that contains unique features produced by the object that emits the observed radiation. Analysing them it is possible to infer valuable information like composition, rotational velocity, or temperature.

Furthermore, this is the first release that includes detailed information about extragalactic objects (distant galaxies that are also routinely observed by the spacecraft while it is continuously scanning the Universe), several catalogues of binary stars, and a substantial increment in the number of stars with measured radials velocities and inferred astrophysical parameters (like age, temperature, surface gravity, or metallicity).

Yes, there is even more data that will be published in the next years. Towards the end of 2023 there will be the Focused Product Release, containing dedicated catalogues for six selected data products. After it, but not before late 2025, Gaia Data Release 4 will happen. This release will contain the products generated by DPAC after analysing 66 months of data.

This coveted release will include the full astrometric, photometric and radial-velocity catalogues, as well as a list probably containing thousands of exo-planets and sub-stellar companions orbiting nearby stars. In addition, this release will include what we call epoch data. Since it became operative, each object detected by Gaia has been observed, on average, 70 times. The data published in the current releases contains the average results of these multiple detections.

Gaia DR4 will include the data associated to each individual observation, and this will open the window to the time domain analysis. In other words, it will be possible to study how the stars change some of their properties (like brightness) in time with unprecedent detail. This will be one of the largest astronomical datasets ever published.

The contents of the Gaia Data Release 5 are not yet publicly defined, but currently it is anticipated that this release will contain all the data collected during the entire mission lifetime. The date for this release has not yet been announced. 

There are many technical challenges associated with this mission. Ensuring that the spacecraft spins at a constant rate during its lifetime (five years for the nominal mission) while it orbits at the Lagrange L2 point (at 1.5 million km from Earth) was certainly a tough one. It was solved by designing a complex and highly precise cold gas micropropulsion system.

Another problem that had to be solved was how to broadcast to Earth the vast amount of data that Gaia is continuously generating. 

Before explaining how this was solved, let me put you in context. Think of an image of the starry night acquired with a normal telescope. In most cases, the stars in that picture are distributed across the entire image frame, but most of it is dark and empty of any features. Now imagine that you are only interested in the stars on that image; you could trim small, squared windows of just a few pixels around each star and ignore the rest of the image. By doing this, you would end up with a collection of small pictures having one star at their centre. The total size of this collection would be smaller than the size of the original image, but you would still have all the information needed. Gaia’s on-board computers are doing something like this, all the time. They are equipped with an autonomous algorithm that detects an object as soon as it enters the Gaia focal plane. If this object meets certain criteria, then the computers extract a small (few pixels across) window centred around it and store that information.

This is an example of the data that is downloaded to Earth. Every day, Gaia sends millions of these small images to the ground antennas that communicate with the satellite. And then, of course, processing the raw telemetry to extract the final science products is a huge task that requires the aid of supercomputers, and years of hard work by the (hundreds of) scientists that form DPAC.

Gaia was designed with one single (but very ambitious) objective: to investigate the origin and evolution of our Galaxy, which in turn allows to better understand the lifecycle of stars and our place in the Universe.

To do so, Gaia is collecting data with unprecedent accuracy for more than one billion stars. This dataset contains fundamental information like distance, position, velocity, temperature, chemical composition, brightness and even more. This huge Galactic census is being used to create the largest, most-precise 3D map of the Milky Way ever made.

As a result of this titanic effort, several secondary (but extremely useful) products are emerging. By the end of the mission, Gaia will have observed hundreds of thousands of asteroids and comets from our Solar System and it will have revealed thousands of failed stars (we called them brown dwarfs) and supernovae.

The measurements provided by Gaia will also detect the movement that the planets induce in their host stars, and thousands of exo-planets (planets outside the Solar System) are expected to be discovered in this way. Because of similar reasons, Gaia is expected to discover a population of black holes with very interesting properties in our Galaxy.

And Gaia will also allow us to further test Einstein’s General Relativity by measuring the bending of the star light that is caused by the major bodies in our Solar System. It is compiling really exciting data for generations of scientists.