Raising Gaia, Europe’s Brainchild

CARRASCOSO (University of Barcelona):

Working on a space mission is a bit like raising children: it takes years, patience and some suffering, but it is also very rewarding. For me parenthood and the work on a space mission started around 2001, when my wife, Isabel, gave birth to our daughter Ana and the European Space Agency (ESA) approved the Gaia mission.

Gaia’s main goal is to measure the distance to one billion stars (as I tell my kids, this is about two stars for each member of the European Union, so four stars are for them). Precisely measuring stellar distances is very difficult. It is done by measuring the stellar parallax, a very small angular displacement of the apparent position of a star in the sky caused by the movement of the Earth around the Sun (a perspective effect). The parallax is smaller for large distances and larger for short distances, which allows us to derive the distance to the star.

The first parallax was measured in 1838 and since then the efforts to obtain more parallaxes with increasing precision has continued. The latest results were produced in 1997 by ESA’s Hipparcos satellite, a stellar catalogue containing parallaxes for about 118,000 stars. This very same year I married Isabel and I joined a group of scientists to propose to ESA its next astrometric mission, Gaia.

It may seem strange to start preparing a new space mission when the previous one has just delivered its results, but space projects are a lengthy affair. Ana has seen me working in Gaia since she was born and will see its completion while she is graduating in medicine. So, as she asks me, why so much effort if you already have the 118,000 stars? This may seem a lot, I answer, but it’s just a tiny fraction of the Milky Way, consisting of more than 100,000 million stars. Also, Hipparcos’ precision only allows us to reliably measure distances to about 1500 light years, which is just our close neighbourhood in galactic terms. To be able to really understand our galaxy, we need more and better data.

Thus, our small group of scientists worked on the concept of a follow-up mission aiming to observe a billion stars with precision in parallaxes 100 times better. In 2000 ESA approved the Gaia mission and for the next five years its technology study was carried out: its basic design was established and the key technological elements for its building were identified. I was involved in the scientific guidance of the design and the development of the mission simulator, and it was a bit like raising Ana: complicated, exhausting, sometimes frustrating, but always wonderful when you can see them grow and imagine the adults they will become.

In 2006 the scientific community around Gaia faced a new challenge. The processing of the huge amount of data Gaia will produce (more than 150 terabytes of raw data, the equivalent of some 35,000 DVDs) will require a complex processing to convert it into scientifically useful data. To carry out this task, the Gaia Data Processing and Analysis Consortium (DPAC) was formed with the daunting responsibility of carrying out a processing that will require 10 20 FLOPS (FLoating-Point Operations Per Second) and will generate more than a petabyte of data. DPAC started its activities in 2007, the same year that David, my second child, was born. I had survived the childhood of Ana and Gaia, and I now faced the childhood of David and DPAC. But I was better prepared this time; you face second children with a much more Zen attitude.

Gaia was launched in December 2013 and is now in space being prepared for the start of its scientific operations. During the next five years Gaia will measure with exquisite precision the positions, distances, movements, photometry and spectra of one billion stars, and we expect that around 2022 the DPAC will be able to publish its final catalogue. It will be the culmination of more than two decades of work, the brainchild of Europe’s science and technology — a priceless scientific legacy for future generations.

Xavier Luri Carrascoso
University of Barcelona
www.atomiumculture.eu

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