Whilst best known for its surveys of the stars and mapping the Milky Way in three dimensions, ESA's Gaia has many more strings to its bow. Among them, its contribution to our understanding of the asteroids that litter the Solar System. Now, for the first time, Gaia is not only providing information crucial to understanding known asteroids, it has also started to look for new ones, previously unknown to astronomers.
Credit: Observatoire de Haute-Provence & IMCCE
Since it began scientific operations in 2014, Gaia has played an important role in understanding Solar System objects. This was never the main goal of Gaia – which is mapping about a billion stars, roughly 1% of the stellar population of our Galaxy – but it is a valuable side effect of its work. Gaia's observations of known asteroids have already provided data used to characterise the orbits and physical properties of these rocky bodies more precisely than ever before.
"All of the asteroids we studied up until now were already known to the astronomy community,"
explains Paolo Tanga, Planetary Scientist at Observatoire de la Côte
d'Azur, France, responsible for the processing of Solar System
observations.
These asteroids were identified as spots in the Gaia data that were
present in one image and gone in one taken a short time later,
suggesting they were in fact objects moving against the more distant
stars.
Gaia's asteroid detections
Credit: ESA/Gaia/DPAC/CU4, L. Galluccio, F. Mignard,
P. Tanga (Observatoire de la Côte d'Azur)
Once identified, moving objects found in the Gaia data are matched
against known asteroid orbits to tell us which asteroid we are looking
at. "Now," continues Tanga, "for the first time, we are finding moving
objects that can't be matched to any catalogued star or asteroid."
The process of identifying asteroids in the Gaia data begins with a
piece of code known as the Initial Data Processing (IDT) software –
which was largely developed at the University of Barcelona and runs at
the Data Processing Centre at the European Space Astronomy Centre
(ESAC), ESA's establishment in Spain.
This software compares multiple measurements taken of the same area and
singles out objects that are observed but cannot be found in previous
observations of the area. These are likely not to be stars but, instead,
Solar System objects moving across Gaia's field of view. Once found,
the outliers are processed by a software pipeline at the Centre National
d'Etudes Spatiales (CNES) data centre in Toulouse, France, which is
dedicated to Solar System objects. Here, the source is cross matched
with all known minor bodies in the Solar System and if no match is
found, then the source is either an entirely new asteroid, or one that
has only been glimpsed before and has never had its orbit accurately
characterised.
Although tests have shown Gaia is very good at identifying asteroids,
there have so far been significant barriers to discovering new ones.
There are areas of the sky so crowded that it makes the IDT's job of
matching observations of the same star very difficult. When it fails to
do so, large numbers of mismatches end up in the Solar System objects
pipeline, contaminating the data with false asteroids and making it very
difficult to discover new ones.
"At the beginning, we were disappointed when we saw how cluttered the
data were with mismatches," explains Benoit Carry, Observatoire de la
Côte d'Azur, France, who is in charge of selecting Gaia alert
candidates. "But we have come up with ways to filter out these
mismatches and they are working! Gaia has now found an asteroid barely
observed before."
Asteroid Gaia-606 on 26 October 2016.
Credit: Observatoire de
Haute-Provence & IMCCE
The asteroid in question, nicknamed Gaia-606, was found in October 2016
when Gaia data showed a faint, moving source. Astronomers immediately
got to work and were able to predict the new asteroid's position as seen
from the ground over a period of a few days. Then, at the Observatoire
de Haute Provence (southern France), William Thuillot and his colleagues
Vincent Robert and Nicolas Thouvenin (Observatoire de Paris/IMCCE) were
able to point a telescope at the positions predicted and show this was
indeed an asteroid that did not match the orbit of any previously
catalogued Solar System object.
However, despite not being present in any catalogue, a more detailed
mapping of the new orbit has shown that some sparse observations of the
object do already exist. This is not uncommon with new discoveries
where, as with Gaia-606 (now renamed 2016 UV56), objects that first
appear entirely new transpire to be re-sightings of objects whose
previous observations were not sufficient to map their orbits.
"This really was an asteroid not present in any catalogue, and that is
an exciting find!" explains Thuillot. "So whilst we can't claim this is
the first true asteroid discovery from Gaia, it is clearly very close
and shows how near we are to finding a never-before-seen Solar System
object with Gaia."
Asteroid search region
Credit: ESA
Gaia is an ESA mission to survey one
billion stars in our Galaxy and local galactic neighbourhood in order to
build the most precise 3D map of the Milky Way and answer questions
about its origin and evolution.
The mission's primary scientific product will be a catalogue with the
positions, motions, brightnesses, and colours of the more than a
billion surveyed stars. The first intermediate catalogue was released in
September 2016. In the meantime, Gaia's observing strategy, with
repeated scans of the entire sky, is allowing the discovery and
measurement of many transient events across the sky: among these are the
detection of candidate asteroids which are subsequently observed by
astronomers in the Gaia Follow-Up-Network. During the five-year nominal
mission, Gaia is expected to observe about 350 000 asteroids of which a
few thousand will be previously unknown.
About Gaia
Gaia is an ESA mission to survey one
billion stars in our Galaxy and local galactic neighbourhood in order to
build the most precise 3D map of the Milky Way and answer questions
about its origin and evolution.
The mission's primary scientific product will be a catalogue with the
positions, motions, brightnesses, and colours of the more than a
billion surveyed stars. The first intermediate catalogue was released in
September 2016. In the meantime, Gaia's observing strategy, with
repeated scans of the entire sky, is allowing the discovery and
measurement of many transient events across the sky: among these are the
detection of candidate asteroids which are subsequently observed by
astronomers in the Gaia Follow-Up-Network. During the five-year nominal
mission, Gaia is expected to observe about 350 000 asteroids of which a
few thousand will be previously unknown.
Credit: Google Earth
The nature of the Gaia mission leads to
the acquisition of an enormous quantity of complex, extremely precise
data, and the data-processing challenge is a huge task in terms of
expertise, effort and dedicated computing power. A large pan-European
team of expert scientists and software developers, the Data Processing
and Analysis Consortium (DPAC), located in and funded by many ESA member
states, and with contributions from ESA, is responsible for the
processing and validation of Gaia's data, with the final objective of
producing the Gaia Catalogue. Scientific exploitation of the data only
takes place once the data are openly released to the community.
Contacts
Paolo Tanga
Observatoire de la Côte d'Azur, France
Email: Paolo.Tang@aoca.eu
Benoit Carry
Observatoire de la Côte d'Azur, France
Email: benoit.carry@oca.eu
William Thuillot
Observatoire de Paris, France
Email: William.Thuillot@obspm.fr
Timo Prusti
Gaia Project Scientist
Directorate of Science
European Space Agency
Email: timo.prusti@esa.int
Source: ESA/Gaia
