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Gaia and asteroid hunting

on 23 August 2019

Whilst best known for its surveys of the stars and mapping the Milky Way in three dimensions, ESA's Gaia mission has many more strings to its bow. Among them, it’s the contribution to our understanding of the asteroids that litter the Solar System. In 2019, the mission released an image showing the orbits of more than 14 000 known asteroids, among which a few new ones.

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.

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.

Once identified, moving objects found in the Gaia data were matched against known asteroid orbits to tell us which asteroid we are looking at.

This image based on information from Gaia’s second data release shows the orbits of more than 14 000 known asteroids with Sun at the centre. The majority of asteroids depicted in this image, shown in bright red and orange hues, are main-belt asteroids, located between the orbits of Mars and Jupiter; Trojan asteroids, found around the orbit of Jupiter, are shown in dark red. In yellow, towards the image centre, are the orbits of several tens of near-Earth asteroids observed by Gaia: these are asteroids that come to within 1.3 astronomical units (AU) to the Sun at the closest approach along their orbit. The Earth circles the Sun at a distance of 1 AU (around 150 million km) so near-Earth asteroids have the potential to come into proximity with our planet.

Most asteroids that Gaia detects are already known, but every now and then, the asteroids seen by ESA's Milky Way surveyor do not match any existing observations. This is the case for the three orbits shown in grey in this view: these are Gaia’s first asteroid discoveries.

The three new asteroids were first spotted by Gaia in December 2018, and later confirmed by follow-up observations performed with the Haute-Provence Observatory in France, which enabled scientists to determine their orbits.

While they are part of the main belt of asteroids, all three move around the Sun on orbits that have a greater tilt (15 degrees or more) with respect to the orbital plane of planets than most main-belt asteroids.

Gaia has the potential to make discoveries at high ecliptic latitudes. Not because ground-based surveys of Solar System objects cannot observe there, but because they tend not to. The vast majority of asteroids exist in the ecliptic plane and, as a result, it is here that most surveys concentrate their efforts. Gaia has no such prejudices and scans the entire sky, giving it the potential to discover new asteroids in the less crowded areas missed by other surveys.

Gaia is an ESA mission to survey one billion stars in our Galaxy in order to build the most precise 3D map of the Milky Way and answer questions about its origin and evolution.

Image credit: ESA/Gaia/DPAC