Gaia snaps photo of Webb at L2

on 17 March 2022

On 18 February, the NASA/ESA/CSA James Webb Space Telescope was photographed by ESA’s Gaia observatory, a mission where Romania contributes as well.

Both spacecraft are located in orbits around the Lagrange point 2 (L2), 1.5 million km from Earth in the direction away from the Sun. Gaia arrived there in 2014, and Webb in January 2022.

On 18 February 2022, the two spacecraft were 1 million km apart, with an edge-on view of Gaia towards Webb’s huge sunshield. Very little reflected sunlight came Gaia’s way, and Webb therefore appears as a tiny, faint spec of light in Gaia’s two telescopes without any details visible.

Gaia is not designed to take real pictures of celestial objects. Instead, it collects very precise measurements of their positions, motions, distances, and colours. However, one part of the instruments on board takes a sort of sky images.

Every six hours, Gaia’s sky mapper scans a narrow 360-degree strip around the entire celestial sphere. The successive strips are slightly tilted with respect to each other, so that every few months the entire sky is covered – touching everything that’s there and that’s bright enough to be seen by Gaia. Within seconds, these slices are automatically scrutinized for star images, the positions of which are then used to predict when and where those stars could be recorded in Gaia’s main scientific instruments. Then they are routinely deleted.

After Webb had reached its destination at L2, the Gaia scientists calculated when the first opportunity would arise for Gaia to spot Webb, which turned out to be 18 February 2022.

In Romania, the Astronomical Institute of the Romanian Academy is involved in four working groups of the CU9 (Coordination Unit 9) with regards to access to the GAIA catalogue, in the global GAIA-FUN-SSO network for tracking Solar System objects discovered by the Gaia Mission and in the Gaia Science Alert working group.

More details here.

Image credit: ESA/Gaia/DPAC; CC BY-SA 3.0 IGO