The James Webb Space Telescope doesn’t orbit the Earth as the Hubble Space Telescope does. Instead, it orbits the sun in a position called the second Sun-Earth Lagrange point, or L2, where it can remain in a stable orbit with one side pointing toward the sun and the other side remaining in the shade. Webb isn’t alone in this L2 orbit though — other spacecraft are there too, including the European Space Agency (ESA)’s Gaia observatory.
That meant there was an opportunity for Gaia, which arrived at L2 in 2014, to capture an image of its new companion. Last month, the two spacecraft were 600,000 miles apart and Gaia was able to snap a picture of Webb. As Webb is edge-on from the view of Gaia, it only reflects a small amount of light and so it appears as a small speck of light in the image.
Capturing this image took some planning, which two Gaia scientists, Uli Bastian of Heidelberg University in Germany and Francois Mignard of Nice Observatory in France, began before Webb arrived at L2. As Gaia images the entire sky, they realized it would be able to see Webb as the new telescope passed Gaia’s field of view.
“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,” ESA wrote. “After Gaia’s two telescopes had scanned the part of the sky where Webb would be visible, the raw data was downloaded to Earth. In the morning after, Francois sent an email to all people involved. The enthusiastic subject line of the email was ‘JWST: Got it!!'”
It is an impressive feat for Gaia to have taken this image, as the observatory is not designed for taking images of individual objects such as stars or planets. Instead, it creates a 3D map of the entire galaxy, looking for changes in position and motion in the one billion stars of the Milky Way. However, the scientists were able to use the observatory’s finder scope to capture this image.
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