Interstellar comet 3I/ATLAS emits a greenish glow in new images

According to the researchers responsible for the publication, the new observations reveal how the comet changed after getting closer to the Sun. After emerging behind the star, 3I/ATLAS reappeared in the sky near Zaniah, a triple star system located in the constellation Virgo.

In previous images of the comet, it appeared to have a reddish color. In the new image it has a slight greenish glow.

Scientists say this is due to light emitted by gases in the comet’s coma (a diffuse atmosphere of gas and dust surrounding its core) that evaporate as it heats up, including diatomic carbon (C₂), a highly reactive molecule made of two carbon atoms that emits light at green wavelengths.

What we don’t yet know, they explain, is how the comet will behave when it moves away from the Sun’s neighborhood and cools. Many comets respond late to solar heat because of the time it takes to penetrate their planet’s interior. This delay could trigger the evaporation of new chemical compounds or trigger a comet explosion.

The observations were made as part of a public outreach initiative organized by NOIRLab in collaboration with Shadow the Scientists, a project created to connect the public with scientists and promote participation in authentic science experiences, such as astronomical observing experiments with world-class telescopes.