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Green glow detected in Mars atmosphere

Christian Fernsby ▼ | June 17, 2020
Scientists have identified a green light in the atmosphere of Mars.
Mars glow
Trace Gas Orbiter   Mars glow
A similar glow is sometimes seen by astronauts on the space station when they look to the Earth's limb.

The glow comes from oxygen atoms when they're excited by sunlight.

The phenomenon has long been predicted to occur on other planets, but the Trace Gas Orbiter (TGO) - a joint European-Russian satellite at Mars - is the first to make the observation beyond Earth.

"It's a nice result," said Dr Manish Patel from the UK's Open University.

"You'd never plan a mission to go look for this kind of thing. Today, we have to be very clear about the science we're going to do before we get to Mars. But having got there, we thought, 'well, let's have a look'. And it worked."

The green glow seen by astronauts at the edge of the Earth and now by the TGO on Mars has a separate origin. It's sunlight that's doing the work. Oxygen atoms are raised to a higher energy level and when they fall back to their resting state, they produce the tell-tale green emission.

Earth has abundant oxygen in its atmosphere. But on Mars it's largely present only as a breakdown product of carbon dioxide. Sunlight will free one of the oxygen atoms in CO2, and it's the transition of this atom that's glowing green on the Red Planet.

The TGO detects the excited oxygen not with an imaging camera but with its Nomad spectrometer package. This instrument sees the oxygen at very particular altitudes.