If – or when – people colonize Mars, they may be able to enjoy the dazzling natural light show of auroras similar to those seen on Earth.
The European Space Agency's Mars Express satellite first detected auroras on Mars in 2005 — but it was only able to pick up ultraviolet light, which is invisible to human eyes. A recent study published in the journal Planetary and Space Science, however, shows that Martian auroras give off visible light as well.
"We wanted to know whether an astronaut standing on the surface of Mars would be able to see the aurora's light," said study author Cyril Wedlund in an interview. "What we show in this study is that the emissions you get are actually bright enough in certain conditions to be seen with the naked eye."
On Earth, auroras are primarily red and green, light displays in the sky people recognize as the aurora borealis or aurora australis, but Martian auroras feature streaks of blue as well. The color differences are a result of differences in the atmospheres of the two planets. Earth's atmosphere contains a lot of oxygen, which gives off red or green light, depending on its chemical state. Mars' atmosphere, by contrast, is rich in carbon dioxide.
Auroras occur as a result of the planet's magnetic field. Anyone who has ever played with iron filings and a magnet has seen that magnetic fields are organized in field lines that run alongside one another. A planet's magnetic fields are also organized this way.
In auroras, they serve as a sort of racetrack for electrons, the tiny particles that provide us with electricity. Interactions with radiation from the sun can cause the electrons to accelerate along the magnetic field lines. The electrons collide with molecules in the atmosphere, and this can cause those molecules to emit light — with different molecules emitting light of different colors.
The researchers studied Mars' carbon dioxide-laden atmosphere, using both numerical models and experimenting with a vacuum chamber called a Planeterrella. Utilizing this chamber, they were able to mimic the atmosphere and magnetic fields of Mars.
"We created an atmosphere of carbon dioxide just like on Mars and then we shot electrons at a magnetized sphere and suddenly we saw some blue light," Wedlund said.
Mars' atmosphere also contains some oxygen, and the researchers surmised from their work that Martian auroras would also feature green and red light.
Auroras are simply beautiful — but the elaborate combination of conditions that produce them are highly complex. As a result, Wedlund sees auroras as a great starting point for studying a variety of planetary features.
"The aurora in general is such a fantastic subject of investigation because it combines so many different aspects that you can trace back to the source using the aurora," he said.
The paper in Planetary and Space Science can be found here.