Turns out that the first men and women to visit Mars might be in for a show. Experts from NASA, the European Space Agency (ESA), and several respectable institutes have determined that full and colorful auroras occasionally streak across the Red Planet's skies - confirmation that visible versions of the phenomenon occur on terrestrial planets other than Earth.
To be clear, experts have long known that auroras occur on many planets and moons in our solar system, but as they are being observed with scientific instruments (spectroscopes and surveys of magnetic activity), it remained unclear if they would actually be visible for a human on the surface of that alien world.
Seeing the Invisible
Traditionally, auroras are caused by a complex interplay between charged solar particles (which come in waves of solar wind), a planet's magnetosphere, and atmospheric gases that glow when heated. However, due to the nature of these particles' light, or simply because of a world's atmosphere, it is never a sure thing that an aurora is visible to the naked eye. For instance, humans cannot see infrared light, yet it is a wavelength at which many things in the Universe glow at. We then have to rely on technologies like the Hubble Space Telescope to see this hidden glow of the cosmos. (Scroll to read on...)
Additionally, past research has revealed that some of the Red Planet's auroras are unexpectedly unique, glowing in strong and erratic waves of ultraviolet light - a spectrum that humans, for the most part, also cannot see.
"What's especially surprising about the aurora we saw is how deep in the atmosphere it occurs - much deeper than at Earth or elsewhere on Mars," Arnaud Stiepen, who works with the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft's Imaging Ultraviolet Spectrograph (IUVS), said in a past statement.
He's talking about one unusual aurora in particular, which happened just last December and astronomers came to call the 2014 "Christmas Lights" of Mars. It was reportedly "unusually energetic," producing about 100 times more energy than you get from a spark of everyday house current.
And thanks to that intensity and how close to the Marian surface the aurora occurred, there is a small chance that it would have even been visible for a person on Mars - namely if that person was a child or young adult with eyes still adjusting to the world. The light can reportedly appear whitish blue or a bright violet. (Scroll to read on...)
However, the Christmas Lights of Mars were, as Stiepen and his colleagues agree, an unusual occurrence. What then, about other auroras, namely near the Red Planet's icy poles? Are they usually invisible as well, or do they look more like the aurora borealis of Earth?
A Familiar Sight on Foreign Ground
Visible Martian lights first seemed possible after the ESA satellite Mars Express spotted aurorae from space in 2005. However, it took nearly a decade to confirm this suspicion, with new information from over 1,000 MAVEN orbits showing that visible Martian aurorae are actually a common event.
Experts then simulated these lights in a lab, replicating the gas of the Martian atmosphere as best they could and then bombarding it with a subtle electrical discharge. The results were recently published in the journal Planetary and Space Science.
"The study indicates that the strongest color in the Martian aurorae is deep blue. Green and red also occur, just like on Earth," researcher Cyril Simon Wedlund of Aalto University's Department of Radio Science said in a statement. "An astronaut looking up while walking on the red Martian soil would be able, after intense solar eruptions, to see the phenomena with the naked eye."
The study also revealed that unlike the Earth, these aurorae are best seen around the Red Planet's southern pole. Perhaps NASA astronauts, who plan to make their way towards Mars by the 2030s, will be the first to see these lights for themselves.
"And to think," Denise Lineberry of NASA's Langley Research Center added in a recent release, "Mars' southern lights could eventually become as much of a draw to aurorae admirers as Earth's northern lights."
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