Mars’ Hope orbiter discovers green aurora spanning thousands of miles

Rather than little green men, astronauts who put their boots down on Martian soil are more likely to be greeted by green-streaked skies.

Scientists have known for more than 15 years that auroras, vibrant light shows in the atmosphere, exist on Mars. The planet’s auroras were found in small specks that seemed to sprout from the ground like mushrooms. The glowing canopies they formed are thought to come from what remains of a magnetic field that disintegrated billions of years ago.

But researchers have just spotted a gigantic new aurora on Mars unlike any other aurora seen before. They call the phenomenon a “discreet meandering aurora” to describe its enormous worm-like shape: a brilliant twisting band of ultraviolet light stretching thousands of miles from the dayside, which faces the sun, to the back of the planet.

A United Arab Emirates Space Agency probe orbiting Mars, known as Hope, took the picture using an ultraviolet spectrometer. The discovery raises new questions about Mars’ atmosphere, the makeup of its ancient magnetic field, and the effects of solar wind – the gases flowing from the sun that make up what is known as “space weather”.

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A snapshot from the United Arab Emirates’ Hope orbiter shows a new green worm-like aurora wrapping around from the day side of the planet to the night side.
Credit: Emirates Mars Mission

When the Hope probe arrived on Mars last year, mission leaders quickly realized its distance from the planet offered them the opportunity to “zoom out” and study the planet on a large scale. After the first images came in from the 3,000-pound SUV-sized spacecraft, they decided to focus on the aurora, Hessa Al Matroushi, who is leading the mission, said in a statement.

What scientists saw in the Hope snapshots blew them away, said Rob Lillis, a planetary space physicist and Emirates Mars mission collaborator based at the University of California, Berkeley. Since November, the team has seen several other cases of worm-like lights, he said.

Most people associate the Northern Lights with the Aurora Borealis, a brilliant light show sometimes seen on Earth at night near the North Pole. A similar effect also occurs near Antarctica. Electrons that are thrown from the sun during solar storms travel along magnetic field lines at the planet’s poles in the atmosphere, interacting with the air.

Auroras “were mysterious for a very long time on Earth before we understood that they were actually space weather and high-energy streams of electrons, originally from the sun and essentially guided by a field planetary magnetic,” Lillis told Mashable. “Whether it’s Earth or Mars, these electrons smash through the atmosphere and make the atmosphere glow.”

Electrons always follow the magnetic field lines and cannot deviate from their trajectory. So why does this region of the Mars sky look like a winding, twisting worm?

“Something funny is going on with this magnetic tail,” Lillis said, referring to the intricate network of magnetic field lines behind Mars. “We don’t yet understand what is causing this, or what is causing such a high flow of electrons on these particular magnetic field lines.”

That’s the mystery the researchers want to solve using a combination of spacecraft operated by the United Arab Emirates Space Program, NASA and the European Space Agency.

“We don’t yet understand what is causing this.”

NASA launched the Mars Maven mission in 2013.

Maven from Mars
Credit: NASA

ESA's Mars Express mission began in 2004.

Mars-Express
Credit: ESA

One is NASA’s Mars Maven mission, launched in 2013. The other is Mars Express, an ESA mission that began operations in 2004. Both probes observe the planet closely, sometimes dropping to less of 200 miles. The UAE hope is much further away, with its lowest point over 12,000 miles away.

Its distance gave the Emirates orbiter a distinct advantage. For the first time, scientists had unprecedented insight into the planet and its atmosphere, revealing Mars at different times of day and through different seasons. Lillis suspects the other probes may have already snapped pictures of tiny parts of these massive worm-like auroras, but they were only able to capture the tips of the iceberg, so to speak.

The next step in the study will be for NASA and ESA orbiters to take measurements of electrons moving toward Mars during a turbulent solar storm when they are in the vermiform aurora region. At the same time, Hope will take pictures of the lights.

“That would be the real holy grail,” Lillis said, “if we could get simultaneous measurements of cause and effect.”

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