NASA’s MAVEN spacecraft has found signs of layers and rifts in the Martian atmosphere
NASA

Earth’s upper atmosphere has strange dense layers of ions that are constantly appearing and disappearing and which can hamper radio communication. Now, the same thing has now been found on Mars, offering a new chance to crack understand this poorly studied phenomenon.

The ionosphere is the layer of the atmosphere about 60 to 1000 kilometres up that is full of charged particles. When those particles are temporarily blown into clumps by the wind, they form what researchers call sporadic E layers in the lower reaches of the ionosphere.

“They act like a mirror in the sky, and radio signals bounce off of them,” says Glyn Collinson at NASA’s Goddard Space Flight Center in Maryland. “When you turn on your favourite radio station and it’s jammed by another station, you have probably been the victim of a sporadic E layer.”

They don’t just interfere with commercial radio stations, though – they can also block radar signals that are used to detect aircraft and ballistic missiles, he says.

E layers are difficult to study on Earth, because they appear and disappear unpredictably and they are at an altitude that is too high for aircraft to reach and too low for satellite orbits. But Collinson and his colleagues have spotted them in the Martian atmosphere for the first time, where they might be far easier to study.

The team found signs of 34 E layers in data from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. The layers form higher in the Martian atmosphere, so MAVEN is flying right through them and they are probably too high to interfere with any future radio communications on the ground, Collinson says.

MAVEN observations of a proton aurora. In the top panel, natural variability of the solar wind results in occasional dense flows of solar wind protons bombarding Mars. At bottom, observations by MAVEN’s Imaging Ultraviolet Spectrograph show increased ultraviolet emission from the atmosphere when the solar wind is enhanced.
Credits: NASA/MAVEN/University of Colorado/LASP/Anil Rao

Auroras appear on Earth as ghostly displays of colorful light in the night sky, usually near the poles. Our rocky neighbor Mars has auroras too, and NASA’s MAVEN spacecraft just found a new type of Martian aurora that occurs over much of the day side of the Red Planet, where auroras are very hard to see.

Auroras flare up when energetic particles plunge into a planet’s atmosphere, bombarding gases and making them glow. While electrons generally cause this natural phenomenon, sometime protons can elicit the same response, although it’s more rare. Now, the MAVEN team has learned that protons were doing at Mars the same thing as electrons usually do at Earth—create aurora. This is especially true when the Sun ejects a particularly strong pulse of protons, which are hydrogen atoms stripped of their lone electrons by intense heat. The Sun ejects protons at speeds up to two million miles per hour (more than 3 million kilometers per hour) in an erratic flow called the solar wind.

The MAVEN (Mars Atmosphere and Volatile Evolution mission) team was studying Mars’ atmosphere with the Imaging UltraViolet Spectrograph (IUVS), and observed that on occasion, the ultraviolet light coming from hydrogen gas in Mars’ upper atmosphere would mysteriously brighten for a few hours. They then noticed that the brightening events occurred when another MAVEN instrument, the Solar Wind Ion Analyzer (SWIA), measured enhanced solar wind protons.

It vanished into thin air. Around 90 per cent of the Red Planet’s atmosphere was probably lost to space over just a few hundred million years, according to a key measurement from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft.

Today Mars is a freezing, arid desert with an atmosphere 1 per cent as dense as Earth’s and its water mostly locked up in polar ice caps.

But most planetary scientists think it was not always so. Certain Mars soils contain minerals that on Earth are produced in the presence of water, and some Martian features seem to point towards ancient lakebeds and even fast-flowing rivers. To have retained this liquid water, the planet’s carbon dioxide-dominated atmosphere must once have been much thicker to limit surface evaporation.

MAVEN has been orbiting Mars since 2014 on a quest to find out where all that CO2 went. It could have gone into the ice caps, into the rocks as carbonate minerals or it could have been lost to space.

New global images of Mars from the MAVEN mission show the ultraviolet glow from the Martian atmosphere in unprecedented detail, revealing dynamic, previously invisible behavior. They include the first images of “nightglow” that can be used to show how winds circulate at high altitudes. Additionally, dayside ultraviolet imagery from the spacecraft shows how ozone amounts change over the seasons and how afternoon clouds form over giant Martian volcanoes. The images were taken by the MAVEN Imaging UltraViolet Spectrograph (IUVS).

“MAVEN obtained hundreds of such images in recent months, giving some of the best high-resolution ultraviolet coverage of Mars ever obtained,” said Nick Schneider of the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder. Schneider is presenting these results Oct. 19 at the American Astronomical Society Division for Planetary Sciences meeting in Pasadena, California.

The close encounter between comet Siding Spring and Mars flooded the planet with an invisible tide of charged particles from the comet’s coma. The dense inner coma reached the surface of the planet, or nearly so. The comet’s powerful magnetic field temporarily merged with, and overwhelmed, the planet’s weak field, as shown in this artist’s depiction. Illustration credits: NASA/Goddard.

Just weeks before the historic encounter of comet C/2013 A1 (Siding Spring) with Mars in October 2014, NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft entered orbit around the Red Planet. To protect sensitive equipment aboard MAVEN from possible harm, some instruments were turned off during the flyby; the same was done for other Mars orbiters. But a few instruments, including MAVEN’s magnetometer, remained on, conducting observations from a front-row seat during the comet’s remarkably close flyby.
The one-of-a-kind opportunity gave scientists an intimate view of the havoc that the comet’s passing wreaked on the magnetic environment, or magnetosphere, around Mars. The effect was temporary but profound.

“Comet Siding Spring plunged the magnetic field around Mars into chaos,” said Jared Espley, a MAVEN science team member at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We think the encounter blew away part of Mars’ upper atmosphere, much like a strong solar storm would.”