Mars Spacecraft reveal comet flyby effects on Martian atmosphere

Two NASA and one European spacecraft, including NASA's MAVEN mission led by the University of Colorado Boulder, have gathered new information about the basic properties of a wayward comet that buzzed by Mars Oct. 19, directly detecting its effects on the Martian atmosphere.

Data from observations carried out by MAVEN, NASA's Mars Reconnaissance Orbiter (MRO) and the ESA's Mars Express spacecraft revealed that debris from the comet, known officially as Comet C/2013 A1 Siding Spring, caused an intense meteor shower and added a new layer of ions, or charged particles, to the ionosphere.

The ionosphere is an electrically charged region in the atmosphere that reaches from about 75 miles (120 kilometers) to several hundred miles above the Martian surface.

ESA's Mars Express spacecraft

Using the observations, scientists were able to make a direct connection between the input of debris from the meteor shower to the subsequent formation of the transient layer of ions, the first time such an event has been observed on any planet, including Earth, said the MAVEN research team.

The comet traveled from the most distant region of our solar system called the Oort Cloud and made a close approach at 2:27 p.m. EDT within about 87,000 miles (139,500 kilometers) of the Red Planet.

That is less than half the distance between Earth and our moon and less than one-tenth the distance of any known comet flyby of Earth.

"MAVEN is well suited for studying the effects of the dust from the comet in the Martian atmosphere, because it makes measurements at the altitudes where the dust was expected to have an effect," said CU-Boulder Professor Bruce Jakosky of the Laboratory for Atmospheric and Space Physics, the principal investigator on the $671 million Mars Atmosphere and Volatile EvolutioN (MAVEN) mission.

"We also should be able to see if there are long-term effects from the comet dust in that same region of the atmosphere."

The places where the red line on this graph extends higher than the blue line show detection of metals added to the Martian atmosphere from dust particles released by a passing comet. 

The graphed data are from the Imaging Ultraviolet Spectrograph (IUVS) on NASA's MAVEN spacecraft, which recorded the intensities of emission by ingredients in the Martian atmosphere just before (blue line) and after (red line) comet C/2013 A1 Siding Spring sped within about 87,000 miles (139,500 kilometers) of Mars on Oct. 19, 2014. 

The "before" line records the usual main gases in the atmosphere, primarily carbon dioxide and its byproducts.

The "after" line includes those plus peaks at 280 nanometer wavelength, a fingerprint of ionized magnesium, and other wavelengths that are fingerprints of iron.

Researchers interpret this change as a result of vaporisation of dust particles that came from the comet and entered the Martian atmosphere at high speed.

Imaging Ultraviolet Spectrograph (IUVS)

IUVS uses limb scans to map the chemical makeup and vertical structure across Mars' upper atmosphere.

Dust from the comet was vaporized high in the Martian atmosphere, producing what was likely an impressive meteor shower.

The debris resulted in significant but temporary changes to the planet's upper atmosphere and possible longer-term changes.

A host of Earth-based and orbiting telescopes also observed the unique celestial event.

The MAVEN spacecraft, recently arrived at Mars, detected the comet encounter in two ways.

The remote-sensing Imaging Ultraviolet Spectrograph (IUVS) designed and built at CU-Boulder observed intense ultraviolet emissions from magnesium and iron ions high in the atmosphere in the aftermath of the meteor shower.

Not even the most intense meteor storms on Earth have produced as strong a response as this one:

The emission dominated Mars' ultraviolet spectrum for several hours after the encounter and then dissipated over the next two days, according to the MAVEN science team.

MAVEN also was able to directly sample and help scientists determine the composition of some of the vaporised comet dust in Mars' atmosphere.

Analysis of these samples by the spacecraft's Neutral Gas and Ion Mass Spectrometer (NGIMS) designed and developed at NASA Goddard Space Flight Center in Greenbelt, Maryland, detected eight different types of metal ions, including sodium, magnesium and iron.

These are the first direct measurements of the composition of dust from an Oort Cloud comet.

The Oort Cloud, well beyond the outermost planets that surround our sun, is a spherical region of icy objects believed to be material left over from the formation of the solar system.

An illustration of Maven spacecraft at Mars. Credit: NASA

"They call this comet encounter a once-in-a-lifetime event, but it's more like once-in-a-million years," said CU-Boulder Associate Professor Nick Schneider, a LASP research associate and lead IUVS scientist for the mission.

"MAVEN got there just in time, and we were ready.

The numbers suggest a Martian would have seen many thousands of shooting stars per hour, possibly enough to be called a meteor storm, so it must have been a spectacular event that night on Mars."

Elsewhere above Mars, a joint U.S. and Italian instrument on Mars Express observed a huge increase in the density of electrons in the Martian ionosphere following the comet's close approach.

"This historic event allowed us to observe the details of this fast moving Oort Cloud comet in a way never before possible using our existing Mars missions," said Jim Green, director of NASA's Planetary Science Division at the agency's headquarters in Washington.

"Observing the effects on Mars of the comet's dust slamming into the upper atmosphere makes me very happy that we decided to put our spacecraft on the other side of Mars at the peak of the dust tail passage and out of harms way."

There are three CU-Boulder undergraduates and two graduate students on the IUVS science team, said Schneider, and there will be a number of additional CU-Boulder students working on MAVEN in the coming years.

Currently there are more than 100 students working on research projects at LASP, which provides hands-on training for future careers as engineers and scientists.

New type of dust in Martian atmosphere discovered

A group of French and Russian scientists, including three specialists from Moscow Institute of Physics and Technology, has discovered a new peculiarity of the Martian atmosphere.

The scientists had analyzed satellite-acquired data and concluded that the dust particles in the planet's atmosphere can be of two types.

The scientific article which presents the results of the research in detail has been published in Icarus.

The Russian contributors to the research, Anna Fedorova, Alexander Rodin and Oleg Korablev, are the specialists of MIPT and SRI (IKI) RAS.

These scientists and their French colleagues from the Paris Observatory and LATMOS research laboratory have carried out a simultaneous analysis of the ultraviolet and infrared atmospheric extinctions from SPICAM, the spectrometer on the board of the orbital station Mars Express.

The results were received during the solar occultations at the beginning of Northern summer on Mars.

Before the Sun is completely eclipsed by the planetary disk, its rays pierce through the atmosphere and then get "caught" by the spectrometer's detector.

Having gone through the atmosphere, the solar rays show a different spectrum with the changes hinting at the atmosphere's makeup, the amount of various aerosols and the size of their particles.

This method was applied to understand the way the particles are distributed in the atmosphere.

The researchers have found out that the dust particles in the Martian atmosphere are not homogeneous, but can be roughly grouped into two modes.

• The first – coarser - mode is represented by both H2O ice grains with the average radius of 1.2 μm, and slightly smaller dust particles (R = 0.7 μm).
• The second mode is a lot finer, it is an aerosol which consists of much smaller particles with a radius of 0.04–0.07 μm.

Interestingly, the density number of the both modes is not that high. Even in the most "dusty" layers of the planet's atmosphere at altitudes of 20–30 km there are about 3.000 particles of the finer mode per 1 cm³, and not more than 2 particles of the coarser mode per 1 cm³.

If compared with what is considered the norm on Earth, the air with such dust density is rather clean (rooms are usually a lot dustier); yet, aerosols are important because they, according to the scientists, play a key role in forming the planet's climate.

Because of fine dust particles in the higher layers of the atmosphere, ice "embryos" are formed faster, which, in turn, influences clouds' build-up. The clouds are responsible for both precipitation and temperature condition on the planet's surface.

Analyzing the way the dust is spread in the atmosphere of the planet with regard to the altitude and geographical coordinates is crucial for forming the full picture of what is happening on Mars.

Besides that, the dust modes which the scientists have discovered confirm that Martian dust storms ("dust devils") are able to lift large quantities of substance from the planet's surface.

The researchers point out that the fact of fine dust presence in the atmosphere can contradict the previously obtained data on the existence of the supersaturated steam at the same altitude.

More information: Icarus, www.sciencedirect.com/science/… ii/S0019103513005332