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.

NASA MAVEN: Probe Snaps 1st Red Planet Images

The first observations of Mars' upper atmosphere made by NASA's MAVEN probe, which reached the Red Planet on Sept. 21, 2014.

Credit: Laboratory for Atmospheric and Space Physics, University of Colorado; NASA

NASA's MAVEN spacecraft isn't wasting any time at Mars.

MAVEN sent home its first images of Mars' upper atmosphere early Monday morning (Sept. 22), just eight hours after entering orbit around the Red Planet.

The false-colour images, which NASA released Wednesday (Sept. 24), were captured by MAVEN's Imaging Ultraviolet Spectrograph (IVS) instrument when the probe was 22,680 miles (36,500 kilometers) above the surface of Mars, agency officials said.

"Blue shows the ultraviolet light from the sun scattered from atomic hydrogen gas in an extended cloud that goes to thousands of kilometers above the planet’s surface," NASA officials wrote in an online description of the image.

"Green shows a different wavelength of ultraviolet light that is primarily sunlight reflected off of atomic oxygen, showing the smaller oxygen cloud," they added.

"Red shows ultraviolet sunlight reflected from the planet’s surface; the bright spot in the lower right is light reflected either from polar ice or clouds."



The $671 million MAVEN mission is NASA's first effort to study the Red Planet's upper atmosphere.

MAVEN will use its three onboard instrument suites to measure the rate of gas escape into space, in an attempt to better understand why Mars lost most of its atmosphere over the eons.

NB: The planet's air was relatively thick in the ancient past but is now just 1 percent as dense as that of Earth.

MAVEN's observations should shed light on how and why Mars transitioned from a warm and wet world billions of years ago to the cold, dry planet we know today, mission scientists have said.

The spacecraft is now in a commissioning phase, during which mission team members will lower MAVEN to its final orbit and check out its science gear.

The probe's one-year science mission is scheduled to start in early November.

NASA Maven: Looking for Mars' missing atmosphere - Video

NASA's MAVEN satellite will measure the process affecting the remaining atmosphere on Mars. 

These include incoming Solar Energetic Particles (SEPs), escape on a molecule-by-molecule basis (Jeans Escape), the effect of Coronal Mass Ejections (CMEs) and extreme solar ultraviolent radiation (EUVs). 

Credit: The Lunar and Planetary Institute and LASP

Ninety kilometers over our heads, the sky is glowing. During the day, the Sun turns the top of our sky into a sea of electrons.

They flow over one another without friction, creating plasma. Radio waves that hit these electrons bounce back to Earth, allowing transmissions to literally turns corners and circle the globe.

The free electron layer conducts current and responds to magnetic fields. As a result, during solar storms this part of the atmosphere lights up, creating undulating auroras.

While liberated, the electrons devise visual spectacles and technical challenges, but the atoms they leave behind must content themselves with being ions.

For this reason, this part of our atmosphere is known as the ionosphere. It's the largest part of our atmosphere, and does a commensurately big job.

It absorbs x-rays that would otherwise destroy life on Earth. If it weren't for our atmosphere, Earth might look a good deal more like Mars.


Why Mars doesn't look more like Earth is the subject of ongoing study. The loss of most of the atmosphere is believed to have been a major factor in Mars turning away from the path of water, warmth and habitability.

Uncovering where that atmosphere went, when and why is the mission of the Mars Atmosphere and Volatile Evolution (MAVEN) satellite.

Scheduled to arrive in September, MAVEN carries with it two instruments designed to probe the remaining ionosphere for clues about the past four billion years, and what will happen going forward.

Our first direct glimpse at ions in the upper atmosphere will be courtesy of the Neutral Gas and Ion Mass Spectrometer (NGIMS). Mass spectrometers like NGIMS are ubiquitous in the world of physical science.

They function like the ionosphere itself: by bombarding specimens with electrons and creating ions. This process allows mass spectrometers to divine the contents of a liquid, solid or gas.

Small and durable, as well as extremely useful, mass spectrometers have been placed on dozens of satellites and rovers, including NASA's Mars rover Curiosity.

To find Mars' missing atmosphere, NGIMS will search for certain elements and molecules in the Martian ionosphere: helium, argon, nitrogen, oxygen, carbon monoxide, and carbon dioxide.

It will note how often each occurs in its neutral and ionized states over 170 miles of sky. It will also count the abundance of heavy and light versions of atoms, also known as isotopes.

Counting isotopes may hold the key to atmospheric loss. The Earth, the Sun and Jupiter have balanced amounts of heavy and light argon isotopes.

These bodies have also retained their atmospheres over time. Mars has too much heavy argon and almost no atmosphere. The heavy argon left behind likely represents the original volume of the atmosphere; light argon reflects the lost air.

"The lighter atom in an isotope pair is able to leave the upper atmosphere just a bit faster than the heavier atom," said NGIMS principle investigator Paul Mahaffey.

"Our direct measurement of the vertical distribution of these isotope pairs will let us understand the physics of escape better and ultimately understand how much of the atmosphere has been lost in the past several billions of years."

22kg IUVS instrument. Credit: LASP, Colorado

As NGIMS tries to catch light argon in the act of leaving the planet, it will also watch space weather and dust storms change the composition of the atmosphere: mixing up molecules near the bottom of the ionosphere and sending others on one-way trips into deep space.

While NGIMS picks out particles one by one, the UltraViolet Spectrograph (IUVS) will be making sweeping, planetary-wide maps.

"IUVS and NGIMS are backups for each other," said IUVS Principle investigator Nick Schneider, "They both measure the composition & structure of the atmosphere.

Nick Schneider

And we're complementary in measuring different isotopes. IUVS measures the [ratio of heavy to light hydrogen] and NGIMS measures isotopes of heavier elements."

As the most powerful ultraviolent spectrograph to ever be sent to another planet, IUVS is exquisitely sensitive to composition and temperature variations of entire upper atmosphere.

The temperature and composition of Mars' atmosphere varies dramatically, not only by altitude, but also by orbit.

At perihelion, when Mars is closest to the Sun, it is 40 million miles closer than at aphelion, when it is farthest away.

The difference in distance means that much more of the Sun's energy will be reaching Mars during certain times of year. As a result, we expect ultraviolet readings at perihelion and aphelion to vary widely.

"But we anticipate seeing changes from other causes too: solar storms like flares and Coronal Mass Ejections (CME's), and dust storms on Mars too," said Schneider.

"These each have the potential to control atmospheric escape on Mars, so we'll be watching them all."

NGIMS instrument, just prior to integration with into the MAVEN spacecraft. Credit: NASA/Goddard