Mars Methane Gets Even More Mysterious

Map of methane concentrations in Autumn (first martian year observed) on Mars. Credit: NASA/Università del Salento

Mars’ atmosphere consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains small amounts of oxygen and water, as well as trace amounts of methane. The methane – although small in percentage – might be the most intriguing because the source of this very short-lived gas remains a mystery. And the mystery has just gotten a little more puzzling, as the lifetime of methane in Mars atmosphere appears to be even shorter than scientists had originally thought. Using observations from the Mars Global Surveyor — which functioned in orbit around for almost ten years – a group of scientists from Italy have determined the methane in the atmosphere of Mars lasts less than a year.

Scientists Sergio Fonti (Università del Salento) and Giuseppe Marzo (NASA Ames) reported their findings of evolution of the methane over three Martian years at the European Planetary Science Congress in Rome.

“Only small amounts of methane are present in the Martian atmosphere, coming from very localized sources,” said Fonti. “ We’ve looked at changes in concentrations of the gas and found that there are seasonal and also annual variations. The source of the methane could be geological activity or it could be biological – we can’t tell at this point. However, it appears that the upper limit for methane lifetime is less than a year in the Martian atmosphere.”

Levels of methane are highest in autumn in the northern hemisphere, with localized peaks of 70 parts per billion, although methane can be detected across most of the planet at this time of year. There is a sharp decrease in winter, with only a faint band between 40-50 degrees north. Concentrations start to build again in spring and rise more rapidly in summer, spreading across the planet.

“One of the interesting things that we’ve found is that in summer, although the general distribution pattern is much the same as in autumn, there are actually higher levels of methane in the southern hemisphere. This could be because of the natural circulation occurring in the atmosphere, but has to be confirmed by appropriate computer simulations,” said Fonti.

Top: Map of methane concentrations in Autumn (first martian year observed). Peak emissions fall over Tharsis (home to the Solar System's largest volcano, Olympus Mons), the Arabia Terrae plains and the Elysium region, also the site of volcanos. Bottom: True colour map of Mars. Credit: NASA/Università del Salento

There are three regions in the northern hemisphere where methane concentrations are systematically higher: Tharsis and Elysium, the two main volcano provinces, and Arabia Terrae, which has high levels of underground water ice. Levels are highest over Tharsis, where geological processes, including magmatism, hydrothermal and geothermal activity could be ongoing.

“It’s evident that the highest concentrations are associated with the warmest seasons and locations where there are favorable geological – and hence biological – conditions such as geothermal activity and strong hydration. The higher energy available in summer could trigger the release of gases from geological processes or outbreaks of biological activity,” said Fonti.

The mechanisms for removing methane from the atmosphere are also not clear. Photochemical processes would not break down the gas quickly enough to match observations. However, wind driven processes can add strong oxidisers to the atmosphere, such as the highly reactive salt perchlorate, which could soak up methane much more rapidly.

Martian years are nearly twice as long as Earth years. The team used observations from the Thermal Emission Spectrometer (TES) on Mars Global Surveyor between July 1999 and October 2004. The team studied one of the characteristic spectral features of methane in nearly 3 million TES observations, averaging data together to eliminate noise.

“Our study is the first time that data from an orbiting spectrometer has been used to monitor methane over an extended period, “ Fonti said. “The huge TES dataset has allowed us to follow the methane cycle in the Martian atmosphere with unprecedented accuracy and completeness. Our observations will be very useful in constraining the origins and significance of Martian methane.”

Methane was first detected in the Martian atmosphere by ground based telescopes in 2003 and confirmed a year later by ESA’s Mars Express spacecraft. Last year, observations using ground based telescopes showed the first evidence of a seasonal cycle.

Source: European Planetary Science Congress

New Theory Says Phobos Formed From Re-Accretion of Impact Debris

Spatial locations of PFS and observations of Phobos used for the compositional analysis. Credit: Giuranna and Rosenblatt

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Most theories on the formation of Phobos and its sister moon of Mars, Deimos, hold that the two moons did not form along with Mars, but were captured asteroids. However, new research indicates that Phobos formed relatively near its current location via re-accretion of material blasted into Mars’ orbit by some catastrophic event, such as a huge impact. This could be an event similar to how Earth’s moon formed. Thermal infrared spectra data from two Mars missions, ESA’s Mars Express and NASA’s Mars Global Surveyor have provided independent researchers similar new conclusions of how Phobos formed.

The origin of the two Martian satellites has been a long standing puzzle. Previous researchers have postulated that because of Phobos small size and highly cratered surface, as well as the fact that Mars is reasonably close to the asteroid belt, that Phobos was a captured asteroid. Recently, alternative scenarios suggested that both moons were formed in-situ by the re-accretion of rocky-debris blasted into Mars’s orbit after a large impact or by re-accretion of remnants of a former moon which was destroyed by Mars’s tidal force.

Today, Dr. Giuranna from the Istituto Nazionale di Astrofisica in Rome, Italy, and Dr. Rosenblatt from the Royal Observatory of Belgium presented their new findings at the European Planetary Science Congress in Rome, saying that the thermal data from the two spacecract, as well as the measurements of Phobos’ high porosity from the Mars Radio Science Experiment (MaRS) on board Mars Express, supports the re-accretion scenario.

“Understanding the composition of the Martian moons is the key to constrain these formation theories,” said Giuranna.

Spatial locations of TES and observations of Phobos used for the compositional analysis. Credit: Giuranna and Rosenblatt

Previous observations of Phobos at visible and near-infrared wavelengths suggest the possible presence of carbonaceous chondritic meteorites, carbon-rich and likely from the early formation of the solar system, commonly associated with asteroids dominant in the middle part of the asteroid belt. This finding would support the early asteroid capture scenario. However recent thermal infrared observations from the Mars Express Planetary Fourier Spectrometer, show poor agreement with any class of chondritic meteorite. They instead argue in favor of the in-situ scenarios.

“We detected for the first time a type of mineral called phyllosilicates on the surface of Phobos, particularly in the areas northeast of Stickney, its largest impact crater,” said Giuranna. “This is very intriguing as it implies the interaction of silicate materials with liquid water on the parent body prior to incorporation into Phobos. Alternatively phyllosilicates may have formed in situ, but this would mean that Phobos required sufficient internal heating to enable liquid water to remain stable. More detailed mapping, in-situ measurements froma lander, or sample return would ideally help to settle this issue unambiguously.”

But other observations appear to match up with the types of minerals identified on the surface of Mars. From that data, Phobos appears more closely related to Mars than objects from other locations in the solar system.

“The asteroid capture scenarios also have difficulties in explaining the current near-circular and near-equatorial orbit of both Martian moons,” said Rosenblatt.

The MaRS instrument used the frequency variations of the radio-link between the spacecraft and the Earth-based tracking stations in order to precisely reconstruct the motion of the spacecraft when it is perturbed by the gravitational attraction of Phobos, and from this, the team was able provide most precise measurement of Phobos’ mass, with a precision of 0.3%.

Additionally, the team was able to give the best estimate yet of Phobos’s volume, with a density of 1.86±0.02 g/cm3.

“This number is significantly lower than the density of meteoritic material associated with asteroids. It implies a sponge-like structure with voids making up 25-45% in Phobos’ interior,” said Rosenblatt.

“High porosity is required in order to absorb the energy of the large impact that generated Stickney crater (the large crater on Phobos) without destroying the body,, said Giuranna. “In addition a highly porous interior of Phobos, as proposed by the MaRS team, supports the re-accretion formation scenarios”.

The researchers said a highly porous asteroid would have probably not survived if captured by Mars. Alternatively, such a highly porous Phobos can result from the re-accretion of rocky-blocks in Mars’ orbit. During re-accretion, the largest blocks re-accrete first because of their larger mass, forming a core with large boulders. Then, the smaller debris re-accrete but do not fill the gaps left between the large blocks because of the low self-gravity of the small body in formation. Finally, a relatively smooth surface masks the space of voids inside the body, which then can only be indirectly detected. Thus, a highly porous interior of Phobos, as proposed by the MaRS team, supports the re-accretion formation scenarios.

The researchers said they would like more data on Phobos to verify their findings, and the upcoming Russian Phobos-Grunt mission (Phobos Sample Return), scheduled for launch in 2011, will help to provide more understanding regarding the origin of Phobos.

Source: Europlanet Conference

Mars Global Surveyor

Mars Global Surveyor

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The Mars Global Surveyor was a spacecraft sent to Mars in 1996. It arrived at Mars and studied the planet for 10 years, until it broke down in 2006, and controllers on Earth lost contact with it. But while it was operating, the spacecraft took thousands of images, and made some major discoveries about Mars.

Mars Global Surveyor was launched on November 7, 1996, and made its orbital insertion on September 11, 1997. It used a technique called aerobraking to reduce its orbit and bring it into an orbit that brought it to an average distance of 378 km from the surface of Mars. It circled the planet in a polar orbit once every 117 minutes, which allowed it to photograph the entire Martian surface.

The spacecraft was equipped with 5 major scientific instruments: Mars Orbiter Camera, Mars Orbiter Laser Altimeter, Thermal Emission Spectrometer, Magnetometer and electron reflectometer and the Ultrastable Oscillator for Doppler measurements. These instruments allowed the spacecraft to study the atmosphere and surface composition of Mars. But it also sent back the highest resolution photographs ever seen of Mars. The newer Mars Reconnaissance Orbiter has returned better images with its larger telescope, but when the first MGS images first came back from Mars, they were stunning.

It made some incredible discoveries about Mars. Thanks to the observations from MGS, astronomers determined that Mars had a layered crust that was more than 10 km thick. It found ancient craters that had been buried and then later exposed by erosion, and it found evidence of ancient lava flows.

But perhaps the biggest discovery was made in 2006, which researchers announced that they had uncovered evidence of recent water activity on Mars. Images from the Mars Global Surveyor showed gullies on Mars which looked like they’d been formed by water. It’s possible that water had erupted out of an underground aquifer and spilled down the slope of a hill before evaporating in the pressure of the Martian atmosphere.

After a decade of service, Mars Global Surveyor went silent on November 2, 2006. It went into safe mode after being issued commands to change the orientation of its solar panels, and it stopped communicating. NASA said that it was, “battery failure caused by a complex sequence of events involving the onboard computer memory and ground commands.” But we’ll never really know what happened to it.

We’ve written many articles about the Mars Global Surveyor for Universe Today. Here’s an article about how we lost contact with the Mars Global Surveyor, and here’s a picture of Earth taken by MGS.

If you’d like more info, check out the Mars Global Surveyor homepage.

Source: NASA