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Follow the Water

August 5, 2013

The Curiosity rover takes a self-portrait from Mars

By Whitney Heins

It’s the middle of the day in sunny southern California. Aluminum foil blacks out windows in the apartments rented by sleeping scientists Linda Kah and Jeffrey Moersch. As the sun begins to fade into the Pacific, they awaken to join hundreds of others like them in analyzing datasets beamed from millions of miles away.

Kah and Moersch are part of NASA’s Curiosity Mars rover team that is looking for evidence that Mars is or ever was capable of supporting life. “These clues could be water-bearing minerals, organic compounds, or other chemical ingredients related to life,” said Moersch.

A Sol in the Life

For the first three months, the two associate professors from UT’s Department of Earth and Planetary Sciences worked at the mission’s home base, the Jet Propulsion Laboratory (JPL) in Pasadena. The odd hours were a necessity because they were living on Mars time, where a day–called a sol–is roughly forty minutes longer than Earth’s.

“We were typically working more than twelve hours a day,” said Kah. “Our schedules moved each day, usually forward about an hour for several days, then jumped back a couple of hours, then forward again.”

They have since returned home to Knoxville, with its familiar twenty-four-hour days, and continue their duties remotely. To help accommodate both life and work, schedules are now compressed to seven-hour shifts that begin in the mid-morning. The team has also moved to pre-planning several days of activity at once, so researchers can have the weekends with their families.

Kah, who studies the role of microbial life in the formation of some of Earth’s earliest rocks, is responsible for closely inspecting Martian rocks the same way.

Complex mineralized veins and abundant round masses of sedimentary rock

The “John Klein” area on Mars was chosen for the first rock drilling sample due to the presence of complex mineralized veins (white arrow) and abundant round masses of sedimentary rock (black arrow). Both imply the presence of mineral-forming fluids at the time these rocks were first deposited. Credit: NASA/JPL-CALTECH/MSSS

“For years, I have used the same set of observations that Curiosity is making to investigate ancient rocks,” said Kah. “I look for microscopic details visible in layers of rock, unusual assemblages of minerals, and the chemistry of both mineral and organic material to decipher clues to the presence of life.”

Kah does not work with the naked eye. She uses Curiosity’s sophisticated array of cameras and technology to inspect the Martian surface.

For example, as the rover slowly moves across Gale Crater, a robotic arm is used to gather, sieve, and transfer soil and powdered rock samples into the rover’s analytical system.

“We then use instruments capable of detecting both organic molecules and the isotopic signatures often left in rocks. On Earth, these signatures often indicate microbial metabolisms,” said Kah. “The rover has the most advanced technology of any yet sent to Mars. It’s like a field geologist with an analytical laboratory on her back.”

While Kah was at JPL, datasets were downlinked from Mars twice a sol. She recalls the anticipation as 250 scientists from several scientific teams–geology, mineralogy and geochemistry, and environmental science–made a “mad dash” to retrieve and examine the data. They would then use their combined expertise to develop the best targets to answer the most pertinent questions.

“After this, representatives essentially got together in a room and fought it out,” Kah said. “Also in that room were long-term planners that reminded everyone what the goals of the mission were so we didn’t get sidetracked by every interesting little rock that we passed by. In order to draw a coherent picture, we need to be sure to collect a coherent set of data.”

Seeking Hidden Hydrogen

Moersch is working things from a different angle. He uses a neutron spectrometer called the Dynamic Albedo of Neutrons (DAN) to search for hydrogen, an ingredient important for life that is chemically bound in water or hydrated minerals such as clays or some sulfates. The objective is to map the abundance of hydrogen from the surface down to about one meter below.

Curiosity's first drill holes

Curiosity's first drill holes at the “John Klein” area. Each hole is about 0.6 inches in diameter. The deepest hole penetrated 2.5 inches into the Martian subsurface. Credit: NASA/JPL-CALTECH/MSSS

DAN, supplied to the mission by the Russian Space Agency, operates in two modes: passive and active.

The passive mode operates naturally as a result of neutrons produced in the subsurface by cosmic rays raining down from space through the Martian atmosphere. Neutrons produced continuously by the rover’s nuclear power plant also contribute. These neutrons interact with other particles in the subsurface, with some eventually leaking out to where they can be detected by the instrument.

DAN characterizes the energies of these escaped neutrons, enabling the science team to determine how much hydrogen is present.

“We do this by characterizing the speed, or energy, of the neutrons,” said Moersch, who worked on five previous missions to Mars, including the Spirit and Opportunity rovers.

“Neutrons and hydrogen are of comparable mass, so if a neutron hits a hydrogen nucleus, it will bounce back at half speed on average–like a pool ball colliding with another pool ball. If a neutron hits something that is heavier–any nuclei other than hydrogen–it would be like a ping pong ball hitting a bowling ball, with very little speed lost by the neutron,” he explained.

The active mode uses a small particle accelerator onboard the rover to produce neutrons in pulses that interact below the surface. This mode offers the additional benefit of being able to measure the time neutrons arrive after each pulse.

“Neutrons that interacted with hydrogen fifty centimeters deep take longer to return to the spectrometer than those that interacted with hydrogen close to the surface,” said Moersch. “So it is possible to make a crude estimate of the vertical distribution of hydrogen using this mode.”

In addition to their scientific duties at JPL, both Kah and Moersch served as Payload Uplink Leads for their respective instruments. In these roles, Kah and Moersch acted as the critical interface between the science and engineering teams, converting the science team’s wishes into tasks the instruments were capable of performing.

Chris Tate, a UT graduate student in physics who is being mentored by Moersch, served as a second-shift Payload Uplink Lead. Each sol, Tate would translate the scientific tasks into instrument-level commands to be executed by the rover.

“Sometimes we’d look up in the sky and see this red dot and know that we were commanding a spacecraft on something millions of miles away,” said Moersch. “It’s pretty astonishing.”

A Curious Discovery

Less than a year into the mission, NASA announced some major discoveries based on an analysis of powder from the first drilled sample from Mars.

Analysis chart by instruments onboard Curiosity

Analysis by instruments onboard Curiosity confirmed the drilled rock sample contained water-bearing smectite clay minerals and sulfate (bassanite). Combined, it suggests Mars once had neutral-pH liquid water, which is a favorable environment for a variety of microbial metabolisms. Credit: NASA/JPL-CALTECH/MSSS

Using critical data from Curiosity’s instrument payload, including DAN and the spectral-imaging capability of onboard cameras, the team was able to determine that a mudstone rock sample–named “John Klein” by the research team–recorded past environmental conditions favorable for microbial life. Additional findings suggest these conditions likely extend far beyond the analysis site.

“This allows us to tell a new story about Mars that we haven’t been able to tell before,” Kah said. “The excitement is high that we can consider part of our mission accomplished. But the fun has only just begun!”

Kah and Moersch feel certain they will find more evidence of the building blocks of life. If they are proven right, then the question becomes, “is life on Earth a unique phenomenon, or can life evolve wherever the conditions are right, as it may have been on Mars billions of years ago?”

“If that is the case, then perhaps life is all over the galaxy,” Moersch said. The question then becomes “where wouldn’t there be life?”