Searching for Mars microbes by the PIXL

Searching for Mars Microbes by the PIXL

Joel Hurowitz with a poster explaining the PIXL instrument, which will probe the chemistry of rocks on Mars.

By Danielle Hall

A model of the PIXL resides in Joel Hurowitz’ lab at Stony Brook University.

On July 31, 2014, Joel Hurowitz and colleagues in the Stony Brook Geosciences Department sat in a lab, glued to a widescreen television set linked to NASA. In labs and conference rooms across the country, scientists waited in anticipation of an announcement from Michael Myers, the Mars lead scientist, in Washington, DC. The reveal was for the 2020 rover. Out of 60 proposals for instruments that would sample and record the Martian landscape, only seven would be chosen. The Stony Brook team was hoping their instrument, the PIXL, would make the cut.

“Up flashes this picture and everyone is looking around to see if their instrument was on it,” said Hurowitz, deputy lead of the PIXL research team and a co-investigator on the RIS4E team. “There was PIXL. It was a really exciting day until we realized how much work we had to do.”

PIXL — the Planetary Instrument for X-Ray Lithochemistry — is one of seven scientific instruments on the Mars 2020 rover tasked with finding signs of past microbial life on Mars. Roughly the size of a basketball, PIXL will sit on the end of the rover’s arm, where it can be strategically placed near an interesting rock.  Its role is to identify the elements in Martian rocks at a scale the size of a grain of salt in the hope of finding geological formations created by some kind of life form.

Microbes leave a trace in the places where they live. This is documented in Earth’s geological history through formations like stromatolites, sedimentary rocks that have a distinct layering pattern and chemical signature formed by mats of cyanobacteria. A visual picture of a Martian rock, combined with a chemical map created using PIXL, could identify a similar structure on Mars.

“If you find two examples of life that evolved independently in one solar system, then that changes all views about how life evolves in the universe. We have two planets in our habitable zone, maybe three. If two of them have life, that’s pretty impressive,” said Scott McLennan, a Geosciences professor at Stony Brook University who has been involved in the mission science of rovers since the Mars Exploration Rover program that began in 2003.

A computer rendering of the Mars 2020 rover, which will carry the PIXL. (Courtesy: NASA)

 

The design of PIXL relied heavily on information and technologies supplied by predecessors — four freely roaming rovers. The Pathfinder mission of 1996 proved a remotely operated vehicle could land on the Martian surface and collect geological data. The next missions aimed to piece together the puzzle of whether life exists or existed on Mars.

“It’s a fundamental way NASA does these missions. Each mission is the foundation of the next mission. There’s always a sense that the next mission has to move in a strategic way,” McLennan said.

Spirit and Opportunity came next. These two sister rovers, launched in 2003, were tasked with finding environments that showed signs of water. And they did. First, Opportunity detected evidence of paleolakes, small lakes in desert environments, and then Spirit found evidence of water that seeped beneath the surface in a manner similar to an environment at Yellowstone National Park. Curiosity, launched in 2011, showed that the building blocks for life (hydrogen, carbon, nitrogen, oxygen, phosphorous, and sulfur) were readily available and that sources of energy would also be available to sustain a living microbe.

Past rover missions, however, failed to measure up to the precision and scale scientists wished they could have for determining the composition of rocks on Mars. Since the Pathfinder mission, the Alpha Particle X-Ray Spectrometer, APXS, was the best way to measure the elements in a rock. The APXS excites electrons in the atoms of targeted materials, like rocks, by bombarding them with high-energy particles, alpha particles, and high energy X-rays. The excited electrons then give off their own energy in the form of X-rays. Each element has a unique energy level that it emits, so scientists can identify the element like using a thumbprint. But APXS has a shortcoming. On Curiosity it can only average a rock’s elemental composition throughout an area the diameter of a quarter.

“For the longest time people that do geochemistry on Mars have wished that we had a chemical tool that could do a point by point analysis,” Hurowitz said.

PIXL became the solution. Its main components include a camera, an X-ray tube, and a detector. The instrument is similar to APXS in that it focuses X-rays on a targeted material and measures the emitted X-rays that the excited electrons give off. The energy level tells which element is there, and the strength of that signal tells how much. But PIXL works at a much finer scale. While APXS uses radioactive material to produce the X-rays, PIXL uses a system similar to X-ray machines in hospitals. The X-ray source is electrical and allows for higher precision. PIXL creates a detailed map of a surface’s composition by measuring an area point by point and then combining the measurements like pixels in a photograph.

When the 2020 rover begins its mission on Mars, PIXL will work at night when the rest of the instruments power down. This is mostly because of time demands. One line of point measurements will take about a half hour to travel the 33.9 million miles back to scientists at NASA’s Jet Propulsion Laboratory in Pasadena. An image the size of a postage stamp will take 16 hours.

Renee Schofield, PhD candidate in Geosciences at Stony Brook University, explains the different components of the PIXL prototype she built using factory parts.

There are two working PIXL instruments, one at the Jet Propulsion Lab and another at Stony Brook University, but they are too small and fragile to endure a bumpy flight and Martian landing. They are homemade, put together piece-by-piece from factory parts, by the scientists who operate them.

“Taking a commercial part and making it play on Mars is a unique challenge,´ Douglas Dawson, PIXL’s X-ray engineer at the Jet Propulsion Laboratory, said in an email.  “On the one hand, you like having something that works, so you don’t want to mess with it too much.  On the other hand, there are temperature, vibration from launch and landing, and contamination and cleanliness constraints that might not be addressed in a commercial build.”

Since the PIXL proposal was accepted in 2014, Dawson and the engineers at the Jet Propulsion Lab have been busy designing and testing an instrument that will withstand the harsh environment of space. This includes creating functional prototypes that use all the materials and size specifications that will be used on the rover.  Between 20 and 35 people work full time on the instrument, but nearly 350 people have contributed to its design and creation.  The final instrument will be built later this year.

Once the rover and its rocket blast off into space the new environment can cause issues unforeseen on Earth. Some materials can give off gases in the vacuum of space that fog up optical lenses. The instrument needs to be light, too. It weighs about 10 pounds.

“Sometimes the competing constraints can box you in pretty tightly in terms of the design options you can really use,” Dawson said.

Two weeks before PIXL’s final review by NASA, the Critical Design Review, where the project gets the final green light, Hurowitz received good news. The beam of the newly designed X-ray tube was working perfectly and was on track to make its voyage to Mars.

Joel Hurowitz with a poster explaining the PIXL instrument, which will probe the chemistry of rocks on Mars.

By Danielle Hall

A model of the PIXL resides in Joel Hurowitz’ lab at Stony Brook University.

On July 31, 2014, Joel Hurowitz and colleagues in the Stony Brook Geosciences Department sat in a lab, glued to a widescreen television set linked to NASA. In labs and conference rooms across the country, scientists waited in anticipation of an announcement from Michael Myers, the Mars lead scientist, in Washington, DC. The reveal was for the 2020 rover. Out of 60 proposals for instruments that would sample and record the Martian landscape, only seven would be chosen. The Stony Brook team was hoping their instrument, the PIXL, would make the cut.

“Up flashes this picture and everyone is looking around to see if their instrument was on it,” said Hurowitz, deputy lead of the PIXL research team and a co-investigator on the RIS4E team. “There was PIXL. It was a really exciting day until we realized how much work we had to do.”

PIXL — the Planetary Instrument for X-Ray Lithochemistry — is one of seven scientific instruments on the Mars 2020 rover tasked with finding signs of past microbial life on Mars. Roughly the size of a basketball, PIXL will sit on the end of the rover’s arm, where it can be strategically placed near an interesting rock.  Its role is to identify the elements in Martian rocks at a scale the size of a grain of salt in the hope of finding geological formations created by some kind of life form.

Microbes leave a trace in the places where they live. This is documented in Earth’s geological history through formations like stromatolites, sedimentary rocks that have a distinct layering pattern and chemical signature formed by mats of cyanobacteria. A visual picture of a Martian rock, combined with a chemical map created using PIXL, could identify a similar structure on Mars.

“If you find two examples of life that evolved independently in one solar system, then that changes all views about how life evolves in the universe. We have two planets in our habitable zone, maybe three. If two of them have life, that’s pretty impressive,” said Scott McLennan, a Geosciences professor at Stony Brook University who has been involved in the mission science of rovers since the Mars Exploration Rover program that began in 2003.

A computer rendering of the Mars 2020 rover, which will carry the PIXL. (Courtesy: NASA)

 

The design of PIXL relied heavily on information and technologies supplied by predecessors — four freely roaming rovers. The Pathfinder mission of 1996 proved a remotely operated vehicle could land on the Martian surface and collect geological data. The next missions aimed to piece together the puzzle of whether life exists or existed on Mars.

“It’s a fundamental way NASA does these missions. Each mission is the foundation of the next mission. There’s always a sense that the next mission has to move in a strategic way,” McLennan said.

Spirit and Opportunity came next. These two sister rovers, launched in 2003, were tasked with finding environments that showed signs of water. And they did. First, Opportunity detected evidence of paleolakes, small lakes in desert environments, and then Spirit found evidence of water that seeped beneath the surface in a manner similar to an environment at Yellowstone National Park. Curiosity, launched in 2011, showed that the building blocks for life (hydrogen, carbon, nitrogen, oxygen, phosphorous, and sulfur) were readily available and that sources of energy would also be available to sustain a living microbe.

Past rover missions, however, failed to measure up to the precision and scale scientists wished they could have for determining the composition of rocks on Mars. Since the Pathfinder mission, the Alpha Particle X-Ray Spectrometer, APXS, was the best way to measure the elements in a rock. The APXS excites electrons in the atoms of targeted materials, like rocks, by bombarding them with high-energy particles, alpha particles, and high energy X-rays. The excited electrons then give off their own energy in the form of X-rays. Each element has a unique energy level that it emits, so scientists can identify the element like using a thumbprint. But APXS has a shortcoming. On Curiosity it can only average a rock’s elemental composition throughout an area the diameter of a quarter.

“For the longest time people that do geochemistry on Mars have wished that we had a chemical tool that could do a point by point analysis,” Hurowitz said.

PIXL became the solution. Its main components include a camera, an X-ray tube, and a detector. The instrument is similar to APXS in that it focuses X-rays on a targeted material and measures the emitted X-rays that the excited electrons give off. The energy level tells which element is there, and the strength of that signal tells how much. But PIXL works at a much finer scale. While APXS uses radioactive material to produce the X-rays, PIXL uses a system similar to X-ray machines in hospitals. The X-ray source is electrical and allows for higher precision. PIXL creates a detailed map of a surface’s composition by measuring an area point by point and then combining the measurements like pixels in a photograph.

When the 2020 rover begins its mission on Mars, PIXL will work at night when the rest of the instruments power down. This is mostly because of time demands. One line of point measurements will take about a half hour to travel the 33.9 million miles back to scientists at NASA’s Jet Propulsion Laboratory in Pasadena. An image the size of a postage stamp will take 16 hours.

Renee Schofield, PhD candidate in Geosciences at Stony Brook University, explains the different components of the PIXL prototype she built using factory parts.

There are two working PIXL instruments, one at the Jet Propulsion Lab and another at Stony Brook University, but they are too small and fragile to endure a bumpy flight and Martian landing. They are homemade, put together piece-by-piece from factory parts, by the scientists who operate them.

“Taking a commercial part and making it play on Mars is a unique challenge,´ Douglas Dawson, PIXL’s X-ray engineer at the Jet Propulsion Laboratory, said in an email.  “On the one hand, you like having something that works, so you don’t want to mess with it too much.  On the other hand, there are temperature, vibration from launch and landing, and contamination and cleanliness constraints that might not be addressed in a commercial build.”

Since the PIXL proposal was accepted in 2014, Dawson and the engineers at the Jet Propulsion Lab have been busy designing and testing an instrument that will withstand the harsh environment of space. This includes creating functional prototypes that use all the materials and size specifications that will be used on the rover.  Between 20 and 35 people work full time on the instrument, but nearly 350 people have contributed to its design and creation.  The final instrument will be built later this year.

Once the rover and its rocket blast off into space the new environment can cause issues unforeseen on Earth. Some materials can give off gases in the vacuum of space that fog up optical lenses. The instrument needs to be light, too. It weighs about 10 pounds.

“Sometimes the competing constraints can box you in pretty tightly in terms of the design options you can really use,” Dawson said.

Two weeks before PIXL’s final review by NASA, the Critical Design Review, where the project gets the final green light, Hurowitz received good news. The beam of the newly designed X-ray tube was working perfectly and was on track to make its voyage to Mars.