NASA’s Mars Exploration Rover Opportunity has found veins of a mineral, apparently gypsum --the “Homestake” deposit--deposited by water, likely formed from water dissolving calcium out of volcanic rocks. The calcium combined with sulfur that was either leached from the rocks or introduced as volcanic gas and deposited as calcium sulfate into an underground fracture that later became exposed at the surface.
“It could have formed in a different type of water environment, one more hospitable for a larger variety of living organisms,” said Opportunity science-team member Benton Clark of the Space Science Institute.
The false-color image the mineral vein above comes from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity. The vein is about the width of a thumb and about 18 inches (45 centimeters) long. Opportunity examined it in November 2011 and found it to be rich in calcium and sulfur, possibly the calcium-sulfate mineral gypsum.
When the Mars Curiosity rover and science lab lands at Mars Gale Crater during August of 2012, one of its prime goals will be testing for ancient signs of water. Because of its history, this 96 mile wide crater with its strangely sculpted mountain --three times higher than the Grand Canyon is deep--is the ideal place for Curiosity to conduct its mission of exploration into the Red Planet's past. Joy Crisp, MSL Deputy Project Scientist from NASA's Jet Propulsion Laboratory, explains:
"This may be one of the thickest exposed sections of layered sedimentary rocks in the solar system. The rock record preserved in those layers holds stories that are billions of years old -- stories about whether, when, and for how long Mars might have been habitable."
An instrument on Curiosity can check for any water that might be bound into shallow underground minerals along the rover's path.
"If we conclude that there is something unusual in the subsurface at a particular spot, we could suggest more analysis of the spot using the capabilities of other instruments," said this instrument's principal investigator, Igor Mitrofanov of the Space Research Institute, Russia.
Today the Red Planet is a radiation-drenched, bitterly cold, bleak world. Enormous dust storms explode across the barren landscape and darken Martian skies for months at a time. But data from the Mars Reconnaissance Orbiter suggest that Mars once hosted vast lakes and flowing rivers.
"Gale Crater and its mountain will tell this intriguing story," says Matthew Golombek, Mars Exploration Program Landing Site Scientist from JPL. "The layers there chronicle Mars' environmental history."
In the gentle slopes around the mountain, Curiosity will prospect for organic molecules, the chemical building blocks of life. Mars Reconnaissance Orbiter has found an intriguing signature of clay near the bottom of the mountain and sulfate minerals a little higher up. Both minerals are formed in the presence of water, which increases potential for life-friendly environments.
"All the types of aqueous minerals we've detected on Mars to date can be found in this one location," explains Golombek.
Clay settles slowly in water and forms little platelets that conform around things, hardening over time and encasing them in ''casts." Clay could seal organics off from the outside environment much like it preserved dinosaur bones on Earth.
"If organics ever existed on Mars, they could be preserved in the clay."
Even on planet Earth, teeming with life, finding billion year-old well-preserved organics is difficult. But Curiosity will find them if they're present in the samples it takes. The rover is equipped with the most advanced suite of instruments for scientific studies ever sent to the Martian surface1. When these are brought to bear on Gale crater’s mysteriously layered mountain, the odds of a discovery will be at an all-time high.
As seasoned travelers know, however, the journey is just as important as the destination. Curiosity can travel up to 150 meters per Mars day, but will stop often to gather and analyze samples.
"It could take several months to a year to reach the foot of the mountain, depending on how often the rover stops along the way," says Golombek. "There will be plenty to examine before getting to the central mound."
A high-resolution camera on the rover's mast will take pictures and movies of the scenery, taking Earthlings on an extraterrestrial sightseeing tour.
"As Curiosity climbs toward higher layers, you'll see spectacular valleys and canyons like those in the U.S. desert southwest. The walls on either side of the rover will rise over 100 feet. The sights alone will be worth the trip."
The Mars Science Laboratory mission will use 10 instruments on Curiosity to investigate whether the area selected for the mission has ever offered environmental conditions favorable for life and favorable for preserving evidence about life.
"The strength of Mars Science Laboratory is the combination of all the instruments together," Mitrofanov stressed.
The Dynamic Albedo of Neutrons instrument, or DAN, will scout for underground clues to a depth of about 20 inches (50 centimeters).
DAN will bring to the surface of Mars an enhancement of nuclear technology that has already detected Martian water from orbit. "Albedo" in the instrument's name means reflectance -- in this case, how original high-energy neutrons injected into the ground bounce off atomic nuclei in the ground. Neutrons that collide with hydrogen atoms bounce off with a characteristic decrease in energy, similar to how one billiard ball slows after colliding with another. By measuring the energies of the neutrons leaking from the ground, DAN can detect the fraction that was slowed in these collisions, and therefore the amount of hydrogen.
Oil prospectors use this technology in instruments lowered down exploration holes to detect the hydrogen in petroleum. Space explorers have adapted it for missions to the moon and Mars, where most hydrogen is in water ice or in water-derived hydroxyl ions.
Mitrofanov is the principal investigator for a Russian instrument on NASA's Mars Odyssey orbiter, the high-energy neutron detector (HEND), which measures high energy of neutrons coming from Mars. In 2002, it and companion instruments on Odyssey detected hydrogen interpreted as abundant underground water ice close to the surface at high latitudes. That discovery led to NASA's Phoenix Mars Lander going to far northern Mars in 2008 and confirming the presence of water ice.
"You can think of DAN as a reconnaissance instrument," Mitrofanov said. Just as Phoenix investigated what Odyssey detected, Curiosity can use various tools to investigate what DAN detects. The rover has a soil scoop and can also dig with its wheels. Its robotic arm can put samples into instruments inside the rover for thorough analyses of ingredients. Rock formations that Curiosity's cameras view at the surface can be traced underground with DAN, enhancing the ability of scientists to understand the geology.
The neutron detectors on Odyssey rely on galactic cosmic rays hitting Mars as a source of neutrons. DAN can work in a passive mode relying on cosmic rays, but it also has its own pulsing neutron generator for an active mode of shooting high-energy neutrons into the ground. In active mode, it is sensitive enough to detect water content as low as one-tenth of one percent in the ground beneath the rover.
The neutron generator is mounted on Curiosity's right hip. A module with two neutron detectors is mounted on the left hip. With pulses lasting about one microsecond and repeated as frequently as 10 times per second, key measurements by the detectors are the flux rate and delay time of moderated neutrons with different energy levels returning from the ground. The generator will be able to emit a total of about 10 million pulses during the mission, with about 10 million neutrons at each pulse.
"We have a fixed number of about 10 million shots, so one major challenge is to determine our strategy for how we will use them," said Maxim Litvak, leading scientist of the DAN investigation from the Space Research Institute.
Operational planning anticipates using DAN during short pauses in drives and while the rover is parked. It will check for any changes or trends in subsurface hydrogen content, from place to place along the traverse. Because there is a low possibility for underground water ice at Curiosity's Gale crater landing site, the most likely form of hydrogen in the ground of the landing area is hydrated minerals. These are minerals with water molecules or hydroxyl ions bound into the crystalline structure of the mineral. They can tenaciously retain water from a wetter past when all free water has gone.
"We want a better understanding of where the water has gone," said Alberto Behar, DAN investigation scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "DAN fits right into the follow-the-water strategy for studying Mars."
Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology in Pasadena said, "DAN will provide the ability to detect hydrated minerals or water ice in the shallow subsurface, which provides immediate clues as to how the geology of the subsurface might guide exploration of the surface. In addition, DAN can tell us how the shallow subsurface may differ from what the rover sees at the surface. None of our other instruments have the ability to do this. DAN measurements will tell us about the habitability potential of subsurface rocks and soils -- whether they contain water -- and as we drive along, DAN may help us understand what kinds of rocks are under the soils we drive across."
Information from DAN will also provide a ground-truth calibration for the measurements that the gamma-ray and neutron detectors on Odyssey have made and continue to make, all around the planet, enhancing the value of that global data set. The team leader of Odyssey's gamma-ray spectrometer suite, William Boynton of the University of Arizona in Tucson, is a co-investigator on the DAN investigation, with the major responsibility to provide DAN data products to NASA's Planetary Data System for usage by scientists everywhere.
Besides heading the team that developed and will operate DAN, Mitrofanov is the principal investigator for a passive neutron-detector instrument to check for hydrated minerals on Mars' moon Phobos as part of the Phobos Soil Return mission that Russia plans to launch in November 2011. "Measurements by DAN on the Mars surface will be useful for the interpretation of Phobos data," he said.
The Daily Galaxy via nasa.gov/msl and kurzweilai.net
Image credit: NASA/JPL-Caltech/Cornell/ASU