October 4, 2013

Hopes that microbes may be living beneath the harsh surface of Mars have been seriously dampened by new findings from the Curiosity rover. Over the past 10 years, Mars-orbiting satellites and telescopes on Earth have produced data showing small but significant amounts of methane gas in the red planet’s atmosphere. Although methane can be produced by geological processes, most of the methane in Earth’s atmosphere is a by-product of animal digestion or comes from decaying plants. Perhaps, scientists thought, the same was true on Mars. However, a study by Curiosity failed to detect any methane at all, scientists at NASA’s Jet Propulsion Laboratory reported.

From October 2012 to June 2013, Curiosity searched for signs of methane in samples of the Martian atmosphere using its Sample Analysis at Mars (SAM) laboratory. The previous research had revealed methane levels of up to 45 parts per billion (ppb). But Curiosity’s data showed nothing above 1.3 ppb, the minimum detectable by the SAM laboratory. Curiosity’s findings suggest that the satellite and telescope readings were incorrect or that the gas has disappeared. But Sushil Atreya of the University of Michigan, Ann Arbor, one of the paper’s co-authors, said, “There’s no known way for methane to disappear quickly from the atmosphere. Methane is persistent. It would last for hundreds of years in the Martian atmosphere. Without a way to take it out of the atmosphere quicker, our measurements indicate there cannot be much methane being put into the atmosphere by any mechanism, whether biology, geology, or by ultraviolet degradation [breakdown] of organics delivered by the fall of meteorites or interplanetary dust particles.” Scientists who reported finding methane argued that more research was needed to rule out the existance of microbial life.

Gravel at this site photographed by Curiosity shows evidence of an ancient streambed. (NASA/JPL-Caltech/MSSS)

The search for existing life on Mars is not quite over, however. Curiosity scientists plan to retune the SAM laboratory to enable it to detect amounts of methane of less than 1 ppb. Moreover, Curiosity’s findings don’t totally rule out the presence of life on Mars. “This important result … reduces the probability of current methane-producing Martian microbes, but … addresses only one type of microbial metabolism. As we know, there are many types of terrestrial microbes that don’t generate methane,” said Michael Meyer, NASA’s chief scientist for Mars exploration.

The SAM laboratory findings also don’t affect efforts to determine whether life existed on Mars in the past. Only two months after landing, Curiosity found direct evidence that billions of years ago, a deep, fast-moving stream of water once flowed across Gale Crater, the rover’s landing site. This discovery showed that Mars had once been capable of supporting life. Whether it did is an open question.

Additional World Book articles:

• Mars Pathfinder
• Mars Science Laboratory
• Space exploration
• The Search for Water on Mars (a special report)

August 6, 2012

The largest and most advanced robotic laboratory ever sent to another planet made a perfect landing on Mars early Monday morning after a descent so complicated and perilous that mission controllers referred to it as “the seven minutes of terror.” The automobile-sized rover, named Curiosity, touched down at 1:32 a.m. Eastern Daylight Savings Time, capping an 8 ½-month, 354-million-mile (570-million-kilometer) journey from Earth. Its mission is to answer one of the most important questions in planetary science–whether Mars is, or ever has been, capable of supporting microbial life. Mission controllers at NASA’s Jet Propulsion Laboratory erupted into cheers and high-fives as Curiosity set down in Gale Crater, an impact crater that may once have held a lake. Moments after landing, Curiosity beamed back its first photographs of the Martian surface.

One of the first images of Mars taken by Curiosity after landing. (Image credit: NASA/JPL-Caltech)

The rover’s nail-biting landing involved a rocket-powered sky crane, the world’s largest supersonic parachute, and the incredibly precise detonation of 79 explosive devices. A failure at any stage of the descent would have doomed the mission. Curiosity, officially named the Mars Science Laboratory, began its plunge through the Martian atmosphere seven minutes before landing. At an altitude of 7 miles (11 kilometers), the parachute deployed to slow the lab, which was traveling at 13,200 miles (21,243 kilometers) per hour. At precise moments, the heat shield then the parachute and part of the rover’s protective shell broke away, leaving only the rover and its sky crane, which fired its rockets. At about 65 feet (20 meters) above the surface, the crane began lowering the rover using three cables. Once Curiosity touched down, the cables broke away and the crane flew off to crash land away from the drop site.

The rover carries a scientific payload about 15 times as massive as those carried by NASA’s Mars rovers Spirit and Opportunity. Curiosity, which has been described as a self-contained geology laboratory, holds 10 sophisticated instruments, two of which were provided by Spain and Russia. Unlike earlier rovers, Curiosity will be able to gather samples of rock and soil, process them, and then distribute them to on-board instruments.

NASA's Curiosity rover is lowered onto the Martian surface by the sky crane, new technology designed specifically for this mission. (Image credit: NASA/JPL-Caltech)

Curiosity’s prime target is Mount Sharp (also known as Aeolis Mons), a mysterious 3-mile- (5-kilometer-) high mountain in Gale Crater consisting of layers of rock that may have been laid down over billions of years. Although the mountain looks similar to layered mountains on Earth, scientists do not know how it formed because, unlike Earth, Mars has not been shaped by plate tectonics. As the rover scales the mountain, it will analyze the layers in an attempt to discover how Mars, which was once warmer and wetter, became so cold and dry. It will also search for organic (carbon-bearing) molecules necessary for life as we know it. Curiosity is scheduled to explore the surface of the red planet for two Earth years (one Martian year). However, because it is powered by a nuclear generator, its mission may be extend for much longer.

Additional World Book articles:

• Mars Pathfinder
• Phoenix [spacecraft]
• Space exploration (Probes to Mars)
• The Search for Water on Mars (a Special Report)