In a release,
The Age of 'Cumberland'
The second rock Curiosity drilled for a sample on Mars, which scientists nicknamed "Cumberland," is the first ever to be dated from an analysis of its mineral ingredients while it sits on another planet. A report by
"The age is not surprising, but what is surprising is that this method worked using measurements performed on Mars," said Farley. "When you're confirming a new methodology, you don't want the first result to be something unexpected. Our understanding of the antiquity of the Martian surface seems to be right."
The analysis of Cumberland from a sample drilled by Curiosity was a fundamental and "unprecedented" measurement considered unlikely when the rover landed in 2012. Farley and his co-authors adapted a 60-year-old radiometric method for dating Earth rocks that measures the decay of an isotope of potassium as it slowly changes into argon, an inert gas. Argon escapes when a rock is melted. This dating method measures the amount of argon that accumulates when the rock hardens again.
Before they could measure rocks directly on Mars, scientists estimated their ages by counting and comparing the numbers of impact craters on various areas of the planet. The crater densities are correlated with ages based on comparisons with crater densities on the moon, which were tied to absolute dates after the Apollo lunar missions returned rocks to Earth.
Farley and co-authors also assessed how long Cumberland has been within about an arm's reach of the Martian surface, where cosmic rays that hit atoms in the rock produce gas buildups that Curiosity can measure.
Analyses of three different gases yielded exposure ages in the range of 60 million to 100 million years. This suggests shielding layers above the rock were stripped away relatively recently. Combined with clues of wind erosion Curiosity observed, the exposure- age discovery points to a pattern of windblown sand chewing away at relatively thick layers of rock. The eroding layer forms a retreating vertical face, or scarp.
"The exposure rate is surprisingly fast," Farley said. "The place where you'll find the rocks with youngest exposure age will be right next to the downwind scarps."
From Rocks to
Finding rocks with the youngest exposure age is important in the mission's investigations of whether organic chemicals are preserved from ancient environments. Organic chemicals are building blocks for life, although they also can be produced without any biology.
"We're making progress on the path to determining whether there are Martian organics in there,"
Favorable for Life
Ming is the lead author of a new report about a site called "
Not only has Curiosity accomplished its primary goal of finding evidence for an ancient environment that could have supported life, but it also has provided evidence habitable conditions existed more recently than expected and likely persisted for millions of years.
Additional new results from Curiosity are providing the first readings of radiation hazards at Mars' surface, which will aid planning of human missions to Mars. Other findings will guide the search for evidence of life on Mars by improving insight about how erosion may expose buried clues of molecular building blocks of life.
New estimates of when habitable conditions existed at
"Smectite is the typical clay mineral in lake deposits," Vaniman said. "It is commonly called a swelling clay -- the kind that sticks to your boot when you step in it. You find biologically rich environments where you find smectites on Earth."
"This habitable environment existed later than many people thought there would be one," Grotzinger said. "This has global implications. It's from a time when there were deltas, alluvial fans and other signs of surface water at many places on Mars, but those were considered too young, or too short-lived, to have formed clay minerals. The thinking was, if they had clay minerals, those must have washed in from older deposits. Now, we know the clay minerals could be produced later, and that gives us many locations that may have had habitable environments, too."
Research suggests habitable conditions in the
Implications for Human Explorers
Today's reports include the first measurements of the natural radiation environment on the surface of Mars. Cosmic rays from outside our solar system and energetic particles from the sun bombarded the surface at Gale Crater with an average of 0.67 millisieverts per day from
Results from the surface-radiation monitoring provide an additional piece of the puzzle for projecting the total round-trip radiation dose for a future human mission to Mars. Added to dose rates Curiosity measured during its flight to Mars, the Mars surface results project a total round-trip dose rate for a future human mission at the same period in the solar cycle to be on the order of 1,000 millisieverts.
Long-term population studies have shown exposure to radiation increases a person's lifetime cancer risk. Exposure to a dose of 1,000 millisieverts is associated with a 5 percent increase in risk for developing fatal cancer.
The radiation detected by Curiosity is consistent with earlier predictions. The new data will help
"Our measurements provide crucial information for human missions to Mars," Hassler said. "We're continuing to monitor the radiation environment and seeing the effects of major solar storms on the surface at different times in the solar cycle will give additional important data. Our measurements also tie into Curiosity's investigations about habitability. The radiation sources that are concerns for human health also affect microbial survival as well as preservation of organic chemicals."
If any organic chemicals that are potential signs of life did exist within rocks at about 2 inches (5 centimeters), the depth of Curiosity's drill, Hassler estimated they would be depleted up to 1,000-fold in about 650 million years by radiation at the exposure rate measured in Curiosity's first 10 months. However, the Cumberland rock that Curiosity sampled with its drill at
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In a release,