Orbiters can count new craters forming on Mars, refining cratering rates. One spectacular new crater has appeared since 2010 with vivid rays.
The BBC News published a photo of the new crater taken with the HiRise camera on board the Mars Reconnaissance Orbiter. Seen in false color, with its 9-mile-long rays surrounding a 100-foot-wide crater , it looks like a blue starburst. The crater formed sometime between July 2010 and May 2012; the hi-resolution photo was taken last November. This and other craters lead scientists to estimate that “impacts producing holes at least 3.9m (12.8ft) in diameter occur at a rate exceeding 200 per year across the planet.” Astrobiology Magazine also announced the crater. See also 5/21/13.
Mars scientists never cease wondering if water flowed on Mars, and if so, whether life appeared. Space.com teased with a headline, “Ancient Mars May Have Been Habitable for Hundreds of Millions of Years,” based on the supposition that clay-rich minerals at the rim of Endeavor Crater, found by the Opportunity rover, suggest that neutral-acidic water once existed there. Astrobiology Magazine called the outcrop “livable mud.” Meanwhile, on the other side of the planet, the Curiosity rover supposedly found a dry lake bed. Mission scientist John Grotzinger introduced five papers in Science about Mars habitability. Exercising some restraint on imagination, he agreed, “These results demonstrate that early Mars was habitable, but this does not mean that Mars was inhabited.”
One real-Mars factor that cannot be ignored is the radiation environment. The top few meters of Mars’ surface is exposed to ionizing radiation, likely to degrade organic molecules. From measurements reported by others in the special issue, Grotzinger said, “Extrapolating these rates over geologically important periods of time and merging with modeled radiolysis data yields a predicted 1000-fold decrease in 100–atomic mass unit organic molecules in ∼650 million years” – just 14% of Mars’ assumed age. One paper proposes that mudstone with organics was buried till recently exposed; that’s about the best hope for possible life to escape the radiation barrage. “Earth’s thick atmosphere and magnetic field greatly reduce incoming radiation,” Grotzinger noted.
Evidence of flowing water on the rims of craters has been hard to prove, Science Daily reported. The “recurring slope lineae” keep reappearing in the Martian summer, but scientists cannot rule out non-watery processes for their formation.
There is life on Mars now, if you can include the most Mars-like environment on Earth. The Conversation tells about volunteers who are working in simulated Martian conditions out in a remote stretch of Utah desert near Hanksville. Ashley Dale tells about his experiences as crew commander in a 14-day experiment to prepare human beings for the rigors of a trip to the red planet. As visionary as such a trip sounds, reality checks will be needed. “I had to keep a calm head and remind myself of the expedition’s priorities,” he said; “Human ingenuity has been perfecting the technology we will need on Mars, but what we can’t do is eliminate human follies.”
Update 2/13/14: Astrobiology Magazine posted a graph showing that the daily Martian radiation dosage exceeds the annual limit for a Department of Energy Worker. What does this do for life? If it’s in the Martian soil within a meter of the surface, “gamma rays and neutrons are easily capable of breaking molecular bonds in the soil, destroying evidence of past life, as well as any life that may be presently trying to survive there.”
Human follies, alas. They are evident right here, in the vain imaginations of astrobiologists.
Let’s do a simple back-of-the-envelope calculation of cratering on Mars from the figure given: at least 200 new impacts per year 12 ft across or more. That should yield 900 billion craters over the lifetime of Mars – close to a trillion. Assuming a fraction of those would be large enough to loft debris to form secondary craters, and some of those could create orbiting bodies that would fall later, that total seems unreasonably high. The same rate would produce over a million craters in just 6,000 years – plenty, but credible. If anyone would like to refine these estimates, they would need to consider the rate of erasure of craters by dust storms and other impacts, and factors that could vary the impact rate from a steady state. The rate we measure today, for instance, may not reflect rates in the past. Planetary scientists frequently propose a “Late Heavy Bombardment” of large impactors, for instance, but such hypotheses are speculative (1/09/12).