Why even consider spending billions of Euro's on sending experts to Mars. Can they find anything by hand, they can't find through robots?

A group of scientists are hunched over, their eyes intently scanning the jumble of rocks on the ground. Every now and then, someone picks one up for closer inspection, turning it over and over again in their hand. Occasional comments ring out in the still desert air:

“Is this one?”
“Hmm.. This probably isn’t anything...”
“Look at that - you found a good one!”

We were hunting for fossils in an ancient seabed that dates back to the Devonian Period, roughly 400 million years ago. At our feet, rock fragments are embedded with trilobites, brachiopods, corals and other sea creatures both extinct and still existing in the oceans today. Although some of the fossils look quite alien, they are unmistakably remnants of life.

This field trip in the Morocco desert was organized by the International Research School of Planetary Sciences’s Ibn Battuta Centre. The various locations we visited were meant to illustrate how this region of Africa has many similarities to the alien landscape of Mars.

Finding evidence for life on Mars will entail much more than scooping fossils up from the arid surface. Most scientists think that if Mars ever had life, it was microbial, and special instruments will be needed to detect it. Deep-digging drills will be required to access any possible remains, since they might be buried in marine sediments dating back to 3.5 billion years ago. Such drills also could help us discover whether life exists on Mars today, surviving in underground reservoirs where it would be protected from the harsh surface conditions.

It’s still just a hypothesis that the surface of Mars was once awash with liquid water, but over the past 40 years different missions have gathered a compelling amount of evidence that supports this scenario.

Whether life ever existed on Mars, however, is still an open question.

NASA’s first search for life on Mars took place in the 1970s, as part of the Viking mission. Looking for chemical signs of existing microbial life, Viking’s Labeled Release experiment added liquid nutrients to martian soil. The presumption was that any microbes living in the soil would eat the nutrients and expel certain gases as a waste product. Scientists are still arguing about the results, but most think the instantaneous gas release that occurred was due to a purely chemical reaction, since life presumably would need more time to process food.

The controversial Viking experiment caused NASA to turn to the basics, and look for the liquid water and organic molecules that life on Earth needs for its survival. That’s been the focus of missions like the Phoenix lander, the Mars Exploration Rovers Spirit and Opportunity, and various satellites such as the Mars Reconnaissance Orbiter.

The search for life itself will begin again with the Mars Science Laboratory, scheduled for launch this year. MSL, renamed “Curiosity” rover, will look for biosignatures and evidence of microbial metabolisms. The planned 2016 and 2018 ExoMars missions, joint ventures of NASA and the European Space Agency, also will hunt for life on Mars.

Reading Life’s Signature 
Our fossil-hunting grounds in Morocco included mud mounds that -- although today high and dry -- were born in a relatively shallow sea. Such submarine mud volcanoes can be the result of gas escaping from underneath Earth’s crust, forcing great quantities of liquid and fine-grained rock to the surface.

To my eyes, the mounds looked like ogres in a science fiction film, the ancient vents forming drooping eyes and a sagging, crumbling mouth. The monstrous mounds remained mute during our visit, but scientists are trying to learn their story by other means.

A vein of travertine, for instance, is a clue that at least one of the mounds we visited had a hydrothermal origin. Other mounds may have been built by so-called “cold seeps,” which have milder temperatures. Several mounds are lined up in a row, indicating they bubbled up along a natural fault in the Earth’s crust. First identified by scientists in the 1930s, many of the Morocco mounds are made of carbonate mud (The term “mud” refers to the grain size of the rocks -- micrite and fine-silt -- rather than a composition of sediment mixed with clay).

One question scientists are trying to answer is how much of the mounds were generated by geological processes, and how much do they owe their existence to life? The abundance of fossils in and around the mounds may have caused the mounds to grow ever larger, as structures like corals acted as catchment basins for sediments and life’s waste products that piled up over time.

The “overprinting” by fossils also masks a deeper truth - the role played by life that we can’t see with the naked eye. Microbes may have been crucial in building the mounds, since the anaerobic bacterial oxidation of methane can lead to carbonate precipitation, and also turn mud into stone. Barbara Cavalazzi of the University of Johannesburg, one of the field trip leaders, published a 2007 study in the journal Astrobiology that discussed the various microfossils found within the mounds.

But even after years of analysis, the mounds remain frustratingly impenetrable. There aren’t any fresh cross-sections available for easy viewing; the few mounds that were cleaved in half through fortuitous natural processes are now so weathered that the details have faded away.

Another way to inspect the inside layers of a mud mound would be to arduously drill holes at different points along them. A less strenuous study would look at rocks that have fallen down off the mounds.

However, “those studies don’t provide a full picture of the mounds, and are really just random shots in the dark,” says Abigail Allwood, a geologist with the Jet Propulsion Laboratory who attended the field trip. To date, there is no complete picture of the structure and method of formation of the mud mounds.

Studying such mounds on Earth can inform our investigations of Mars. Research published in the journal Icarus last year pointed to possible mud volcanoes in the northern plains of Mars. 

The Icarus study mapped more than 18.000 circular mounds thought to be mud volcanoes in the Acidalia Planitia region, and estimated that more than 40,000 eventually could be found. Using data obtained from the Mars Reconnaissance Orbiter, the scientists were able to investigate the structure and mineralogy of some of the mounds. This allowed them to rule out other means of mound construction, such as meteorite impacts, lava flows, or ground deformation caused by ice or evaporation. 

Life probably didn’t play a role in building the martian mounds as it did on Earth. However, because volcanoes bring up fluids from deep underground, any biosignatures of past or present life also could have been brought up to the planet’s surface. The study authors therefore point to the mounds as key places to search for evidence of life on Mars.

Source: NASA's Astrobiology Magazine