A Big Deal: Organic Molecules Found on Mars

by David Weintraub

MarsIn 1976, both Viking 1 and Viking 2 touched down on the surface of Mars. Both landed on vast, flat plains, chosen because they were ideal locations for landing safely. Perhaps the most important Viking experiment for assessing whether life could exist on Mars was the gas chromatograph and mass spectrometer (GCMS) instrument, built by a team led by Klaus Biermann of MIT. Ultimately, Biermann and his GCMS team reported a definitive answer: “No organic compounds were found at either of the two landing sites.” None, nada, zilch.

This scientific discovery had enormous importance for our understanding Mars. Summing up what we learned from the Viking missions in 1992, and in particular what we learned from the absence of any organics in the sampled Martian soil, a team of Viking scientists wrote, “The Viking findings established that there is no life at the two landing sites.” Furthermore, because these two sites were thought to be extremely representative of all of Mars, they concluded that this result “virtually guarantees that the Martian surface is lifeless everywhere.” 

If Mars is sterile, then SpaceX and NASA and Blue Origin and Mars One can all move forward with their efforts to land colonists on Mars in the near future. They needn’t wrestle with any ethical issues about contaminating Mars.

Fast forward a generation. In a paper published in Science last week, Jennifer Eigenbrode and her team, working with data collected by the Mars Science Laboratory (i.e., the Curiosity rover), report that they discovered organic molecules in Martian soil. The importance of this discovery for the possible existence of life on Mars is hard to overstate. The discovery of organics on Mars is a BIG deal.

Let’s be careful in discussing organic molecules. An organic molecule must contain at least one carbon atom and that carbon atom must be chemically bonded to a hydrogen atom. All life on Earth is built on a backbone (literally) of organic molecules (DNA). And life on Earth can produce organic molecules (for example, the methane that is produced in the stomachs of cows). But abiological processes can also make organic molecules. In fact, the universe is full of such molecules known as PAHs (polycyclic aromatic hydrocarbons), which are found in interstellar clouds and the atmospheres of red giant stars and which have absolutely nothing to do with life.

Repeat: the presence of organic molecules on Mars does not mean life has been found on Mars. The absence of organic molecules in the Martian soil, as discovered in the Viking experiments, however, almost certainly means “no life here.” 

Were the Viking scientists wrong? Yes, in part. Their conclusion that the plains of Mars are representative of every locale on Mars was an overreach. When assessing whether the environment on Mars might be hospitable to life, local matters. That conclusion shouldn’t surprise anyone. After all, we find significant differences on Earth between the amount and kinds of life in the Mojave Desert and the Amazon River basin. Why? Water.

The vast, flat plains of Mars are free of organics, but they are unlike Gale Crater. Gale Crater was once a lake, full of water and dissolved minerals. We know now that certain locations on Mars that were warm and wet for extended periods of time in the ancient past have preserved a record of the organic molecules that formed in those environments.

Could life have played a role in creating these molecules?  Maybe, but we don’t know, yet. We do know, however, where to keep looking. We do know where to send the next several generations of robots. We do know that we should build robotic explorers that can drill deep into the soil and explore caves in places similar to Gale Crater.

Abigail Allwood, working at NASA’s Jet Propulsion Laboratory, is building a detector called PIXL that will be sent to Mars on a rover mission that is scheduled for launch in 2020. PIXL will be able to make smart decisions, based on the chemistry of a rock, as to whether that rock sample might contain ancient, fossilized microbes. A later mission might retrieve Allwood’s PIXL specimens and bring them back to Earth for more sophisticated laboratory studies. With instruments like PIXL, we have a good chance of definitively answering the question, “Does Mars or did Mars ever have life?”

What does the presence of organic molecules in the Martian regolith mean, as discovered by Curiosity? Those molecules could mean that life is or once was present on Mars. Finding those molecules just raised the stakes in the search for life on Mars. The jury is still out, but the betting odds just changed.

Given all we currently know about Mars, should we be sending astronauts to Mars in the next decade? Do we have the right to contaminate Mars if is already home to native Martian microbes? These are important questions that are more relevant than ever. 

David A. Weintraub is professor of astronomy at Vanderbilt University. He is the author of Life on Mars: What to Know Before We GoReligions and Extraterrestrial Life: How Will We Deal with It?How Old Is the Universe?, and Is Pluto a Planet?: A Historical Journey through the Solar System. He lives in Nashville.

“Dreams of Other Worlds”: The Mars Rovers #WSW2013

MERHouston, we have lift off!

All week long for World Space Week, we will be posting exclusive excerpts from Chris Impey and Holly Henry’s new book, Dreams of Other Worlds: The Amazing Story of Unmanned Space Exploration. Each day will include an excerpt from a different chapter about a different unmanned spacecraft, along with a picture of the craft that doubles as an iPhone background!

Today’s excerpt is from Chapter 3, and it talks about our strategy for learning more about Mars, and what the Mars Rovers, Spirit and Opportunity, are doing to help us with that.

Tomorrow will bring another chapter and another adventure, so stay tuned!

Decoding the Red Planet

As we saw in the last chapter, Mars seems dead to the orbiters that daily send back images of the surface. The atmosphere is tenuous, ultraviolet radiation and cosmic rays scorch the soil, and it rarely gets above freezing even on the balmiest summer day.15 It’s unlikely any form of life could exist on the surface now, but Mars has not always been so inhospitable. NASA’s strategy in searching for life in the Solar System is to “follow the water,” and even if there’s no surface water now, there was in the past. Each of the Mars Exploration Rovers, Spirit and Opportunity, was designed for just a ninety-day mission. In the end, they have vastly exceeded expectations with their indomitable traverses of the forbidding Martian terrain. Think of them as twin robotic field geologists whose primary goal is to search for the signposts of water.16 The record of past water can be found in the rocks, minerals, and landforms on Mars, particularly those that could only have formed in the presence
of water.

Think you know all about these missions? Take our quiz and find out!
Proud of your score? Tweet it! #WSW2013