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.

Steven S. Gubser & Frans Pretorius: The Little Book of Black Holes

Black holes, predicted by Albert Einstein’s general theory of relativity more than a century ago, have long intrigued scientists and the public with their bizarre and fantastical properties. Although Einstein understood that black holes were mathematical solutions to his equations, he never accepted their physical reality—a viewpoint many shared. This all changed in the 1960s and 1970s, when a deeper conceptual understanding of black holes developed just as new observations revealed the existence of quasars and X-ray binary star systems, whose mysterious properties could be explained by the presence of black holes. Black holes have since been the subject of intense research—and the physics governing how they behave and affect their surroundings is stranger and more mind-bending than any fiction. The Little Book of Black Holes by Steven S. Gubser and Frans Pretorius takes readers deep into the mysterious heart of the subject, offering rare clarity of insight into the physics that makes black holes simple yet destructive manifestations of geometric destiny. Read on to learn a bit more about black holes and what inspired the authors to write this book.

Your book tells the story of black holes from a physics perspective. What are black holes, really? What’s inside?

Black holes are regions of spacetime from which nothing can escape, not even light. In our book, we try to live up to our title by getting quickly to the heart of the subject, explaining in non-technical terms what black holes are and how we use Einstein’s theory of relativity to understand them. What’s inside black holes is a great mystery. Taken at face value, general relativity says spacetime inside a black hole collapses in on itself, so violently that singularities form. We need something more than Einstein’s theory of relativity to understand what these singularities mean. Hawking showed that quantum effects cause black holes to radiate very faintly. That radiation is linked with quantum fluctuations inside the black hole. But it’s a matter of ongoing debate whether these fluctuations are a key to resolving the puzzle of the singularity, or whether some more drastic theory is needed.

How sure are we that black holes exist?

A lot more certain than we were a few years ago. In September 2015, the LIGO experiment detected gravitational waves from the collision of two black holes, each one about thirty times the mass of the sun. Everything about that detection fit our expectations based on Einstein’s theories, so it’s hard to escape the conclusion that there really are black holes out there. In fact, before the LIGO detection we were already pretty sure that black holes exist. Matter swirling around gigantic black holes at the core of distant galaxies form the brightest objects in the Universe. They’re called quasars, and the only reason they’re dim in our sight is that they’re so far away, literally across the Universe. Similar effects around smaller black holes generate X-rays that we can detect relatively nearby, mere thousands of light years away from us. And we have good evidence that there is a large black hole at the center of the Milky Way.

Can you talk a bit about the formation of black holes?

Black holes with mass comparable to the sun can form when big stars run out of fuel and collapse in on themselves. Ordinarily, gravity is the weakest force, but when too much matter comes together, no force conceivable can hold it up against the pull of gravity. In a sense, even spacetime collapses when a black hole forms, and the result is a black hole geometry: an endless inward cascade of nothing into nothing. All the pyrotechnics that we see in distant quasars and some nearby X-ray sources comes from matter rubbing against itself as it follows this inward cascade.

How have black holes become so interesting to non-specialists? How have they been glorified in popular culture?

There’s so much poetry in black hole physics. Black hole horizons are where time stands still—literally! Black holes are the darkest things that exist in Nature, formed from the ultimate ashes of used-up stars. But they create brilliant light in the process of devouring yet more matter. The LIGO detection was based on a black hole collision that shook the Universe, with a peak power greater than all stars combined; yet we wouldn’t even have noticed it here on earth without the most exquisitely sensitive detector of spacetime distortions ever built. Strangest of all, when stripped of surrounding matter, black holes are nothing but empty space. Their emptiness is actually what makes them easy to understand mathematically. Only deep inside the horizon does the emptiness end in a terrible, singular core (we think). Horrendous as this sounds, black holes could also be doorways into wormholes connecting distant parts of the Universe. But before packing our bags for a trip from Deep Space Nine to the Gamma Quadrant, we’ve got to read the fine print: as far as we know, it’s impossible to make a traversable wormhole.

What inspired you to write this book? Was there a point in life where your interest in this topic was piqued?

We both feel extremely fortunate to have had great mentors, including Igor Klebanov, Curt Callan, Werner Israel, Matthew Choptuik, and Kip Thorne who gave us a lot of insight into black holes and general relativity. And we owe a big shout-out to our editor, Ingrid Gnerlich, who suggested that we write this book.

GubserSteven S. Gubser is professor of physics at Princeton University and the author of The Little Book of String Theory. Frans Pretorius is professor of physics at Princeton.