David Weintraub on Life on Mars: What to Know Before We Go

WeintraubDoes life exist on Mars? The question has captivated humans for centuries, but today it has taken on new urgency. NASA plans to send astronauts to Mars orbit by the 2030s. SpaceX wants to go by 2024, while Mars One wants to land a permanent settlement there in 2032. As we gear up for missions like these, we have a responsibility to think deeply about what kinds of life may already inhabit the plane—and whether we have the right to invite ourselves in. This book tells the complete story of the quest to answer one of the most tantalizing questions in astronomy. But it is more than a history. Life on Mars explains what we need to know before we go.

Why does Mars matter?

Are we alone in the universe? Earth might be an oasis of life, the only place in the universe where living beings of any kind exist. On the other hand, life might be as common across the universe as the hundreds of billions of stars and planets that populate it. Mars is the closest habitable world in the universe where we can begin to learn about extraterrestrial life. If life is common, if the genesis of life is possible given the right environment and the necessary elemental materials, some form of life might exist right next door, on Mars, and if life were discovered on Mars that is of an independent origin than life on Earth, we could safely predict that life is common throughout the universe. Such a discovery would be extraordinary. Mars Matters.

Haven’t we already discovered life on Mars?

Maybe. Maybe not. Some astronomers believe that evidence from NASA’s Viking Lander biology experiments strongly suggest the presence of past or present life on Mars. Other astronomers believe that evidence found in a meteorite from Mars is evidence of ancient life on Mars. Still others believe that methane gas discovered in the atmosphere of Mars is evidence for life on Mars today. However, no consensus exists. None of the data is definitive that would prove or disprove the hypothesis that Mars once harbored or still nurtures life. The jury is still out.

Could life on Mars and life on Earth be related?

Could be. In order for a meteorite to get knocked off Mars and arrive on Earth, several things must happen. First, an asteroid of significant size must hit the surface of Mars and some of the debris from that impact must be lofted off the surface intact and at high speed. The impact debris kicked off the surface then must drill a hole through the Martian atmosphere and emerge above the atmosphere with a high enough velocity (known as “escape velocity”) to escape the gravitational clutches of Mars. Then that object has to end up on an orbit that intersects with that of Earth. All of these things are improbable but possible. Have they actually happened?

A meteoritic breakthrough occurred in 1982, when the leader of the 1981–1982 U.S. search party looking for meteorites in Antarctica found a tiny, unusual-looking rock now known as ALH 81005, which showed mineralogical similarities to lunar rocks. By 1983, several teams of meteoriticists, working independently, had confirmed that this specimen was, without any doubt, a lunar meteorite. For the first time, we had evidence that meteorites can come from objects as large as our Moon.

Then, in 1985, a geochemist proved that the gases trapped inside air bubbles inside EETA 79001, another Antarctic meteorite, this one collected in 1979 in the Elephant Moraine region, were a perfect match to the gases found by NASA’s Viking lander in the atmosphere of Mars. Therefore, without any doubt, EETA 79001 itself was a piece of Mars. We now know of several dozen meteorites that are, without question, of Martian origin.

If a meteorite can travel from Mars to Earth (or vica versa), then life could be transported by this vehicle from one planet to the other.

Why should you care about microscopic Martians?

Do microscopic Martians matter? Yes. Microscopic Martians, if they exist, would be astoundingly important to our understanding of life in the universe. A second genesis, life that began completely independently of terrestrial origins, might have occurred on Mars. Even if life on Mars is limited to bacterial-sized beings, buried underground or hiding deep in a crevice where they are protected from dangerous ultraviolet radiation and cosmic rays and where they can find water, those beings would teach us something of enormous importance about the existence of life beyond Earth. Life on Mars that is independent of life on Earth would send us a clear message about exobiology: life could happen anywhere and everywhere that conditions allow. Alternatively, if we find microscopic life that is DNA-based, we also receive an enormously important message about exobiology and clues about our distant, evolutionary past: such a discovery would tell us that life is easily transported across interplanetary space. Once life gets started, it can spread, and thus, whether we are Martians or the Martians are us, we’re all related. Finally, if we discover that Mars is barren and sterile, without even microscopic Martians, we will know that we are more alone in the solar system and perhaps in the galaxy and universe than many of us currently think.

How Earth-like is Mars? And does that matter?

Mars is very nearly a twin of Earth. Like Earth, Mars is a small rocky planet with a solid surface and an atmosphere.  Mars orbits the Sun at a similar distance as Earth, where the amount of solar heating is sufficient, for at least part of every year, to allow the possibility of the existence of liquid water on at least parts of the surfaces of both planets. The length of the day and night of Mars — 24 hours, 39 minutes — is extremely similar to the day/night spin (24 hours) of Earth. The obliquity of Mars (the 25 degree tilt of Mars’ rotation axis with respect to the plane of its orbit around the Sun) is almost the same as the tilt of Earth (23.5 degrees). These tilts generate seasonal changes, and the seasonal changes of Mars are very similar to the seasons we find here on Earth. The polar caps on Mars, which are mostly water ice, closely resemble the ice caps on Earth. The thin Martian atmosphere behaves like the thicker atmosphere of Earth, with clouds, frost that condenses on the surface, and winds that blow across the surface of the planet. And Mars has large reservoirs of water, just like Earth.  Yes, differences exist. The mass of Mars is smaller than the mass of Earth; the density and composition of the Martian atmosphere are different from those of Earth; Earth has a strong magnetic field while Mars does not; Mars’ water is either frozen or buried deep beneath the surface, while most of Earth’s water is either frozen or liquid and is at or near the surface.  But if you’re looking for an Earth-like planet where Earth-like forms of life could thrive, Mars is a great place to look.

Why did you decide to write this book?  Why should someone read your book?

I think, without any doubt, that humanity will colonize Mars in the near future, perhaps within a decade, and most certainly by the end of the twenty first century. When we settle on Mars, we will contaminate Mars. If any life exists there today, we almost certainly will alter or destroy it in the same way that human and animal diseases have devastated the native species on every continent and island on Earth to which human explorers have extended their reach, putting life forms that have been isolated and protected from other life forms in harm’s way. After we place human colonies on Mars, we will lose the opportunity to discover, with certainty, whether Mars ever was or still is inhabited.

We have one chance to make these discoveries, and that is the present time before we colonize Mars. I think the knowledge we might gain about Mars and Martian life before we send colonists to the red planet is so unique and valuable that we humans should, collectively, debate whether the 2020s and 2030s are the right time to send the first wave of settlers to Mars. Perhaps we should wait just a bit longer, and let robotic exploration continue until the debate about life on Mars is settled. With this book, I hope to help trigger that public debate before it is too late.

David A. Weintraub is professor of astronomy at Vanderbilt University. He is the author of How Old Is the Universe? and Is Pluto a Planet?: A Historical Journey through the Solar System. He lives in Nashville.