Does 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 planet – and whether we have the right to invite ourselves in. Life on Mars 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.
David Weintraub tells why, of all the celestial bodies in our solar system, Mars has beckoned to us the most. He traces how our ideas about life on Mars have been refined by landers and rovers, terrestrial and Mars-orbiting telescopes, spectroscopy, and even a Martian meteorite. He explores how finding DNA-based life on the Red Planet could offer clues about our distant evolutionary past, and grapples with the profound moral and ethical questions confronting us as we prepare to introduce an unpredictable new life form – ourselves – into the Martian biosphere.
Life on Mars is also a book about how science is done – and undone – in the age of mass media. It shows how Mars mania has obscured our vision since we first turned our sights on the planet and encourages a healthy skepticism toward the media hype surrounding Mars as humanity prepares to venture forth.
"Life on Mars is a valuable lesson in science. Weintraub's well-written and easy-to-read book will appeal to anyone interested in Mars and the search for life."
– Alfred McEwen, director of the Planetary Image Research Laboratory, University of Arizona
Our planetary neighbour Mars has long fascinated us, and the idea of there being Martian life holds a strong grip on our collective imagination. NASA and others are becoming serious about sending people to Mars. Before we do so, astronomy professor David Weintraub would like to give you this readable history of our fascination with the Red Planet and the research that tries to answer the question: is there life on Mars? (Admit it, you were crooning that David Bowie song there).
Having fond memories of regularly spinning Jeff Wayne’s Musical Version of The War Of The Worlds on my parents’ record player when I was a child, I was aware that our fascination with Mars goes back to Welles’s 19th century book and the radio play that caused such a stir at the time (though not as much as legend would have it, see Broadcast Hysteria: Orson Welles’s War of the Worlds and the Art of Fake News). But as Weintraub shows, our fascination goes back much further and all the classic civilisations had a name for this planet. Pretty much as soon as telescopes had been invented, Western scientists pointed them at the Red Planet and Weintraub starts his exploration of the Western scientific interest in Mars in 1636.
What follows is a fascinating historical foray, taking us back to a time before empirical science as a practice had really been invented. In a period where theology and natural philosophy dominated, the assumption was that, of course, Mars was inhabited. Why else would God create other worlds but to fill them with inhabitants to worship him? Surely, he would not waste his energy by creating barren worlds? Suggesting that is tantamount to heresy! We have been predisposed ever since to assuming there had to be life on Mars.
Weintraub walks us through what in hindsight seems like an almost comical period in which the wildest assumptions were taken to be true based on very few observations or actual data. What did not help is that Mars is quite like Earth in many respects. Its days are only slightly longer, its tilt relative to the Sun (i.e. its obliquity, which causes our seasons here on Earth) is almost the same, and it has an atmosphere. But without much solid ground, people assumed Mars had seas, ice caps, vegetation, even large canals that must have been constructed by intelligent life forms.
As telescopes grew more powerful and other scientific instruments were invented to analyse light with, more and more of these claims fell apart. Scientist tried to prove the existence of chlorophyll (the molecules that make plants green and do the hard work of converting the Sun’s energy into more plant) and failed. Claims were then backpedalled to lichens which could survive in the dry climate of Mars, and when support for that failed others opined algae. Eventually, the claims were backpedalled to hopes for microbial life. Many of you might remember the ruckus in the mid-nineties when NASA announced they had found fossils of a bacterium in a Martian meteorite (ALH 84001, see The Rock from Mars: A Detective Story on Two Planets).
Whether Mars has an atmosphere, and what it is made of, is another important area of research. You can use a spectrometer to analyse what colours of light are reflected off a planet’s surface and which ones are absorbed. This can give you information about the chemical composition of a planet’s atmosphere. Once it turned out that the Martian atmosphere is primarily carbon dioxide, the hope of finding water evaporated. And although water would be found, the quantities are small. Since the ’60s until today, scientists have been trying to find evidence for methane in Mars’s atmosphere. Although abiotic (i.e. non-living) processes can form this gas as well, it is a byproduct of life’s metabolism. Weintraub gives a detailed treatment of the findings and claims back and forth. So far, the levels of methane measured – first from earth-bound telescopes, then from satellites passing or orbiting Mars, and finally from the rovers that NASA has landed on the planet – are so low that they can hardly be told apart from background noise and instrument inaccuracies. It is just as likely that there is no methane at all. There certainly is no evidence for large amounts of it.
To this day though, scientists remain hopeful, and Weintraub highlights how they almost habitually keep the door open for the possibility of life. It has been very hard to shake this notion, even when the data over the centuries have not stacked up in its favour. The other idiosyncrasy Weintraub highlights is the extraordinary influence of the press that predictably overstates findings in sensational headlines. He is, quite rightly, critical of the science-by-press-conference debacles that we have seen. It is embarrassing how often scientists have had to backpedal, or have just stopped talking about some of their previous claims that didn’t hold up in the end. This is why we need peer review.
So far, so good, Weintraub delivers a very readable history of research on Mars. Even if you do not have much of a background in physics or astronomy, he explains the science well and makes good use of illustrations to do so. But there was one thing missing, something the blurb promised and the title implied. I was looking forward to reading Weintraub “grapple with the profound moral and ethical questions confronting us as we prepare to introduce an unpredictable new life form – ourselves – into the Martian biosphere”. He briefly mentions the likelihood of ethical and moral quandaries in the first chapter, but he never explicitly returns to it. As the sprawling history of Martian research was laid out and the remaining pages melted away under my hands, I realised he was not going to return to this topic. That’s a shame, as he opens the book with some tantalising questions, and I would have loved to see him develop these further in a dedicated chapter.
That point notwithstanding, Life on Mars is a fascinating history of our interest in the Red Planet, and an up-to-date overview of the search for life.
David A. Weintraub is professor of astronomy at Vanderbilt University. He is the author of Religions 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.