John Mustard

Gathering evidence toward the possibility of life on Mars

There have been many extraordinary claims of life on Mars, yet none has proffered extraordinary evidence. During the next 20 years the continued exploration will bring us closer to answering that question.

Over the last few weeks, a bright reddish “star” has been piercingly clear in the southern sky, even through the murky urban atmosphere of the Northeast. This is Mars orbiting closer to Earth than it has in more than a decade.

Mars holds a special place in the solar system and in our imaginations. Our fascination with this planet stems from the very real possibility that life once existed, or even presently exists, on Mars. The vision of Mars as a life-sustaining planet, complete with water, vegetation, and an intricate canal system built by intelligent beings, was first evoked by the 19^th-century amateur astronomer Percival Lowell. This vision defined Mars in the public’s eye for much of the 20^th century.

Science fiction classics such as H. G. Wells’ War of the Worlds, Ray Bradbury’s Martian Chronicles, and more recently Kim Stanley Robinson’s Mars books-of-color (Red Mars, Green Mars, and Blue Mars) also have painted a vivid picture of a dynamic planet populated by a culturally rich species. Scientific measurements of Mars through the first half of the century were not completely able to dispel these imaginative notions as these observations were limited to what we could see through telescopes.

At the dawn of the space age, the first high-resolution images of the planet taken by the Mariner 4 spacecraft in 1964 decidedly shattered popular notions. Instead of an oasis, the surface of Mars appeared as battered and barren as that of the Moon. We saw Mars as a place of bitter cold, with a thin, suffocating atmosphere, more parched than the driest places on Earth. The prospects that life could exist on such a hostile world were suddenly very remote. This revelation was perhaps one of the greatest disappointments of the space age.

Seven years later, the Mariner 9 spacecraft revealed a planet in startling contrast with earlier observations. Mars, in fact, was home to the largest volcano in the solar system, Olympus Mons at more than 80,000 feet high; a canyon, Valles Marineris, plunging five miles deep that would stretch from New York to Los Angeles; water-carved channels that approximate the size of Earth’s rivers, as well as gargantuan scars scoured by floods of unimaginable size. What happened between missions? Had Mars suddenly come to life?

No. Improved technology meant that Mariner 9 had instruments with better resolution. Subsequent missions to Mars have continued the tradition of all science: to make discoveries by advancements in technology and observations.

By looking at new places, increasing magnification by 10 times, or increasing the accuracy, scientists are almost guaranteed to make a discovery. This is occurring right now with the Mars Global Surveyor spacecraft. Its tenfold increase in technology makes it possible to image objects as small as an automobile or elevation differences equivalent to the height of a table. A new vision of Mars is emerging, based on solid observations, that brings water back to the fore and shows that it has played a key role in Mars’ history and may even be reshaping the surface of the planet today.

The Surveyor’s measurements show that a large ocean, almost one mile deep, may have existed in the vast northern plains. While the ocean has long since disappeared, evidence of its existence revives some of Lowell’s grand imaginations of a water world. Last summer, scientists reported on the existence of many small, very young channels that appear to have been carved by water – so young, in fact, they may even be forming today. My colleagues and I have found evidence of a recent ice age on Mars. The young channels and the ice age together may point to an active water cycle and that liquid water may exist, however briefly, on the surface today.

A seminal discovery during the last 30 years is that life on Earth is found anywhere liquid water is present, including such extreme environments as the interior of nuclear reactors, ice-covered Antarctic lakes, suboceanic hydrothermal vents, and deep subsurface rock. The existence of an active water cycle on Mars brings us closer to considering the possibility that life may have existed. One of the most profound questions we face is: are we alone in the universe? Answering that question in the affirmative has the potential to transform our perceptions of ourselves, much like the Copernican realization that the Earth was not the center of the universe. Carl Sagan said, “I believe that the extraordinary should be pursued. But extraordinary claims require extraordinary evidence.” There have been many extraordinary claims of life on Mars, yet none has proffered extraordinary evidence. During the next 20 years the continued exploration will bring us closer to answering that question. However, the definitive, extraordinary evidence of life will undoubtedly require the return of samples to Earth or perhaps the exploration of the planet by astronauts.