On November 26, 2018 after seven months of traveling through space, NASA’s InSight mission navigated a soft landing on Mars to the cheers at Mission Control at NASA’s Jet Propulsion Laboratory. InSight will study Mars’ underworld, collecting data that will provide a map of the interior of the red planet and help scientists understand how Mars and other rocky planets formed. “We can basically use Mars as a time machine to go back and look at what the Earth must have looked like a few tens of millions of years after it formed,” said Bruce Banerdt, the principal investigator of the InSight mission. Later missions will address even more intriguing questions – did Mars once harbor microscopic life, and could microscopic life possibly exist beneath Mars’ surface today. The answers will have profound implications for the origin of life here on Earth.
Billions of years ago, early after its formation, Mars may have been very much like Earth with vast amounts of water on its surface and a thick supporting atmosphere. Images from earlier missions to Mars – NASA’s Viking Mission, Mars Pathfinder Mission, and Mars Global Surveyor – have identified deep channels and canyons on Mars’ surface believed to have been formed by streams, rivers, and lakes that existed in the early years of the planet. Mars must have had moderate temperatures and a robust atmosphere in its early years to provide conditions that would support liquid water on the surface of the planet. Today Mars’ has lost almost all of its atmosphere and has become a frigid wasteland no longer suitable for life. What happened?
Mars, like Earth, was initially hot due to volcanic eruptions and continued bombardment by meteorites. As the bombardment abated and Mars began to cool, a thick atmosphere with a blanket of greenhouse gases – water vapor and carbon dioxide – helped to keep the planet warm. But this was not to last. In the early days of our solar system our young Sun was very active and tumultuous, blasting huge quantities of charged particles that bombarded the planets. When these charged particles collided with Mars’ atmosphere, they energized atmospheric molecules, allowing them to escape Mars’ gravitational field and drift into space. Over time as Mars began to lose its atmosphere, it also lost some of its greenhouse effect due to loss of greenhouse gases (water vapor and carbon dioxide), and the planet began to cool. As the planet cooled, water vapor condensed on its surface, further reducing the greenhouse effect and further cooling the planet. Cooling begot more condensation of water vapor and more cooling in a freezing cycle known as the runaway refrigerator effect. Over time Mars lost almost all of its atmosphere and almost all of its greenhouse effect and became the frigid wasteland we know today no longer suitable for life.
Luckily for us, Earth is larger than Mars and has a strong gravitational field better able to hold on to its atmosphere. Perhaps even more importantly, Earth has a magnetic field that deflects solar charged particles, providing protection for our atmosphere. Earth’s magnetic field is created deep within the planet by its liquid outer core, which contains molten iron that moves by convection. Since moving electric charges create magnetic fields, scientists believe that charged particles within the molten iron are generating Earth’s magnetic field. Mars has an iron core that is solid rather than liquid, so it cannot generate moving electric charges and has little or no magnetic field. Scientists with the NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) mission have documented the profound effects solar radiation has on dissipating Mars’ atmosphere in the absence of a protective magnetic field (Fecht 2015).
It’s a sad story – the evolution of Mars from a hospitable planet in its early life to the frigid wasteland it is today. But perhaps this enhances the intrigue and mystery of early Mars and the question whether life was once present on the red planet. Almost four decades ago, Mars sent us a messenger that may have provided answers to this question and raised new possibilities about the origins of life on our planet Earth. In 1984, while most Americans were enthralled with the launch of Challenger 4, Ronald Reagan’s presidency, or the newest episode of “Night Court,” United States government scientists were busy examining newly found remnants of a meteorite that had crashed into Antarctica 13,000 years before. The meteorite was called, rather unceremoniously, Rock 84001. The remnants of the meteorite were estimated to be 4 billion years old, and evidence indicated that the meteorite had broken off from Mars and traveled a 16 million-year journey to Earth.
Years after its discovery, and long into a new Presidency, further studies suggested that the meteorite might contain fossils of nanobacteria. The findings, while controversial, were published in the prestigious journal Science, and received great public attention including a televised press conference in 1996 by President Bill Clinton. At his press conference, Clinton waxed philosophical:
Today, Rock 84001 speaks to us across all those billions of years and millions of miles. It speaks of the possibility of life. If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered. Its implications are as far-reaching and awe-inspiring as can be imagined. Even as it promises answers to some of our oldest questions, it poses still other questions even more fundamental (Clinton 1996).
While there remains controversy over whether the microscopic etchings found on Rock 84001 are true fossils of bacterial life or mere artifacts, the discovery popularized panspermia as a possible source for the origin of life on earth. Panspermia, the idea that Earth could have been seeded with cells from extraterrestrial sources, may sound like an absurd proposition, but many respected scientists—including astronomer Fred Hoyle, Frances Crick of DNA fame, and even the late brilliant physicist Stephen Hawking—have voiced support for the concept. If the findings in Rock 84001 are true, they raise many more questions than answers, as President Clinton suggested. The search for where and how life began, then, becomes even more complex. InSight and subsequent Mars’ missions may soon help to provide answers.
Fecht, S. (2015, November 5). Why Can’t We Live on Mars? Blame the Sun. Popular Science. Retrieved November 2018 from https://www.popsci.com/how-did-mars-lose-its-atmosphere
Williams, M. (2015, December 15). Mars Compared to Earth. Universe Today. Retrieved November 2018 from https://www.universetoday.com/22603/mars-compared-to-earth/
Mars, Water and Life. (2018) Retrieved November 2018 from https://mars.jpl.nasa.gov/msp98/why.html
Chang, K. (2018, November 26). NASA’s InSight Mission Has Touched Down onMars to Study the Red Planet’s Deep Secrets. The New York Times. Retrieved Novmeber 2018 from https://www.nytimes.com/2018/11/26/science/nasa-insight-mars-landing.html
This post is adapted from Bruce Brodie’s recently published book Why Are We Here? The Story of the Origin, Evolution, and Future of Life on Our Planet.