David Morrison: Waystations to Mars
David Morrison is a senior scientist at the NASA Astrobiology Institute, where he participates in a variety of research programs. Internationally known for his research on small bodies in the solar system, Dr. Morrison is the author of more than 135 technical papers, has published a dozen books, and asteroid 2410 Morrison is named in his honor. He testified before the President’s Commission on the Moon, Mars and Beyond on April 16, 2004.
If you had to summarize astrobiology in an elevator, in 30 seconds, (you would say) it’s the study of how life begins and evolves – that is, where did we come from? Does life exist elsewhere in the universe – are we alone? And, what is life’s future on Earth and beyond – where are we going in space? These are the defining terms for astrobiology, but you’ll notice they also appear in other forms in the NASA vision and mission statements.
Astrobiology is naturally directed toward the planet Mars. It is the most likely abode of life elsewhere in the solar system, and is also the only planet that I can imagine humans establishing a permanent presence within the 21st century. While it’s hostile by Earth standards, the gravity, atmosphere, temperatures, diurnal cycle, and resources like water on Mars make it a uniquely attractive target for human exploration. I would like to emphasize that Mars is equally attractive because of the possibility of finding evidence for life – past or perhaps present probably microbial life, but that is really no less interesting to the biologist. We will need to search carefully for evidence of life on Mars and do so before we send astronauts. I’d like to point out that there are profound implications of almost anything we learn about life on that planet.
If there is no life on Mars today, or if life once existed there but has perished, then clearly we want to understand what went wrong with Mars and to draw lessons for the stewardship of our own planet. If we find life, and it’s genetically related to Earth life with DNA and RNA, then we will probably have established that microbial life forms can be exchanged between worlds by hitchhiking on meteorites. We will have the opportunity to study how our cousins have evolved for four billion years in a completely independent and alien environment on Mars.
If there’s life there and it’s not related to us, if it does not use the same sort of genetic system we do, then we will truly have discovered independent origin, a second genesis for life within the solar system. And that discovery will infinitely enrich our understanding of the fundamentals of life and also encourage us to look for other inhabited worlds. Any of these discoveries would surely rank among the most important scientific results of this or any other century.
Clearly, once we send humans to Mars, we will carry a vast load of terrestrial microbes at the same time. So, I would like to stress the importance of carrying out a careful robotic search for evidence of life before we land humans. This is not to delay sending humans to Mars, but to argue for a robust robotic system over the next 25 years.
I’d like to speak a little bit about asteroids. Asteroids is one of the places where astrobiology really, really counts because the “astro” part the asteroids can collide with planets and have profound effects on biological evolution. The near-Earth asteroids come closer to us than any other objects in space and sometimes collide with our planet. They should be a part, I think, of any long-term plan for the future.
|“I was sitting in the porch of the house at the trading station of Vanovara at breakfast time and looking towards the north… suddenly the sky was split in two, and high above the forest the whole northern part of the sky appeared to be covered with fire.” -Farmer Sergei Semenov of the Tunguska event, 1908|
Asteroids are important for three reasons: They’re leftover building blocks of the planets, which makes them of great interest to scientists. As a potential resource, they could provide important material such as iron and water in space. And since they do occasionally collide with the Earth, we may someday need to defend our planet against such an impact. It’s only in the last 15 years that we recognized this asteroid impact hazard is serious. We know in particular that the impact 65 million years ago did away with the dinosaurs and, incidentally, with most mammals and most other life forms on Earth at the same time. That could happen again. It is improbable. That is to say, impacts don’t happen very often. But without better knowledge, we cannot be sure that our generation won’t be the one to experience such a threat.
|Fragments of Comet P/Shoemaker-Levy 9 colliding with Jupiter (July 16-24, 1994).|
Today, NASA, with support from the Air Force and many individuals, is carrying out the Spaceguard survey to find asteroids and chart their orbits before they hit the Earth, to provide decades of warning. And that is going very well. Probably as studies that are under way come to fruition, we will extend that survey to smaller objects and ultimately should be able to predict the next impact – whether it’s a large object that could kill us all, or a small one that would simply obliterate a city.
These are intrinsically unlikely events. We’re not in the business of calculating the probabilities of impact any more. We’re looking at asteroids one at a time and determining if there are any out there that will hit in our lifetime, or our children’s or grandchildren’s lifetime. And the final note is that in addition to searching for asteroids, I think it’s only prudent that we begin to develop the technology for defending ourselves. This is the one natural hazard that we can defend ourselves from. An incoming asteroid, given decades of warning, can be deflected so it will miss the planet entirely. We understand that in principle. It’s probably reasonable that we should start to develop that technology.
One particular proposal that intrigues me is to use one of the three Prometheus missions to do a demonstration. To go to a small asteroid, use the electric propulsion and deflect it a tiny bit, make a measurable change in its orbit, so we can stand up to the people of the world and say, “We’re not only searching for potential threats from asteroids, we’re beginning to develop the technology that ultimately could defend our planet from this sort of threat from space.”
Related Web Pages
Spirit’s Sol images and slideshow
Opportunity image gallery and slideshow
Mars Berries Once Rich in Iron-Water
NASA’s RATs Go Roving on Mars
Pancam- Surveying the Martian Scene
Alpha Proton X-ray Spectrometer