The Mars Exploration Program is a science-driven program that seeks to understand whether Mars was, is, or can be, a habitable world. To find out, we need to understand how geologic, climatic, and other processes have worked to shape Mars and its environment over time, as well as how they interact today.
Mars is similar to Earth in many ways, having many of the same “systems” that characterize our home world. Like Earth, Mars has an atmosphere, a hydrosphere, a cryosphere and a lithosphere. In other words, Mars has systems of air, water, ice, and geology that all interact to produce the Martian environment.
What we don’t know yet is whether Mars ever developed or maintained a biosphere–an environment in which life could thrive.
To discover the possibilities for past or present life on Mars, NASA’s Mars Exploration Program is currently following an exploration strategy known as “Seek Signs of Life.” This science theme is built on the prior science theme of “Follow the Water,” which guided missions such as 2001 Mars Odyssey, Mars Exploration Rovers, Mars Reconnaissance Orbiter, and the Mars Phoenix Lander.
Progressive discoveries related to evidence of past and present water in the geologic record make it possible to take the next steps toward finding evidence of life itself. The Mars Science Laboratory mission and its Curiosity rover mark a transition between the themes of “Follow the Water” and “Seek Signs of Life.” In addition to landing in a place with past evidence of water, Curiosity is seeking evidence of organics, the chemical building blocks of life. Places with water and the chemistry needed for life potentially provide habitable conditions. Future Mars missions under the science theme “Seek Signs of Life” would likely be designed to search for life itself in places identified as potential past or present habitats.
Goal 1: Determine if Life Ever Arose On Mars
During the next two decades, NASA will conduct several missions to address whether life ever arose on Mars. The search begins with determining whether the Martian environment was ever suitable for life.
Conditions Needed for Life to Thrive
On Earth, all forms of life need water to survive. It is likely, though not certain, that if life ever evolved on Mars, it did so in the presence of a long-standing supply of water. On Mars, we will therefore search for evidence of life in areas where liquid water was once stable, and below the surface where it still might exist today. Perhaps there might also be some current “hot spots” on Mars where hydrothermal pools (like those at Yellowstone) provide places for life. Recent data from Mars Global Surveyor suggest that liquid water may exist just below the surface in rare places on the planet, and the 2001 Mars Odyssey will be mapping subsurface water reservoirs on a global scale. We know that water ice is present at the Martian poles, and these areas will be good places to search for evidence of life as well.
In addition to liquid water, life also needs energy. Therefore, future missions will also be on the lookout for energy sources other than sunlight, since life on the surface of Mars is unlikely given the presence of “superoxides” that break down organic (carbon-based) molecules on which life is based. Here on Earth, we find life in many places where sunlight never reaches–at dark ocean depths, inside rocks, and deep below the surface. Chemical and geothermal energy, for example, are also energy sources used by life forms on Earth. Perhaps tiny, subsurface microbes on Mars could use such energy sources too.
Looking for Life Signs
NASA will also look for life on Mars by searching for telltale markers, or biosignatures, of current and past life. The element carbon, for instance, is a fundamental building block of life. Knowing where carbon is present and in what form would tell us a lot about where life might have developed.
We know that most of the current Martian atmosphere consists of carbon dioxide. If carbonate minerals were formed on the Martian surface by chemical reactions between water and the atmosphere, the presence of these minerals would be a clue that water had been present for a long time–perhaps long enough for life to have developed.
On Earth, fossils in sedimentary rock leave a record of past life. Based on studies of the fossil record on Earth, we know that only certain environments and types of deposits provide good places for fossil preservation. On Mars, searches are already underway to locate lakes or streams that may have left behind similar deposits.
So far, however, the kinds of biosignatures we know how to identify are those found on Earth. It’s possible that life on another planet might be very different. The challenge is to be able to differentiate life from nonlife no matter where one finds it, no matter what its varying chemistry, structure, and other characteristics might be. Life detection technologies under development will help us define life in non-Earth-centric terms so that we are able to detect it in all the forms it might take.
Goal 2: Characterize the Climate of Mars
A top priority in our exploration of Mars is understanding its present climate, what its climate was like in the distant past, and the causes of climate change over time.
What’s the Martian Climate Like Today?
The current Martian climate is regulated by seasonal changes of the carbon dioxide ice caps, the movement of large amounts of dust by the atmosphere and the exchange of water vapor between the surface and the atmosphere. One of the most dynamic weather patterns on Mars is the generation of dust storms that generally occur in the southern spring and summer. These storms can grow to encompass the whole planet. Understanding how these storms develop and grow is one goal of future climatic studies.
What Can the Current Climate on Mars Reveal about the Past?
A better understanding of Mars’ current climate will help scientists more effectively model its past climatic behavior. To do that, we’ll need detailed weather maps of the planet and information about how much dust and water vapor are in the atmosphere.
Monitoring the planet for this information over one full Martian year (687 Earth days) will help us understand how Mars behaves over its seasonal cycle and guide us toward understanding how the planet changes over millions of years.
The layered terrain of the Martian polar regions also holds clues about the planet’s past, much like the rings of a tree provide a record of its history. When and how were these polar layers deposited? Was the climate of Mars ever like that of Earth? And if so, what happened to change the planet into the dry, cold, barren desert it is today? Those are the questions that our missions still have to answer.
Goal 3: Characterize the Geology of Mars
How did Mars become the planet we see today? What accounts for the differences and similarities between Earth and Mars? These questions will be addressed by studying Mars’ geology. As part of the Mars Exploration Program, we want to understand how the relative roles of wind, water, volcanism, tectonics, cratering and other processes have acted to form and modify the Martian surface.
For example, Mars is home to incredibly large volcanoes, which can be 10 to 100 times larger than those on Earth. One reason for this difference is that the crust on Mars doesn’t move the way it does on Earth. That means the total volume of lava piles up into one, very large volcano.
The Magnetism of Mars Gives Clues to the Planet’s Interior and More
A recent discovery by the Mars Global Surveyor spacecraft of large areas of magnetic materials on Mars indicates that the planet once had a magnetic field, much like Earth does today. Because magnetic fields in general act to shield planets from many forms of cosmic radiation, this discovery has important implications for the prospects for finding evidence of past life on the Martian surface. Study of the ancient magnetic field also provides important information about the interior structure, temperature and composition of Mars in the past. The presence of magnetic fields also suggests that Mars was once more of a dynamic Earth-like planet than it is today.
Rocks on Mars Can Tell Us About the Planet’s History and Its Potential for Harboring Life
Of fundamental importance are the age and composition of different types of rocks on the Martian surface. Geologists use the age of rocks to determine the sequence of events in a planet’s history. Composition information tells them what happened over time. Particularly important is the identification of rocks and minerals formed in the presence of water. Water is one of the keys to whether life might have started on Mars.
What other materials might be trapped in those rocks with information about the planet’s history? How are the different rock types distributed across the surface? Future orbiting and landed missions will carry special tools designed to help answer these questions.
Goal 4: Prepare for the Human Exploration of Mars
Eventually, humans will most likely journey to Mars. Getting astronauts to the Martian surface and returning them safely to Earth, however, is an extremely difficult engineering challenge. A thorough understanding of the Martian environment is critical to the safe operation of equipment and to human health, so the Mars Exploration Program will begin to look at these challenges in the coming decade.
Astronaut Safety in the Hostile Martian Environment
The safety of astronauts is of paramount importance to NASA. Mars lacks an ozone layer, which on Earth shields us from lethal doses of solar ultraviolet radiation. We do not have good information about the amount of ultraviolet radiation that reaches the Martian surface. A more detailed understanding of the radiation environment will provide the information necessary to assess the effects of UV radiation on astronauts, as well as help engineers design protective space suits and habitats.
We do know that the Martian soil contains “superoxides.” In the presence of ultraviolet radiation, superoxides break down organic molecules. While superoxides’ effect on astronauts is probably not serious, their impact and that of any other unique chemical aspects of the Martian soil must be assessed before human exploration of Mars can begin.
Robotic Spacecraft Will Pave the Way for Human Exploration of Mars
To pave the way for human exploration, 2001 Mars Odyssey will begin to analyze the radiation environment on Mars. This mission and the Mars Reconnaissance Orbiter will continue to search for water resources that, if discovered, could be used to support future human explorers. Eventually, robotic spacecraft, rovers, and drills could be used to access water resources in advance of, and during, human exploration.
Advanced entry, descent and landing techniques that reduce the G-forces on landers will also be developed for spacecraft and astronaut safety.