Water: The Common Thread of a Mars Exploration Strategy

Donna Shirley

The "Water Strategy"

NASA Administrator Dan Goldin and NASA Associate Administrator for Space Science Wes Huntress have agreed on a strategy for the exploration of Mars for the next 10 years. The strategy is to explore and study Mars in three areas/

Evidence of past or present life
Climate (weather, processes and history)
Resources (environment and utilization)

Each of these areas is connected with the search for water on Mars. When and where was water present in the past, and what is its current form and amount? We know from previous missions that the Martian polar caps include water ice as well as frozen carbon dioxide. The Viking and Mariner 9 orbiter images show evidence of past great floods (the Pathfinder lander is planning to land in such an area), and of dry rivers and lake beds. Where did the all the water go?

If life ever did arise on Mars it would almost surely have been connected with water. And understanding the processes which led (or didn't lead!) to life on Mars will help us understand the potential for life elsewhere in the Universe.

Water is a key to climate, both on Earth and Mars, and understanding the history of the Martian climate will help us better understand the Earth's climate change processes.

Water will be a major resource for future human exploration of Mars, and if we understand how the solid Mars evolved (including what happened to produce water and make it disappear), we may be able to predict or find reservoirs of water available for human use.

A Series of Missions to Build Up "Water" Knowledge

How do we go about finding out about water on Mars? Dan McCleese of JPL, the Mars Exploration Program Scientist, and Steve Squyres of Cornell, the head of the Mars Science Working Group, led that group to define a strategy for the "water search." They looked at how small Mars orbiters, landers, "networks" of landers, and sample returns could be combined in a logical progression of missions that will build up an understanding of how water existed and exists now on Mars.

The small orbiter missions will search for accessible water (we know that ice is accessible at the poles, but are there reserves underground or in the soil?). They will search for ancient sediments and hydrothermal deposits (dry lake beds and geysers). They will provide data to understand the present Mars climate and study how water escapes from the atmosphere into space. The orbiters will also study the surface of Mars and identify good landing sites for the landers, and will provide a radio link between the landers and the Earth.

The small lander missions will search for carbonates and evaporites, minerals that could only have formed in the presence of water. Landers can investigate water reserves in detail/ for example they can measure the amount of water that has been bonded to the soil, or drill into the polar ice caps to see how many layers of snow have been built up. Investigation of surface chemistry and how the rocks and soil have "weathered" due to water will tell us about the past climate. And the landers may be able to find organic compounds or even evidence that life may have been present at one time in Mars' past.

"Networks" of more than a dozen very small landers scattered over the planet could be used as weather stations to see how the Martian weather changes over the whole planet and the whole Martian year. If the networked landers have seismometers on board, and if they detect "marsquakes," that information will tell us about what Mars is like deep inside, and how it might have evolved.

Finally, sample return missions can bring back rocks and soil for analysis on Earth with very sensitive instruments (too large to take to Mars) which can tell us about the climate history, the dates of different rocks, and may even allow us to detect compounds that could have led to life, or which are evidence of past life. (The odds of being able to select a rock with a fossil, however, are very low, even if fossils exist on Mars.)

Olympus Mons Mosaic from Mariner 9. JPL-P-13074

A "Strawman" Mission Set

All of these missions must be done within the very tight cost constraints of the Mars Exploration Program (about $100M per year). The Mars Science Working Group laid out a "strawman" strategy for fitting the science goals into a set of missions which can gradually build up our knowledge of Mars over the next 10 years, following the themes of life, climate, and resources.

First Mars Global Surveyor, which will orbit Mars from 1997 through 2002, will study the surface of the planet and acquire information on the weather, the magnetic and gravity fields, and the mineralogy. The 1997 landing of Mars Pathfinder, with its stereo camera and rover, will send back to Earth information on the geology and surface chemistry of a specific site.

Next, in 1998, another orbiter and lander (half the size and cost of Mars Global Surveyor and Pathfinder) will be launched. The orbiter will carry either a surface measuring instrument (the Gamma Ray Spectrometer - GRS) or an atmospheric instrument (the Pressure Modulated Infrared Radiometer - PMIRR), plus a small camera and a radio relay for the '98 lander. The lander will carry the first of a series of lander payloads specifically designed to carry out the "water strategy." The payloads will be selected as total packages in a competition between science and engineering teams. They may look for certain chemicals that give information on the history and existence of water, they may analyze rocks to tell the history of the climate, they may (if the lander is targeted to one of the poles), drill into polar ice. In 2001 and 2003 there are opportunities to send additional landers, which can continue to carry out the "water" investigations.

Any of these landers could be targeted to ancient lake beds to search for "fossil slime." They could be sent to river valleys to investigate how water once flowed on Mars. The landers could include rovers and/or sampling arms to put instruments on the surface or retrieve samples for analysis.

In 2003 an alternative to sending more "large" landers would be to send a network of meteorology/seismology stations, or a network of penetrators that can make chemical measurements below the surface all over the planet.

And finally, in 2005, the Mars Science Working Group recommended that the Mars Exploration Program attempt a Sample Return Mission - very challenging within the cost constraint of about $200M!

An Augmented Mission Set

Even better opportunities for the "water strategy" will occur if we can form teams with international partners. We are still exploring the possibilities of "Mars Together " in 1998 with the Russians, which would allow the U.S. to fly both the GRS and the PMIRR instruments on the U.S. orbiter. This would let us study both the atmosphere and the surface in a very complementary way starting in 1999. In 2003 the European Space Agency (ESA) is proposing to send a joint ESA/U.S. mission to orbit Mars and land three or four of the "large" U.S. landers, supported with a radio link on a European orbiter.

And more instruments can be carried, or more landers sent, if new technology improvements can be introduced into U.S. spacecraft to make them smaller, lighter, and cheaper. A program called "New Millennium" is currently being planned to develop and demonstrate a new generation of space technologies to do this for both planetary and Earth missions. The Mars Exploration Program will be a "customer" for this new technology, and some of the New Millennium demonstrations may "piggyback" on Mars missions.