Scientists know that in order for life to exist on Mars, there has to be water. And although the red planet is covered with ancient riverbeds, it now seems to be as dry as a bone. What happened to all the water? When the Mars Polar Lander and its two probes reach the planets south pole this Friday, we may be one step closer to solving this Martian mystery.
Water, Water Everywhere and Not a Drop to Drink?
|Channels are evidence of past erosion.|
The possibility that water might exist on Mars was first raised in the late 1870s when Italian astronomer Giovanni Schiaparelli observed "canali," or channels, through a telescope. But when spacecraft were first sent there in the 1960s, images revealed a stark world, with not a drop of water to be found. The Viking missions in the 1970s showed signs of deep canyons, and even what appeared to be ancient lake shorelines, but still no flowing water. The search for life on our next door neighbor appeared to be fruitless.
In the 1990s however, a glimmer of hope surfaced in the form of a meteorite believed to have originated on Mars. Discovered on the Allan Hills ice field in Antarctica in 1984, the meteorite, known as ALH84001, contains what may be ancient fossils of microorganisms from billions of years ago, when the Martian climate may have been much warmer and wetter. Although this conclusion is controversial, it has opened the door to a renewed search for water on Mars.
Today, Mars is too cold and its atmosphere is too thin to have liquid water on its surface, but that wasnt always the case. It may have been much warmer at one time, or water trapped beneath the surface may have been periodically released. In either scenario, the Martian climate changed a great deal—either abruptly or gradually—and scientists believe its water was either lost to space, absorbed by the surface, or both. The Mars Polar Lander may very well help scientists piece together the planets climate history.
How Do You Get Beneath the Surface?
|Mars Microprobe Mission Flipbook by Russell Crotty.|
As the Mars Polar Lander makes its careful descent to the Martian surface on December 3, two tiny passengers, called microprobes, will take a very different approach. About 10 minutes before the Lander touches down, the Deep Space 2 probes, which are not much bigger than softballs, will slam into the south pole at 400 miles per hour. "Probably the most exciting thing about Deep Space 2 is that its only a protective shell to carry us into the atmosphere," says Sue Smrekar, project scientist at NASAs Jet Propulsion Lab. "We have no rockets, parachutes, airbags, nothing like that to slow us down, so we [just] hit the ground.... Think of getting your laptop to work after running into a wall at 400 miles per hour."
|A DS2 probe. The part that drops down is the "forebody."|
To test the probes, scientists first dropped them out of planes over the Mojave desert, then shot them out of huge air guns in New Mexico. Due to the high impact speed, part of the probes (the forebody—see image on left) will penetrate the Martian surface to about three feet underground. Named for Ronald Amundsen and Robert Falcon Scott, the first explorers to reach the Earths South Pole, they are the first probes to penetrate another planets surface.
How Do They Test For Water?
Once theyre beneath the surface, the probes will drill for samples, melt them on the spot, and beam the results back to Earth, where scientists will look for signs of water. Martian polar ice caps are similar to the ones on Earth in that they are believed to contain layers of dust and snow that can help scientists decipher Martian climactic history, much like growth rings in trees reveal their history.
"One of the big questions for Mars is, where has the water gone?" says Smrekar. "If you estimate how much water it took to form the channels you would get a total water depth of on the order of 100 yards or maybe more.... The ice thats present in the polar caps, even if the southern cap is water as well, is much less." Scientists already know the northern cap is composed of water and carbon dioxide ice, and that there are traces of water vapor in the Martian atmosphere.
|What About the Polar Lander? |
The Mars Polar Lander is more than a vessel for the microprobes. It is a robot with a mechanical arm that will dig about 20 inches deep and obtain soil samples. These samples will then be heated in an onboard oven and analyzed. From this the scientists hope to gain clues to how much ice is beneath the surface and what minerals might once have been found on Mars.
The Lander is also equipped with three cameras that will take images of the Martian surface as the spacecraft is landing, stereo panoramic views from the top, and closeup views of the soil that the arm scoops up.
If They Find Water, So What?
"Wed really like to find water," says Smrekar. "Itd be a really exciting confirmation of our theory that theres water near the surface of Mars and that all the water that was there billions of years ago is still on the planet and not gone into space."
Since Mars is the planet with an environment most similar to Earths, finding water there may also help scientists unravel our own climate enigmas. "We have no record of what conditions were like early on on the Earth, so its really a laboratory to understand the early phases of planetary evolution," says Smrekar. Mars weather data may even shed some light on the debate as to to whether Earths climate changes are natural or driven by people.
If the probes do reveal liquid water or ice beneath the Martian surface, it doesnt automatically follow that life will be found, but its a start. "[Water alone is] not a sufficient condition, but its definitely a necessary condition," says Smrekar. The fact that life has been found in extremely harsh conditions on Earth—such as ancient microbes deep beneath the ice pack in Greenland—leads scientists to believe the same sorts of conditions on Mars could have allowed organisms to survive there. At the very least, hidden water could mean a supply of drinking water for future Mars colonies.
Elsewhere on the web:
Listen to the Dec. 3 installment of National Public Radios Science Friday, when host Ira Flatow and guests talked about the upcoming mission.
MPL entry, descent and landing.
"An Exiobiological Srategy for Mars Exploration," a 1995 document.
Mars Lander Game
Mars Fact Sheet