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First-of-Its-Kind Antenna to Probe the Depths of Mars
During the next couple of weeks, if all goes as planned, the martial arts champion of radar antennas will kickbox its way into space.

The image shows a box-shaped spacecraft in orbit above the cratered surface of Mars with a black sky in the background. On either side of the spacecraft are two long, rectangular solar panels. Attached to the top of the spacecraft are three long, wirelike objects arranged like an inverted that make up the two horizontal and one vertical segment of MARSIS. Image left: Mars Express
This artist's concept shows the three segments of MARSIS as they will appear after deployment, two of the segments extending horizontally on either side of the Mars Express spacecraft and one extending vertically. Image credit: NASA/JPL/Caltech.
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Weighing in at a mere 4 pounds (1.8 kilograms) and packing a pyrotechnic punch, the MARSIS antenna, which stands for Mars Advanced Radar for Subsurface and Ionospheric Sounding, will spring into operation in May. On each of its two main "arms," thirteen segments will quickly uncoil, taking a few seconds to reach their full length of 20 meters (65 feet) after tiny explosive charges open a pair of compartment doors. The motion will cause the spacecraft, the European Space Agency probe called the Mars Express, to rotate slowly 45 degrees, temporarily losing contact with Earth. In this case, losing the signal for a short time will be the first sign of success.

Radar Will Uncover What Is Hidden

"There is no camera to tell us if the antenna has deployed correctly," notes electrical engineer and radar scientist Daniela Biccari, of the University of Rome. "We will monitor the spacecraft’s orientation with gyroscopes and accelerometers."

The photo shows Daniela Biccari, a brunette with dark sunglasses wearing a long-sleeve white pullover and dark brown slacks, seated on a ledge beside a grassy area and a small shade tree in front of a building at JPL. Image right: Daniela Biccari
Italian radar specialist Daniela Biccari will monitor the antenna's function without being able to see it. Image credit: NASA/JPL
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Scientists will use MARSIS to probe beneath the surface of Mars. The radar will search for underground features much the way an ultrasound device looks at an unborn child inside a mother's womb. When radar waves encounter a boundary between different materials, some energy is reflected and some is transmitted. MARSIS will use radar signals with wavelengths hundreds of meters long to detect features up to 5 kilometers (3.1 miles) deep. One of the things scientists will look for are aquifers, zones in buried rocks that are rich in liquid water. If spaces between rock grains are empty, most of the radar waves will penetrate. If spaces are filled with water, the signals will bounce back.

MARSIS Antenna is a First

"MARSIS will let us 'see' the invisible Mars," says Ali Safaeinili, an electrical engineer and radar scientist at the Jet Propulsion Laboratory in Pasadena, California. "So far, for the most part, we have only observed the surface of Mars, but with MARSIS we can see rock and ice beneath the surface."

The photo shows a smiling Ali Safaeinili with his hands clasped in front of him, seated on a patio beside the blue waters of the Mediterranean Sea. He has curly, short-cropped, dark brown hair and is wearing a long-sleeve blue shirt and black wristwatch. Image left: Ali Safaeinili
JPL engineer Ali Safaeinili helped design MARSIS to see what would otherwise be hidden from view. Image credit: NASA/JPL
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Concerned about its unconventional design, mission controllers in Europe have delayed the deployment of MARSIS more than once. A week before its originally scheduled deployment in April of 2004, an engineer at Astro Aerospace, the California company that designed the antenna, ran a computer simulation suggesting the antenna might spring backward and graze the spacecraft.

Testing and More Testing

Since then, engineers and scientists on both sides of the Atlantic have run multiple simulations, using computers and spare flight hardware, to ensure minimal risk to the spacecraft. To give humans adequate time to check all systems, deployment will occur in three stages – twice for the two main arms and once for a third, smaller antenna.

This image taken from orbit by the European Space Agency's Mars Express spacecraft, shows rolling hills of layered rocks covered with patches of bright snow or ice. Image right: North Pole of Mars
Scientists will use MARSIS to look below the surface of Mars. This image, taken by the European Space Agency's Mars Express spacecraft, shows layers of water ice at the north pole. Image credit: ESA
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“No one has ever sent an antenna with this material design into space before,” says deputy principal investigator Roberto Seu, of the University of Rome. “It’s a very exciting project.”

What Happened to the Water?

Based on orbital images, scientists know that Mars once had flowing water on its surface that carved rivers and canyons.

"If you took all the water we see in the ice on Mars and spread it all over the planet, you would get a global ocean about 10 to 20 meters (33 to 66 feet) deep," notes JPL geologist Jeffrey Plaut, lead U.S. investigator for MARSIS. "But if you calculated the amount of water needed to carve the channels, you would find it is on the order of hundreds of meters. That's a big difference."

Some water may have disappeared into space. Hydrogen and oxygen ions in water can be broken apart by ultraviolet radiation or other chemical processes and carried away in the solar wind.

The photo shows a close-up of Jeff Plaut, with sandy hair parted on the right, a short beard and moustache, and just a hint of a smile on his face, in front of a wall bearing a global elevation map of Mars. Image left: Jeff Plaut
JPL geologist Jeff Plaut will use MARSIS to study layers of buried rock, ice, and water on Mars. Image credit: NASA/JPL
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Some water may have been trapped underground. Scientists hope to see what’s beneath layers of icy material at the martian poles. During the polar winter, the water ice is covered by a layer of dry ice – frozen carbon dioxide – that evaporates in summer. Year-round, frozen water is mixed with martian soil similar to permafrost beneath the Alaskan tundra.

Water: Key to Life

Finding liquid water on Mars is important for several reasons. The first is the search for life elsewhere in the solar system. In the presence of water, microbes may have a potential habitat.

"These are some of the biggest questions of all," said Plaut. "Is there life on Mars or has there been life on Mars in the past?"

The image shows a global map of Mars with different colors denoting different amounts of water on the planet. A broad swath north and south of the equatorial regions is relatively dry, while the polar regions are relatively rich in water. Image right: Mars Water Map
Scientists used the Gamma Ray Spectrometer aboard NASA's Mars Odyssey spacecraft to produce a global water map of Mars. The areas with the highest concentrations are at or near the martian poles. MARSIS will enable scientists to take a closer look at the extent of water and water ice on Mars and how deeply it is buried. Image credit: NASA/JPL
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Water is also important to eventual human exploration, both for consumption and as an energy source. Though Mars today is different from Earth, it started out with many of the same raw materials.

"The most exciting result would be to find present-day liquid water on Mars," says Plaut. "We have lots of evidence of ancient water on Mars and good evidence of ice on Mars but no ability to detect buried liquid water before now."

More at Mars Rovers or Mars Exploration Program .