Martian radars to peer beneath Red Planet's surface
BY STEPHEN CLARK
Posted: August 10, 2005
Interplanetary geologists are busy this week analyzing the first sets of data from an Italian subsurface sounding radar currently orbiting Mars, as a crucial counterpart sits on a Florida launch pad ready to join the hunt for conjectured underground ice and water.
A similar radar is awaiting launch Thursday morning aboard NASA's Mars Reconnaissance Orbiter spacecraft, set to head to the Red Planet to conduct its most detailed survey ever. See Spaceflight Now's extensive coverage of that mission here.
The Shallow Subsurface Radar, also from Italy, will complement information from MARSIS after it arrives in its science orbit late next year.
Launched in June 2003 aboard the European Mars Express orbiter, the activation of MARSIS was delayed by a year to allow engineers to ensure the violent deployment of three radar antennas would not damage the spacecraft. Two fiberglass 20-meter dipole antennas and one 7-meter monopole antenna were housed in small containers during the first two years of the mission, but were commanded to spring free over the past few months.
The first 20-meter boom deployed in early May, but controllers could not confirm all segments were locked in place. A later maneuver exposed the suspect area to the Sun, and the heating coaxed the hinge into place. The second dipole antenna was released without incident in the middle of June.
After the instrument was checked out during a two-week commissioning phase, radar beams began piercing the Martian soil on July 4 to probe the region for evidence of potential ice and water layers that could exist after deteriorating climate conditions forced them off the surface.
"The commissioning phase confirmed that the radar is working very well, and that it can be operated at full power without interfering with any of the spacecraft systems," said Robert Seu, MARSIS instrument manager at the University of Rome.
MARSIS was developed by contractor Alenia Spazio, with project management by the Italian space agency and scientific guidance from the University of Rome. NASA's Jet Propulsion Laboratory also took part, providing the actual antenna built by Astro Aerospace.
The additional testing period will focus on the checkout of the 7-meter boom, which is used to refine MARSIS data in parts of Mars where rough topography can disrupt raw data.
MARSIS operates as the Mars Express orbit approaches it closest point to the Red Planet, so the radar can obtain the highest resolution possible. During night passes, the radar waves are best suited for studying the subsurface, while ionospheric data is gathered in daytime. During each orbit, the instrument is turned on for a total of 36 minutes, with the central period devoted to subsurface observations, bookended by a pair of five-minute ionospheric studies.
Initial results indicate the Martian upper atmosphere may be much more active than originally thought, with a higher number of charged particles than expected. Data from the subsurface is still being glossed over, and officials say they will release it once they have a full understanding of what it means.
"The instrument is working pretty closely to our expectations. It is working properly," said Enrico Flamini, director of solar system programs for the Italian space agency.
"Obviously we will have to clean up the data...but it is very encouraging and I think very shortly we will have clearance from the PI (principal investigator) to provide this data."
"The data are extremely complex to be understood due to the fact that it is the first time ever with MARSIS there are sounding radars flying around another planet," he said.
MARSIS will continue operating in a subsurface mode through the about the next week, when the night portion of the orbit become insufficient to support the observations.
"The biggest part of our work just started, as we now have to be sure that we clearly identify and isolate these echoes that come from the subsurface," said Giovanni Picardi, MARSIS principal investigator from the University of Rome. "To do this, we have to carefully screen all data and make sure that signals that could be interpreted as coming from different underground layers are not actually produced by surface irregularities. This will keep us occupied for a few more weeks at least."
With a vertical resolution of 50-100 meters in the underground, MARSIS has already proven it can probe up do a depth of five kilometers based on the first science products.
MRO's instrument, on the other hand, will offer data with a resolution of just 20 meters. However, SHARAD's radar will only focus on the first kilometer below the Martian surface.
"With MARSIS we are going to have the broad picture of the distribution of water on Mars, while with SHARAD we are going to have the defined picture. We will be able to provide the position, the depth, and the extension of the possible ice and water layers that are under the Martian surface at a depth that can be reached by future Mars exploration."
SHARAD will operate in the 15 to 25 megahertz range of frequencies, which allows it to gather sharper images of the upper tier of the subsurface. MARSIS radar waves are in the range of 0.1 to five megahertz, meaning it can pierce the deeper layers.
"The sounding radars are the first opportunity to explore Mars beneath the surface," said MARSIS co-principal investigator and SHARAD team member Jeffrey Plaut from NASA's Jet Propulsion Laboratory.
"We hope to extend our understanding of the surface geology into the subsurface. We are attempting to address a major question in the evolution of Mars, 'Where did all the water go?' If large amounts of water or ice are stored in the upper regions of the Martian crust, these instruments may be able to detect it."