September 16, 1998
Concurrently, three Los Alamos researchers are part of a 17-member international team working on a feasibility study for NASA to determine the technical requirements for an instrument to study the moon's icy surface. The preliminary report is due Nov. 1.
Called the Ice Penetrating Radar, the instrument would use a three-antenna array that sends millions of radar signals at different frequencies to map out the thickness of Europa's ice surface and detect, if present, a subsurface Europan ocean. The IPR also would characterize Europa's ice surface.
A liquid ocean is the most important ingredient in the development and sustenance of life; detecting and characterizing Europa's oceans, if present, are an integral part of scientists' search for evidence of life in the solar system.
"If we can confirm the existence of a water ocean on Europa, it would be the only ocean known to exist in our solar system outside of Earth's," said Brad Edwards of Los Alamos' Space and Remote Sensing Sciences Group. Edwards also is part of the 17-member Instrument Definition Team, which includes researchers from around the world.
Because ice is transparent to a large range of radar signals, the IPR will be able to record waves reflected off the top layer of ice and the ice-water interface, ultimately converting them into three-dimensional images.
"We think the ice crust surface could be as deep as 100 kilometers, but data we received from the Galileo spacecraft indicate that the ice could be as thin as hundreds of meters," explained Edwards. Photos transmitted by the Galileo spacecraft in 1994 presented the first evidence of the possible existence of liquid water on Europa.
"If a water ocean does exist on Europa, the IPR can map thin areas of the ice surface for future lander missions to Europa to sample the water for signs of life," said Edwards.
Edwards said the Instrument Definition Team currently is studying many things, including how to distinguish the different radar reflection signals returned by rocks, cracks in the ice, salty and nonsalty ice, and other conditions on the moon's surface. Another obstacle is making sure the IPR survives Jupiter's intense radiation that surrounds Europa, he added.
"The radiation around Europa measures about 25 megarads per month. That's enough radiation to fry a desktop computer in about five minutes," he said.
Still another important consideration is determining just how much power the IPR will need in order to transmit and receive its radar signals and the kinds of antennas that need to be used, said Xuan-Min Shao of Los Alamos' Space and Atmospheric Sciences Group and fellow IDT member. Shao said he hopes to begin testing the IPR prototype's antennas within the next couple of months. The testing will take place at Los Alamos.
Shao said the instrument's weight is another major factor in designing and building the prototype. "We think the Ice Penetrating Radar should weigh no more than eight kilograms," he said, or about 17 pounds.
The final draft design for the IPR is scheduled to be submitted to NASA sometime in March 1999, said Edwards. At that time, NASA will put out an announcement for opportunities for the Europa mission, scheduled for launch sometime in 2004. It would take anywhere from five to seven years for the instruments to reach Europa, after which time measurements would be taken for about a month.
The IPR is one of a suite of instruments -- called a strawman's payload -- that NASA currently is considering sending to Europa, the other instruments being an optical camera, transponder and laser altimeter. The IPR is the primary instrument; the laser altimeter would be used to measure the tidal bulge of Europa's surface caused by Jupiter's tremendous gravitational pull on the moon. "The laser altimeter will measure the moon's tides. If they're small, then we'll know that there's little or no water underneath the surface," said Edwards.
Shao said although it is conceivable that NASA may choose an instrument suite that does not include the IPR for the Europa mission, because the IPR is one of only a few instruments that can both measure Europa's ice surface depth and characterize its structure, there is a good chance that it will remain part of the suite that ultimately makes the 400-million-mile trek.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.
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