Lorenz Named to Cassini Radar Science Team

Oct. 2, 2000

WRITER: Agnieszka Przychodzen
UA Lunar and Planetary Lab

NASA has named Ralph Lorenz of the University of Arizona Lunar and Planetary Laboratory (LPL) as a member of the Cassini RADAR science team.

RADAR, on NASA's Cassini spacecraft heading toward Saturn, will begin mapping the surface of Saturn's moon Titan in 2005. One objective is to map a landing site on Titan for the European Space Agency (ESA) Huygens Probe. The Cassini orbiter and the Huygens Probe constitute the biggest, most complex interplanetary spacecraft ever built.

Arizona is heavily involved in Cassini/Huygens. UA planetary scientists and their teams with major responsibilities are:

  • Carolyn C. Porco, who leads the Imaging Science Subsystem (ISS) team
  • Robert H. Brown, who leads the Visible and Infrared Mapping Spectrometer team
  • Martin G. Tomasko, who leads the Descent Imager/Spectral Radiometer (DISR) experiment on the Huygens Probe
  • Jonathan I. Lunine, one of three interdisciplinary scientists (and the only American) for the Huygens Probe.

In addition, Alfred S. McEwen, who directs LPL's Planetary Image Research Lab, is on the 14-member ISS team. The LPL's Peter H. Smith and Lyn R. Doose are DISR scientists. Lunine is a member of the Gas Chromatograph Mass Spectrometer science team, as is Donald H. Hunten. Hunten is a member of the original Cassini mission science definition team of 1983.

Lorenz , 31, a senior research associate at LPL, has been working on the mission since 1990, He first worked for ESA in the Netherlands, engineering experiments for the Huygens Probe. He continued work on the probe package for three years while completing his doctorate at the University of Kent in the United Kingdom. Lorenz joined the UA in 1994 to work with planetary sciences Professor Jonathan I. Lunine on models of Titan's surface and with Peter H. Smith to photograph the satellite's surface with the Hubble Space Telescope. They got first-ever glimpses of the Titan landscape.

Lorenz said the 1994 Hubble data convinced him that scientists needed to rethink how radar might complement optical images taken with cameras aboard the Cassini orbiter. He soon began collaborating with the Cassini RADAR team.

As a RADAR science team member, Lorenz is responsible for helping plan the best possible radar observations. It's no small job: The Cassini spacecraft will fly by Titan 40 times during its four-year tour of the Saturn system. Voyager flew by Titan only once in the 1980s - and that single encounter took six months' planning, Lorenz notes.

"We have to be many times more efficient at planning the observations. There is a lot of work in setting up the software and deciding which places to look at. This is a very difficult decision making process because there are lots of good instruments on Cassini, and you have to think about what you can learn from each observation," says Lorenz.

Cassini's RADAR will penetrate both clouds and darkness in mapping the entire surface of Titan, which is the second largest satellite in the solar system. It will map about a third of the moon in sharp detail, or at high resolution.

RADAR will operate an hour or so before closest approach to its target. The instrument uses the large 4- meter high-gain antenna and microwave radiation to send out signals to the moon. Scientists will build a picture of the surface from the echoes returned.

Cassini's RADAR could solve such mysteries as whether the large, bright region on Titan is a range of ice mountains washed clean of dirty organics by methane rainfall, as Smith and other scientists theorize. It will tell scientists about surface composition and layering, the extent of any methane lakes and oceans -- and certainly surprises impossible to anticipate, Lorenz said.

"Radar is a different way of seeing. Only the Earth and Venus have been studied extensively with radar, and Venus is a poor example because we haven't seen much of its surface optically. Radar is great for measuring topography and shapes of surface features, such as mountains. To do that with a camera you need sharp shadows, and because Titan's atmosphere is so fuzzy that might be difficult to achieve. With both radar and optical instruments, Cassini then is a very powerful science experiment," Lorenz said.

"I've thought about Titan's landscape a lot," Lorenz added. "One of the key questions I'd like to answer is what it's like on the surface.

"I think the view will be spectacular - weird, but strangely familiar. Titan is made of very different stuff than is the Earth...but many of the processes that shape the Earth's landscape could be occurring on Titan in a slightly different form. ...Anything is possible with Titan. That's why it's so exciting."

The Cassini mission, which is managed by the NASA Jet Propulsion Lab in Pasadena, was launched on Oct.15, 1997, from Cape Canaveral and will fly by Jupiter in December. At launch the spacecraft weighed about 5, 600 kilograms. Only the two Phobos spacecraft sent to Mars by the former Soviet Union were heavier.


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