Fascination with Distant Worlds
In 1989, when Voyager 2 hurtled through the far reaches of our solar system passing the planet Neptune, a live feed from JPL opened a window onto an exotic world nearly 3 billion miles away. Entitled "Neptune All Night," the PBS television coverage enraptured a young Cynthia Phillips, who recalls watching the fly-by in her Boston home, late into the night until "caught" by her parents. The grainy images from outer space set this SETI Institute planetary scientist on a future career path that stretched far beyond the confines of our warm blue planet.

The icy cracks of Jupiter's moon Europa.
The icy cracks of Jupiter's moon Europa continue to intrigue astrobiologists. The white sheen is likely frost and the moon's heat source is a combination of an underground ocean and tidal heating under the strong gravitational pull of Jupiter. Credit: Galileo Project, JPL, NASA
With an undergraduate degree from Harvard in Astronomy and Physics, Phillips completed graduate studies in Planetary Science at the University of Arizona. There she first worked with then UA professor and now SETI Institute scientist, Dr. Christopher Chyba, who sparked her interest in the possibility of life on Europa in a graduate seminar on astrobiology.

While at Arizona, Phillips developed image processing techniques that allowed her to compare satellite images taken at different times of the same geologic locations of two Jovian moons, Europa and Io. Her algorithms allowed researchers to view any geological changes that had taken place in the time interval between imaging surveys of the Voyager and the Galileo missions.

In 2000, Phillips joined Chyba at the SETI Institute's Center for the Study of Life in the Universe, where today she continues her work on Europa as a NASA Astrobiology Institute (NAI) co-investigator on the SETI Institute's lead team.

Europa Research

Phillip's NAI research consists of two phases. First, she will complete a large database of images consisting of 95 separate observations from the five and one-half year long Galileo mission. "We have between one and twenty frames from each observation," says Phillips. The separate images were taken with different filters and at different resolutions. With the database, Phillips will determine which images cover the same area of the surface multiple times. Overlapping images allow Phillips to look for any changes on the surface that indicate current or recent geological activity. "Examples would be areas where the surface may have cracked open or where a feature has grown wider or taller," she explains.

In the second phase of the project, Phillips and Chyba will use the results of phase one to evaluate a number of models proposed by different researchers for Europa's surface features to understand implications of those models for life's prospects on Europa.

One model, she says, offers a theory for the creation of long linear cracks and ridges that "suggests they could be formed by the tides on Europa opening and closing the surface. One version of this model suggests the ice layer is quite thin. If there is actually liquid water close to the surface of Europa, this could mean a number of things," she continues. "It could mean there may be interesting biological or organic compounds created at the surface that then have a chance to work their way down into Europa's ocean layer." Conversely, "it is also possible that if there are any interesting signs of life or biological compounds within the ocean, then if the water is close to the surface, these materials can work their way up to the surface." Both possibilities offer tantalizing prospects for astrobiologists seeking evidence of life on this cold, distant world.

Remarkable frozen texture on Jupiter's moon, Europa.
Remarkable frozen texture on Jupiter's moon, Europa.
Credit: NASA/JPL
Asked how the imaging and model evaluation are integrated, Cynthia again offers an example. "If we found a domed feature that had gotten bigger over the five years, we would know to focus on a model that includes such features in the second half of the study." She would then estimate from the images how much larger the dome has grown in the specific time interval, and how much material would have had to be brought to surface for the growth to take place. A variety of models might account for the growth, "upwarping or instrusions of solid and liquid materials," she says, naming two. "I can look at parameters for what is seen to be happening, and how much material the model predicts."

So far, her preliminary studies have not detected change however, if she finds any evidence at all, she'll be very excited. "I'd know that there is geological activity taking place currently, and it would mean that Europa is one of a very few places in our solar system where such activity is taking place."

Europa Will Never be Done

Although the Galileo satellite is scheduled to dive into Jupiter's atmosphere on September 21, 2003, Phillips states with confidence that "Europa will never be done," and adds, "I could happily work on Europa for another 20 years."

A probe to drill into the Europan oceans.
Missions beyond Europa orbiters, like a probe to drill into the Europan oceans, may not have to go far into the ice to find evidence of life.Credit:NASA/JPL
For the next five of those years, she'll be using the Galileo data set, but she acknowledges that this data has limitations. The failure of Galileo's high gain antenna limited the quality of the images. Also, the satellite spent a relatively limited amount of time observing Europa as it orbited Jupiter, imaging the planet and its other moons in addition to the object of her study.

The quality of the combined images of Galileo and Voyager is frustratingly inconsistent. "Some areas," she says, "have a resolution of 20 kilometers per pixel some are very sharp, some are very fuzzy." While scientists do have images of the entire surface, some are, in Phillips' words, "pretty lousy." In some areas of Europa, "Voyager 2 images are better than Galileo we're using these."

Phillips worked with the U.S. Geological Survey building a map of Europa, "trying to blend a hodge-podge of images into smoothest map possible." Looking at a globe of the moon, it is possible to see large areas where the features are still sketchy. "There are regions where we just need better data."

She eagerly anticipates the next NASA mission to the mysterious planet, tentatively planned as the "Jupiter Icy Moons Orbiter" or JIMO mission, which may launch in "about a decade" and would orbit Europa for up to a month. "JIMO would take a very nice consistent data set of the kind I've been hoping for," she explains. "I'm crossing my fingers."

Written by Cynthia Phillips
NASA's Astrobiology Institute
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