Dec 3, 1998

The frosty plains of Europa

Updated: June 18th, 2018

As Galileo returns new images of Europa, NASA scientists prepare to study samples from a potentially similar environment here on Earth

Dec. 3, 1998: The large Jovian moon Europa may be hiding liquid water beneath its frozen crust. We won't know for sure until robotic explorers one day venture below the surface of that icy moon in search of oceans and possibly life. For now we must learn what we can from surface photos of Europa, like this one captured by the Galileo spacecraft, and from studies of a mysterious subterranean lake here on Earth.


Galileo image of a region of Europa


Above: North is to the lower left of the picture and the sun illuminates the surface from the upper left. The image, centered at -40 degrees latitude and 225 degrees west longitude, covers an area approximately 800 by 350 kilometers (500 by 220 miles). The resolution is 230 meters (250 yards) per picture element. More information from the Planetary Photojournal.

The picture above is a mosaic of images from Europa's southern hemisphere. The brown, linear ridges extending across the scene are thought to be frozen remnants of cryo-volcanic activity. "Cryo-volcanoes" (cold volcanoes) occur when liquid or partially frozen water erupts onto the Europan surface, freezing instantly in the extremely low temperatures so far from our sun.

a closer view
of icy ridges and water ice on Europa
A geologically older, smoother surface, bluish in tone, underlies the ridge system. The blue surface is composed of almost pure water ice, whereas the composition of the dark, brownish spots and ridges is not certain. One possibility is that they contain mineral salts in a matrix of high water content.

Left: A closer view of the volcanic ridges and areas of blue that scientists believe are frozen water on Europa. Europa's frosty surface has intrigued scientists ever since the Voyager spacecraft missions flew through the Jupiter system in 1979. At -260° F, the moon's surface temperature could deep-freeze an ocean over several million years, but it's possible that warmth from a tidal tug of war with Jupiter and neighboring moons could be keeping large parts of Europa's ocean liquid. Tidal friction from Jupiter is also thought to be responsible for volcanic activity on Europa's neighbor Io, and for a similar underground ocean on Callisto.


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The next best thing to being there....

Many scientists would love to travel to Europa to study conditions there first-hand, but regular flights to Jupiter probably won't begin for some time. Meanwhile, there is an environment right here on Earth with significant similarities to Europa and Callisto, a place called Lake Vostok.

Below: In 1993 altimetric and radar data were used to trace this outline of Lake Vostok, located about 1000 miles from the South Pole. Image used is copyrighted by the Canadian Space Agency. More Information from Caltech-JPL.

In 1974 a team of scientists conducting airborne research passed over the Soviet research station Vostok in Antarctica. Their sounding instruments detected an expanse of water beneath the ice roughly the size of Lake Ontario. Although Antarctica records some of the coldest temperatures on Earth, Lake Vostok is buried under four kilometers of ice. The ice sheet acts as a blanket, shielding the lake from cold temperatures on the surface. It is also thought that geothermal heat helps keep the water liquid.

Earlier this year Richard Hoover of NASA's Marshall Space Sciences Lab and Dr. S.S. Abyzov of the Russian Academy of Sciences examined ice cores from above Lake Vostok for evidence of microbiotic life, using an Environmental Scanning Electron Microscope. What they found surprised them. "We've found some really bizarre things - things that we've never seen before," said Richard Hoover of NASA's Marshall Space Flight Center. "There are all sorts of microorganisms in the ice. Some are readily recognizable as cyanobacteria, bacteria, fungi, spores, pollen grains, and diatoms, but some are not recognizable as anything we've ever seen before," Hoover said.

Above, right: One of the more exotic forms Hoover and Abyzov found in the deep ice. Many of these microbes will undoubtedly fall into known categories when identifications are made.


Hoover is about to begin new studies of the deep ice microorganisms in collaboration with Academician Mikhail V. Ivanov, Director of the Institute of Microbiology of the Russian Academy of Sciences to search for microorganisms in very deep samples of Vostok ice. Extremely deep ice samples from approximately 100 meters above the surface of the lake (about 400,000 years old) were obtained earlier this year by an international team of US, Russian, and French scientists.

According to Richard Hoover, "These are the deepest samples ever obtained, and the deepest that ever will be obtained until new technology makes it possible to actually penetrate the surface of Lake Vostok without contaminating it." Although scientists are anxious to know what lies within the pristine waters of the lake itself, they are contenting themselves for now with ice from above. "Lake Vostok is an incredibly precious resource," Hoover continued, "and it would be a colossal mistake to take samples before it can be done without contaminating the waters with chemicals or surface microorganisms."

Lake Vostok is clearly a valuable new laboratory for astrobiologists, and they intend to proceed very, very carefully. The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.


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Author: Dr. Tony Phillips & JPL press releases
Curator: Bryan Walls
NASA Official: John M. Horack