Europa Diary II
Life on Ice
|Jupiter's moon Europa.Credit: NASA
The Europa Focus Group is a collaboration of scientists who study Jupiter's moon, Europa. This ice-covered world may be one of the few places in our solar system other than Earth that has a water ocean, and liquid water is believed to be one of the key factors in the development of life. Astrobiologists and other scientists eager to learn more about Europa recently headed to Alaska's North Slope.
The scientists studied the region's unique terrain, providing insight for future missions to the icy landscape of Europa. Flying in small aircraft to study geographical features, driving snowmobiles over glacial terrain, digging bore holes to get a glimpse of ice history -- all the activities pursued by these hardy adventurers may someday be duplicated on the surface of Europa by robotic spacecraft.
Matt Pruis , a support scientist with NorthWest Research Associates in Seattle, Washington, attended the North Slope conference and kept a journal of the events.
Thursday, 24 April 2003
This morning I arose to the continual twilight of the Arctic north. Although the sky had dimmed during the night, it never really got what I would call dark. After a breakfast fit for a polar explorer at the cafeteria, I headed for our first meeting. I grabbed an extra cup of coffee on the way, hoping to counteract the excess quantity of food I'd just consumed.
We gathered this morning to discuss research conducted since our last workshop. One of the goals of the Europa Focus Group is to share new information among all the scientists, engineers and mission planners. Either because the Starbucks coffee I was drinking was having sufficient effect or, more likely, because of my fascination with the discussed topics, I was captivated by the presentations. The talks covered the gamut of developing technologies, on-going research and future mission planning -- all with an emphasis on understanding the astrobiological potential of icy worlds.
|Inspecting the core from an ice-drilling experiment, Alaska's North Slope. Credit: M. Pruis
Current plans call for a mission launch to Jupiter's ice-covered moons Callisto , Ganymede and Europa in the year 2011. Paul Holland led a discussion about new technologies we can use to collect and process subsurface samples. By determining the elemental chemistry and volatile content of fluids and ice, we could gather clues about the potential for life.
For instance, NASA's Jet Propulsion Laboratory is developing a "cryobot" vehicle that could drill through the icy shell of Europa and sample the ice along its descent. This would allow scientists to examine the evolution of Europan volcanic activity since the formation of its icy surface. Volcanoes beneath Europa's proposed ocean could provide both a birthplace and a heated abode for life. The cryobot also would be able to detect if there are any nutrients available for microbes.
With the tone set by the presentations, we geared up for an afternoon excursion to near-shore ice. Although there was only a gentle breeze, the temperature was in the low teens -- cold enough to test our heavy parkas and boots. We had more people than snowmobiles, so we used a loose rope tether to attach sleds to the machines. Each snowmobile carried one passenger, while two people rode behind, standing up in the dog sleds.
It was not long before we had arrived at a site worthy of study. Hajo Eicken led a demonstration on ice coring. A sea ice drill is, in essence, a chain saw engine that has been adapted to drive a rotary shaft instead of a blade. The drill drives a 4-inch diameter core barrel that has a metal-tipped PVC corkscrew glued to its outer edge. This pseudo-drill bit both drills the ice and removes excess ice fragments from the core barrel. Two people are needed to keep the drill vertical, and they can get a 1-meter-long ice core sample in only two or three minutes.
Examination of our sample core showed that it was full of small channels. These channels allow brine (salty water) to escape from the ice. Normal seawater is composed of about 35 parts per thousand of salt, but when sea ice first forms it is only about 16 parts per thousand. That means a lot of salt is rejected into the seawater during ice formation. For every cubic meter of ice formed, roughly 20 kilograms (44 pounds) of salt are essentially poured into the upper ocean!
|Sectioned ice core held in its drill bit, Alaska's North Slope. Credit: M. Pruis
So as 1.5-meter-thick ice forms over the Arctic Basin each year, 300 billion tons of salt pours into the upper Arctic Ocean and significantly affects the ocean's density. Even salt that is initially trapped within newly formed sea ice eventually drains out of the channels that we could see in our ice core. After a couple of summers, the salt content of the ice is only around 1 or 2 parts per thousand.
I was in for a surprise when we looked at the bottom of the ice core sample. I grew up in Michigan and spent my winters boring fishing holes into Lake Huron, so I was familiar with freshwater ice. But unlike that ice, the bottom surface of sea ice is not smooth. It has a very rough surface and is distinctly greenish-brown in color. The color is caused by a large increase in biological material --mostly algae such as diatoms .
The color also comes from dissolved organic material that supports the growth of bacteria. There is a surprisingly high diversity of viruses and fungi as well. Crustaceans feed on the several hundred different species of algae that live in this bottom-most layer of ice, and fish feed on the crustaceans. It's a complex food web. Yet standing here on the icy surface, you'd never know this ecosystem was there. You have to penetrate down through the ice to have any chance of discovering it.
The Arctic ice provides us with important lessons for when we start looking for life on Europa. For instance, the concentration of cell biology in the bottom of the Arctic ice is 10 to 100 times that of the seawater only a few centimeters away. Such information could be useful in designing future missions to sample Europa's ice. It would be tragic to send a probe all the way to Europa and not find any evidence of life, when life is just a centimeter away!
After analyzing some local ice structures, we drove back to prepare for an evening flight over the pack ice. Everyone in the group decided to skip dinner. The flight was going to involve steep banking and tight turns to give the best views of the ice, and nobody wanted to do it on a full stomach.
We had to split our group between two airplanes, but the pilots from Cape Smythe Air flew in formation so that everyone would see the same ice features. I was in the second ( "chase") airplane and wore a headset to communicate with the pilots. The flight reminded me of scenes from "Top Gun" as we continually dove and weaved to keep in visual contact with the lead plane. Several people had to their airsickness bags.
When I was able to pull my eyes away from the dance of the airplanes, I realized there was incredible complexity in the pack ice below. Ice floes ranging from 20 to several 100 meters in size appeared to be constantly bumping into one another. Ice ridges had formed and collapsed, leaving behind vast fields of "brash" ice. Young " nilas" less than 10 centimeters thick formed interesting structures, where regions had interwoven and rafted upon one another.
|View of expansive floating continent of ice sheets, from plane's cockpit, Alaska's North Slope. Credit: M. Pruis
All the ice we saw had formed during this past winter. The summer of 2002 was unusually warm, and by the end of the summer there was less ice covering the region than since they began collecting satellite imagery of the Arctic about 25 years ago. We could see that there wasn't any older ice located within 50 kilometers of the coastline.
After our bird's eye view of the Earth's sea ice cover, I have a gnawing fear that deciphering the dynamics of Europa's icy shell will be an extraordinary challenge. The structures we saw today were the sum of a complex history of repeated cycles of ice deformation and growth. Using only a snapshot image, it would not be possible to unravel the entire ice history of a planet.
Perhaps our hope for Europa lies in our ability to recognize the most important processes, without over-emphasizing insignificant features that are unique, unusual or eye-catching. Geologists in the past misinterpreted the history of our planet and the importance of different processes, simply because they tended to pick up the most interesting and unusual rocks, ignoring the boring rocks that were everywhere in the field.
Yet in times of doubt, I take great comfort from these scientists and philosophers of earlier ages. They, too, faced challenges of the unknown. Despite frequent mistakes, they were confident that someday these challenges would be overcome:
"There shall come a time when the bands of ocean
shall be loosened, and the vast earth
shall be laid open; another Tiphys shall
disclose new worlds, and Thule shall no longer
be the extreme point among the lands."
- Seneca, from his play Medea "
Support for the conference was provided by the NASA Astrobiology Institute. Dr. Ronald Greeley (Arizona State University) organized the meeting; Dr. Hajo Eicken (University of Alaska) organized and led the field excursions. The Ukpeagvik Inupiat Corporation allowed the use of their meeting facilities and provided access to key field areas.
Matthew Pruis is a third-year graduate student in Marine Geology and Geophysics at the University of Washington's School of Oceanography. He received his Bachelor of Science in Applied Geophysics from the Michigan Technological University. His graduate advisor is H. Paul Johnson . In addition to his graduate work, Matt also works at NorthWest Research Associates, Inc. as a research scientist. In this multi-part Europa Diary series, Matt Pruis chronicled his impressions for the Astrobiology Magazine, as part of his participation in the Europa Focus Group's recent journey to Alaska's North Slope.
Related Web Pages
Europa Diary I: Landing on Alien Terrain
Europa Diary II: Life on Ice
Europa Diary III: On Polar Bear Time
Europa Diary IV: Walking on Thin Ice
Alaska Europan Photo Gallery (Credit: Matt Pruis/ Jere Lipps )
Ice on Europa
Iñupiat native people
Barrow Arctic Science Consortium
Ukpeagvik Inupiat Corporation
Interpreting Europa's Features
Infrared Spectroscopy: An Overview
Galileo Project Home