the aurora, and their actual role in the auroral process is ... task for him and his co-workers, but their efforts were ... guide me throughout the rest of my life.".
Eos, Vol. 84, No. 1, 7 January 2003 rays, Block used a magnetized plasma flow representing the solar wind. He also built a firm theoretical basis for the experiments by analyzing the laws of scaling phenomena from the cosmos to the laboratory He showed that although complete scaling of the actual magnetospheric configuration to the laborato ry is technically out of reach because of the large scaling factor, important aspects of mag netospheric processes can be properly scaled by using a scaling adjusted to the process concerned.This quantitative approach became the model for a new generation of terrella and lunella experiments. Together with his student Ulf Fahleson, Block conducted experiments on the interaction between plasma and neutral gas in relative motion. Using a rotating-plasma device built for thermonuclear studies, they found that as the relative velocity reached a certain value, the relative motion suddenly ceased and the neutral gas was ionized.This was the first experimental verification of Alfven's hypothesis of the Critical Ionization Velocity, which was an essential element in his theory of how planets formed around the Sun, and moons around some planets.The phenomenon was later verified in a number of experimental configurations and has been invoked by various authors to explain the interaction between the solar wind and gas clouds released from the Moon, and the formation of an ionosphere on Io. It has also been demonstrated in active space experiments in the Earth's ionosphere. Block did pioneering work on the electric double layer phenomenon.This phenomenon was well known from old gas discharge exper iments. Although not well understood theoret ically, the phenomenon was very real and constituted a source of serious technical problems by causing current disruptions in
the industrial mercury rectifiers of that time. Block showed that the same phenomenon could also be an important feature of the auroral process.This was received with con siderable skepticism, but recent in situ meas urements above the aurora have shown that electric double layers do indeed occur above the aurora, and their actual role in the auroral process is subject to considerable interest in the space physics community. In the first Swedish satellite project,Viking, Block was principal investigator for the instru ment that measured electric fields in the plasma above the aurora.This was a very demanding task for him and his co-workers, but their efforts were rewarded by considerable inter national acclaim when the results arrived. Block's scientific expertise was welcomed in various committees nationally as well as in the European Space Organization and the United Nations. While at the Royal Institute, Block spent time in the United States. In the 1960s, he worked with plasmoid experiments at Stevens Institute of Technology in Hoboken, New Jersey and with magnetospheric physics at the Jet Propulsion Laboratory in Pasadena, California. From the 1970s through the 1990s, he cooperated closely with the Air Force Geophysics Laboratory (AFGRL), Hanscom Field, Massachusetts, working on magnetospheric plasma dynamics and their coupling to the auroral current circuit. As part of this collaboration, he spent several short periods of time at AFGRL and the Phillips Laboratory Although his guest scientist visits were limited to the United States, he had welldeveloped scientific contacts with colleagues in Europe, Japan, and Australia, and he was a frequent and welcome participant in interna tional conferences.
In Brief
that this ice seal distinguishes Lake Vida from other lakes that receive meltwater below a floating ice cover and that annually exchange gases with the atmosphere. Using ground-penetrating radar, ice core analysis, and other tools, the researchers determined that the lake water was seven times saltier than sea water and remained in a liquid state at temperatures below -10°C. In addition, they detected organic material and sediment below the ice, and from ice cores, were able to revive microbes determined to be at least 2,800 years old. Said John Priscu of the Land Resources and Environmental Sciences Division of Montana State University/The ice covers of these lakes
PAGE 2 Previously unknown lake system found in Antarctica There may be nothing new under the Sun. But under the deep ice in the McMurdo Dry Valleys of Antarctica, geophysical scientists believe they may have uncovered a previously unknown lacustrine ecosystem, which they have named Lake Vida. Beneath 19 meters of ice—the thickest non-glacial lake ice cover on Earth— researchers, including Peter Doran of the Uni versity of Illinois at Chicago, have reported finding an "ice-sealed" lake. They concluded
Block and I met for the first time in 1956, during my final undergraduate year, when he was my advisor. His commitment and helpful ness was of great value to me. Although he was not my formal thesis advisor, Block was an important discussion partner, and he fos tered my development as a scientist. As colleagues for more than 40 years, we had a very fruitful collaboration and developed a profound friendship. In addition to his scientific merits, Block had a very pleasant personality and contributed much to the good personal relations that have been, and still are, characteristic of the Alfven Laboratory, and which has meant so much to all who have worked there. Block's personality was well characterized in a letter of condolence from one of his many international friends: "Lars Block was a brilliant scientist as well as a humble and deeply religious person. His strong sense of ethics and his generosity were characteristic of how he worked with and mentored others. He had a piercing physical insight that would often enable us to obtain solutions to very difficult space plasma prob lems. I will miss his dry humor. His spirit will guide me throughout the rest of my life." Block's many friends are left with a feeling of great loss, but also deep gratitude for what he meant as a scientist and as a friend.
Author Carl-Gunne Fdlthammar Division of Plasma Physics, Alfven Laboratory, Royal Institute of Technology Stockholm, Sweden represent an oasis for life in an environment previously thought to be inhospitable." Doran said,"Lake Vida provides insight into a novel terrestrial ecosystem. What happened at Lake Vida may have been the fate of other Antarctic lakes, during even colder times, and more tropical aquatic ecosystems during extreme global glaciations of the past." The research,funded by the U.S.National Sci ence Foundation and NASA, is published in the 7 January issue of the Proceedings of the National Academy of Sciences.
Randy Showstack,
Staff Writer
