Professor James Van Allen

Space scientist who discovered the belts of intense high-energy radiation that surround the Earth

James Alfred Van Allen, physicist: born Mount Pleasant, Iowa 7 September 1914; Research Fellow, then Physicist, Carnegie Institution of Washington 1939-42; Physicist, Applied Physics Laboratory, Johns Hopkins University 1942, Supervisor of High-Altitude Research Group and of Proximity Fuse Unit 1946-50; Professor of Physics, University of Iowa 1951-85, Head of Department 1951-85, Carver Professor of Physics 1972-85, Regent Distinguished Professor 1985-2006; married 1945 Abigail Halsey (two sons, three daughters); died Iowa City, Iowa 9 August 2006.

James Van Allen was one of the true pioneers of the space age. He was a creative experimental space scientist and scientific leader and, possibly, the most famous Iowan ever. Universally known to space scientists as "Van", Van Allen came to the front page of Time magazine and world fame when his experiment flew on the first successful American satellite, Explorer 1, launched on 31 January 1958.

The image of Van Allen with Wernher von Braun and William H. Pickering holding aloft a model of Explorer 1 following its successful launch is iconic and marked for Americans the nation's first space triumph at long last. The greatest triumph came for Van Allen, as he made an immediate major scientific discovery with Explorer 1; that the Earth was surrounded by belts of intense high-energy radiation, known now as the Van Allen belts.

His instrument had been designed to look for cosmic radiation (cosmic rays) originating from the far universe - he found rather that the Earth had its own local store of intense radiation. Initially it was felt that the belts had their ultimate origin in radiation from the cosmos interacting with the atmosphere of Earth. In time, it became clear that the bulk of the charged particles constituting the belts gained their very high energy locally in the region surrounding Earth, now known as the Earth's magnetosphere, an extraordinary finding at the time and one whose implications for what goes on elsewhere in the universe was not fully absorbed by astrophysicists for long afterwards.

Van Allen had luck. His instrument was on the second rostered US satellite launch; the first had failed spectacularly and publicly the previous December. The first detection of the belts was what is called a null detection; the instrument count rate increased in the atmosphere with height, steadily, but then dropped sharply to zero counts in the belts, because the instrument saturated in the (unexpectedly) extreme environment of space near Earth. A second instrument, flown on Explorer 3, launched in May 1958, not only confirmed directly that there was intense radiation at high altitude but also that it was made up of high-energy electrically charged particles, primarily protons and electrons.

It was subsequently realised that a Russian instrument on Sputnik II had already detected the radiation belts in question, but that the spacecraft orbit only rose high enough to do so over the Southern hemisphere, where Australian radio astronomers had recorded the signal but not passed it on, because of the Russians' refusal to share the scientific results. For years afterwards, in Russia, the belts were known as the Vernov belts.

Despite his luck, few would begrudge Van Allen his triumph; indeed Explorer (and Sputnik) were part of the world-wide International Geophysical Year (IGY), an idea conceived in 1950 at a dinner party in Van Allen's suburban Washington home. Even had it not marked the inauguration of space science and exploration, the IGY itself was a great success in bringing Earth scientists together in a massive co- ordinated effort across national boundaries to understand better how our planet worked in a world bitterly divided at the time by the Cold War .

To concentrate alone on the discovery of the belts that bear his name is to severely underestimate Van Allen's scientific acumen and overall contribution. As Head of the Department of Physics and Astronomy at his Alma Mater, the University of Iowa, in Iowa City, from 1951 onwards he had built up a formidable school, using rockets and balloons and a combination of the two, unique to Van Allen, known as "rockoons", well before the space age began.

With the space age, he developed a group that not only investigated the radiation belts of Earth but also pioneered instruments to measure the low-energy charged particles, the plasma, in the Earth's magnetosphere, whose interaction with the extended solar environment not only ultimately gives rise to the belts but also is the source of the aurora and all the rapid changes in the Earth's magnetic field (geomagnetic storms and substorms, etc.)

Van Allen himself was responsible for instruments which first mapped the even more intense radiation belts of Jupiter and Saturn with the Pioneer 10 and 11 spacecraft. Unlike at the Earth, the belts were known in advance to be present at the giant planets, on the basis of measurements of radio waves by radio astronomers. In this area also, the Iowa group led by Van Allen's student Don Gurnett subsequently not only made pioneering measurements of the radio and plasma wave environment of Jupiter, Saturn, Uranus and Neptune, but also showed, against many expectations, that the Earth was a major radio source, the waves emanating from the aurora rendering the Earth the brightest solar system source in the kilometric band, apart from the Sun itself.

James Van Allen bravely defended the need for science to underpin the rationale for robotic space exploration but did not feel that science could be used as the rationale for putting man into space. Most famously, he spoke up loudly against the impact of Nasa's budgetary difficulties in developing manned space (particularly the shuttle) on progress in robotic planetary exploration.

An early victim of the post-Apollo era was the so-called "Grand Tour" mission which had been planned to use a fortuitous alignment (every 179 years) to visit Jupiter, Saturn and Uranus in one mission. Despite the words Grand Tour never being used again, a programme did get resuscitated and the Voyager spacecraft did complete a magnificent voyage to Jupiter, Saturn, Uranus and Neptune between 1977 and 1989, with the Iowa radio and plasma wave instruments making major discoveries.

Although involved in its inception, Van Allen took a back seat on Voyager, but was very much a leader of the development of the subsequent Galileo mission to Jupiter where he was an interdisciplinary scientist. Several of his ex-students made not only Voyager a success but also played major parts in Galileo. Right now, his legacy can be seen in the Cassini Saturn orbiter radio, plasma and energetic charged particle teams.

James Alfred Van Allen was born about 50 miles south of Iowa City, in Mount Pleasant, in 1914. He grew up, the son of a lawyer, in a classic Mid-West pioneering farming community. His education and outstanding performance at Iowa Wesleyan College and then the University of Iowa led him eventually to leave Iowa, first for the Carnegie Institute of Washington, then to Second World War work on proximity fuses which led him directly into the Pacific combat zone (with a naval commission) with a charge to ensure the practical implementation of the developments.

After the war, he joined the new Applied Physics Laboratory of Johns Hopkins University in Maryland and started experimenting using V2 rockets captured from the Germans. The call to return to Iowa came in 1951. There he stayed and, despite official retirement from the university in 1985, retained an office and was regularly on campus until very recently.

He was a very likeable man, as generations of undergraduates and graduate students can attest, not to speak of numerous colleagues world-wide. He was unfailingly courteous and modest; 30 years ago, my wife, failing to catch his name at a social event, could not believe afterwards that she had been talking to such a giant.

Van Allen was awarded many honours - the Crafoord medal awarded by the Swedish Academy in "non-Nobel" disciplines was his in 1989. The US National Medal of Science and the Gold Medal of the Royal Astronomical Society are among numerous other awards and distinctions.

David Southwood