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Number 379, June 25, 1998 by Phillip F. Schewe and Ben Stein
NEAREST EXTRA-SOLAR PLANET. The existence of a planet around the star Gliese 876, only 15 light years distant from Earth, was announced this week by planeteer Geoffrey Marcy of San Francisco State University at a meeting in Victoria, British Columbia. The star, whose presence is inferred not from direct observation but by the wobble it imparts to the star, has a mass about 1.6 that of Jupiter. Gliese itself only has a mass of about one third that of our sun, making it the lightest known star to have a planet. The planet circles the star every 61 days at a radius of one-fifth the Earth-Sun distance. The discovery was soon confirmed by other astronomers. (Science News, 27 June 1998.) Still other extra-solar planets (perhaps a half dozen) will be presented by several observing teams at a meeting a week from now in Santa Barbara. (Science NOW, 24 June 1998.)
LIFE EXTINCTIONS BY COSMIC RAY JETS. Several reasons have been put forward to explain past periods of mass extinction on the Earth. An asteroid, for example, is thought to have killed off the dinosaurs in the Cretaceous/Tertiary era 60 million years ago. A new theory by physicists at the Technion in Israel suggests that jets of cosmic rays coming from the collapse of neutron stars or the merger of two such stars could initiate a lethal batch of muons in our atmosphere. They argue that the ensuing ionizing radiation might have affected the biosphere in two ways---by killing many species outright and by causing the sort of mutations that might result in the abrupt appearance of many new species in the aftermath of the of the jet event. Furthermore, the coming of the cosmic rays might be heralded a few days before by the arrival of a gamma ray burst (GRB), presumably from the same energetic source. The mechanism behind GRBs is itself now the subject of intense astronomical scrutiny. Arnon Dar et al., Physical Review Letters, 29 June; Arnon Dar, arnon@physics. technion.ac.il, 011-972-4-829-3529; science journalists can obtain the article from AIP.)
THE MOON WAS THE FIRST OBJECT OF PURE SCIENCE, according to Martin Gutzwiller of IBM (gutzwil@watson.ibm.com). The Babylonians (c1000 BC) recordedthe comings and goings of the Moon arithmetically without understanding the geometry. The Greeks (c200 BC) went further; they viewed the solar system as sitting in an immense vacuum surrounded by the fixed stars. But even the clever Greeks knew nothing about the underlying physics of the solar system. This fell to Newton (1687) in the "Principia," and the 18th century mathematician/physicists such as Laplace. These thinkers proposed the principle of universal gravitation and tried to check it out on the complicated Moon-Earth-Sun system. The study of this oldest of three-body problems is the true subject of Gutzwiller's article in the April 1998 issue of Review of Modern Physics. In many physics problems, the dynamics of two interacting bodies (a planet and a star or two electrical charges, say) is easy. Add a third body and things get complicated, indeed chaotic, which is why Newton and his 18- century followers were largely stumped in their efforts to nail down the Earth-Sun-Moon dynamics. Gutzwiller compares the study of this problem with the history of particle physics: the amassing of cross sections, branching ratios and other particle properties (the kinds of things published in tables) corresponds to the "Babylonian phase," while the advent of the standard model represents the "Greek phase." The third, or Newtonian, age, in which the masses of the quarks and fundamental parameters such as the fine structure constant will be explained, has not yet arrived. (For a study of the 3-body problem with ions, see Update 372)
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