trophysical Journal, Sorokin and Glownia propose that DIBs can be explained by a Case for life on Mars strengthens combination of efficient light scattering Only a few months after U.S. scientists tion you cannot get by an inorganic pro(similar to the process that makes the sky announced possible evidence of micro- cess,'' Wright tells C&EN. appear blue) and complex nonlinear optiscopic life on Mars, British scientists reIn EETA79001, the scientists found cal interactions related to those that make port that they, too, have found evidence "nonspecific organics" that match those lasers possible. Out of about 130 known suggesting the Red Planet may have har- occurring in ALH84001. The group now sharp DIBs, they so far have been able to bored life—possibly as recently as half a plans to look for evidence of methaneprecisely assign more than 70 to specific million years ago. producing bacteria in EETA79001. molecular transitions of H2 using their theAt a Royal Society meeting in London Some scientists express skepticism oretical model. at the end of October, astronomers Ian about the British findings. OceanograSorokin and Glownia believe DIBs origWright and Colin T. Pillinger of the Open pher Jeffrey L. Bada and colleagues at inate in cold, thin hydrogen clouds within University, Milton Keynes, England, and Scripps Institution of Oceanography, Monica Grady of the Natural History Mu- La Jolla, Calif., found amino acids in 30 light-years of very bright stars along a seum, London, discussed their studies of EETA79001 that are similar to those in the line of sight to Earth. These clouds are two martian meteorites. Antarctic ice where the meteorite was deflooded with scattered vacuum ultraviolet The first one, ALH84001, is the same posited [Geochim Cosmochim Acta, 59, (VUV) light from the star. This light is so 3.6 billion-year-old meteorite believed 1179 (1995)]. This similarity, Bada says, is intense that it triggers a nonlinear optical by a team of National Aeronautics & "strong evidence" for contamination. process called two-photon absorption, in Space Administration and Stanford Uni- Water flowing through the meteorite which a hydrogen molecule simultaneousversity scientists to contain evidence for could explain the carbon isotope ratios ly absorbs a photon of a specific wavelife on Mars (C&EN, Aug. 12, page 6). the British group found, he says. length of VUV light and a photon of a speThe second meteorite, EETA79001, is Wright counters that such a water cific color of starlight. When the star's much younger, only about 175 million flow "would have left its mark in other light is observed from Earth, the absorbed years old. It is believed to have been ways." Minerals would have become hyejected from Mars about 600,000 years drated, he says, and the oxygen isotopic visible wavelengths show up as DIBs. ago. ratio would have changed. Their theory—which has been reIn ALH84001, the British scientists Both scientists agree the meteorite worked several times in the past three found isotopic ratios of carbon that are studies will continue to generate debate years—has been received skeptically in indicative of methane-producing bacte- and invite much more scrutiny. the astrophysics community, says Wim ria. "In effect, it's an isotopic composiElizabeth Wilson Ubachs, a lecturer in physics at the Free University, Amsterdam. The IBM scientists are outsiders in that community, he notes, and the concepts of nonlinear optics they use are probably not familiar to most astronomers. Two laser physicists doing blue-sky reUbachs, a laser physisearch at IBM may have solved a mystery cist, finds the new theothat has puzzled astronomers for 75 ry stimulating. But its vayears. lidity is "not definite," The mystery centers on the origin of h e tells C&EN, and the so-called diffuse interstellar bands some DIBs appear to be (DIBs), a complex pattern of some 200 visdue to other molecules. ible absorption bands of varying widths Aware that previous observed in the spectrum of many bright DIBs explanations have stars. In the 1930s, scientists showed these not been well supported bands were due to light absorption by by experimental data, Sosome interstellar material. rokin and Glownia have Many candidates have been proposed suggested specific experfor the light-absorbing material, including iments to test the validity polycyclic aromatic hydrocarbons, fuller- IBM's Sorokin (left) and Glownia propose explanation for of their ideas. They say enes, porphyrins, carbon-chain molecules, the origin of the mysterious diffuse interstellar bands early results from the solid oxygen, and even alien bacteria. But (DIBs) spectrum (in background). first series of tests (from no candidate accounts for more than a Ubachs' lab) seem to be consistent with smattering of the DIBs. abundant molecule in the universe, it was Now, Peter P. Sorokin and James H. not suspected because "the DIBs pattern their predictions. Glownia of IBM Research Division's T. J. doesn't match the well-known absorption The duo's DIBs work was partially Watson Research Center in Yorktown spectrum for hydrogen at all," the re- supported by the U.S. Army Research OfHeights, N.Y., believe they have assem- searchers explain. But astronomers have fice. IBM spokesman Michael Ross notes bled the strongest case yet for a photon assumed the mystery interstellar material that this is the kind of "pure" research filcher that previously seemed to have an absorbs the missing starlight by the simple that was more common at IBM in the process of linear absorption. ironclad alibi: molecular hydrogen. past than it is now. Even though H 2 is by far the most In a paper to appear in the Dec. 20 AsRon Dagani
Hydrogen proposed as solution to stellar puzzle
NOVEMBER 11, 1996 C&EN
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