PLANETARY SCIENCE: Making a Splash With a Hint of Mars Water

A wave of chatter about water and therefore possible life on Mars swept a paper at Science into headline news a week before its scheduled publication. The paper, on page 2330 of this issue, features high-resolution pictures of muddy-looking gullies on the sides of martian craters, suggesting the prospect of liquid water on, or at least near, the surface of the planet. But a number of skeptical planetary scientists are already coming up with alternative explanations for the rivulet-ridden piles of debris that exclude stores of liquid water and therefore readily accessible life.     

PLANETARY SCIENCE: Fountains of Youth

The search for geologic features indicative of past or present water is central to Mars exploration programs. As Tanaka explains in his Perspective, such features have tended to be associated with very old (> 1 billion years) regions. However, a study by Malin and Edgett indicates that the youngest geologic features on Mars show signs of fluid discharge and runoff. If the results hold up, then some very unusual event must have occurred in the recent past on Mars.     

PLANETARY SCIENCE: Beating Up on a Young Earth, and Possibly Life

Lunar meteorite analyses reported on page 1754 of this issue reveal a burst of impacts on the moon 3.9 billion years ago and nothing before that; the cosmochemists conclude that the moon and Earth endured a storm of impacts 100 times heavier than anything immediately before or after. Such a lunar cataclysm would have scarred the moon with the great basins that now shape the man in the moon. On Earth, the same bombardment would have intervened in the evolution of life, perhaps forcing it to start all over again.     

PLANETARY SCIENCE: Asteroids Come of Age

Since the discovery of the first asteroid almost 200 years ago, these celestial bodies have advanced from nuisances hampering stellar studies to the focus of geological studies aimed at understanding the early solar system. Binzel describes the history of their study, which has now culminated in NASA's NEAR mission to the asteroid Eros. Four papers report first results from this first rendezvous mission with an asteroid.     

PLANETARY SCIENCE: Enhanced: Salty Old Rocks

Small grains of halite in meteorites are generally interpreted as a sign of the former presence of water. In his Perspective, Ott discusses the unexpected discovery of halites in relatively highly metamorphosed meteorites. According to the age determined by Whitby et al. for halite crystals in one of these meteorites, they are among the oldest known materials in the solar system.     

PLANETARY SCIENCE: 'Spiders' Channel Mars Polar Ice Cap

Scientists studying the latest high-resolution photos of the martian south polar ice cap think they may have found additional clues to its ebb and flow. These hints of the planet's bizarre atmosphere come from a new class of dramatic-looking terrain features whose dark, multilimbed, vaguely radial designs have earned them the moniker "black spiders," and another group of dusky, spreading features called "dark fans." At a recent gathering here of Mars researchers, a planetary scientist proposed that the spiders might be subsurface gas channels, visible through an unusually transparent section of the martian ice.     

PLANETARY SCIENCE: Enhanced: A Meteorite Falls on Ice

Primitive meteorites provide a glimpse into the early history of our solar system, but some of the most primitive meteorites are also rarely found on Earth. In his Perspective, Grossman explains why the fall of the Tagish Lake meteorite on 18 January 2000 in British Columbia, Canada, was a lucky event for meteorite researchers. The first analysis of the meteorite is reported by Brown et al. Well-preserved organic matter in the meteorite provides a unique opportunity to study the nature and origin of organic matter that may have accreted on early Earth and played a role in the origin of life.     

PLANETARY SCIENCE: Imaging Spat Pits Amateur Against Pros

A long-running dispute over who should get credit for first reporting landmarks on Mercury's uncharted hemisphere burst into public view on 26 May, when a Boston University press release claimed honors for a BU team without mentioning the contributions of an erstwhile collaborator, amateur astronomer Ron Dantowitz. The row, which has left both sides bitter and unwilling to work with each other, "was the opposite of how a collaboration between amateurs and professionals should be," says one of the scientists involved.     

PLANETARY SCIENCE: Saturn Wins Satellite Title With New Moons

This week an international team of astronomers announced the discovery of four new moons of Saturn, restoring the ringed planet to its status as commander of the largest retinue of satellites in the solar system. Their appearance should help researchers understand not just how the new moons were formed but also how the giant planets themselves came to be.     

PLANETARY SCIENCE: Most-Common Meteorites Find a Home Among the Asteroids

Meteoriticists have long been puzzled by the fact that the most common meteorites, so-called ordinary chondrites, don't appear to have come from the most common asteroids, the S-types. Last week, however, a group of researchers attending the spring meeting of the American Geophysical Union here announced that the 31-kilometer-long S-type asteroid Eros now being orbited by the NEAR Shoemaker spacecraft is made of the same stuff as ordinary chondrites. That conclusion comes from NEAR Shoemaker's first-ever analysis of the elemental composition of an asteroid.     

PLANETARY SCIENCE: Solar System Scientists Look to Find an Edge

For several years, ever-improving telescope technology has allowed astronomers to peer farther and farther beyond Neptune to discover a rapidly increasing number of bodies littering the outer reaches of the solar system. Now many researchers agree that an end is in sight, although some remain skeptical.     

Life at high temperatures

Water environments with temperatures up to and above boiling are commonly found in association with geothermal activity. At temperatures above 60 degrees C, only bacteria are found. Bacteria with temperature optima over the range 65 degrees to 105 degrees C have been obtained in pure culture and are the object of many research projects. The upper temperature limit for life in liquid water has not yet been defined, but is likely to be somewhere between 110 degrees and 200 degrees C, since amino acids and nucleotides are destroyed at temperatures over 200 degrees C. Because bacteria capable of growth at high temperatures are found in many phylogenetic groups, it is likely that the ability to grow at high temperature had a polyphyletic origin. The macromolecules of these organisms are inherently more stable to heat than those of conventional organisms, but only small changes in sequence can lead to increases in thermostability. Because of their unique properties, thermophilic organisms and their enzymes have many potential biotechnological uses, and extensive research on industrial applications is under way.     

MATERIALS SCIENCE: Weird Gold Nanowires

When the dimensions of matter are reduced to the nanometer scale and beyond, strange properties often emerge. In their Perspective, Tosatti and Prestipino discuss the weird gold nanowire structures reported by Kondo and Takayanagi. They explain why the wires may be helical and only form certain "magic" sizes. Other metals may form similarly strange structures with unusual properties.     

MATERIALS SCIENCE: Deformations in Extreme Matter

Most materials become narrower in cross section when stretched, but some materials, such as foams, have the counterintuitive property of becoming fatter when stretched (they have a negative Poisson's ratio). In this Perspective, Lakes discusses how his unusual property may arise in isotropic and anisotropic materials. He highlights the study by Baughman et al., who show that anisotropic materials with a negative Poisson's ratio in one direction can be incompressible, i.e., without an overall change in volume upon stretching. This behavior is predicted for materials with very high density, such as neutron star crusts, or very low density, such as ion plasmas, and the validity of the prediction is demonstrated with experimental data for ion plasmas.     

SCIENCE PRIORITIES: An Opportunities-Based Science Budget

Newt Gingrich introduces the concept of an "opportunities-based budget", as an approach to federal research and development funding. Policy-makers should not frame the debate on science funding in terms of percentage of increase. Rather, a systematic analysis of the promise of opportunities should be conducted and the funds allotted accordingly. This article is a call to rethink how lawmakers are funding the discoveries upon which future generations will rely.     

HISTORY OF SCIENCE: Science and Sputnik

Sputnik led to an energetic U.S. space program and new discoveries about the cosmos.     

ESSAYS ON SCIENCE AND SOCIETY: Taking Responsibility

Joseph Rotblat was born in Warsaw in 1908. He trained in nuclear physics and later specialized in radiation biology. He was awarded the Nobel Peace Prize in 1995, with the Pugwash Conferences on Science and World Affairs, "for their efforts to diminish the part played by nuclear arms in international politics and in the longer run to eliminate such arms." In this essay, he reflects on his experiences and recounts how he has applied his ethical principles to his work as a scientist and educator in Poland, the United Kingdom, and the world. He urges other scientists to apply ethical considerations for the survival of humankind above all others.