Last year, when Michel Mayor and Didier Queloz of the Geneva Observatory reported the first

solid evidence of a planet circling a sun-like star outside the solar system, manyastrophysicists were taken aback. Theseobservations showed what could be a

Jupiter-size planet orbiting quite close tothe star 51 Pegasi; it was about sevenmillion kilometers away—only a smallfraction of the distance between the sunand Mercury. Yet existing theories forthe development of planetary systemsindicated that such giant planets shouldform at much greater distances from astar. What was a big planet doing soclose in?

Some initially believed that the oldtheories were fine and that 51 Pegasiwas simply the exception that provesthe rule. After all, the technique thatMayor and Queloz had used was mostsensitive to large planets in tight orbits.

But further discoveries over the past yearhave uncovered nine other “extrasolar”planets, and three of these bodies, inaddition to the one around 51 Pegasi,are rapidly circling at a celestial hair’sbreadth from their stars. Astronomersnow surmise that such “hot Jupiters”might, in fact, be commonplace.

“I don’t think any of us were preparedto see these three-day- or four-day-periodJupiters,” says George D. Gatewood,director of the University of Pittsburgh’sAllegheny Observatory, referring to theshort times needed for such planets tocomplete their diminutive orbits. Indeed,just seven months before the discovery

News and Analysis20 Scientific American November 1996

F I E L D N O T E S

Bring Me a Shrubbery

Iam on an experimental farm near Syracuse in upstate NewYork, standing next to dense thickets of a tall woody shrub

that is bereft of any edible fruit and would certainly lose in anarboreal beauty contest. The shrub, a hybrid willow, sends outa vigorous green spray of whiplike stems that climb as high as11 feet in a single year. Although the double rows of identicalplants are five feet apart, the stands are impenetrable: theprofusion of wood and leaves is literally arresting. The willowwould seem an unlikely crop, but if Edwin H. White of theState University of New York’s College of Environmental Sci-ence and Forestry has his way, it could become common in

much of the northern U.S. By 2010, farmers may be growing50,000 acres of the stuff in New York alone.

Shrubbery would not normally warrant an intensive re-search effort, but to White and local power companies—andnow the Department of Energy—the prodigious growth rateof these hybrid willows makes them a potential source ofclean-burning fuel. They produce five to 10 times more woodevery year than any natural forest. A 50,000-acre crop wouldbe worth $20 million.

White, who is dean of research, has spent the past 10 yearsinvestigating how to cultivate the plant. He is convinced that

the U.S. and other countries should make more use of woodfor energy. Burning farmed wood in power stations reducesreliance on foreign oil and curtails emissions of carbon diox-ide (although trees produce the gas when they are burned,they take it out of the atmosphere while growing).

Hybrid willow shrubs—which look nothing like the familiartree—appear to be the most promising biomass fuel for theU.S., White says. Once established they are extremely hardy,tolerating marginal land with only irrigation and some addednitrogen. The basic cultivation scheme was developed inSweden; 50,000 acres are now grown in Europe. The shoots,which readily grow from sticks, are cut back at one year, andthe wood is harvested every three years thereafter for about20 years. Researchers are studying a patchwork of varieties.

Burning wood is, of course, hardly a new idea, but its highcost means that very little is used in the U.S. New York StateElectric and Gas Corporation (NYSEG) is one of a small num-ber of power companies nationwide that have investigatedusing waste wood, chipped into two-inch lumps, for burningalong with coal. Michael Tesla of NYSEG says he aims eventu-ally to burn willow in 1/4-inch flakes.

Although willow will cost hardly less than coal for the sameamount of energy when equipment costs are figured in, pow-er companies see it as a valuable way of cutting about 10 per-cent from their sulfur emissions, which are limited by tradablepermits, as well as emissions of nitrogen oxides, which maybe limited in the future. The companies also recognize its po-tential as a hedge against the possibility that carbon dioxideemissions from fossil fuels might someday be taxed.

The federal government is offering willow a jump start. TheDOE and the U.S. Department of Agriculture earlier this yearsigned an agreement with a consortium of New York powercompanies, agencies and academic institutions to establish2,600 acres of willow as a demonstration project. The energydepartment will provide 36 percent of the estimated $14-mil-lion cost. Although in New York the project will initially focuson burning wood directly, in other states it will eventually in-clude burning gas produced by heating the wood. Whitenotes that there are 200 million acres of abandoned farmlandin the U.S. I don’t need to ask what he would like to see grow-ing on them 20 years from now. —Tim Beardsley

SCIENCE AND THE CITIZEN

HOT JUPITERS

Why do some giant planets hug their stars?

ASTRONOMY

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Copyright 1996 Scientific American, Inc.