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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Strange Force on Spacecraft Deflated
9 October 1998 7:00 pm
The mysteriously aberrant motion of the two Pioneer spacecraft in the distant solar system may not be so mysterious after all. Last month, an apparently inexplicable force prompted NASA scientists to speculate that Einstein's theory of general relativity might need some updating, but a new analysis suggests a more mundane cause: tiny gas leaks from the spacecraft control system.
Four weeks ago, a team led by John Anderson of NASA's Jet Propulsion Laboratory in Pasadena, California, announced that as the spacecraft travel away from the sun, they have been slowing more than gravity alone can explain, as if a mysterious force were pulling on them (ScienceNOW, 9 September). The team tried to rule out all possible causes, leaving the prospect of a flaw in the laws of physics. But according to team member Philip Laing of the Aerospace Corp. in El Segundo, California, they have now noticed that minor variations in the anomalous speed change seem to have occurred as valves opened and closed during routine adjustments of the spacecraft's spin and orientation--suggesting that gas leaks are braking the craft. The team now suspects that other, more constant gas leaks may account for the bulk of the anomaly.
The same process is almost certainly affecting the European Ulysses spacecraft, which also appears to be pulled toward the sun. "Ulysses is leaking all over the place, probably because of sticking valves," says Laing. A few grams of leaking gas per year would be enough to slow the craft.
Jonathan Katz of Washington University in St. Louis, Missouri, has another, equally mundane explanation for the effect: He thinks it may be due to waste heat from the radioactive power source aboard the spacecraft. Heat radiation from the generator would be reflected by the backside of the communications antenna on each Pioneer, giving a tiny push toward the sun, says Katz. But Laing doesn't think this is happening. He notes that the radioactive decay of plutonium--and the heat waste--should decrease over time, while the mystery acceleration remained constant between 1980 and 1988.