Puzzling
hyper-gravity proves weighty mystery
May
21, 2001 Posted: 2:32 p.m. EDT (1832 GMT)
By Richard Stenger,
CNN
(CNN) -- An unknown force seeming to pull on a pair of distant space
probes has left astronomers with a weighty mystery, one that appears to defy the
conventional laws of physics.
The Pioneer 10 and Pioneer 11 spacecraft,
which for decades have steadily traveled in opposite directions in the solar
system, have covered significantly less space then they should have, astronomers
said.
A team of NASA researchers has systematically attempted to
determine what has slowed the sibling NASA robot ships, to no
avail.
"Something is slowing down the spacecraft. And we have not been
successful in finding the source of that. There is more slowing than you would
expect from Newtonian gravity," said John Anderson, a senior scientist at NASA's
Jet Propulsion Laboratory in Pasadena, California.
Mystery force a real drag
The
probes have traveled far beyond Jupiter since their launch in the early 1970s.
But astronomers have been able to measure with great precision the trajectories
and distances of the pair.
Noticing that Pioneer 10 was unexpectedly
lagging on its journey away from the sun, they speculated that an unknown object
could been exerting an influence.
But they had to revise that theory when
they realized that a mysterious force was acting in an identical manner on
Pioneer 11, which on the other side of the system.
"It's the same
magnitude and the same direction, namely pointed toward the sun. The force
points to the sun in both cases," said Anderson.
Astronomers studied the
Doppler shift of the radio signals to help calculate the distances of the
probes. After extensive analysis, they dismissed instrumentation error,
propellant leaks and minor heat emissions as causes of the negative
thrust.
Perhaps the spacecraft inadvertently produced an unknown force
that is not yet understood, Anderson said. Perhaps scientists will have to
reconsider basic assumptions about the laws of physics.
"No one has come
up with a conventional explanation," he said. One possible reason "is that it is
a modification of gravity."
Pioneer sends shocking
signal
Launched in the early 1970s, the Pioneers were the first
probes to explore the outer solar system, astounding the world when they sent
home flyby images of giant planets like Jupiter, Saturn and their
moons.
The resilient Pioneer 10, now far beyond the orbit of Neptune,
surprised astronomers in April when it managed to send a transmission back to
Earth as directed. Radio communications with Pioneer 11 ceased in
1995.
The scientists were unable to calculate the effects of distant
gravity on other deep space probes, like Voyager I or Voyager 2, because they
employ a different kind of orientation and propulsion system, Anderson
said.
Anderson and his colleagues have submitted their work to the
journal Physical Review D. Their findings are currently available on the
Internet scientific archive site of the Los Alamos National
Laboratory.