New science : Mysterious force holds back Nasa probe


Richard Moore


Mysterious force holds back Nasa probe in deep space 
By Robert Matthews, Science Correspondent 
(Filed: 10/02/2002) 

A SPACE probe launched 30 years ago has come under the
influence of a force that has baffled scientists and could
rewrite the laws of physics.

Researchers say Pioneer 10, which took the first close-up
pictures of Jupiter before leaving our solar system in
1983, is being pulled back to the sun by an unknown force.
The effect shows no sign of getting weaker as the
spacecraft travels deeper into space, and scientists are
considering the possibility that the probe has revealed a
new force of nature.

Dr Philip Laing, a member of the research team tracking
the craft, said: "We have examined every mechanism and
theory we can think of and so far nothing works.

"If the effect is real, it will have a big impact on
cosmology and spacecraft navigation," said Dr Laing, of
the Aerospace Corporation of California.

Pioneer 10 was launched by Nasa on March 2 1972, and with
Pioneer 11, its twin, revolutionised astronomy with
detailed images of Jupiter and Saturn. In June 1983,
Pioneer 10 passed Pluto, the most distant planet in our
solar system.

Both probes are now travelling at 27,000mph towards stars
that they will encounter several million years from now.
Scientists are continuing to monitor signals from Pioneer
10, which is more than seven billion miles from Earth.

Research to be published shortly in The Physical Review, a
leading physics journal, will show that the speed of the
two probes is being changed by about 6 mph per century - a
barely-perceptible effect about 10 billion times weaker
than gravity.

Scientists initially suspected that gas escaping from tiny
rocket motors aboard the probes, or heat leaking from
their nuclear power plants might be responsible. Both have
now been ruled out. The team says no current theories
explain why the force stays constant: all the most
plausible forces, from gravity to the effect of solar
radiation, decrease rapidly with distance.

The bizarre behaviour has also eliminated the possibility
that the two probes are being affected by the
gravitational pull of unknown planets beyond the solar

Assertions by some scientists that the force is due to a
quirk in the Pioneer probes have also been discounted by
the discovery that the effect seems to be affecting
Galileo and Ulysses, two other space probes still in the
solar system. Data from these two probes suggests the
force is of the same strength as that found for the

Dr Duncan Steel, a space scientist at Salford University,
says even such a weak force could have huge effects on a
cosmic scale. "It might alter the number of comets that
come towards us over millions of years, which would have
consequences for life on Earth. It also raises the
question of whether we know enough about the law of

Until 1988, Pioneer 10 was the most remote object made by
man - a distinction now held by Voyager 1. Should Pioneer
10 make contact with alien life, it carries a gold-plated
aluminium plaque on which the figures of a man and woman
are shown to scale, along with a map showing its origin
that Nasa calls "the cosmic equivalent of a message in a


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