- 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
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
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
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 system.
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 Pioneers.
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 gravity."
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 bottle".