Posted on 02/09/2002 6:34:49 PM PST by blam
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 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".
So, why isn't the red shift of all stars the same? (If they aren't at different distances.)
The acceleration due to gravity of a small mass toward a large mass can be calculated, and is 32.17405 ft/sec-sec at sea level (average) on Earth. The small body moves toward the large body and the large body hardly moves at all (when a rock falls down, the earth would fall up toward it if the rock was large enough).
As stated before, my view is that the value of G is not known with sufficient accuracy and errors of 6 mph out of 10 billion are bound to happen.
Awwww, there ya go with the gratuitous "Uranus" allusion again.
Is there some sort of prize for the poster who uses "Uranus" more times than anyone else on an astronomy thread?
That's the equation for the FORCE, not the acceleration.
The acceleration due to gravity acting on an object is constant, regardless of its mass. That's what Galileo was trying to find out when he dropped objects of differing masses off the balcony of the Tower of Pisa; they all fell at the same rate.
The mass of the spacecraft is irrelevant to how much acceleration it experiences due to gravity; it is very much relevant to how much FORCE is produced as a consequence of it.
Well, actually, no. I searched and since no one else had decided to field this one, I thought I would. It has to do with the notion of escape velocity. If you "throw" a ball or a rock hard enough it will travel far enough away from the earth that the pull of the earth's graviational field will fall off faster than the rock (whatever) loses velocity. The escape velocity from the surface of the earth is about 11.2 km/sec. Even if you attained this velocity it would not allow you to escape from the sun's attraction. At the radius of the earth's orbit, the escape velocity from the sun is more than 42 km/sec. But you could lauch to the east at midnight and let the earth's orbital and rotational motion give you a 30 km/sec head start.
Nor is the mass of the sun. However, the graviational constant of the sun is very well know, since it determines the sidereal period of planetary orbits. We have a baseline of observations stretching back over two thousand years based on well documented planetary occulations of distant stars, which tell us precisely when a planet was where.
True, that is the equation for the force the two bodies exert on each other. However the equation for the accelleration, say of the smaller mass, is
A = F/M (from F=M*A) So let M==M2 the much smaller mass.
Substituting we get
A = F/M2 = ( (G*M1*M2) / (R*R) ) / M2 = (G*M1)/(R*R)
with M2 canceling. Ergo it doesn't matter for the accelleration. However G is just as important as before. And it may indeed be known to the proper precision. I have my doubts about M1, the mass of the solar system, being known with sufficient precision.
FYI that would be (G * M1) in the equation above. Of course it's not just the mass of the Sun that counts, but the mass of everything else in the solar system too. However since the mass of all the rest is small compared to the mass of the sun, it need not bee known to the same precision as the total effective mass , and I suspect the net (G*M) is known to the required precision, in fact I'd bet on it, else there would not be all this who-hah. The astronomers understand those equations much better than most of us, I say most, because I suspect some of us are astronomers or astrophysicts, orbit mechanics specialists and so forth. (but not me, I do airplanes and such)
Since the craft is ten billion miles away from our Sol (I think that was the number - is that 11 light years?), it is outside the solar system. So we need the mass and distance from the stars in the neighborhood. If it is accelerating then it may be attracted to something ahead of it or to the side. Or its path may be curving if it is out of the plane of the galaxy. Seems to me that this error is really pretty small...
Why don't we just send that Pioneer some Viagra and then its bound to make its way back to Earth?
The staircase would eventually meet the last, topmost tread where, in order to maintain the same integral volume, the classical pull would be slightly greater than the quantum pull. This quantum limit effect would isolate the effect of gravity to a finite region surrounded by the last tread.
The concept could also explain the acceleration of expansion in the universe, for as various gravitational subsystems, such as solar systems and galaxies, converge within gradually smaller regions, the size of the topmost tread regions becomes greater. In this way, the effect of gravity is increased within the gravitational subsystems, and it is decreased outside of them.
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