* Astronomy

Pioneer 10 and 11 were two of NASA’s most successful space missions of the 1970s. Launched in 1972, Pioneer 10 was the first spacecraft to travel through the Asteroid belt and the first to obtain close-up images of Jupiter.
Pioneer 11 was launched in 1974 and went on to make the first direct observations of Saturn in 1979. But there was something else that made them special: each carried a golden plaque with a message from mankind to alien civilisations.


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The plaques, for instance, depict our solar system and the path followed by the spacecrafts. The trajectory shows their way past Jupiter and out of the solar system. However unrealistic the aim of contacting aliens may be, there is no doubt of the symbolism. The Pioneers were the product of a generation of astronomers eager to communicate with the cosmos. It now seems that the cosmos has responded in a surprising way.
In 1980, John Anderson, one of the leaders of the Pioneer team at the Jet Propulsion Laboratory (JPL) in California, noticed something unexpected. Astronomers should have been able to exactly predict the trajectory of their spacecrafts by using the standard Newtonian-Einsteinian laws of gravity. But Anderson’s calculations were all wrong. The spacecrafts were not where they were supposed to be. It was as if they were being slowed down by an unknown, mysterious force.
Anderson was later joined in his efforts by Michael Martin Nieto, from the Los Alamos National Laboratory and Slava Turyshev, a colleague at JPL. Turyshev was one of the first Soviet scientists to work in the United States after the Cold War. When he first heard of the Pioneer anomaly, he volunteered to work on the project for free.
Convinced that there was an error in the way astronomers were calculating the trajectories, Turyshev studied more than 60 possible effects that could cause an abnormal reaction in the spacecraft. Every conceivable cause was taken into account, from gas leaks to the effect that ocean waves, hitting the shores in the Mojave Desert, had on the radio instruments receiving Pioneer’s transmissions. After more than a decade of careful analysis, they realised that these effects were not even close to explaining the Pioneer anomaly.
The mystery then got even more interesting when similar effects were reported on two other spacecrafts, Ulysses and Galileo. How can we explain the same anomaly occurring simultaneously in four different spacecrafts? The scientific community was now paying attention.
Today, an increasing number of people believe that the Pioneer anomaly could actually be a discovery, a very big one. The call for new laws of gravity is getting stronger.
In fact, a solution may have already been proposed a long time ago. It dates back to 1983, when Mordehai Milgrom, a physicist at the Weizmann Institute in Israel, first considered a modification to the standard laws of gravity.
Back then, one of biggest riddles in physics was related to the motion of galaxies. Galaxies were observed to be rotating in a way that physicists could not understand. Milgrom, using a different law of gravity, was able to successfully predict such behaviour.
Nonetheless, his attempt was considered heresy against one of the most well-established physical theories. The Universal Law of Gravity was first formulated by Isaac Newton and had managed to describe how the planets moved with one single equation. But in the 17th century, Newton knew nothing about galaxies. Stacy McGaugh, a physics professor at the University of Maryland, suggests that Newton would probably be the first to propose a different law if he knew the facts about the galaxies as well.
Milgrom’s theory on galaxies did not predict the Pioneer anomaly, but an increasing number of people feel that it may well do so. There are already several proposals for more complete versions of modified gravity in which the anomaly is accounted for. There is still a long way to go, though, both in developing the theory and getting attention.
“I’m still shocked by how so few of us have heard about this theory, let alone know anything serious about it.” - Stacy McGaugh.
In the meantime, at the Jet Propulsion Laboratory, Turyshev and his colleagues have initiated the development of a dedicated mission to study the Pioneer effect and understand the source of the anomaly. Whether it is a gas leak or modified gravity, Turyshev feels obligated to go to the bottom of this. “What if this is something that nature is telling us?” he asks, “We must be careful and patient to listen and understand what we are being told”.
Sadly, the main characters of this story will not be around for its conclusion. NASA has received its last, very weak, signal from Pioneer 10 in 2003, and Pioneer 11 sent its last signal in 1995. The spacecrafts are probably plodding their way into deep space, in a way no-one yet understands.

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-- Edited by Blobrana at 18:05, 2005-05-20