Einstein Wrong About Gravity?

JPL’s Anderson uncovers a 24 year mystery

John Anderson is a physicist at NASA’s Jet Propulsion Laboratory. For the past 24 years he has been collecting data on the first two Pioneer satellites, and what he found is something

rather astonishing:

Rather than traveling at a constant velocity of more than 25,000 mph toward the edge of the solar system, Pioneers 10 and 11 were inexplicably slowing down. Even factoring in the gravitational pull of the sun and its other planets couldn’t explain what he was seeing.

How could that be?

At first, Anderson figured there must be a simple explanation. Maybe there was a malfunction on board the spacecraft. Maybe his calculations were wrong.

Shy, bookish and soft-spoken, Anderson was not the type to call a news conference to announce that two U.S. spacecraft appeared to be disobeying the physical laws of the universe.

‘I assumed something was going on that I didn’t understand,’ said Anderson, now 70. ‘So I just kept at it.’

For years.

What did he discover? The Pioneer Anomaly. Pioneer, it seems, was slowing down to the point where it was a quarter of a million miles slower than it should be. Planets and other sources of gravity were factored in, but scientists were stumped.

The explanations? Either dark matter is slowing the spacecraft down, or we are wrong about gravity. The European Space Agency plans a mission to discover the reason for the anamoly in 2015. Great article.

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