Archived Blog Post: May 16, 2001

Mystery force tugs distant probes - "The mystery deepened further when an analysis of the trajectory being followed by its sister spacecraft, Pioneer 11, launched in 1973, showed that it too was being subjected to the same mysterious effect. But Pioneer 11 is on the opposite side of the Solar System from Pioneer 10, about 22 billion km (about 14 billion miles) away."

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