A study of GPS satellite orbits suggests the Earth is heavier than thought, perhaps due to a halo of dark matter, a U.S. researcher says.

Dark matter is thought to make up about 80 per cent of the universe's matter, but scientists have been unable to determine much else about it, including its presence in the solar system.

In 2009, researchers at the Institute of Advanced Studies in Princeton, N.J., theorized that observed changes in the speeds of space probes as they flew past the Earth could be explained by dark matter bound by Earth's gravity.

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