Scientists puzzled as Earth gets fatter round the middle

THE Earth has suddenly become fatter round the middle in the last four years, researchers have found.

Like a pumpkin, the planet is a little bit wider around the equator than a perfect sphere would be. For 19 years its waistline shrank, but since 1998 it has been expanding, according to a study in the journal Science.

American scientists Christopher M. Cox and Benjamin F. Chao noticed the bizarre phenomenon after studying space-based observations from the past 25 years.

They found that a measurement of the Earth's width had generally been decreasing for most of that time. The main reason was that the melting of the ice caps had caused the mantle - the thick layer of nearly-molten rock between the crust and the Earth's core - to rebound. But they subsequently discovered that around four years ago the Earth's "dynamic oblateness"- its girth began to increase. The trend is continuing, the study said.

According to their calculations, neither global sea level rise nor faster melting of glacial ice could have produced such a sharp change.

Cox, of Raytheon Information and Scientific Services, and NASA scientist Chao suggested that shifting of mass at the boundary between the Earth's core and the mantle may be responsible.

But Mr Cox said the increase in the Earth's width was only in the order of a few millimetres.