Scientists have known for some time that the Earth is not a perfect sphere.
It is shaped a little like a pumpkin – wider at the middle and narrower at the poles. It is a difference of more than 20 kilometres.
But now new research published in the journal Science suggests our planet is getting even wider – if only by the odd millimetre.
The scientists behind the report, Christopher Cox and Benjamin Chao, base their findings on space-based observations from past 25 years.
Since the early 1980s, satellite laser-ranging studies that have been used to work out the planet’s gravity field have demonstrated how the Earth has lost a bit of its pumpkin look – it has actually become slightly more spherical.
This has been put down to a rebound effect in the mantle – a thick layer of nearly molten rock between the Earth’s crust and its core – following the loss of the heavy mass of ice at the poles after the last Ice Age.
But Cox and Chao say their work suggests this trend was reversed abruptly from about four years ago.