Want to lose weight fast? No need to adjust your diet – just move to higher ground. This weight change is the result of fluctuations in Earth's gravity, which a new high-resolution map shows are greater than thought.
Gravity is often assumed to be the same everywhere on Earth, but it varies because the planet is not perfectly spherical or uniformly dense. In addition, gravity is weaker at the equator due to centrifugal forces produced by the planet's rotation. It's also weaker at higher altitudes, further from Earth's centre, such as at the summit of Mount Everest.
NASA and the European Space Agency
Christian Hirt of Curtin University in Perth, Western Australia, and colleagues combined gravity data from satellites and topographic data to map gravity changes between latitudes 60° north and 60° south, covering 80 per cent of Earth's land masses.
The map consists of more than 3 billion points, with a resolution of about 250 metres. Computing gravity would take 5 seconds per point on an ordinary PC, but the team used a supercomputer to do the whole lot in three weeks.
Free fall favourite
The model pinpoints more extreme differences in gravitational acceleration than previously seen. Standard models predict a minimum gravitational acceleration of 9.7803 metres per second squared at the equator and 9.8322 m/s2 at the poles. Hirt's model pinpoints unexpected locations with more extreme differences. Mount Nevado Huascarán in Peru has the lowest gravitational acceleration, at 9.7639 m/s2, while the highest is at the surface of the Arctic Ocean, at 9.8337 m/s2.
"Nevado was a bit surprising because it is about 1000 kilometres south of the equator," says Hirt. "The increase in gravity away from the equator is more than compensated by the effect of the mountain's height and local anomalies."
These differences mean that in the unlikely event that you found yourself falling from a height of 100 metres at each point, you would hit the surface in Peru about 16 milliseconds later than in the Arctic. You would also lose 1 per cent of your body weight in moving from the Arctic to the Peruvian mountaintop, although your mass would not change.
Journal reference: Geophysical Research Letters, DOI: 10.1002/grl.50838
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