The Earth has recorded its personal best time for a single rotation and scientists are now theorising that it may have been caused by the melting polar ice caps.
Earth from space. File photo. Photo: Creative commons
Smashing a Personal Best is always satisfying, and on 29 July the Earth recorded its own personal best time for a single rotation.
It's not a record most people would have noticed - the day was just 1.59 milliseconds short of the usual 24 hours.
Earth records fastest rotation
University of Auckland astrophysicist Dr Jan Eldridge told Morning Report it was surprising discovery as as theory suggests the Earth should instead be slowing down.
"We have tides on the earth for our oceans and that's actually dragging trying to slow the earth down and that's from the gravity of the moon that's slowing it down so it is a surprise that this kind of sped up.
"Even by that little amount we can measure it accurately enough that if those few milliseconds add up over a few years you have to have a leap second when we have a new year each year or we might start getting the time wrong," Eldrige said.
Any need for a "leap second" would likely require decades of incremental increases to the Earth's rotation speed, she said.
The Earth's rotation rate naturally changed by a matter of seconds over the space of centuries and millennia, she said.
However, the invention of atomic clocks meant scientists were now able to more accurately measure the rate at which the Earth was spinning, she said.
Eldridge said the speeding up of the Earth's rotation would not have any impact on day-to-day life but it would be important to check GPS satellites which needed the correct time to correctly locate destinations on Earth.
"I think we'll be pretty safe, it's a GPS system and that's why we've got to make sure we keep the time on track to make sure where the Earth is at different times is where the satellites think it is."
Meanwhile, mobile phones would have automatically updated to the correct time in accordance with atomic clocks, she said.
Eldridge said it was surprising that scientists could find such a tiny difference in the Earth's spin-rate - detecting a thousandth of a seconds difference out of the 86,000 seconds in a single day.
Scientists were unsure exactly why the Earth's rotation had sped up but there were a few theories being floated, she said.
"The Earth is a really complex body and this spinning up is happening because it's probably something similar to if you spin on a spinny chair with your arms and your legs sticking out and then you bring your arms and legs you spin up, so something is probably changing in the Earth which is making it spin up by this very tiny amount," Eldridge said.
One theory suggested the melting of the planet's polar ice caps meant there was less weight pushing down on the Earth's poles.
The theory argued that this subsequently caused magma underneath the Earth's crust to push back out which may have led to a slight alteration to the way the Earth spins.
The Earth's axis is also known to wobble, another theory which could explain the planet speeding up, Eldridge said.