Did it feel like time flew in November 2009? It turns out the days were actually going a wee bit faster for part of that month, according to a team of NASA and European scientists.
Earth spun about 0.1 millisecond faster for a two-week stretch, said study co-author Steven Marcus, a researcher at NASA’s Jet Propulsion Laboratory in Pasadena, California.
The planet’s speedier spin appears to have been due to a slowdown in an ocean current that whips around Antarctica.
“The Earth speeding up is just like a [twirling ice] skater pulling in her arms,” he explained. When the skater does this, she spins faster, because the laws of physics dictate that her body must conserve what’s called angular momentum.
“When [the skater] sticks out her arms, they move pretty fast, because there’s a big circle. When she pulls in her arms, the circle is smaller, so in order to have the same angular momentum, she has to speed up,” Marcus said.
“It is the same with the Earth,” in the sense that if an ocean current slows down, the planet’s spin must speed up to conserve angular momentum.
Scientists have long known that changes in the speed of ocean and atmospheric currents can—and do—slightly affect the rate of Earth’s rotation and, hence, the length of a day.
“The thing is, with the ocean the effect is a lot weaker, since the ocean flows a lot slower than the atmosphere,” Marcus said.
But in November 2009, he said, a slowdown in the Antarctic Circumpolar Current “seemed to be a lot stronger than usual, and that’s probably what made it large enough to be detected in the Earth’s spin data.”