When life gives you lemons, make lemonade, right? That, at least, is the motto the European Space Agency seems to have embraced with respect to two wayward satellites, which are being repurposed to provide the most accurate assessment yet of how gravity affects the passage of time.

Last year, a Russian Soyuz rocket accidentally placed two ESA-operated GPS satellites into elliptical, rather than circular, orbits. The faulty launch leaves the satellites unfit to perform their intended duties as part of a global Galileo GPS system. It would have been a huge waste of money and resources, but there’s a silver lining.

To wit, physicists now have a unique opportunity to test one of the key predictions of Albert Einstein’s theory of general relativity: That clocks run more slowly when they’re close to heavy objects, because of how gravity warps the fabric of spacetime. (Remember Miller’s planet from Interstellar, where an hour is actually seven years of Earth time thanks to the monster black hole next door? Same principle).


As the two Galileo satellites swing toward and away from the Earth in their oblong orbits, German and French physicists will track the speeding and slowing of time using the spacecrafts’ on-board atomic clocks. To date, our best measurements of the so-called time dilation effect were made in 1976, in an experiment that lasted a mere two hours. The Galileo satellites will be tracked for a year, enabling physicists to make measurements up to four times more accurate.

By this time next year, we’ll have a better idea of exactly how much gravity causes time to dilate. The impromptu experiment is a great reminder that in science, a failure can often be turned into an opportunity. And that in space, one should never, ever waste anything.

[Nature News]

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