Nasa's Juno spacecraft has become the fastest man-made object in history - despite mysteriously partly shutting down.
The Jupiter-bound satellite was performing a slingshot manoeuvre around Earth which boost its speed to an incredible 87,000 mph (140,013kph).
But Nasa scientists noticed it was not transmitting as much data as it should have been and had reverted to its "safe mode" which it is programmed to do when there is a problem.
Rick Nybakken of the NASA Jet Propulsion Laboratory (JPL), said ominously: "We did not plan for this."
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He added the development was causing "a moderate level of concern", reports the Montreal Gazette.
What caused the satellite to switch to safe mode is still unknown but the trajectory of the craft has not been affected.
A spokesman for the JPL told the Register: "It was in safe mode as it came out of the Earth flyby.
"Two-way communications have been established. The spacecraft is in a safe stable state receiving power from the solar arrays as expected."
The slingshot manoeuvre was need as there are not rockets powerful enough to boost the satellite to such speeds.
University of Iowa research scientist Bill Kurth told FoxNews.com: "Juno will be really smoking as it passes Earth at a speed of about 25 miles per second relative to the Sun."
When it reaches Jupiter it will orbit the planet 33 times from pole to pole and gaze beneath the gas giant's obscuring cloud cover to see what lurks beneath.
The mission will greatly enhance our understanding of the planet's origins, structure, atmosphere and magnetosphere, and could even look for a potential solid planetary core.
Kurth said: "The mission is very exciting. We’ll come the closest we've ever come to Jupiter, within just a few thousand miles of the planet's cloud tops."
Juno's name comes from Greek and Roman mythology. The god Jupiter drew a veil of clouds around himself to hide his mischief, and his wife, the goddess Juno, was able to peer through the clouds and reveal Jupiter's true nature.