An alarm clock in deep space was set to wake up Rosetta, an unmanned comet probe, before a key phase in its 10-year mission, according to the European Space Agency.
Rosetta's onboard computer system was programmed with a wakeup call of 5 a.m. EST (1000 GMT,) but it will take over seven hours before mission control knows if it actually worked or not.
Launched back in 2004, the probe has traveled 4.3 billion miles around the Solar System, according to AFP.
ESA said the probe's goal is to meet up with comet 67P/Churyumov-Gerasimenko this August, and by next November it will be the first space craft to place a lander on a comet.
The comet is predicted to then move around the sun as the lander conducts experiments
"It's the first time we've made a rendezvous with a comet, that's never been done before, and it's going to be the first time we've escorted a comet past its closest approach to the Sun," ESA project scientist Matt Taylor said to CNN.
Rosetta has been in hibernation the past 31 months, according to AFP.
The wakeup signal is expected to take a couple of hours, which will then be followed by a "all is well" signal, which will take 45 minutes to cross a distance of over 500 million miles.
"The window in which we expect the nominal signal, if everything goes according to plan, is of about an hour, between 1730 and 1830 GMT," Paolo Ferri, ESA's head of solar and planetary missions, said to AFP.
The probe cost $1.36 billion and was named after the Rosetta stone, according to CNN.
The main objective of Rosetta's mission is to try understanding the origin of the solar system and how it has evolved over the years. ESA believes that during the mission, they'll be able to figure out if comets have anything to do with the water found on Earth.