The launch of the first ever space mission to Pluto has been delayed for the second time this week.
Nasa's New Horizon's take-off has been postponed for "at least one more day" because of a problem with the power at the laboratory managing the mission.
It missed its slot on Tuesday because of strong winds, and Nasa scientists were hoping to launch it on Wednesday.
The latest delay is unlikely to make much difference, as the probe will take nine years to reach the planet Pluto.
Pluto is the furthest planet from Earth and is three billion miles away. The probe will move at a speed of 10 miles per second to get there by 2015.
The mission will cost $700m
A jet liner would take 1,000 years to do the same journey
An 87-year-old retired teacher from Surrey gave Pluto its name
Some scientists say Pluto is more of a giant comet than an actual planet
Pluto is made of rock and ice
Once the probe arrives at the mysterious planet it will take pictures of the icy surface and atmosphere and beam them back to Earth.
New Horizons - which cost £396m ($700m) won't actually land on Pluto, but will pass close by to examine the planet and check out its three moons.
It's an unmanned mission, but Nasa has put an American flag inside the craft and a CD containing the names of around half a million people who signed up to their website.