The Messenger space probe was set to be launched aboard a Delta II rocket from Cape Canaveral, Florida, at 2:16 am Monday (0616 GMT) on a journey of several years to probe the solar system's planet closest to the sun.

NASA said ground controllers decided on the delay due to heavy clouds resulting from a tropical storm hitting the region north of the launch area.

"Similar weather is predicted tomorrow," NASA said in a statement. "However, if Tropical Storm Alex moves farther away, the forecast would likely improve."

Messenger is to fly over Mercury three times in 2008 and 2009 before entering the planet's orbit in March 2011.

It will travel a total of 7.9 billion kilometers (4.9 billion miles), even though Mercury is 91 million kilometers (56 million miles) from Earth.

It is the first US mission to Mercury since the Mariner 10 spacecraft flew over 30 years ago.

SPACE.WIRE