BBC correspondent Sue Nelson reports on Japan's Mars mission

It is Japan's first interplanetary mission and is designed to gather evidence about whether life might once have existed on Mars, and if there is water under the planet's surface.

Instruments on board the probe will begin sending back information from October next year, when the craft goes into orbit around Mars.

Probe carried by rocket

Up until now, only the United States and Russia have sent space probes there.

The space probe is trying to spend one Martian year - the equivalent of two Earth years - studying the atmosphere and moons of Mars.

It will measure the Red Planet's magnetic field and look for a "water signature" - signs of water being present on or below the surface.

Dr Chris Welch, a space technologist at Kingston University in Britain, says: "We certainly know that water existed on Mars in the past. You just have to look at the surface - there are so many features which can only be explained by water."

'Where did Mars' water go ?'

"The question is where did the water go ? One explanation is that it has all evaporated into space, the other is that it is still on the planet, but not in liquid form. Most likely it is under the surface."

The 31-metre long rocket, named Nozomi (Hope), blasted off from Uchinoura cosmodrome on the island of Kyushu early on Saturday.

Dr Chris Welch: "Japan wants to become a space power"

The rocket is expected to launch into orbit a probe, Planet B, which has 14 on-board instruments designed by specialists from Japan, Germany, Canada, the United States and Sweden.

Japan's space programme suffered a major setback in February when an H-2 rocket failed to put one of the world's largest satellites into a geostationary orbit, thus sending about $500m down the drain.

Dr Welch says: "For the Japanese as a nation it is important as a form of technology development.

"All their space activities to date have been towards developing the expertise they need to become a space power in the future."

The cost of space research has been criticised in Japan at a time when the country is in severe economic difficulties.