The first European spacecraft sent to the moon has entered lunar orbit, the European Space Agency (ESA) said on Tuesday.

The SMART-1 spacecraft reached its closest point from the moon so far, coming within 5,000 kilometers (3,100 miles) of the lunar surface on Monday, the ESA said. Scientists were now seeking to stabilize the spacecraft in orbit around the moon.

"By about mid-January, SMART-1 will be orbiting the moon at altitudes between 300 kilometers (over the lunar south pole) and 3,000 kilometers (over the lunar north pole), beginning its scientific observations," the ESA said in a statement.

The small spacecraft will make the first comprehensive inventory of key chemical elements in the lunar surface and investigate the theory that the moon was formed following the collision of a smaller planet with Earth, 4.5 billion years ago.

SMART-1 has also been the test flight for a new solar-electric propulsion technology, a kind of solar-powered thruster that is ten times more efficient than the usual chemical systems employed when traveling in space.

The so-called "ion" engine was tested over a long spiraling trip to the moon of more than 84 million km, a distance comparable to an interplanetary cruise, ESA said.

It does not burn fuel like chemical rockets do but instead converts sunlight into electricity via solar panels and uses it to electrically charge heavy gas atoms, which speed away from the spacecraft and thereby drive it forward.

"Overall, the engine performed extremely well, enabling the spacecraft to reach the moon two months earlier than expected," the EAS said.

"The extra fuel available also allowed the mission designers to significantly reduce the altitude of the final orbit around the moon. This closer approach to the surface will be even more favorable for the science observations that start in January."

SMART-1 was launched from Kourou, French Guiana, on Sept. 27, 2003.