The close flyby, at an altitude of just 770 metres, provides new insights into the formation, size and surface features of the 4.75 kilometre wide object.

The images, captured by the Chang'e-2 spacecraft and published in the Nature journal Scientific Reports, allowed the authors to develop a 3D image of the asteroid, showing it has two lobes, one much larger than the other.

"We have high resolution images indicating the asteroid consists of two major parts ... forming a contact binary," says the study's lead author Professor Jianghui Ji of the Chinese Academy of Sciences, in Beijing.

"It looks like a ginger root, with the big lobe the body, and the smaller one the head."

Contact binaries are asteroids made up of two smaller objects held together by gravity.

Its irregular, surface is peppered with more than 50 impact craters including an 800-metre wide basin at the end of the large lobe.

Long journey

"This asteroid comes from the main asteroid belt, where it was affected by the gravitational perturbations of Jupiter," says Ji.

Toutatis tumbles on an orbit that brings it close to Earth every four years.

Previous studies concluded the asteroid's tumbling rotation is primarily caused by the gravitational influence of the Earth.

A second contributing effect is heat from the Sun being absorbed and re-radiated unevenly from the asteroid's irregular surface. The warmed areas radiate photons, which carry momentum and act as tiny thrusters.

"This is part of an emerging picture of smaller asteroids being rubble piles, rather than single distinct bodies," says Dr Craig O'Neil from the University of Southern Queensland, who was not involved in the research.

"Large asteroids have sufficiently strong gravity to form as single large spherical bodies, and like planets, can undergo differentiation with heavier elements such as iron moving to the core, leaving lighter materials such as silicates to form a surrounding mantle."

China's lunar missions

The new images of Toutatis were taken by one of Chang'e-2's onboard engineering cameras, originally designed to monitor the deployment of the spacecraft's solar panels and photograph objects, such as the Earth and Moon.

Chang'e-2, which was launched on 1 October 2010 to explore the Moon and search for lunar mineral resources.

This was Beijing's second mission to the Moon, and also photographed candidate landing sites for the Chang'e-3 mission now underway, which is carrying China's first lunar rover, known as Yutu, or Jade Rabbit.

After completing its primary mission, Chang'e-2 was sent on an extended mission studying the space environment, before eventually intercepting Toutatis and performing a close flyby 13 December 2012.

Chang'e-2 is still operational and is now more than 50 million kilometres from Earth.