Earth is not on a collision course with a massive asteroid, detailed pictures of the nearby flying object have revealed.

Astronomers have been in awe as it approached the planet and provided the opportunity to obtain radar images of the asteroid's surface and shape.

NASA said the pictures would help observers understand the object's orbit.

The asteroid, first discovered in 2003, is classified as "potentially hazardous" due to its size and close approaches to Earth's orbit.

However, the latest radar measurements confirm it does not pose a future impact threat to Earth.


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The asteroid - called 2003 SD220 - flew safely past Earth on Saturday at a distance of about 1.8 million miles (2.9 million kilometres) - its closest approach in more than 400 years.

It will be the closest approach until 2070, when it will come slightly closer.

The radar photos released by the space agency reveal the asteroid is at least one mile (1.6km) long. NASA said its shape was similar to that of the "exposed portion of a hippopotamus wading in a river".

The pictures were obtained by coordinating NASA's 70m (230ft) antenna in California, the National Science Foundation's 100m (330ft) telescope in West Virginia and the Arecibo Observatory's 305m (1,000ft) antenna in Puerto Rico.

"The radar images achieve an unprecedented level of detail and are comparable to those obtained from a spacecraft flyby," said Lance Benner, the scientist leading the observations from California.

"The most conspicuous surface feature is a prominent ridge that appears to wrap partway around the asteroid near one end. The ridge extends about 330ft above the surrounding terrain.

"Numerous small bright spots are visible in the data and may be reflections from boulders. The images also show a cluster of dark, circular features near the right edge that may be craters."

Scientists said the images confirmed the asteroid had a slow rotation period of about 12 days and that it had a complex rotation - like a "poorly thrown football".