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The new James Webb Space Telescope has been hit by a piece of space rock.

The incident appears to have occurred sometime towards the end of last month.

Nasa says one of the main mirrors on the huge space observatory has been damaged by the small meteoroid.

However, the space agency doesn't think it will affect the mission's overall performance.

James Webb was launched in December to succeed the ageing Hubble Space Telescope.

Nasa says that a tiny rock fragment collided with the space observatory sometime between 23 and 25 May.

Even though the meteoroid was small in space terms - it was larger than anything the telescope was tested against before it was launched.

The super high speed at which things move through space means even the smallest object can cause a lot of damage if it hits something.

Nasa said that engineers had built the telescope to withstand such impacts, even though the piece of rock was larger than was expected.

"We always knew that Webb would have to weather the space environment, which includes harsh ultraviolet light and charged particles from the Sun, cosmic rays from exotic sources in the galaxy, and occasional strikes by micrometeoroids within our Solar System," said Paul Geithner, technical deputy project manager at Nasa's Goddard Space Flight Center in Greenbelt, Maryland.

"We designed and built Webb with performance margin - optical, thermal, electrical, mechanical - to ensure it can perform its ambitious science mission even after many years in space."

The US space agency are still trying to check the damage, although they say that the telescope appears to be operating well enough.

Nasa scientists say it was the was the fifth time that the James Webb telescope has been hit since it was launched last year on Christmas Day, but this latest event has been the most significant.

The telescope is currently gathering observations of the Universe, near and far, to demonstrate its capabilities. Astronomers are due to release the telescope's first proper pictures of space on 12 July.

Longer term, the scientists intend to use Webb to try to see the very first stars to light up the cosmos more that 13.5 billion years ago.

They'll also train the telescope's big "eye" on the atmospheres of distant planets to see if those worlds might be habitable.