A bridge too far(side)

Rock bridge on the Moon

NASA's Lunar Reconnaissance Orbiter spacecraft snapped this image of a natural rock bridge on the far side of the Moon. The bridge spans what appears to be two cave-ins in an underground lava tube.

An image taken by the main camera aboard NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft—currently orbiting the Moon—has revealed a natural bridge of rock that apparently crosses two holes in the lunar crust.

The bridge appears to be about 20 metres long and 7 metres wide.

On Earth, natural rock bridges are usually formed from long-term erosion by wind and flowing water.

But the Moon has neither of those phenomena, so how did the bridge form?

The answer seems to be a collapsed lava tube.

Images of Moon, going all the way back to the Apollo days of the 1960s, have shown that numerous lava tubes can be found across its face.

Lava tubes are where a stream of molten rock moves across a surface. The outside of the stream cools and solidifies, insulating the still-moving lava within and forming a tunnel. Eventually the lava flow is depleted and an empty tube or tunnel is left behind.

Two views of a rock bridge on the Moon

What a difference an angle can make. The image on the left shows the bridge with sunlight slanting in from a 42-degree angle. The image on the right is with the sunlight at 82 degrees, or almost overhead.

Occasionally parts of the tunnel roof collapses, sometimes leaving a bridge or arch where the roof was a bit thicker or stronger.

This is what seems to have happened in the case of the newly-discovered bridge on the Moon.

But instead of the lava coming from a volcano, in this instance it appears to have been a flow of rock that formed when a large meteoroid hit the lunar surface and melted everything around it.

The location in question is called King Crater, and the bridge is found on the floor of the crater, where a large pool of molten rock would have been formed after the meteoroid struck.

Story by Jonathan Nally, editor SpaceInfo.com.au

Images courtesy NASA / Goddard / ASU.

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  1. Steve says:

    bloody brilliant as always

  2. […] This post was mentioned on Twitter by Peter Gossner, Jonathan Nally. Jonathan Nally said: A bridge too far(side) http://goo.gl/fb/Z4GEc […]