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.
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.
Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz