Lunar rock and roll

Crater Tycho

The 85-kilometre-wide crater Tycho on the Moon. The arrow marks the location of the huge boulder shown in detail below.

THE 85-KILOMETRE-WIDE CRATER Tycho is one of the standout features of the side of the Moon that faces Earth.

Named after the 16th century Danish astronomer Tycho Brahe, it is thought to have formed 108 million years ago when an asteroid smashed into the lunar surface.

Southern region of the Moon

Like the spokes of a wheel, rays of lighter-coloured ejected rock stretch away from the crater Tycho (the prominent crater near centre, with the central peak). Photo by Joe Huber, sourced from Wikipedia.

The impact formed the crater, and also flung out huge amounts of molten rock—called ejecta— in all directions.

That ejecta can still be seen today, in the form of bright ‘rays’ stretching away from Tycho.

Astronauts of the final Apollo mission, Apollo 17, managed to collect samples of Tycho ejecta from their landing site in the Taurus-Littrow valley, thousands of kilometres away.

Like many craters, it has a central peak that rises high above the crater floor. This peak was formed as the molten rock splashed back upwards immediately after the impact…just as a central splash back occurs when an object is dropped into a glass of milk.

Tycho’s central peak rises 1.6 kilometres above the floor.

Along with the rest of the lunar surface, Tycho has been imaged in detail by NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft, currently still operating.

Large boulder in crater Tycho

A 320-metre-long block of ejected rock sits near the rim of Tycho. It has a smooth top, thought to be a veneer of solidified molten rock droplets.

One of LRO’s most startling images of Tycho shows a huge boulder, 320 metres long, perched near the crater’s rim.

This boulder is thought to have been blasted out of the lunar surface when the impactor that formed the crater, struck.

It has a smooth top, which scientists think is the result of a rain of molten rock droplets settling on it and solidifying.

Images courtesy of NASA / GFSC / Arizona State University.

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