Best Images of Crater Rays From The Lunar Reconnaissance Orbiter

A Cosmic Beating

The Moon is battered, scarred, and pummelled from thousands of impacts over billions of years. The Moon though, like the Earth took most of its beating in the early days of the solar system, and yes Earth took just as much punishment as the Moon did. But Earth has weather, erosion, and is geologically very active, covered in forests, deserts, oceans and everything in between. All this activity has done a good job of concealing, and wearing down the craters. Also the Earth has an atmosphere that takes care of the smaller objects, burning them up before they even reach the ground. The Moon though has no atmosphere, meaning it is exposed to every incoming projectile from space.

The Moon is pristine with no wind, erosion, or present geological activity. This means that lunar features are mainly ‘frozen’ in time with nothing to disturb them, apart from maybe the occasional new impact, or darkening action by the Sun on lunar dust. So craters, ravines, lava flows, etc look as fresh as when they were first made. In fact boulders have been photographed on the lunar surface that have rolled down a crater wall or slope, leaving a trail behind them in the lunar dust that looks like it was made yesterday. In reality astronomers and scientists know they rolled down that slope tens of millions of years ago, and with little to disturb them they generally stay like that.

 

The Crater Impact

When a comet or asteroid hits the Moon they can be travelling at many thousands of miles per hour, so the resulting collision is kind of violent to say the least. When a sufficiently large object hits it creates extreme heat, actually melting the rock and compressing it into the surface, the melted rock can then ‘rebound’ producing a central peak which then cools and is often as high as the crater walls themselves.

A bowl shaped depression is dug out of the lunar surface and all the rock, dust, and lunar soil gets thrown upwards and outwards. No surprise there then I hear you say, but this can create some really striking effects. Lunar material gets launched just a few metres, or sometimes hundreds of miles from the original impact, to land back down to the surface as ejecta blanket, or crater rays. Younger lunar craters usually have bright crater rays, because this fresh material has been excavated from beneath the surface and hasn’t had the effect of Sun weathering. The action of sunlight will darken lunar dust over time, giving an idea of the age of craters from the tone of the ejecta. 

Here are some of the best images of crater rays from impacts large and small, as photographed from the Nasa Lunar Reconnaissance Orbiter, CLICK TO ENLARGE…

Unnamed 270 metre crater, image credit Nasa

Bright rays surround this 270 metre diameter crater, with darker tendrils of ejecta nearest to the rim and inside the impact. This darker lunar material may be melt material.

Unnamed 1 kilometre diameter crater, image credit Nasa

This is a stunning example of crater rays, almost taking on a symmetrical flower patten. The fine lunar material is brightest nearest the crater than further out. See the smaller, darker spots surrounding the crater, and the two larger darker impacts to the south and west, these are all secondary impacts from the main collision

Ejecta from a fresh crater, image credit Nasa

Fine impact ejecta coats the lunar surface south of Mare Tranquillitatis, image credit nasa, area 520 metres. Pull out and get the full picture here

Young crater in Balmer Basin, image credit Nasa

Dark thin tendrils of ejecta surround this crater at just a bit smaller than the 1200 metre Meteor Crater in Arizona. The darker material is melted rock that was thrown out in the impact, credit Nasa

A 475 metre crater inside Komarov Crater, image credit Nasa

Thin crater rays extend out from this 475 metre impact, which is inside the much larger 84 kilometre wide Komarov Crater at the south east edge of Mare Moscoviense. The ejecta from this smaller impact have produced rays that go down into the dark region which is actually a fracture in the larger Komarov Crater. The rays from this smaller crater are straight, and not been twisted or warped, showing that the crater is younger than the fracture.

80 metre diameter crater, image credit Nasa

This is a great image of crater rays on a small scale, as this impact is only 80 metres across. Check out both the dark and light tones of ejecta. The action of sunlight on lunar soil darkens it over time, this darker space weathered ejecta has been mixed with fresh brighter material excavated from below the surface by the impact.

A pair of craters, image 1.6 kilometres wide, credit Nasa

Attractive impact ejecta sprays outwards from these two small craters at the edge of the Jura Mountains, in Sinus Iridum. The larger crater has dug down to much darker material deeper below the lunar surface, whereas the smaller crater is shallower and far brighter. Check out the image from afar showing the crater pair at the foot of the Jura Mountains (image width 8.3 kilometres)

30 metre crater, image credit Nasa

Bright crater rays surround this little 30 metre diameter crater like the spokes of a wheel, with dark boulders also ejected from the crater and landing nearby. The dark blocks suggest hard material, and this crater is located on the impact melt of a much larger 8.7 kilometre wide crater.

John Brady

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