Stickney crater on Mars’s moon Phobos

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Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

An image taken in 2008 by the Mars Reconnaissance Orbiter of the Stickney Crater, the largest crater on the martian moon Phobos.

The image was taken from a distance of 6000km. The Stickney crater is over 9km across, nearly half the diameter of the tiny moon itself.

Phobos is the largest of Mars’s two moons and orbits the planet at a distance of a mere 9400km going around the red planet every 7.5 hours or so, twice in every martian day.

Due to its small size and mass, Phobos remains an irregular shape as it is not massive enough to be rounded by its own gravity…. The gravity on Phobos is less than 1000th that on Earth.

Phobos is covered with a layer of fine dust (regolith) up to 100m metres deep which is believed to have originaled from extensive histoical impact cratering. The stripes around Stickney crater were originally thought to have resulted from the impact which formed the crater however it is now understood that these in fact originate from debris ejected into space resulting from impacts on Mars.

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Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

Phobos in its full glory. The moons’ origin is unclear and one school of thought is that it is actually a captured asteroid, originating from the asteriod belt between the orbits of Mars and Jupiter.

This gravitational attraction is continuing to draw Phobos ever closer to Mars and it is likely that within 10 million years or so, Phobos will be torn apart by the ever increasing gravitational tidal forces with its debris forming a new ring system around the red planet.

Phobos is named after the Greek god Phobos which means ‘fear’.

 

 

 

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Tycho crater – central peak

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Credit: NASA

Staying on the crater theme for a bit, the image above is of the central peaks of the prominent crater Tycho on the Moon.

The mountainous formation above is some 15km across and rises 2km from the base of the crater which was formed relatively recently some 100 million years ago.

The central peak forms directly following impact and is due to a phenomena known as uplift which occurs in the larger craters and is due to complex interactions between shock waves, the force of impact and the inherent strength of the impacted area as well as gravity.

This image was obtained at lunar sun rise on 10th June 2011 by the Lunar Reconnaissance Orbiter and shows the central peak casting a long shadow and captures amazing detail at incredible resolution.

Zooming in a little closer, individual boulders can be picked out on the peak, the largest in the image below is 120m in size, the overall image is 1200m across approximately:

Tycho boulder

Credit: NASA

The Tyco crater is a prominent impact crater located on the southern highlands and is named after the Danish astronomer Tycho Brahe.  The crater has an extensive ejecta that radiates out in a spoke formation some 1500km or so from the central crater.

An image of the Tyco crater in its full glory from the LPO and another as seen from London are shown below:

Tycho

Credit: NASA

tyco 10.09

Barringer meteor crater

Barringer Meteor_Crater_-_Arizona

Credit: NASA

The Barringer meteorite crater is one of the best examples of a meteor impact crater on Earth.

Located near Flagstaff Arizona, the crater is a little under 1.2km in diameter and 200m deep and is believed to have formed some 50,000 years ago.

The meteorite that caused the crater is estimated to have been only 50 metres in diameter with a mass of just under 300,000 tonnes and is estimated to have been travelling at a speed of 12.8km/second or 46,000km/hour when it hit Earth.

For comparison, the Copernicus crater on the Moon below is approximately 800 million years old, is 93km wide & 3.8km deep.

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Image of Copernicus crater taken in London in March 2012

However, although large by comparision, both craters are dwarfed by the largest known crater in the solar system…..

The South Pole Aitken (SPA) basin, also located on the Moon is an incredible 2500km in diameter, or 200x as wide as the Barringer crater.

The SPA basin (see below) was created approximately 4 billion years ago (500 million years after the moon was formed) and is 12km deep. It is now thought that the area of low mass formed by the gigantic basin eventually destabilised the Moon casuing it to roll over onto its side within a million years of the impact.

Largest crater on the moon

Credit: NASA/Clementine Project/LPI