It all goes to show that if you look hard enough at a craters, mountain ranges and deserts you will see all kinds of interesting shapes.

Some took that to absurd levels when they claimed that a mountain on Mars was actually a "face" sculpted by a long-extinct civilisation.

The crater Galle smiles

This theory was shown to be nonsense last year with close-up images of the mountain in question. At high resolution, there was certainly no face.

But now there is a heart.

The new image, taken by the Mars Global Surveyor spacecraft, shows a heart-shaped pit formed by collapse within a straight-walled trough known geologically as a graben. Graben are formed along fault lines when the crust of a planet is stretched.

It lies on the eastern edge of the Alba Patera volcano in a region called northern Tharsis. It is about 3.2 kilometres (two miles) across.

Another of the newly released images is of the curious "happy face" that contains some large, windblown sand dunes.

It is in fact the crater Galle, 224 km (140 miles) across. But no doubt some people, disappointed that the original face on Mars was not real, will say it appears to have been constructed.

What it really shows is that Mars has a sense of humour.