Sunday, January 20, 2013

Extraterrestrial rivers - spooky

Perspective view of Reull Vallis, Mars. Image: ESA
The striking image above, taken by ESA’s Mars Express last year, is the upper part of the Reull Vallis region of Mars. 

The river-like structure is believed to have formed when running water flowed in the distant Martian past, cutting a steep-sided channel through highlands before running on towards a vast basin. 

The presumed dried-up river stretches for almost 1500 km (940 miles) across the Martian landscape, flanked by numerous tributaries, one of which can be clearly seen cutting in to the main valley. More images on ESA website.

Not spooky enough?  Then try this

Images of Mars tend to look familiar to us, like desert regions of the Earth. So take a look at a river on Saturn’s huge moon Titan.  The image on the left is just a taster. For the real thing, go to

NASA's Cassini spacecraft has captured a crisp image of a long river cutting across Titan’s surface.  Not a dried-up river: it's flowing as you read this. Flowing not with water, but with hydrocarbons (liquid methane mainly I think). At -180° Centigrade. The river stretches more than 250 miles (400 kilometers) from its source to a large sea near Titan's north pole. Cassini's radar image is the first high-resolution shot ever taken of such a vast river system on a world beyond Earth.  Scientists are comparing it to Earth's Nile River in Egypt; not in length, but in straightness. Like the Nile its course is thought to follow a geological fault.

How big is Titan?

Titan is the second largest moon in our solar system. Only Jupiter's moon Ganymede is larger, with a diameter barely 112 kilometers greater. This graphic shows the relative sizes of Earth, Titan and our Moon. Mars if shown would appear larger than Titan but much smaller than Earth.  One more spooky fact: light takes about 80 minutes to reach Earth from Titan. From the Sun, 8 minutes.

L to R: Earth, Titan, our Moon
        Diameters in km:
        Earth 12,760
        Mars 6,790 (not shown)
        Ganymede 5,250 (not shown)
        Titan 5,140
        Earth’s Moon 3,470

1 comment:

  1. Fascinating stuff. A liquid methane river at -180°C! Also, I was unaware that light from Saturn took 10 times as long to reach us as light from the Sun. (I'm not sure I would call these things spooky though.)