09 February 2014

Curiosity captures rare photo of Earth from the surface of Mars, 100 million miles away

Mars rover Curiosity, which is now roughly half way to its final destination, has taken a brief pause to look up at the sunsetting sky and take a photo of Earth. In the photo above, Earth is roughly 99 million miles away and if you squint, you can also see the Moon. According to NASA, if you were walking on the surface of Mars, the Earth and Moon would be visible to the naked eye and would appear as “bright evening stars.” This is only one of a handful of times that Earth has been imaged from more than a few thousand miles away. It’s always rather humbling to see Earth that mote of dust suspended in a sunbeam just sitting there, tiny and insignificant, dwarfed by the grandest of black expanses.

This photo, PIA17936, was captured by Curiosity’s Mastcam about 80 minutes after sunset on the rover’s 529th sol (Martian day; January 31 in Earthling terms). NASA has processed the photo to remove “effects of cosmic rays,” whatever that means (I kind of wish NASA had published the unaltered version, so that we could find out). At a distance of 99 million miles, Earth and Mars are relatively close in this photo due to their differing orbits, they can be up to 250 million miles apart (at which point the Earth would be a lot dimmer in the sky).

The Pale Blue Dot (Earth), seen by Voyager-1, when it was around 1.6 billion miles away

With this photo, Curiosity joins the lofty ranks of spacecraft such as Cassini, Voyager, and Messenger which have also captured stunning photos of the Pale Blue Dot. Voyager famously captured the photo above, of Earth seemingly nestled within Saturn’s rings, as it continued on its journey to the edge of the Solar System. Below, you can see a photo taken by Cassini a more modern spacecraft with a higher-resolution camera from the dark side of Saturn.

The Earth and Moon as seen from the shadow of Saturn by Cassini

We should also take this opportunity to update you on Curiosity’s progress. The last we heard from the one-ton rover, way back in July 2013, it had just turned on its autonomous driving software and begun the five-mile journey to the base of Mount Sharp the goal of the rover’s primary mission. In six months, it’s completed around 40% (2.1 miles) of the linear distance. The actual driven distance is higher, as Curiosity has had to navigate its way around myriad obstacles.

Curiosity’s progress on Mars, as of Sol 533

Most recently, NASA was faced with a tough decision to attempt to cross a sand dune, or to take a longer, rougher route around it. Both options were fraught with danger. Curiosity’s predecessor, Spirit, died when it got stuck in a Martian sand trap but on the other hand, NASA scientists were concerned that Curiosity’s wheels might be badly damaged by the rougher ground. In the photo below, you can see the damage that Curiosity’s light aluminium wheels have already sustained more damage than NASA had expected after just six months of driving in Gale Crater.

Damage to Curiosity’s aluminium wheels

In the end, Curiosity opted for the sand dune and as of a couple of nights ago, it had successfully made it to the top, and is now surveying the route down the other side. Discovery News created a rather cool animated GIF of the rover scaling the sand dune, pictured below.

Curiosity scaling the Dingo Gap sand dune on Mars



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