Crossing the divide and looking homeward

CuriosityLast time around, I mentioned that the Curiosity team was looking at alternative routes to get the rover down to the crossing-point for the start of its explorations of “Mount Sharp” at the centre of Gale Crater and, more immediately, to a target of interest for further science studies.

The desire to seek alternative routes came as a result of periodic examinations of Curiosity’s aluminium wheels revealing they’d suffered more wear and tear during recent traverses of very rough terrain than had been anticipated. While not a threat to the rover, mission managers would still prefer to lessen the impact of the rover’s southerly transit over what has proven exceptionally rugged ground.

At the time of writing that last update, planners were considering taking Curiosity over a sand dune roughly a metre (3 feet) in height sitting between two rocky scarps, as the terrain beyond the dune, dubbed “Dingo Gap”, appeared to be markedly less rough. While a little more circuitous than a direct-line drive, crossing the dune would still allow the rover to get to its next target for taking samples, a rocky outcrop dubbed “KMS-9″.

The view over “Dingo Gap”, captured on Sol 528 (January 30th, 2014), shows a westward-leading valley of much smoother terrain compared to the rover’s recent drives. The largest of the dark rocks on the sand to the right of the scene are about 60 cm (2 feet) across. This image was captured via Curiosity’s Mastcam and is shown unprocessed: the colours are as the human eye would see them on Mars under local daylight conditions (click to enlarge)

While other routes were under consideration as well, it was decided to take Curiosity “Dingo Gap” after it had been ordered to drive up to the base of the dune and take a peep directly over the top of the mound to get a detailed view of the land on the other side. The rover actually made the crossing  on Sol 535 (February 6th), and a series of nine black-and-white images captured by the rear hazard-avoidance cameras (Hazcams) were later strung together to form a short video of the crossing.

series of nine images captured by the rover’s rear Hazcams show progress over “Dingo Gap”. At the start of the sequence, Curiosity’s front wheels were on the base of the dune’s slope, and the entire traverse covered a distance of some 7 metres (23 feet) – click to enlarge

With the crossing made, Curiosity is set to travel to “KMS-9”, something over half a kilometre away, and which comprises three different terrain / rock types offer a relatively dust-free area for examination and further drilling operations. The area is one of the number of potential “waypoints” identified from orbit that missions scientists hope will help provide greater insight in the soil, rock and climatic conditions which may have once existed around “Mount Sharp” and help build up a clearer picture of changes in conditions which may have occurred within the region through which the rover is travelling.

Looking Home

It’s sometimes hard to understand the gulf which lies between Earth and Mars – a gulf humans will one day cross. Part of the problem is that because both planets move in different orbits (and Mars’ orbit is somewhat more elliptical to Earth’s), the distance can vary greatly over time. When both planets are on the same side of the Sun to one another and their orbits are at their closest, the distance can be as “little” as 56 million kilometres (about 34.4 million miles), but when on  the opposite side of the sun from one another, the distance can be as much as 400 million kilometres (250 million miles).

A recent image from Curiosity helped put these vast distances into some perspective. Around 80 minutes after sunset on Sol 529 (January 31st, 2014), the rover tilted its Mastcam upwards and captured an image of a very distant Earth hanging in the evening sky, with a very faint Moon close by.

In this composition image, the Earth is seen in the main picture as it appears from the surface of Mars. In the inset, the image has been processed to reveal both Earth and her moon (click to enlarge)
In this composition image, the Earth is seen in the main picture as it appears from the surface of Mars. In the inset, the image has been processed to reveal both Earth and her moon (click to enlarge)

At the time the image was captured, Earth lay some 160 million kilometres (100 million miles) from Mars. While Earth is the brightest object next to the Sun in the Martian sky, the Moon’s magnitude is rough equal that of background stars, and so it is harder to identify without additional image processing, as shown in the inset.

The picture marks the first time Curiosity has photographed both the Earth and the Moon as seen from Gale Crater. However, it is not the first time the two of them have been imaged from Mars.

Perhaps the most famous of these images was captured in 2003 by NASA’s now defunct Mars Global Surveyor using its high-resolution Mars Orbiter Camera (MOC). This was the first time the Earth had been seen as a visible disk from another planetary body in the Solar System. Even so, the Moon was still so faint, some post-processing was required to enhance it.

Earth as seen from Mars orbit, May 8th, 2003, as captured by the Mars Orbiter Camera aboard the Mars Global Surveyor vehicle. The original MOC image was black-and-white, colour has been added as a part of post-processing to reveal the prominent shape of South America (click to enlarge)

Like Earthrise, Bill Ander’s iconic images of Earth captured on December 24th, 1968, as Apollo 8 carried humans around the Moon for the first time, The Blue Marble and Pale Blue Dot before them, these images show just how small and remote our world really is. Even our own back yard of the Solar System is amazingly huge. They also serve to give us a glimpse of the future, and a time when human crews, orbiting Mars and exploring its surface, take a moment to look back home.

MSL coverage in this blog

All images courtesy of NASA / JPL