A sense of scale…

There’s now a steady flow of gorgeous images coming back from Mars for us to enjoy, thanks to Opportunity, the fantastic team behind her, and even more people who work hard to get those pictures online quickly, for us to drool over and play about with. Some – wide angle shots – show the far horizon of Endeavour crater, waaay over there to the east. Others, with a smaller field of view, show the northern edge of Cape York, where Oppy will soon be trundling about looking for more Homestakes. Still others, taken through the rover’s microscope, show individual clods of dirt and spills of dust. It’s hard to link between them, I think, but I’d like to give it a try.

Yesterday a set of – I think – beautiful MI images came down from Mars, showing a small area of the “North Pole” dust dunes in great detail. You can see dust flecks, cracked, harder patches of dust, and small gritty stones. Here’s one of those images…

Now, if you take a quartet of those images and stitch them together, play about with the sharpening, brightness and contrast, you can make something like this

Got to be honest, I *love* that picture, I’m really pleased with how it turned out. But what does it actually show? I’ll let “Road to Endeavour” friend Paolo Bellutta explain…

The APXS field of view is about 1cm when in contact with the surface of Mars and therefore each spectra is representative of an area about 1cm in diameter which includes “disturbed” soil (soil that was rearranged by the rover wheels) and “undisturbed” soil (original Martian surface).  In order to have a better measurement of what the subsurface is composed of we took a spectra of the undisturbed Martian surface over the weekend (Sol 2957-58-59) and on Sol 2960 we placed the APXS on a part of the rover tracks that appeared coming from the deepest part of the excavated terrain.  By computing the difference between the two spectra we can have a better understanding of soil composition under the weathered surface. 

Whenever we place the APXS we want to make sure we localize the precise position of the instrument using the Microscopic Imager.  Teh Field of View of the MI is about 3x3cm and in order to make sure we capture the entire imprint of the MB contact plate, which is about 4cm in diameter, we take a mosaic of 2×2 MI frames.  Since there is (intentional) overlap between the images, the area covered ( by the mosaic shown above – Stu) is approximately 5x5cm. 

Since the Microscopic Imager focus cannot be adjusted (as opposed to MSL’s MAHLI) we take images at different distances from the surface.  In order to capture this mosaic we actually captured images at five different distances from the surface and at the distance where we believe we should have the sharpest image we take four images
which will then be processed on the ground to reduce noise due to dust deposition on the MI lens.  At the same “best focus” position we also take a “stereo” image where we move the IDD turret and point the MI to the same spot.  These images allows us to have compute the 3D surface.  These images compose what we call an “MI stack”.

Adding all up for this Sol MI mosaic we captured a total of 36 images!  Typically we take more, 15 images per five-layer MI stack, but in some cases we take up to 23 images per seven-layer stack (one at the bottom, one at the top of the stack, four at each intermediate position in the stack plus one stereo image).

Before taking an MI stack we typically do what we call a ‘Mossbauer touch’, that is we use the MB contact plate to precisely locate the martian surface. The contact plate trips when a force of 1 Newton is applied. If you take 22 sheets of A4 or D format paper from your printer tray, you roll them up to form a cylinder of about 4cm in diameter and lay the cylinder vertically on your hand, that’s about the force that is needed to trip the MB plate. Not much, is it?

In the MI mosaic we see about 1/2 of the imprint of the MB as a result of our MB touch. Why only 1/2? That eas because in order to reach a specific location on the surface we had to rotate the turret and touch only with one side of the MB. This is a result of having lost the Azimuth actuator on the IDD. Whenever we need to reach something that is on the side to the plane where the IDD can move we need to twist the turret to the right or to the left.

Sometimes the surface is too rough, or scientists do not want us to modify the surface and therefore the MB touch cannot be used prior to the MI stack(s), that’s when the seven-layer MI stacks come into play. These accomodate more inaccuracy in surface position knowledge.

Thanks Paolo! So, what you’re seeing on that mosaic of mine is the half circle imprint of the MB, which is about 3cm across, making the whole mosaic between 5 and 6cm on each side. That’s a tiny area of Mars, in which you can see tiny, tiny details and features. Which is pretty cool.

But you know what might be even more cool? A 3D version…

You know what you should do? Click on that to enlarge it, and then imagine you’re an ant crawling around on Mars. I’m sure that’s the view you’d have…

…but you know what would be even MORE cool? Zooming in on that little bit of Mars from further away – much further away. Surely that would help give us a sense of scale..?

Try this – you might need to click on the image to begin the animation, and it only runs through once…

As usual with my posts here, that’s just a bit of fun, I’m not claiming it’s particularly ‘worthy’ or useful, I just liked the idea of zooming-in on that little bit of Mars, that’s all. 🙂

But what about the bigger picture? When Oppy looked up again from that little area of the surface of Mars, having taken pictures of its rocks, stones, dust and dirt, over to the east she saw those gorgeous, gorgeous, crater-pocked hills rearing up on the eastern side of Endeavour. We’ve all got used to those hills, haven’t we? But again, it’s hard to get a sense of scale, and I’ve always wondered what they would look like, how far away they would look, if I was there, standing next to Oppy..?


Just outside Kendal, roughly south-west of our town, is a local beauty spot that Stella and I (and many others) often escape to when the usually-dire Cumbrian weather relents and allows the Sun to break through the Mordor-like clouds, giving us a rare sunny, hot day to enjoy. Just above the little village of Brigsteer is Helsington Church, with a small car park on the edge of a sheep-grazed field, from where we can enjoy a sweeping panoramic view from the east to the west, a view which takes in a patchwork quilt of green fields, criss-crossed by spider cobweb roads, and countless tiny barns, farm buildings and cottages. It’s gorgeous, and if we’re treated to a nice day we often pull together a picnic and flee out of town to sit on the warm grass up there, and just relax. On the SW horizon, far away, are some hills, very pretty, dimmed by distance and the haze of the countryside…

….and it occurred to me yesterday, while I sat there eating my pork pie, crisps and cake, trying to ignore the indignant “Get orf my land!” glares from the rather-to-close-for-comfort sheep and reading my newly-bought copy of Kim Stanley Robinson’s new novel, “2312” (VERY good so far, even though there’s not much Mars in it!) that, well, hmmm, those hills might be as far from our picnic spot as the eastern hills of Endeavour are from Oppy, as she works her way down the northern end of Cape York’s spine?

So, once home, onto Google Earth, to find out. And you know what? It works out! Well, kind of. The hills visible from Helsington Church are just over 23km away, while the hills visible to Oppy over on the other side of Endeavour are around 21km away, so there’s not a lot of difference, not really. So, now, whenever we go up there, with our sandwiches and Coke, and I look out across those fields at these distant hills, I’ll be able to imagine I’m there on Cape York, looking across Endeavour at the hills on its eastern side…

Even if the view on Mars would be different because of the lack of air and haze there, and the closer horizon (smaller planet), I still quite like the idea of just being able to go somewhere and see some mountains that are the same distance away from me as the mountains Oppy is looking at on Mars.. 🙂

Meanwhile, Oppy is still there, on Mars, looking at dust beneath her wheels, mountains on her horizon, and a huge, cathedral dome sky above her. At the moment she’s the only working spaceprobe on the surface of Mars – or on any other world inthe solar system for that matter – but soon she’ll (hopefully) be joined by Curiosity, which, even as you read these words, is screaming towards the Red Planet and her date with destiny.

Exciting times we live in, aren’t they?

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5 Responses to A sense of scale…

  1. Astro0 says:

    Love that animation. Blows my tiny mind 🙂

  2. starbuck5250 says:

    What a stunning post! Love the details that Paolo provided, but your wonderful interpretation makes it all real for me.

  3. hawsey says:

    Love it , especially the animation ,keep up the good work .Your posts are always appreciated .

  4. hawsey says:

    P.S think you should photoshop Oppy in to the car park 😉

  5. Nicole says:


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