Every time the Curiosity rover takes a ‘selfie’ on Mars, we get the same questions: “How was this picture taken?” “Why isn’t the rover’s arm or the camera visible in this picture?” “In all of Curiosity’s selfies, the camera mast is never visible… why?” And (sigh) “What is NASA hiding???”
The answer is simple and quite logical. Look any selfie image you’ve taken. Does your hand show up in the picture?
No, because it is behind the camera.
The same is true with the rover’s arm. It is behind the camera, so it isn’t part of the picture. In your own selfies, if you’ve done a good job of positioning things, your arm doesn’t appear in the photo either.
Just think of the rover’s arm as the ultimate interplanetary selfie stick. The best selfie-stick pictures are where the stick doesn’t show up in the image and it appears you had your own photographer. That’s what happens with the Curiosity rover self-portraits.
Additionally, while the rover selfies look like they are just one single image taken by the wide-angle camera on the rover, it is actually a series of individual images stitched together. The picture above is made from dozens of images the rover took of itself with the Mars Hand Lens Imager (MAHLI) camera at the end of the rover’s robotic arm. Curiosity moves its robotic arm around and over itself and the ground, taking pictures from every angle. These pictures are then stitched, just like panoramic images are put together to form a complete image of your total view.
As Curiosity’s Engineering Camera Team Leader Justin Maki explains in the video below, “The rover is imaging the deck while the arm is behind the camera, and then to image the ground … again the arm is behind the camera when taking these pictures. When we stitch them all together, you don’t see the arm in any of the pictures.”
Click on the image to start the video:
It’s interesting to note, that while the lead image above — the latest rover selfie — does not include the rover’s robotic arm, the shadow of the arm is visible on the ground. You’ll notice there seems to be an extra “joint” in the arm, which is just part of the image editing, particularly the stacking of the images where the ground is, where the image editors used more than one image for that area. For the selfie image below, taken in 2012, the imaging team chose not to include any shadow of the arm.
Why does the rover imaging team take these rover selfies? Are they just joining in on the selfie craze here on Earth?
These images are actually a great way for the rover team to look at all the components on Curiosity and make sure everything looks like its in good shape. The wheels are of particular interest because there has been some damage to them from driving over sharp rocks. These images also document various areas where the rover has worked, and often include things like the holes the rover has drilled into the Martian rocks and soil.
Emily Lakdawalla at The Planetary Society has written an extremely detailed post on how the rover takes self-portraits. She created this composite image of the 72 individual frames the Mars Hand Lens Imager (MAHLI) had to take in order to cover the 360-degree view showing the rover’s underside, a “belly selfie“:
Here’s another longer video from JPL that explains all the rover’s cameras.
Source: Universe Today, written by Nancy Atkinson