The Lunar Reconnoissance Orbiter usually investigates the moon, but in May, the opportunity to photograph both the Earth and Mars in a single shot captured its electronic eye. Here's the story on how the spacecraft pulled of the technical challenge of catching two planets more than 110 million kilometers apart.
Can you see Mars? It's that little speck that can easily hide behind any dust on your screen. Image credit: NASA
At the time this photograph was taken, Earth was 376,687 kilometers away from the satellite, and Mars was roughly 300 times farther away at a staggering 112,500,000 kilometers. To increase the challenge even farther, the camera mounted on the satellite is actually a pair of narrow-angle cameras. Each camera images a single row of pixels that are mosaic together to make a single pair. The cameras can't slew on their own, so if the satellite isn't moving, they would just image the same area over and over and over again. That means the imaging team needed to capture a photograph where the two subjects differed dramatically in scale and intensity, while maneuvering the satellite to cover the entire area of interest.
To make sure they got it right, the team set up the shot and took practice images on May 8, 2014 before the real-deal on May 24, 2014. They tinkered with camera settings to capture both planetary bodies in the same shot, fine-tuning spacecraft motion and camera exposure time. Once they took the image, they gently manipulated it during processing to enhance the shot for puny human eyes. Mars is contrast-stretched to make it visible: a linear scaling was applied to intensity values, improving contrast by adjusting the range of pixel values for the image.
NASA's Earth Observatory highlighted the final picture as an Image of the Day, describing what was happening on our home planet last May:
This view of Earth includes several cloud patterns that satellites observe frequently. A line of rain and thunderstorms are visible in a band near the equator, an area known as the Intertropical Convergence Zone. To the north, off the west coast of North Africa, notice the banks of closed-cell clouds over the Atlantic Ocean. Moving into the high latitudes, we see comma-shaped cloud patterns caused by extra-tropical cyclones.
Download the full-sized, unannotated image here.