On May 15, NASA’s Psyche mission flew just 4500 km above the surface of Mars, en route to a metallic asteroid. It was using the Red Planet’s gravity to increase its speed and adjust its trajectory.
So-called ‘gravity assist flybys’ are common for interplanetary spacecraft. They make travel to the inner or outer solar system more efficient. But they also provide a valuable opportunity to test the spacecraft’s science instruments. Psyche did just that, and captured images of Mars’ dusty surface in the hours before and after its closest approach.
Hearing about Psyche’s flight, the teams behind ESA’s long-running Mars Express and its High Resolution Stereo Camera (HRSC) wondered whether the paths of the two spacecraft would cross, allowing them to point at the same patch of the Red Planet.
Teams working on both missions had coordinated their observing plans weeks in advance, exchanging trajectories and observation timelines to photograph the same parts of the Martian surface as closely as possible.
The images shown here represent one of two coordinated observations. On the left is an image taken by Mars Express. On the right is the same landscape captured by Psyche’s camera just 1 hour 50 minutes later.
Photos show part of Noachis Terra, one of the oldest known parts of the surface of Mars. The area is dotted with sand dunes filled with craters which are shown in dark blue.
Although relatively close in time, the images were taken from very different distances and viewing angles. By the time Psyche passed through this region, about 2.5 hours after its closest approach to Mars, its altitude had increased to about 41,000 km. Meanwhile, Mars Express was at an altitude of only 6000 km; It was looking from an inclined angle, while Psyche was looking almost straight down towards the surface of Mars.
The two coordinated observations are not only good visual comparisons, but can also be used to help calibrate Psyche’s cameras. By comparing the brightness and color recorded in each image pixel, scientists can detect small differences in how the two cameras respond to light. Although more investigation is needed to see whether the observations are similar enough to be useful, these comparisons can help check and adjust Psyche’s camera to ensure it works better in the future.
Image Notes
The resolution of the Mars Express image is 800 meters per pixel. The resolution of the Psyche image is 500 meters per pixel. Although the resolution of Mars Express’s HRSC camera is less than 20 meters per pixel under optimal conditions, its observing settings were adjusted to capture the best image equivalent to Psyche’s image resolution at a large distance of 41,000 km.
Both images are RGB color composites generated from the corresponding red, green and blue filters (Psyche image) or image channels (Mars Express image).
Both images have been enlarged for better comparability.
[Image description: A square image showing a mostly-orange patch of Mars’s surface, scattered with sharp craters, many of which are blue inside. A vertical bar lets viewers slide between two views of exactly the same patch of surface. Whilst the landscape is identical, the left image is slightly more orange and the right image is slightly more blue.]
