Webb’s unique observation post nearly 1.5 million kilometres away at the Sun-Earth Lagrange point 2 (L2) provides a view of Mars’ observable disk (the portion of the sunlit side that is facing the telescope). As a result, Webb can capture images and spectra with the spectral resolution needed to study short-term phenomena like dust storms, weather patterns, seasonal changes, and, in a single observation, processes that occur at different times (daytime, sunset, and nighttime) of a Martian day.

Because it is so close, the Red Planet is one of the brightest objects in the night sky in terms of both visible light (which human eyes can see) and the infrared light that Webb is designed to detect. This poses special challenges to the observatory, which was built to detect the extremely faint light of the most distant galaxies in the universe. Webb’s instruments are so sensitive that without special observing techniques, the bright infrared light from Mars is blinding, causing a phenomenon known as “detector saturation.” Astronomers adjusted for Mars’ extreme brightness by using very short exposures, measuring only some of the light that hit the detectors, and applying special data analysis techniques.

Webb’s first images of Mars, captured by the Near-Infrared Camera (NIRCam), show a region of the planet’s eastern hemisphere at two different wavelengths, or colours of infrared light. This image shows a surface reference map from NASA and the Mars Orbiter Laser Altimeter (MOLA) on the left, with the two Webb NIRCam instrument field of views overlaid. The near-infrared images from Webb are shown on the right.