The James Webb Space Telescope continues making history as it explores our solar system, galaxy and the universe. This time, Webb turned its powerful cameras towards Mars.
NASA’s James Webb Space Telescope continues making sensational history. Although this time, its cameras did not point to some far away galaxy, what the space telescope captured is nonetheless impressive. Using Webb, scientists captured the first images and spectra of Mars on Sept. 5. With its infrared sensitivity, the telescope provides an unprecedented view of our neighboring planet. This complements data collected by orbiters, rovers, and other telescopes.
From Webb’s unique vantage point, nearly a million miles away at the sun-Earth Lagrange point 2 (L2), it is possible to observe Mars’ observable disk (the part of the sunlit side that faces the telescope). This allows Webb to acquire images and spectra at a spectral resolution that allows scientists to study short-term phenomena like dust storms, weather patterns, seasonal changes, as well as processes that take place at different times of the Martian day (daytime, sunset, and nighttime) all in a single observation. Its proximity makes the Red Planet one of the brightest objects in the night sky, both in visible light, which can be seen by human eyes, and in infrared light, which can be detected by Webb.
As a result, the observatory faces special challenges, as it was designed to detect the faint light of the most distant galaxies in the universe. Due to Webb’s sensitive instruments, the bright infrared light from Mars blinds users without special observing techniques, causing a phenomenon known as “detector saturation.” A very short exposure, the measurement of only some light hitting the detectors, and the application of special data analysis techniques were used to adjust for Mars’s extreme brightness.
A region of Mars’ eastern hemisphere is pictured in two different wavelengths of infrared light as captured by Webb’s Near-Infrared Camera (NIRCam). A NASA surface reference map of Mars and the Mars Orbiter Laser Altimeter (MOLA) are shown in the first image in this article, with the two NIRCam fields of view overlaid. On the right, you can see a near-infrared image from Webb. As you can see in the NIRCam image [top right], reflected sunlight dominates the shorter wavelength image and thus reveals surface details similar to those that can be seen in the visible-light image [left]. A photograph of the Hellas Basin offers a glimpse into the Huygens Crater rings, the dark volcanic rock of Syrtis Major, and the brightening in the Huygens Crater.
The NIRCam image [lower right] shows a planet losing heat as it emits longer wavelengths (4.3 microns). In the 4.3-micron wavelength range, brightness is related to surface and atmospheric temperatures. Due to its heat, the region where the sun is near overhead is the brightest on the planet. In the cooler northern hemisphere, which is experiencing winter at this time of year, the brightness decreases toward the polar regions, which receive less sunlight.
It is important to note, however, that temperature is not the only factor affecting how much 4.3-micron light reaches Webb through this filter. CO2 molecules absorb some of the light emitted by Mars as it passes through the planet’s atmosphere. The Hellas Basin, which covers more than 1,200 miles (2,000 kilometers) and is the largest and best-preserved impact structure on Mars, appears darker than its surroundings due to the effect of this dust. Geronimo Villanueva, the principal investigator for these Webb observations at NASA’s Goddard Space Flight Center, explained that this is not a thermal effect at Hellas. As Hellas Basin is located at a lower altitude, air pressure is higher. As a result of pressure broadening, the thermal emission at this wavelength range [4.1-4.4 microns] is suppressed. These competing effects in these data will be very interesting to separate,” the researchers explained in a statement.
A near-infrared spectrum of Mars was also released by Villanueva and his team, showing how powerful Webb’s spectroscopy is. Despite the fact that the images show how brightness varies depending on wavelength based on time of day and location on the planet, the spectrum shows subtle changes in brightness between hundreds of different wavelengths that represent the entire planet. To gain further insight into the planet’s surface and atmosphere, astronomers will analyze features of the spectrum.
Using Webb’s Near-Infrared Spectrograph (NIRSpec)’s six high-resolution spectroscopy modes, this infrared spectrum was obtained. The spectrum of the planet shows rich spectral features that shed light on dust, icy clouds, rocks on the surface, and the composition of the atmosphere. By using Webb, water, carbon dioxide, and carbon monoxide can be detected by their spectral signatures, which include deep valleys known as absorption features. These observations have been analyzed by the researchers, who are preparing a paper to be submitted for peer review and publication in a scientific journal. This imaging and spectroscopic data will be used by the Mars team in the future to investigate regional differences throughout the planet and to search for trace gases such as methane and hydrogen chloride.
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