On September 5, NASA’s James Webb Space Telescope captured its first images and spectra of Mars. The powerful telescope provides a unique perspective with its infrared sensitivity on our neighbor planet, complementing data collected by orbiters, rovers and other telescopes. Webb is an international collaboration with ESA (European Space Agency) and CSA (Canadian Space Agency). Webb’s unique observatory is nearly a million miles from Earth at the Sun-Earth Lagrange 2 (L2) point. Provides a view of the observable disk of Mars (the part of the sunlit side facing the telescope). As a result, Webb can capture images and spectra with the spectral resolution needed to study short-term phenomena such as dust storms, weather patterns, seasonal changes and, in a single observation, processes that occur at different times (day, sunset and night ) of a Martian day. Because it is so close to Earth, 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 for the observatory because it was built to detect the extremely faint light of the most distant galaxies in the universe. In fact, 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 the extreme brightness of Mars by measuring only part of the light that hit the detectors, using very short exposures and applying special data analysis techniques. Webb orbits the Sun near the second Sun-Earth Lagrange point (L2), which is about 1.5 million kilometers (1 million miles) from Earth on the far side of Earth from the Sun. Webb is not exactly at L2, but orbits in a halo around L2 as it orbits the Sun. In this orbit, Webb can maintain a safe distance from the bright light of the Sun, Earth, and Moon, while also maintaining its position relative to Earth. Credit: STScI Webb’s first images of Mars [top image on page], captured by the Near Infrared Camera (NIRCam), shows a region of the planet’s eastern hemisphere in two different wavelengths, or colors, of infrared light. This image shows a surface reference map from NASA and the Mars Orbital Laser Altimeter (MOLA) on the left, with the two Webb NIRCam instrument fields of view superimposed. Near-infrared images from Webb are shown at right. The shorter wavelength NIRCam image (2.1 microns). [top right] is dominated by reflected sunlight and thus reveals surface details similar to those seen in visible light images [left]. The rings of Huygens Crater, the dark volcanic rock of Greater Syrtis, and the glow in the Hellas Basin are all evident in this image. The longer wavelength NIRCam image (4.3 microns). [lower right] shows thermal emission – light emitted by the planet as it loses heat. The brightness of the 4.3 micron light is related to the temperature of the surface and atmosphere. The brightest region on the planet is where the Sun is almost overhead, because it is generally warmest. Brightness decreases toward the polar regions, which receive less sunlight and less light is emitted from the colder northern hemisphere, which experiences winter at this time. The James Webb Space Telescope. Credit: NASA Goddard Space Flight Center However, temperature is not the only factor that affects the amount of 4.3 micron light that reaches Webb with this filter. As the light emitted by the planet passes through the Martian atmosphere, some is absorbed by carbon dioxide (CO2) molecules. The Hellas Basin – which is the largest well-preserved impact structure on Mars, spanning more than 1,200 miles (2,000 kilometers) – appears darker than its surroundings because of this phenomenon. “This is actually not a thermal phenomenon in Hellas,” explained principal investigator Geronimo Villanueva of NASA’s Goddard Space Flight Center, who designed these Webb observations. “The Greek basin is at a lower elevation, and therefore has a higher atmospheric pressure. This higher pressure leads to a suppression of the thermal emission in this particular wavelength range [4.1-4.4 microns] due to an effect called pressure broadening. It will be very interesting to tease apart these competing effects in these data.” Villanueva and his team also released Webb’s first near-infrared spectrum of Mars, demonstrating Webb’s power to study the Red Planet with spectroscopy. Webb’s first near-infrared spectrum of Mars, recorded by the Near-Infrared Spectrograph (NIRSpec) on September 5, 2022, as part of the Guaranteed Time Observing Program 1415, over 3 slits (G140H, G235H, G395H). The spectrum is dominated by reflected sunlight at wavelengths shorter than 3 microns and thermal emission at longer wavelengths. Preliminary analysis reveals that the spectral dips appear at specific wavelengths where light is absorbed by molecules in the Martian atmosphere, namely carbon dioxide, carbon monoxide and water. Other details reveal information about dust, clouds, and surface features. By constructing a model of the best-fitting spectrum, using, for example, the Planetary Spectrum Generator, abundances of atmospheric molecule data can be generated. Credit: NASA, ESA, CSA, STScI, Mars JWST/GTO team While the images show differences in brightness embedded in a large number of wavelengths from place to place across the planet on a particular day and time, the spectrum shows the subtle variations in brightness between hundreds of different wavelengths representative of the planet as a whole. Astronomers will analyze the characteristics of the spectrum to gather additional information about the planet’s surface and atmosphere. This infrared spectrum was obtained by combining measurements from all six modes of the Webb Near-Infrared Spectrometer High Resolution Spectroscopy (NIRSpec). Preliminary analysis of the spectrum shows a rich set of spectral features containing information about dust, icy clouds, the type of rocks on the planet’s surface and the composition of the atmosphere. The spectral signatures—including deep valleys known as absorption features—of water, carbon dioxide and carbon monoxide are easily detected with Webb. The researchers have analyzed the spectral data from these observations and are preparing a paper to submit to a scientific journal for peer review and publication. In the future, the Mars team will use this imaging and spectroscopy data to explore regional differences across the planet and look for traces of gases in the atmosphere, including methane and hydrogen chloride. These NIRCam and NIRSpec observations of Mars were conducted as part of Webb’s Cycle 1 Guaranteed Time Observing (GTO) solar system program led by AURA’s Heidi Hammel.
