Mars seems to be massive in the first Webb images of the Red Planet

Webb’s first images of Mars, captured by its NIRCam instrument Sept. 5, 2022 [Guaranteed Time Observation Program 1415]. Left: Reference map of the observed hemisphere of Mars from NASA and the Mars Orbiter Laser Altimeter (MOLA). Top right: NIRCam image showing 2.1-micron (F212 filter) reflected sunlight, revealing surface features such as craters and dust layers. Bottom right: Simultaneous NIRCam image showing ~4.3-micron (F430M filter) emitted light that reveals temperature differences with latitude and time of day, as well as darkening of the Hellas Basin caused by atmospheric effects. The bright yellow area is just at the saturation limit of the detector. Credit: NASA, ESA, CSA, STScI, Mars JWST/GTO team

On September 5, NASA's James Webb Space Telescope got the first photos and spectra of Mars. The telescope, a partnership between the European Space Agency and the Canadian Space Agency, gives a unique view on our neighboring planet with its infrared sensitivity, supplementing data obtained by orbiters, rovers, and other telescopes. Webb's unique observation site at the sun-Earth Lagrange point 2 (L2) gives a glimpse of Mars' visible disk from roughly a million miles distant (the portion of the sunlit side that is facing the telescope).

As a result, Webb can acquire pictures and spectra with the spectral resolution required to examine short-term phenomena such as dust storms, weather patterns, seasonal variations, and processes that occur at multiple periods (daytime, sunset, and midnight) of a Martian day in a single observation. Because it is so close, Mars is one of the brightest objects in the night sky in terms of both visible light (which human eyes can see) and infrared light (which Webb is meant to detect). This presents unique problems to the observatory, which was designed to detect the incredibly weak light of the universe's most distant galaxies.

Webb's equipment are so sensitive that the strong infrared light from Mars is blinding without specific observation procedures, resulting in a situation known as "detector saturation." Astronomers compensated for Mars' extraordinary brightness by taking extremely brief exposures, detecting only a portion of the light that struck the detectors, and used advanced data analysis techniques. The Near-Infrared Camera (NIRCam) took Webb's first photographs of Mars, which show an area of the planet's eastern hemisphere at two distinct wavelengths, or hues of infrared light. The first picture in this article displays a NASA surface reference map on the left, with the Mars Orbiter Laser Altimeter (MOLA) and two Webb NIRCam sensor fields of view superimposed. Webb's near-infrared photographs are presented on the right.

Webb’s first near-infrared spectrum of Mars, captured by the Near-Infrared Spectrograph (NIRSpec) Sept. 5, 2022, as part of the Guaranteed Time Observation Program 1415, over 3 slit gratings (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 the spectral dips appear at specific wavelengths where light is absorbed by molecules in Mars’ atmosphere, specifically carbon dioxide, carbon monoxide, and water. Other details reveal information about dust, clouds, and surface features. By constructing a best-fit model of the spectrum, for example, the Planetary Spectrum Generator, abundances of given molecules in the atmosphere can be derived. Credit: NASA, ESA, CSA, STScI, Mars JWST/GTO team

The NIRCam shorter-wavelength (2.1 micron) image [top right] is dominated by reflected sunlight, revealing surface features comparable to those visible in visible-light photographs [left]. This view shows the rings of the Huygens Crater, the black volcanic rock of Syrtis Major, and the brightening in the Hellas Basin. The NIRCam longer-wavelength (4.3 microns) picture [bottom right] shows the planet emitting thermal emission light as it loses heat. The brightness of 4.3-micron light is affected by surface and atmospheric temperatures. Because it is typically the hottest, the brightest place on the earth is when the sun is nearly above.

The brightness falls toward the polar areas, which receive less sunshine, and less light is released from the chilly northern hemisphere, which is currently experiencing winter. The temperature, however, is not the only factor influencing the quantity of 4.3-micron light reaching Webb through this filter. Some of the light released by Mars is absorbed by carbon dioxide (CO2) molecules as it travels through the planet's atmosphere. Because of this effect, the Hellas Basin, Mars' most well-preserved impact feature spanning more than 1,200 miles (2,000 kilometers), seems darker than its surroundings.

Geronimo Villanueva of NASA's Goddard Space Flight Center, who designed these Webb observations, stated that this is not a thermal effect at Hellas. Because the Hellas Basin is lower in elevation, the air pressure is higher. Because of a process known as pressure widening, the greater pressure suppresses thermal emission at this specific wavelength range [4.1-4.4 microns]. It will be fascinating to separate these opposing impacts in this data.

Villanueva and his colleagues recently published Webb's first near-infrared spectrum of Mars, proving Webb's ability to investigate the Red Planet using spectroscopy. The photos illustrate variances in brightness summed across a large number of wavelengths from place to place throughout the world on a certain day and time, whereas the spectrum reveals minor variations in brightness between hundreds of distinct wavelengths indicative of the whole planet. Astronomers will examine the spectrum's characteristics in order to learn more about the planet's surface and atmosphere.

This infrared spectrum was created by merging observations from all six of Webb's Near-Infrared Spectrograph's high-resolution spectroscopic modes (NIRSpec). Preliminary study of the spectrum reveals a diverse range of spectral signatures containing information about dust, frozen clouds, the types of rocks on the planet's surface, and the makeup of the atmosphere. Webb detects spectral characteristics like as deep troughs known as absorption features of water, carbon dioxide, and carbon monoxide. The researchers have been studying the spectrum data from these sightings and are preparing a report for peer assessment and publishing in a scholarly journal.

The Mars team will use these imagery and spectroscopic data in the future to investigate regional variances throughout the planet and to seek for trace molecules in the atmosphere, such as methane and hydrogen chloride. The NIRCam and NIRSpec observations of Mars were made as part of Webb's Cycle 1 Guaranteed Time Observation (GTO) solar system mission, which was directed by AURA's Heidi Hammel.