First Webb Space Telescope images of the Red Planet


Webb’s first images of Mars, captured by his NIRCam instrument on September 5, 2022 [Guaranteed Time Observation Program 1415]. Left: Reference map of the Mars hemisphere observed by NASA and the Mars Orbiter Laser Altimeter (MOLA). Top right: NIRCam image showing reflected sunlight from 2.1 microns (F212 filter), revealing surface features such as craters and layers of dust. Bottom right: Simultaneous NIRCam image showing about 4.3 micron emitted light (F430M filter) 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 captured its first images and spectra of[{” attribute=””>Mars. The powerful telescope provides a unique perspective with its infrared sensitivity on our neighboring planet, complementing data being 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 observation post is nearly a million miles away from Earth at the Sun-Earth Lagrange point 2 (L2). It 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 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 to 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 Mars’ extreme brightness by measuring only some of the light that hit the detectors, using very short exposures, and applying special data analysis techniques.

Webb's Orbit

Webb orbits the Sun near the second Sun-Earth Lagrange point (L2), which lies approximately 1.5 million kilometers (1 million miles) from Earth on the far side of Earth from the Sun. Webb is not located precisely at L2, but moves in a halo orbit 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), show a region of the planet’s eastern hemisphere at two different wavelengths, or colors of infrared light. This image shows a surface reference map of[{” attribute=””>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 on shown on the right.

The NIRCam shorter-wavelength (2.1 microns) image [top right] is dominated by reflected sunlight, and thus reveals surface detail similar to that apparent in visible light images [left]. The rings of the Huygens crater, the dark volcanic rock of Syrtis Major, and the brightening of the Hellas Basin are all apparent in this image.

The longest wavelength NIRCam image (4.3 microns) [lower right] shows thermal emission – the 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 the atmosphere. The brightest region of the planet is where the Sun is almost overhead, as it is usually the hottest. Brightness decreases towards the polar regions, which receive less sunlight, and less light is emitted from the cooler northern hemisphere, which experiences winter at this time of year.

James Webb L2 Space Telescope

The James Webb Space Telescope. Credit: NASA Goddard Space Flight Center

However, temperature is not the only factor affecting the amount of 4.3 micron light reaching Webb with this filter. When the light emitted by the planet passes through the atmosphere of Mars, some of it is absorbed by carbon dioxide (CO2) molecules. Hellas Basin – which is the largest well-preserved impact structure on Mars, spanning more than 1,200 miles (2,000 kilometers) – appears darker than the surroundings because of this effect.

“It’s actually not a thermal effect at Hellas,” explained lead researcher Geronimo Villanueva of NASA’s Goddard Space Flight Center, who engineered these Webb observations. “The Hellas Basin is at a lower elevation and therefore experiences higher atmospheric pressure. This higher pressure results in a suppression of 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 disentangle these competing effects in these data. »

Villanueva and her team also published Webb’s first near-infrared spectrum of Mars, demonstrating Webb’s power to study the Red Planet with spectroscopy.

Composition of the atmosphere of Webb Mars

Webb’s first near-infrared spectrum of Mars, captured by the Near-Infrared Spectrograph (NIRSpec) on September 5, 2022, as part of the 1415 Guaranteed Time Observing Program, across 3 slit arrays (G140H, G235H, G395H). The spectrum is dominated by reflected sunlight at wavelengths below 3 microns and thermal emission at longer wavelengths. Preliminary analysis reveals that 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, using, 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

While the images show integrated differences in brightness over a large number of wavelengths from place to place on 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 spectra features to gather additional information about the planet’s surface and atmosphere.

This infrared spectrum was obtained by combining measurements from the six high-resolution spectroscopy modes of the Webb Near Infrared Spectrograph (NIRSpec). Preliminary spectrum analysis shows a rich set of spectral features that contain information about dust, icy clouds, the type of rocks on the planet’s surface, and the composition of the atmosphere. Spectral signatures – including deep valleys called 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 that they will submit to a scientific journal for peer review and publication.

Going forward, the Mars team will use this imaging and spectroscopic data to explore regional differences across the planet and to search for traces of gases in the atmosphere, including methane and hydrogen chloride.

These NIRCam and NIRSpec observations of Mars were made as part of Webb’s Cycle 1 Guaranteed Time Observation (GTO) solar system program led by AURA’s Heidi Hammel.

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