James Webb Space Telescope captures first images of Mars, and the results are phenomenal

Webb can image the entire planet at once in high resolution at a short exposure time, allowing for the study of dust storms, weather patterns and seasonal changes.
Deena Theresa
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Webb’s first images of Mars, captured by its NIRCam instrument.

NASA, ESA, CSA, STScI, Mars JWST/GTO team 

The James Webb Space Telescope has captured its first images and spectra of Mars, revealing atmospheric data that previous instruments couldn't detect.

Captured with its Near InfraRed Camera, or NIRCam instrument from JWST's position around a million miles (1.6 million kilometers) from Mars, on September 5, along with data from its Near InfraRed Spectrometer (NIRSpec), the images were released on Monday, September 19, at the Europlanet Science Congress 2022.

Due to its proximity, the Red Planet is one of the brightest objects in the night sky in terms of visible light and the infrared light that Webb is designed to detect. But, this posed challenges to the observatory as it wasn't the easiest object for the JWST — designed to see incredibly distant and faint objects — to visualize.

"Mars is so bright, that the challenge is how to see it," NASA Planetary Systems Laboratory at Goddard Space Flight Center scientist and lead investigator Giuliano Liuzzi said in an EPSC press conference to mark the release of the images.

According to NASA's blog, 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". Therefore, astronomers had to employ very short exposures, measuring only some of the light that hit the detectors, and applying special data analysis techniques.

"We can see this incredible resolution, we have the diffraction limit of a space telescope in the infrared, which is fantastic. We can see the whole planet," Liuzzi said.

Tricky to capture, but Webb did it

The image below shows a surface reference map from NASA and the Mars Orbiter Laser Altimeter (MOLA) on the left, with the two Webb NIRCam instrument fields of view overlaid.

James Webb Space Telescope captures first images of Mars, and the results are phenomenal
Webb’s first images of Mars, captured by its NIRCam instrument with a reference map of the observed hemisphere of Mars from NASA and the Mars Orbiter Laser Altimeter.

The JWST was able to 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.

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The images reveal a region of the planet's eastern hemisphere at two different wavelengths or colors of infrared light. The NIRCam shorter-wavelength (2.1 microns) image is dominated by reflected sunlight and reveals surface details similar to those apparent in visible-light images. The rings of the Huygens Crater and the dark volcanic rock of Syrtis Major, are evident in the image.

The Hellas Basin, a crater that was created when something gigantic slammed into Mars about four billion years ago, also shows up in Webb's first image of Mars. The crater, which is 2,300 kilometers (1,400 miles) wide and 7 kilometers (4.4 miles) deep just south of the planet’s equator, is a cooler shade in comparison to the rest of the daylit side of the planet.

The NIRCam longer-wavelength (4.3 microns) image shows thermal emission – light that is given off by the planet as it loses heat. It reveals information about heat emitted from the Martian surface and atmosphere, as well as the concentrations of carbon dioxide in the atmosphere.

Webb can also study Mars using spectroscopy

Geronimo Villanueva of NASA’s Goddard Space Flight Center, who designed the Webb observations, also released Webb’s first near-infrared spectrum of Mars, demonstrating Webb’s power to study the Red Planet with spectroscopy.

James Webb Space Telescope captures first images of Mars, and the results are phenomenal
Webb’s first near-infrared spectrum of Mars, captured by the Near-Infrared Spectrograph.

The spectrum shows the subtle variations in brightness between hundreds of different wavelengths representative of the planet as a whole. Astronomers will analyze the features of the spectrum to gather additional information about the surface and atmosphere of the planet. The spectral signatures – including deep valleys known as absorption features – of water, carbon dioxide, and carbon monoxide are easily detected with Webb.

Scientists can also now easily track down the sources of any trace gases that they spot. "Hunting for these particular [chemical] species and, eventually, identifying the sources of these species is a work that can be done in a much more promising way with JWST," said Liuzzi.

The researchers are currently preparing a paper they will submit to a scientific journal for peer review and publication.

The Mars team will be using this imaging and spectroscopic data to explore regional differences across the planet and to search for trace gases in the atmosphere, including methane and hydrogen chloride.

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