by Margaret W. Carruthers, Space Telescope Science Institute
NASA’s James Webb Space Telescope captured its first images and spectra of Mars on September 5. The telescope, an international collaboration with ESA (European Space Agency) and CSA (Canadian Space Agency), provides a unique perspective with its infrared sensitivity on our neighboring planet, complementing data collected by orbiters, rovers and others telescopes.
Webb’s unique vantage point nearly a million miles away at Sun-Earth Lagrange Point 2 (L2) provides a view of Mars’ observable disk (the part of the illuminated side that faces the telescope). As a result, Webb can capture images and spectra with the spectral resolution needed to study near-term phenomena such as dust storms, weather patterns, seasonal changes, and, in a single observation, processes occurring at different times (day, sunset and night). ) of a Martian day.
Because it’s so close, the Red Planet is one of the brightest objects in the night sky in terms of visible light, which human eyes can see, and infrared light, which Webb is designed to detect. This poses particular challenges for the observatory, which was built to detect extremely faint light from the most distant galaxies in the universe. Webb’s instruments are so sensitive that without special observing techniques, Mars’ bright infrared light is blinding, causing a phenomenon known as “detector saturation.” Astronomers adjusted to Mars’ extreme brightness by using very short exposures, measuring only part of the light that hit the detectors, and applying special data analysis techniques.
Webb’s first images of Mars, captured by the Near Infrared Camera (NIRCam), show a region of the planet’s eastern hemisphere in two different wavelengths, or colors of infrared light. The first image in this article shows a NASA surface reference map and the Mars Orbiter Laser Altimeter (MOLA) on the left, with the two fields of view of the Webb NIRCam instrument superimposed. Webb’s near-infrared images are shown on the right.
The shorter wavelength NIRCam image (2.1 microns) [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.
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 over 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 leads to a suppression of thermal emission at 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 this 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.
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.
James Webb Space Telescope’s first exoplanet image revealed
Provided by the Space Telescope Science Institute
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