James Webb goes in deep on Mars temperature and atmosphere

By Georgina Torbet September 24, 2022

Although the James Webb Space Telescope was built primarily for looking back at the earliest and most distant galaxies, it can also be used for a host of other scientific observations — including looking at targets right here in our own solar system. Webb will perform a major study of Jupiter and has already imaged Neptune. Now, Webb has been used to get a fascinating look at our planetary neighbor, Mars.

It’s actually pretty difficult for Webb to study Mars because it is so close, and therefore very bright in both the visible light portion of the spectrum and in the infrared wavelengths at which Webb observes. The brightness can oversaturate the detectors which are designed to pick up very faint light sources. But Webb’s NIRCam camera was able to capture the martian surface, with two images captured at different wavelengths shown below.

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Webb’s first images of Mars, captured by its NIRCam instrument. — 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. NASA, ESA, CSA, STScI, Mars JWST/GTO team

The shorter wavelength image, shown at the top, is similar to a visible light image and shows features like craters and basins. The longer wavelength image, shown below, shows how the planet is radiating heat. The brightest spot is where the sun is directly overhead, with cooler regions toward the poles. The Hellas Basin also appears darker, though this isn’t because of temperature effects but rather due to the effects of altitude and air pressure.

Webb was also able to capture Mars using its spectrometry instruments. These can split light into different wavelengths to see the composition of an object — in this case, looking at the composition of the martian atmosphere as a whole. There are clear indications of carbon dioxide, water, and carbon monoxide, and what is impressive about this is how well the data fits the model of what we already know about Mars’s atmosphere. This shows just how effective Webb’s instruments are for this kind of spectrometry work — and how effective Webb has the potential to be when looking into the atmospheres of exoplanets.

Webb’s first near-infrared spectrum of Mars, captured by the Near-Infrared Spectrograph. — 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. NASA, ESA, CSA, STScI, Mars JWST/GTO team

The research using this Webb data is still being worked on and has not yet been published or peer-reviewed, so it shouldn’t be taken as definitive. But it goes to show just how versatile a tool Webb can be, with more Webb data on Mars still to come.

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