First Webb infrared spectrum of Mars
This is Webb’s first near-infrared spectrum of Mars, demonstrating Webb’s power to study the Red Planet with spectroscopy.
Whereas the Mars images show differences in brightness integrated over a large number of wavelengths from place to place across the planet at 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 analyse the features of the spectrum to gather additional information about the surface and atmosphere of the planet.
This near-infrared spectrum of Mars was captured by the Near-Infrared Spectrograph (NIRSpec) on 5 September 2022, 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, by using, for example, the Planetary Spectrum Generator, abundances of given molecules in the atmosphere can be derived.
