Science

First images of Mars taken by the James Webb Space Telescope reveal the secrets of the atmosphere

The James Webb Space Telescope (JWST) took the first images of Mars by observing infrared light from the Red Planet with high sensitivity.

The first images and spectra of Mars taken by the James Webb Space Telescope were published on Monday (September 19) at the Europlanet Science Congress. (will open in a new tab) (EPSC) 2022. Images and measurements were taken on September 5, 2022 from the JWST position about a million miles (1.6 million kilometers) from Mars.

Images of the observed disk of Mars – the side of the planet illuminated by the sun and facing the telescope – were taken by the Webb near-infrared camera. (will open in a new tab) (NIRCam) and can provide planetary scientists with a unique look at Earth’s close neighbor, providing data that can be used in conjunction with observations made by rovers like NASA’s Perseverance and ships in Martian orbit.

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Since Mars is relatively close and very bright, it is not the easiest object for the JWST to see incredibly distant and faint objects to visualize.

“Mars is so bright that the challenge is how to see it,” said Giuliano Liuzzi, scientist and lead researcher at NASA’s Planetary Systems Laboratory at the Goddard Space Flight Center, at an EPSC press conference to release the images.

To prevent the bright infrared light from Mars from blinding the JWST instruments, scientists used very fast shutter speeds to observe the Red Planet. This meant measuring only a fraction of the light that reached the JWST detectors and then applying special techniques to analyze the collected data.

“We can see this incredible resolution, we have the space telescope’s infrared diffraction limit, and it’s fantastic. We can see the entire planet,” Liuzzi continued.

24/7 observations of Mars

JWST was able to capture images and spectra with the spatial resolution that astronomers need to study short-term phenomena such as Martian weather patterns, dust storms, and even changes caused by the planet’s seasons.

In addition, the Webb Telescope can capture events that occur at different times during the Martian day – during the day, at sunset, and at night – in a single observation.

The first JWST images of Mars show an area in the planet’s eastern hemisphere in two different wavelengths of light.

The shortwave image is dominated by reflected sunlight and shows features on the Martian surface that resemble those seen in visible light. These features include the Huygens crater, an impact crater about 280 miles (450 kilometers) wide, and dark volcanic rock in Sirte Major.

The Webb Space Telescope’s NIRCam camera has captured the light that Mars emits in the longer infrared as it loses heat. The brightness of this light is related to the temperature of Mars and its atmosphere, with the brightest and warmest region being where the sun is almost above the planet.

The brightness decreases towards the Martian polar regions, which are less exposed to sunlight, and in the northern hemisphere of the planet, where it is now Martian winter.

However, the amount of light reaching the JWST is not only related to the temperature of the planet. Images collected by the telescope can also give insight into the chemical makeup of the Martian atmosphere and surface.

Atmospheric cues in the Hella pool

Analyzing the spectrum of light detected from Mars with data collected by the James Webb Space Telescope could help astronomers determine the composition of its atmosphere and its surface.

After analyzing JWST images, Liuzzi and his team found that the 1,200-mile-wide (1,930 km) Hellas basin appears darker than its surroundings, even during the region’s hottest Martian day.

“One of the nice things is that you can see the dark spot, which is a pool on Mars. We didn’t expect this. We saw something very bright, but it got darker,” Liuzzi said. “In fact, this is not a thermal effect in Hellas.”

The darkening seen in this well-preserved impact structure is the result of light passing through the Martian atmosphere and being absorbed by carbon dioxide.

“The Hellas Basin is at a lower altitude and therefore experiences higher atmospheric pressure,” explains researcher Goddard. “This higher pressure leads to the suppression of thermal radiation in that particular wavelength range due to an effect called pressure expansion. It will be very interesting to parse these competing effects in this data.”

The new images also demonstrate the ability of the James Webb Space Telescope to study Mars using a technique called spectroscopy, based on measurements made with the Near Infrared Spectrograph (NIRSpec) instrument.

First Near Infrared Spectrum of Mars taken by the James Webb Space Telescope taken by the Near Infrared Spectrograph (NIRSpec) on September 5, 2022. (Image credit: NASA, ESA, CSA, STScI, Mars JWST/GTO team) (will open in a new tab)

Because chemical elements absorb and emit light at very specific wavelengths, planetary scientists can use spectroscopy to study the “fingerprints” that various chemicals leave in light passing through a planet’s atmosphere to determine its composition.

The scientists’ initial results show spectral features encoded with information about Martian dust, icy clouds, atmospheric composition and the type of rocks found on the planet’s surface.

Observations with JWST should be able to detect the presence of water, carbon dioxide, carbon monoxide and other chemical compounds.

Liuzzi pointed to the debate about the presence of methane on Mars, with initial ground-based observations and rovers suggesting the compound, albeit sporadically. While measurements from the ExoMars Trace Gas Orbiter (TGO) have failed to confirm this, and observations from Earth are complicated by the presence of methane in our planet’s atmosphere, Liuzzi believes the JWST observations could be crucial.

“The big mystery was that the rovers on the surface and the observational data left a gap from zero to 10 kilometers. [6 miles]”, he said. “Now we have James Webb, we can see the full column [of the atmosphere] to the very surface where the rover is located. So we came up with a new way to solve this puzzle.”

Methane is important, Liuzzi added, because it could tell planetary scientists about many of the geologic processes on Mars, including that something big hit the Red Planet from space. Methane can also point to biological activity in the ancient history of the planet.

“This is what is now our main goal,” said Liuzzi.

The JWST team is currently preparing a paper outlining its findings for peer review.

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