Webb’s first images of Mars: a heat map and more


This is one of Webb’s first images of Mars, acquired on September 5, 2022. It shows infrared light — aka heat — emitted from the day side of Mars. See the subsolar point label? This is where the sun was above Mars when Webb acquired this image. Hellas Basin – a huge, roughly circular impact basin in Mars’ southern hemisphere – is also marked. Picture via Nasa/ ESA/ CSA/ STScI/ Mars JWST/ GTO team.

Webb’s first images of Mars

The Hubble telescope sees in visible (or ultraviolet) wavelengths. But the new Webb telescope sees mostly in the infrared. It captures a part of the electromagnetic spectrum that we humans cannot see with our eyes, but can feel as Heat. And now we have the first infrared images and spectra of Mars, published today (September 19, 2022) on the Webb Telescope Blog. Alise Fisher, who wrote about the images for NASA, said they complement each other:

… Data is collected by orbiters, rovers and other telescopes.

And, wow, do they ever! For me, it’s feels as if we were literally seeing Mars with new eyes.

Two smiling humans, in bright yellow, orange and red colors.
We humans cannot see in infrared, but we perceive infrared radiation as heat. This image shows what humans would look like if seen in infrared. By the way, some land creatures see in infrared wavelengths, including some snakes, which use this sense at night to aim and then strike their prey. Image via Cody.pope/Wikimedia Commons (GFDL).

What do we see?

Notice the words “subsolar point” on the images of Mars on this page. It is the point on Mars where the sun is at its zenith (directly overhead). And, of course, Mars rotates. It rotates on its axis at about the same rate as the Earth (Mars completes one revolution every 24.6 hours, so its day is almost the same length as our day). Mars rotates below this subsolar point, and what we see in this image is heat coming from the brightest part of Mars’ dayside (as opposed to its cooler nightside).

What can we learn? Writing on the Webb Telescope Blog, Alise Fisher noted that Webb:

…provides a view of the observable disk of Mars (the part of the sunlit 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.

And NASA said:

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.

These fascinating new observations from Webb remind me of some of the great Mars watchers of the past — like Christiaan Huygens in the 1600s and Percival Lowell in the early 20th century — peering into Mars through their ground-based telescopes. I wish they could have seen those Webb images!

2 photos of part of Mars, one orange and brown, one yellow to brown image of the same region, with labels.
The first images of Mars by Webb! On the left is an image from Webb’s NIRCam instrument at infrared wavelengths of 2.1 microns (reflected sunlight). The left image shows the surface features and dust layers of Mars. The image on the right is a simultaneous NIRCam image at infrared wavelengths of about 4.3 microns (emitted light, aka heat, from the daytime surface of Mars). The image on the right shows temperature differences with latitude and time of day (it’s noon below the subsolar point, for example). “The bright yellow area is just at the saturation limit of the detector,” NASA said. Picture via Nasa/ ESA/ CSA/ STScI/ Mars JWST/ GTO team.

It’s a growing gibbous Mars

By the way, also note that Mars is not quite complete in the image above. Webb’s observation outpost in space is nearly a million miles (1.6 million km) away at Lagrange Sun-Earth 2 (L2) point. That’s four times the moon’s distance from us. This contrasts with the distance from Mars to Earth in September 2022 of about 79 million miles (about 127 million km), according to TheSkyLive.com). So essentially Earth and the telescope are the same distance from Mars.

And, at this moment, Mars appears almost full from Webb’s (or Earth’s) perspective. Almost, but not quite. That’s because Earth is currently racing behind Mars in its smaller, faster orbit. And we will pass between Mars and the sun on December 8, 2022. This is when his day side will fully face us. And that’s why now is the perfect time to start observing Mars, with the eye alone.

But Mars’ relative proximity to Earth now and the brightness of our skies aren’t helpful to those trying to observe Mars with Webb. As explained by Alise Fisher on the Webb Telescope blog:

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.

There is so much more to say about these images. There are many more details in Alise Fisher’s post on the Webb Space Telescope blog. Enjoy the pictures! No doubt there are more to come…

3 views of Mars in varying brightness and detail with labels.
See bigger. | Webb’s first images of Mars, captured by his NIRCam instrument September 5, 2022 [Guaranteed Time Observation Program 1415]. Left: Reference map of the Mars hemisphere observed by NASA and the Mars Orbiter Laser Altimeter (MOLA). Top right: NIRCam image showing reflected sunlight from 2.1 microns (F212 filter), revealing surface features such as craters and layers of dust. Bottom right: Simultaneous NIRCam image showing about 4.3 micron emitted light (F430M filter) 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. Image via NASA/ ESA/ CSA/ STScI/ Mars JWST/GTO team.
Chart with vertical bars of different colors and irregular white lines.
See bigger. | Webb’s first near-infrared spectrum of Mars, captured by the Near-Infrared Spectrograph (NIRSpec) on September 5, 2022, as part of the 1415 Guaranteed Time Observing Program, across 3 slit arrays (G140H, G235H, G395H). The spectrum is dominated by reflected sunlight at wavelengths below 3 microns and thermal emission at longer wavelengths. Preliminary analysis reveals that 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, using, for example, the Planetary Spectrum Generator, abundances of given molecules in the atmosphere can be derived. Image via NASA/ ESA/ CSA/ STScI/ Mars JWST/GTO team.

Conclusion: Webb’s first images and spectra of Mars were released today (September 19, 2022).

Via NASA’s Webb Space Telescope (@NASAWebb on Twitter)

Via the Webb Telescope Blog

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