What new images from the James Webb Space Telescope teach us about the planet Mars

Close collaboration is expected on future missions to Mars for the use of the James Webb telescope.

The James Webb Space Telescope surprises us again with new images of a planet in the Solar System. This time it was the turn of our neighbor: Mars.

Although these are not as spectacular as those of the gas giants Jupiter and Neptune , it is true that they provide a lot of information about the relief of the red planet and the differences in temperature on its surface.

In addition, the James Webb has also obtained the spectrum of the planet: a characteristic curve that allows studying, among other aspects, the chemical composition of the Martian atmosphere.

Structure and relief of the planet Mars

It is called “the red planet” because of its clear reddish hue (distinguishable with the naked eye) due to the large amount of iron oxide present on its surface. His name is associated with Mars, the Roman god of war .

It is the second smallest planet in the Solar System, only behind Mercury. With a rotation period similar to that of Earth (about 24 hours and 39 minutes), Mars takes about 23 months to complete one revolution around the Sun.

Due to its small mass compared to Earth, Martian gravity is about 2.6 times less than that of our planet: if you can jump half a meter high on Earth, you would jump 1.2 meters on Mars .

Being the least dense inner planet , Mars is rocky in composition and is structured in different layers: a dense metallic core (made up mainly of nickel and iron), a surrounding silicate mantle, and an outer crust about 50 kilometers thick. The most abundant elements in this last layer are oxygen, silicon and iron, among others.

Some features of the Martian relief are unique in our Solar System. Mount Olympus, 22.5 kilometers high and with an extension that covers a large part of mainland France, leaves our Mount Everest almost insignificant.

Mars also has large expanses of rocky terrain made up of lower-elevation hills. In the lower image we can see these groups of rocks and hills (the so-called Methuselah outcrop ) taken by the Spirit rover in 2005.

It is a false color image for a better visual interpretation of the Martian relief, from three filters of different colors (red, green and violet), which the Spirit camera had incorporated.

Noteworthy is the Hellas Basin : a plain about 2,300 kilometers in diameter in the southern hemisphere of the planet formed after the impact of a meteorite. The resulting crater is the largest, reaching a maximum depth of about 6 kilometers.

On the other hand, Mars has the longest canyon system in the Solar System: the Valles Marineris . This gigantic depression reaches a length of about 4800 kilometers (practically the distance between California and New York) and 11 kilometers deep. By comparison, it is ten times longer than the Grand Canyon in Arizona.

It is believed that Mars may have contained liquid water on its surface millions of years ago, forming ancient river networks and deltas. In fact, the presence of rocks and minerals on the Martian surface, whose shape was shaped by the action of liquid water, support this statement.

Dry ice and frozen water in the polar ice caps

Our neighboring planet has two permanent ice caps at its poles. When we talk about ice we refer to both dry ice (made up of carbon dioxide) and water ice.

The only place on the planet where frozen water is visible on its surface is the north polar cap. In contrast, at the Martian south pole, solid water is located below a layer of frozen carbon dioxide.

A thin atmosphere made up mostly of carbon dioxide

The red planet has a very thin and sparse atmosphere made up mainly of carbon dioxide (95%), nitrogen and argon.

If you were to stand on the surface of this planet and look up into the Martian sky, it would appear blurry and reddish (due to high concentrations of suspended dust): we would lose the lovely bluish hue of our atmosphere.

The atmospheric pressure on Mars is about a hundred times less than that on Earth. This peculiarity has, among others, two important consequences:

  1. There are no large amounts of liquid water on the planet’s surface. This is due to the very low value of atmospheric pressure, which would cause liquid water to undergo rapid evaporation (or freezing).
  2. The sound on the red planet would be very different from what we would perceive on Earth.

Characteristics such as the speed of sound (almost 1.4 times lower than on our planet), volume (with a lower sound level on Mars) and sound quality (favoring low tones, since high tones are practically absorbed due to the high concentration of CO₂ in the Martian atmosphere) would be very different from those on our planet.

Compared to the large number of satellites possessed by the giant planets Jupiter and Saturn , Mars has only two small natural satellites called Phobos and Deimos.

Phobos is the larger of the two and the closest to the planet. Its shape is irregular, with an average size of about 22 kilometers, and it always presents the same face to Mars (similar to our Moon orbiting around the Earth, due to an effect called tidal coupling or synchronous rotation).

Deimos is the smallest natural satellite in the entire Solar System . With an average size of about 12 kilometers, it orbits the red planet at a greater distance than Phobos (also in synchronous rotation) in about 30 hours.

James Webb’s new images of Mars

Returning to the new images of Mars provided by the James Webb, it should be remembered that this space telescope operates in the infrared range .

This means that the colors shown in the following snapshots are not real: each hue represents areas of Mars where sunlight is reflected to a greater or lesser degree, or warmer or colder regions of the planet.

Thus, for example, the image above left was recorded by Webb’s NIRcam instrument at an infrared wavelength of 2.1 microns (wavelengths that the human eye can detect range from 0.38 microns in violet to the 0.75 microns of the red color).

It should be noted that this snapshot contains a lot of sunlight reflected by the red planet. For this reason, details of the Martian relief such as the Huygens crater, the Syrtis Major volcano and the Hellas basin can be distinguished in a similar way to an image in the visible (that is, in true color).

On the other hand, the upper right image shows the infrared radiation emitted by Mars at a wavelength of 4.3 microns. Warm colors represent areas of the planet at higher temperatures (such as the region surrounding the Hellas Basin), while violet tones are related to colder areas (such as the polar regions, where less energy falls). solar radiation).

The differences in temperature with the latitude of the place are notable, as well as the darkening of the Hellas basin caused by atmospheric effects.

What is the reason for the large yellow area surrounding the subsolar point of Mars, that is, the region that receives the greatest amount of solar radiation? The explanation lies in the enormous sensitivity of the James Webb instruments (originally designed to detect faint infrared signals from distant objects).

Because Mars is so close to the telescope, the planet’s bright infrared light has a blinding effect on James Webb’s instruments: this effect is called detector saturation.

Precisely, this large yellow area is right at the saturation limit of the detector, preventing the telescope from recording higher values ​​of infrared radiation from Mars.

The spectrum tells us about the Martian atmosphere

The James Webb Telescope is not only capable of recording images in the infrared for certain wavelengths, as in the previous snapshots: it can also obtain radiation values ​​in a range of wavelengths (the so-called spectrum ). The James Webb instrument tasked with this task is NIRSpec .

In this way, the graph in the upper figure represents the infrared radiation reflected and emitted by the planet Mars, against the infrared wavelengths in which the NIRSpec instrument operates (horizontal axis, from 1 to 5 microns).

It is notorious that, for specific wavelengths, the curve suffers from certain spectral dips: this is because infrared light is absorbed by molecules in the Martian atmosphere, specifically carbon dioxide, carbon monoxide, and water vapor.

In other words, these spectral curves allow us to identify the chemical compounds present in the Martian atmosphere (and any other planet whose infrared signal James Webb can detect).

Future implications of these new results on Mars

These promising results on the spectrum of Mars will be very useful when looking for traces of other less abundant gases in the Martian atmosphere (such as methane or hydrogen chloride).

In addition, and given its privileged location, the James Webb will be able to study different phenomena such as dust storms or certain weather patterns on the red planet. A close collaboration between this telescope and the different missions deployed on Mars is expected.The Conversation