Infrared Saturn, pictured by James Webb
The astronomer Rafael Bachiller reveals to us in this series the most spectacular phenomena of the Cosmos. Pulsating research topics, astronomical adventures and scientific news about the Universe analyzed in depth.
The James Webb Space Telescope has captured an infrared image of Saturn that shows us an unknown and surprising facet of the ringed giant.
high atmosphere
Among the many tasks that have been entrusted to the Webb telescope are observations of the planets of our solar system.. By working in the infrared, this telescope has already offered us unusual images, for example, of Jupiter with its auroras and of Uranus with its rings. Now it is Saturn's turn.
The image that has recently been made public has been taken in a monochromatic infrared filter centered at 3.23 microns of wavelength, characteristic of methane.. The planet's disk appears quite dark, indicating a high methane content in the upper atmosphere, a compound that absorbs this wavelength of light that the planet is receiving from the Sun.
The northern hemisphere of the planet appears somewhat brighter than the southern hemisphere due to the seasonal differences that one would expect: it is summer in the north, while the southern hemisphere is at the end of winter.. However, a deep darkness is observed at the north pole that is not known to what is due.
A clear brightening towards the limb is also observed, suggesting that, at very high altitudes, methane not only absorbs light, but also emits some radiation, very possibly due to a fluorescence phenomenon (re-emitted light after absorption).
What this infrared image does not show are the characteristic horizontal bands that are visible that are familiar to us from photographs taken in the optical domain.. Such stripes follow the lines of constant latitude of the planet and are due to cloudy areas in deep layers of the atmosphere.
rings
In the infrared image, Saturn's icy rings appear very bright, confirming that they do not have methane in their composition. The strong contrast between the rings and the dark disk is what gives the Webb image its unusual appearance.. Saturn has ten known rings, and in this image it is possible to observe fine details in the three main ones of the system (A, B and C). These three rings have a width of 275,000 kilometers (equivalent to three quarters of the Earth-Moon distance), the F ring is much thinner and paler, but it can also be seen very clearly in the new image.
Saturn's rings in the infrared
The rings are formed by swarms of rocks and pieces of ice, these fragments have very different sizes: from a grain of sand to a terrestrial mountain. One of the most surprising characteristics of the rings is that they are extremely thin: their vertical thickness barely reaches one kilometer.. That is, if we consider the ratio of their thickness to their width, then in proportion the rings turn out to be much thinner than a razor blade.
The Cassini divide, which separates the A and B rings, is about 4,800 kilometers wide, while the Encke divide, an annular gap within the A ring, is only 325 kilometers wide.
moons
Three of Saturn's moons – Dione, Enceladus and Tethys – are also clearly visible on the left side of the new infrared image.. However, these are not the largest moons of the giant planet, the largest – Titan, Rhea and Iapetus – are not observable in this snapshot.. Let's remember that 83 moons are already known in Saturn
The same Webb telescope has recently been used to observe one of the most interesting of these moons: Enceladus, from whose south pole some immense geysers of water vapor emerge.. The results were published in Nature and the article can be consulted at this link. The plumes reach a height of about 10,000 kilometers above the surface of Enceladus, that is, about twenty times greater than the diameter of the moon.. Some of the material from these plumes feeds into Saturn's E ring.
Vapor plume on Enceladus . villanueva
NASA announces that Webb has already taken deeper images of the entire Saturn system, including its moons and rings. Such images should show details of the fainter rings and smaller satellites.. So the images that we show here are only a small appetizer of what is to come.
Rafael Bachiller is director of the National Astronomical Observatory (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain.