The telescopes and instruments at the WM-Keck Observatory in Hawaii allow us to study Jupiter’s large moons. They are all confirmed to have auroras, like Earth’s, but with some differences.
The late André Brahic and Jean-Pierre Bibring told Futura that what struck them and their colleagues during nearly 50 years of exploring the planets of the solar system was their great diversity. There is also another unit so that planetary scientists can partially implement what they have learned from studying the Earth.
Today, a team of astronomers using the instruments of the WM-Keck Observatory on Maunakea in Hawaii, just announced that they have highlighted in the visible wavelengths the phenomenon of the Aurora Borealis on the four main moons of Jupiter, that is the famous Galilean moons. In order of distance from Jupiter there is first Io, the volcanic, Europa, the icy, then Ganymede and Callisto. The researchers published their findings in two articles in The Planetary Science Journal.
Highlighting the polar auroras of the Medici moons, as Galileo named them in honor of his protector of the Medici family, required high-resolution spectrometers, Keck explains in the press release the moons were cast in the shadow of Jupiter. Detection would have been much more difficult anyway, since the moons passed in front of Jupiter’s face during the day, as the light from the auroras was drowned out by that reflected off the gas giant’s clouds.
Auroras speak about the composition of the atmospheres of Jupiter’s moons
The auroras have more or less distinct colors and characteristics and occur at the top of the moons’ atmospheres, which are thinner than in the case of Earth. So we see the emissions from the atoms being bombarded by the charged particles channeled into Jupiter’s powerful magnetosphere. Spectrometers have shown that the four Galilean moons have oxygenated auroral emissions very similar to what we see in the sky near the Earth’s poles, but the atmospheres on Jupiter’s moons are much thinner and thinner, we get a dark red color that nearly 15 times brighter than the familiar green light on Earth.
On Europa and Ganymede, oxygen also glows in the infrared. At Io, Jupiter’s innermost moon, volcanic gas and dust clouds, some hundreds of kilometers high, influence the nature of auroral emissions. These feathers contain salts like sodium chloride and potassium chloride, which break down to create additional colors. So the sodium gives Io’s auroras the same yellow-orange glow that we see in urban streetlights.
Astronomer and planetary scientist Katherine de Kleer sums it up roughly like this: “The brightness of the different colors of the aurora tells us what the atmospheres of these moons are likely made of. We find that molecular oxygen, similar to what we breathe here on Earth, is probably the main constituent of the atmosphere of icy moons. »
Astronomers have used new datasets and archives from NASA’s Hubble Space Telescope to uncover evidence of water vapor in the atmosphere of Jupiter’s moon Ganymede. The vapor is present due to the thermal excitation of water molecules from the moon’s icy surface. For a fairly accurate French translation, click the white rectangle at the bottom right. Then the English subtitles should appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose French. © NASA Goddard
An atmosphere that freezes in a few hours
The research team also brought some additional elements that confirm the thesis of the presence of water vapor in the atmospheres of Europa, Ganymede and Callisto, without really ending the debates on the subject. We expect this presence because we strongly suspect the presence of subterranean oceans, which is actually a certainty in the case of Europa, where probable geysers were discovered with Hubble.
Measurements by planetary scientists of the presence of sulfur dioxide in Io’s atmosphere have also confirmed what Futura already stated in a previous article, from which we reproduce the content in part.
Io appears as a hellish world covered with sulfur deposits. But when the Moon passes through Jupiter’s shadow during a solar eclipse, which occurs about every 42 hours, its atmosphere, which consists largely of sulfur dioxide (SO2), literally freezes and contracts – evidenced by the sudden drop in SO2 in that atmosphere made noticeable by the spectrometer.
We are certainly far from the Sun, so the temperature of Io’s atmosphere is 127 Kelvin (-146 °C) despite its active volcanism. But during the two hours the Moon spends in Jupiter’s shadow, it dips to 105 Kelvin (-168°C) before rising again as it leaves. At this temperature, SO2 suddenly condenses and solidifies before fully sublimating once the eclipse is over.