Nature does not fit into our ideas of neatly contained categories. Many things in nature blur the boundaries we try to draw around them. This is also true of Jupiter’s moon Ganymede, the largest moon in the Solar System. JWST took a closer look at Ganymede, a planet-like moon, to better understand its surface.

Ganymede is actually a planet, except it doesn’t orbit the Sun. If it revolved around the Sun instead of Jupiter, it would be no different from a planet. It has a different internal structure with a molten core that creates a magnetic field. It has a siliceous mantle very similar to Earth’s and a complex icy crust beneath which lies a deep ocean. It has an atmosphere, albeit thin. It is also larger than Mercury and almost as large as Mars. According to the authors of the new study, this is the archetype of the water world.

However, despite all this information about the giant moon, there are details that have not yet been disclosed. This is especially true for its complex surface. “After preliminary observations, several open questions remain about the nature, origin, and processes that produced the current composition of Ganymede’s surface,” the authors of the new paper write. JWST has the ability to conduct observations to answer some of these questions. What did he find?

A team of researchers from the United States, Europe, and Japan examined Ganymede’s surface using JWST’s NIRSpec and MIRI instruments. Their results were published in a paper titled “Composition and thermal properties of the Ganymede surface from JWST/NIRSpec and MIRI data.” Will be published in the journal Astronomy and Astrophysicsand the lead author is French planetary scientist D. Boquely-Morvan of LESIA – Observatoire de Paris. Currently hosted on preprint server arXiv.

Two types of terrain dominate Ganymede’s surface: bright, icy, rugged terrain and dark regions. Light areas cover about two-thirds of the surface, and dark areas cover the rest. Both types are ancient, but the dark regions are older and also have dense craters. These two genres are mixed together; the lighter terrain cuts the dark terrain into strips.

The Galileo and Juno missions examined the chemical composition of Ganymede’s surface, as did ground-based telescopes. But there are still unresolved problems. “After preliminary observations, several unanswered questions remain about the nature, origin, and processes that produced the current composition of Ganymede’s surface,” the authors write.

Ganymede has enough CO2, but it appears to be trapped in other molecules. It is such positions that attract the attention of scientists. CO mapping ₂ This will help explain what the other molecules are and how the situation develops. Ganymede has water ice, but it appears shapeless. JWST mapped the distribution and properties of the ice. Ganymede also has a recently discovered 5.9 μm absorption band, and JWST may help determine its origin.

Ganymede’s temperature range means pure CO₂ No ice is expected on the lunar surface. JWST observations show that some of the CO₂ It is retained in water ice, although it is only 1% by mass. The rest is trapped in various minerals and salts.

As for water ice, JWST found that there is more ice in the polar regions. In these regions, Jupiter’s energetic ions spread across Ganymede’s surface. The authors write that this can be explained by “…a combination of micrometeoroid gardening, ice mining, and ion irradiation.” Water vapor then re-deposits on non-ice materials, forming purer water ice, which JWST easily detects.

Observations have shown that the 5.9 μm absorption band is common in Ganymede, but shows local variations. The researchers accept the possibility that this is due to insoluble organic material delivered by carbonaceous chondrites or comets, but definitively rule out this explanation. “Sulfuric acid H hydrates₂FOR THIS REASON₄+N₂“O are good candidates to explain the 5.9 μm band,” the authors write.

These are detailed results that mean a lot to scientists, but not much to the rest of us. But other findings are easier to understand. For example, Ganymede’s poles and some general differences between the leading and trailing edges. “The spectral properties of the polar regions are very different for the front and back sides,” they write. “The origin of these differences continues to be investigated.” This is partly due to Jupiter’s strong influence on its moons.

The relationship between Jupiter and Ganymede is similar to the relationship between the Sun and the Earth. Just as Jupiter’s plasma hits the backside of Ganymede, the solar wind hits Earth’s magnetosphere. Not only that, Ganymede’s magnetic field interacts with Jupiter’s magnetic field, helping to create Jupiter’s auroras.

Ganymede and Jupiter have a complex relationship, and some of that relationship goes back to Ganymede’s surface chemistry, where Jupiter’s plasma hits the moon’s poles and irradiates the ice. Although this research has improved our understanding of these and other issues, it does not give us the answers we seek. But this is science; It’s not just about fame and headlines.

Ganymede is a magnificent satellite, almost a planet. We know it probably formed from debris from Jupiter’s lower nebula, but that was billions of years ago. A lot has happened since then, leading us to see an intriguing world with a warm and potentially habitable ocean larger than all the oceans on Earth combined. These JWST observations are the most detailed, but according to the authors, we are not yet ready to fully interpret them. There will probably be a few more surprises when we do this.

“From an observational perspective, this JWST study demonstrated that observations aimed at probing diurnal variations in Ganymede’s surface properties can reveal unexpected processes,” the authors write. And, as is often the case, the results will inform and shape our next attempt to understand this fascinating world.

“Overall, the results obtained in this study will undoubtedly help optimize the observation strategies of the Satellite and Jupiter Imaging Spectrometer (MAJIS) on the ESA/JUICE mission that will further explore Ganymede.”

But we’ll have to wait. ESA’s JUICE mission launched last spring and will reach Jupiter in the summer of 2031. Get ready for new surprises from this planet-like satellite.