The NASA probe has discovered huge new craters on Ganymede
Two missions previously photographed Ganymede , the largest moon in the solar system, the Voyager 1 mission in 1979 and the Galileo spacecraft in the mid-1990s. Some of these images, however, were taken at a non-ideal angle, leaving large empty spots of which the scientists knew nothing; technology has also improved dramatically since those missions were launched. So scientists were thrilled when NASA's Jupiter explorer Juno revealed the crater-covered surface of the moon in the greatest detail ever and spotted sparkling auroras extending between Ganymede's poles and the equator.
These images have delineated a plethora of new features on Ganymede's surface, including impact craters up to 100 kilometers wide, explained Goeffrey Collins, a geologist at Wheaton College in Massachusetts, at the Lunar and Planetary Science Conference. it took place from 7 to 11 March in Texas. The images also revealed several smaller craters, 40 to 50 km wide and multiple features that scientists believe may be the result of Ganymede's volcanic activity.
“We found calderas-like, similar features. to what we have seen previously in other parts of Ganymede, ”said Collins. Calderas are volcanic craters which in the case of Ganymede were probably created by cryovolcanoes that emit water and frozen gases from inside the moon. The number of these features seen in Juno's images suggests much more intense volcanic activity on the moon than scientists previously expected.
Europa, the frozen moon of Jupiter. Credits: NASA / ESA / W. Sparks (STScI) / USGS Astrogeology Science Center
“This actually increases the number of total caldera-like features we found across Ganymede by 30 percent,” Collins explained. Not only is Ganymede the largest moon in the entire solar system, 26% larger than the planet Mercury, but it is also the only moon that we know to have its own magnetic field.
Variations in this magnetic field led scientists to conclude that the moon must have a huge subterranean ocean of salt water, which is up to 96km deep and hidden under a 150km thick crust of ice and rock. The ocean makes Ganymede a privileged candidate for the existence of primitive forms of life. Orbiting 1.07 million km away from the gas giant Jupiter, Ganymede is embedded in Jupiter's magnetic field and enormous gravity, which attracts passing asteroids and comets.
“We have now been able to see the exact positions of [auroral] emissions, ”Pippa Molyneaux, a researcher at the Southwest Research Institute in San Antonio, Texas, told the conference. “We were able to see the latitudinal extent of the aurora for the first time and we see that there are very sharp boundaries at the polar edges of both ovals, while as we move towards the equator, the emissions decrease more gradually, so future models should explain it ”. Ganymede will be the main focus of the next European Jupiter Icy Moons Explorer (JUICE), which is expected to be launched next year.
