ALIEN LIFE drenched in HOT FLUID on Jupiter's Ganymede – is that so?
Hubble riddle: What's lurking inside mega-moon's hidden ocean?
The Hubble space telescope is usually eyeing up far away galaxies, but a novel technique has allowed it to peer inside the largest moon in our Solar System – and find signs of water.
Jupiter's Ganymede is massive, about twice the size of Earth's moon, and has both an iron core and its own magnetosphere. Just as with Earth, that magnetosphere causes auroras to form around Ganymede, and by using Hubble to study these, and how they interact with Jupiter's magnetic field, led to the discovery of a hidden ocean.
"I was always brainstorming how we could use a telescope in other ways. Is there a way you could use a telescope to look inside a planetary body?" said Joachim Saur of the University of Cologne in Germany.
"Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon's interior."
The aurora's movements were way out of line with theoretical models, indicating that there must be a large ocean under Ganymede's rock and ice surface that was causing the disruption. Subsequent calculations show that the ocean is massive – 60 miles deep, starting 95 miles below the moon's surface.
Liquid water outside of Earth is very rare indeed, and it's likely Ganymede's hot iron core, and the proximity to Jupiter, will keep the sea rather warm. Under such conditions life could be a possibility, although only in its most basic form.
"This discovery marks a significant milestone, highlighting what only Hubble can accomplish," said John Grunsfeld, assistant administrator of NASA's Science Mission Directorate.
"In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system. A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth." ®