by Danielle Nadin
Now more than ever, eyes are trained to the skies in search of habitable planets, moons and asteroids. Water is key to life, and confirming its presence anywhere other than Earth would be ground-breaking. A team of researchers lead by the University of Cologne’s Joachim Saur, with the help of NASA’s Hubble telescope, recently came forth with some of the best evidence of water beyond our world to date. Their findings were published in the Journal of Geophysical Research: Space Physics.
Jupiter’s largest moon, Ganymede, has long been suspected of hiding an ocean beneath its surface. This assumption was based on models developed in the 1970s.
Ganymede is the only known moon to have its own magnetic field (generated by its iron core), which was confirmed and measured in 2002 during NASA’s Galileo mission. This magnetic field is responsible for an interesting phenomenon called aurorae, which are glowing bands of hot, electrically charged gas that float near the moon’s poles. Ganymede is influenced by both its own magnetic field and Jupiter’s. As Jupiter’s magnetic field fluctuates, the aurorae are expected to rock back and forth as well.
This is not what researchers found. In fact, Ganymede’s magnetic field was powerful enough to create “magnetic friction”, a force capable of “fighting” Jupiter’s magnetic field, diminishing the rocking of the aurorae. Unable to use Hubble to search inside the moon for signs of water, Saur’s idea was to use NASA’s powerful telescope to observe the movement of the aurorae on its surface. His team predicted that, in the absence of a subterranean ocean, the bands would oscillate by approximately six degrees, whereas the force of a magnetic field generated by a large body of salt water would reduce these oscillations to roughly two degrees. As expected, the aurorae only fluctuated by two degrees, supporting predictions that there is a large underground ocean on Ganymede.
Theoretical models estimate this ocean is 150 to 250 kilometers deep, shielded by a 150 kilometer thick crust composed primarily of ice. That is at least ten times deeper than the Earth’s oceans and could contain more water than all of our oceans combined! This unique new method of exploring what lies beneath foreign worlds’ surfaces has put Ganymede in the spotlight.
Although the moon is small, only slightly larger than Mercury, and so cold that any water on its surface would be frozen solid, the liquid gold it may inhabit has it gaining massive interest.
On April 24th, NASA will celebrate the Hubble Space Telescope’s 25th anniversary. Hubble continues to propel astronomical discoveries, enhancing our understanding of our solar system, the universe, and where we fit into the immensity of it all.