In a surprise revelation on the eve of the Hubble Space Telescope’s 25th anniversary, NASA has announced that it has found evidence of the presence of a saltwater ocean on Ganymede, Jupiter’s largest moon. In a press release issued by NASA, they add that the underground ocean on Ganymede could contain more water than all the water on the Earth’s surface.
Scientists have, for years, attempted to find evidence of liquid water on worlds other than the Earth. While several planets and moons, including our own moon, have shown some evidence of water in the form of frozen ice and polar ice caps, so far, there has been no evidence of any of these worlds having enough liquid water to sustain life as we know it. This landmark discovery on Ganymede changes all that. Current estimates put the Ganymede saltwater seas to be a least 60 miles (100 km) deep — making the 11 km deep Marianas Trench, the deepest point on Earth, look silly. Unlike our Earthly ocean, though, Ganymede’s saltwater ocean is covered by a massive sheet of ice, 95 miles thick.
According to John Grunsfeld, associate administrator of NASA’s Science Mission Directorate at NASA Headquarters, Washington, the discovery of liquid water on Ganymede is a significant milestone. He credits the Hubble Space Telescope for the discovery.
“This discovery marks a significant milestone, highlighting what only Hubble can accomplish. 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.”
Ganymede, which also happens to be the biggest of all moons found in the solar system, is so large that it is actually bigger than the planet Mercury. It is also the only moon in the solar system known to have a magnetic field of its own. In fact, it is Ganymede’s magnetic field and its interaction with Jupiter’s much larger magnetic field that resulted in the discovery of water underneath its surface.
According to NASA, Ganymede’s magnetic field causes aurorae on its southern and northern poles — much like the ones observed on Earth. Using the Hubble Space Telescope, NASA observed the changes in Ganymede’s magnetic field and its aurorae when it interfered with Jupiter’s magnetic field. The interference caused the aurorae on Ganymede to move back and forth. Measuring the intensity and frequency of this back and forth movement, scientists were able to deduce that a large amount of saltwater exists underneath the frozen surface of Ganymede.
The idea to study the characteristics of the insides of Ganymede was put forth by a team of scientists under the leadership of Joachim Saur, of the University of Cologne in Germany.
“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? 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.”
After a detailed study of the aurorae observed on Ganymede’s poles, it was deduced that a strong magnetic field from within Ganymede was countering the effect of Jupiter’s magnetic field on it. It was suppressing the rocking of the aurorae on Ganymede’s poles by quite some margin. According to NASA, had it not been for the subterranean ocean, the rocking of the aurorae would have been six degrees instead of the currently observed two degrees.
Using this data, scientists estimated that the saltwater oceans on Ganymede could turn out to be much deeper than the oceans on Earth. The possibility of Ganymede being a world where water could be found was first suspected back in the 1970s during the Voyager missions. In 2002, NASA’s Galileo flew past Ganymede and gave evidence about the moon possessing a strong magnetic field paving way for today’s discovery.
[Image via NASA]