NASA detects subsurface ocean on solar systems largest moon

NASA scientists announced theyve found evidence that Ganymede, the largest moon in the solar system, has a vast subsurface liquid ocean that contains more water than the Earths surface. Ganymede is already unique in other ways its larger than the planet Mercury (but less than half Mercurys mass), twice the mass of our own moon, and the only satellite known to have its own magnetosphere. Like Europa, Ganymede may have an incredibly thin atmosphere of oxygen. The discovery of a liquid ocean on Ganymede increases the chances that life exists or has existed within its depths.

This discovery marks a significant milestone, highlighting what only Hubble can accomplish, said John Grunsfeld, associate administrator of NASAs Science Mission Directorate at NASA Headquarters, Washington. 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.

Ganymedes magnetic field is the reason Hubble was able to peer across the void and detect the presence of subsurface water. Just as Earth has the northern and southern lights (Aurora Borealis and Aurora Australis), Ganymede has its own auroral belts, as shown below:

Water is whats known as dimagnetic, meaning it generates a weak magnetic field in opposition to whatever magnetic field is applied to it. The aurora around Ganymede are expected to rock back and forth in response to Jupiters magnetic field (Ganymedes self-generated magnetic field is embedded in Jupiters as shown below):

What the scientists found is that the rocking motion across the surface was much reduced compared to what theyd expect to see if there was no water underneath the surface of the moon. Current thinking is that the ocean is an estimated 60 miles deep, but buried 95 miles beneath the icy crust.

Weve known for decades that Ganymede contained significant amounts of water ice, but the presence of liquid oceans was less certain. At 95 miles below the surface, the oceans could run quite hot. For reference, the average temperature on the surface at the Kola Superdeep Borehole in July is just 52F / 11C, while the temperature at the bottom of the shaft, 49,000 feet below the surface, was 356F / 180C. At more than 10x the depth, Ganymedes hypothetical ocean would be insulated from the cold vacuum of space and warmed by the moons active core.

Ganymede isnt the only water-related news this week. NASA has also detected hot springs and hydrothermal vents operating beneath the icy crust, within subsurface oceans. Its long been known that Enceladus had significant water reserves, the moon periodically emits particle blasts and weve detected cryovolcanoes volcanos that emit frozen compounds rather than magma actively on the surface.

Finding hydrothermal vents, however, is still a first since Earth was previously the only planet known to have them. Its not clear if Enceladus core is active or if proximity to Saturn and its orbital resonance with other moons keeps it warm via tidal heating, but either way, its another example of how we continue to learn about the planets and moons within the solar system. Recent years have proven that water essential to human life and and to any future colonization efforts is far more common within the solar system than was previously believed.

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NASA detects subsurface ocean on solar systems largest moon