NASA’s Hubble telescope has published virtually conclusive evidence that potential life-giving conditions exist on Ganymede in the form of an immense underground sea. Ganymede joins Jupiter’s other moons Europa and Callisto and Saturn’s moons, Titan and Enceladus which are also believed to have liquid seas.
Scientific American quoted Jim Green, NASA’s director of planetary science, who joked, “The solar system is now looking like a pretty soggy place.”
Regarding the discovery on Ganymemde, Heidi Hammel from the Association of Universities for Research in Astronomy said,
“It is one step further toward finding that habitable, water-rich environment in our solar system.”
Like many of the other moons, conditions on the surface may make life there unlikely, but below the crust is another matter. Temperatures of -171F to -297F on Ganymede’s surface effectively rule out life on top, but it is entirely possible that life forms exist in its subterranean ocean.
“Scientists estimate the ocean is 60 miles (100 kilometers) thick — 10 times deeper than Earth’s oceans — and is buried under a 95-mile (150-kilometer) crust of mostly ice,” says Science Daily. That makes the size of Ganymede’s ocean greater than all of the oceans on Earth combined.
Findings from the Galileo missions to Jupiter between 1995 and 2003 already hinted at the existence of water on the moon, but were inconclusive since it was based on only 6 flybys of 20 minutes each.
Last year, another article in Digital Journal reported that research by NASA suggested that there could even be different layers of ice and liquid below Ganymede’s surface — something like a “multilayered club sandwich” of seas and ice.
However, the latest findings from observations by the Hubble Telescope have provided the most convincing evidence yet.
SpaceFlightNow quoted Joachim Saur, leader of the research team and professor of geophysics at the University of Cologne in Germany, who said,
“Our new HST observations provide the best evidence to date for the existence of an ocean on Ganymede.”
NASA explained how the discovery took place.
Ganymede is the largest moon in our solar system and the only moon with its own magnetic field. The magnetic field causes aurorae, which are ribbons of glowing, hot electrified gas, in regions circling the north and south poles of the moon. Because Ganymede is close to Jupiter, it is also embedded in Jupiter’s magnetic field. When Jupiter’s magnetic field changes, the aurorae on Ganymede also change, “rocking” back and forth.
By watching the rocking motion of the two aurorae, scientists were able to determine that a large amount of saltwater exists beneath Ganymede’s crust affecting its magnetic field.
Jupiter’s “rocking” of Ganymede’s auroae should cause a 6 degree change in its motion but in fact there is only a two-degree change. The only thing which could account for this discrepancy is the countervailing influences of an ocean under Ganymede’s surface.
To make sure, scientists used over 100 computer models to rule out other factors which could be affecting the aurora. The results left them confident that only an electrically conductive salt water ocean creating its own magnetic field could account for the data.
What was unique in these observations was the use of the Hubble telescope to investigate the phenomenon and deliver the answers.
It came about because Professor Saur thought “out of the box” and asked himself if the Hubble telescope could be used to learn more than facts about Ganymede’s surface, but also the inside of the moon.
“I was always brainstorming how we could use a telescope in other ways,” said Saur. “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.”
Heidi Hamme commented that,
“This is a really great example of using a remote sensing technique — using a telescope in orbit around the Earth — to study a moon that’s in orbit around Jupiter and yet be able to make inferences about the interior of that moon just by looking at it from the outside. We aren’t at Jupiter. Hubble is at the Earth, and yet it can probe the internal structure of this moon remotely. That’s a really powerful tool.”
Jim Green described the findings as “an astounding demonstration” of using a new approach to look inside a planetary body with a telescope.
Science Daily quoted John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate, who said,
“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.”
Further investigations of Ganymede will be undertaken by the European Space Agency, which aims to send a probe to Jupiter in 2022 and NASA will also launch its “JUICE” mission to Jupiter and its satellites around the same time.
