Hubble Shows Evidence of Large Underground Ocean on Ganymede

From HubbleSite: "NASA's Hubble Space Telescope observed a pair of auroral belts encircling the Jovian moon Ganymede. The belts were observed in ultraviolet light by the Space Telescope Imaging Spectrograph and are colored blue in this illustration. They are overlaid on a visible-light image of Ganymede taken by NASA's Galileo orbiter. The locations of the glowing aurorae are determined by the moon's magnetic field, and therefore provide a probe of the moon's interior, where the magnetic field is generated. The amount of rocking of the magnetic field, caused by its interaction with Jupiter's own immense magnetosphere, provides evidence that the moon has a subsurface ocean of saline water." Image Credit: NASA, ESA, and J. Saur (University of Cologne, Germany)

From HubbleSite: “NASA’s Hubble Space Telescope observed a pair of auroral belts encircling the Jovian moon Ganymede. The belts were observed in ultraviolet light by the Space Telescope Imaging Spectrograph and are colored blue in this illustration. They are overlaid on a visible-light image of Ganymede taken by NASA’s Galileo orbiter. The locations of the glowing aurorae are determined by the moon’s magnetic field, and therefore provide a probe of the moon’s interior, where the magnetic field is generated. The amount of rocking of the magnetic field, caused by its interaction with Jupiter’s own immense magnetosphere, provides evidence that the moon has a subsurface ocean of saline water.” Image Credit: NASA, ESA, and J. Saur (University of Cologne, Germany)

Water is the building block of life, and evidence of it suggests the possibility of life on other worlds. This week, one of the Great Observatories may have unlocked the key to life on a distant, strange world. The Hubble Space Telescope (HST), which will soon enter its 25th year of operation, recently added another feather to its illustrious cap: its observations have shown strong evidence that a large underground saltwater ocean may possibly exist within Jupiter’s biggest moon, the icy Ganymede. While scientists have suspected since the 1970s that this may have been the case, this week NASA announced that the amount of “rocking” by the moon’s magnetic field supports the idea of such an ocean. Joachim Saur of Germany’s University of Cologne, who led the team that made this finding, enthused, “Our new HST observations provide the best evidence to date for the existence of an ocean on Ganymede.”

Ganymede has its own magnetic field and is able to generate aurorae surrounding its poles (similar to the aurorae seen surrounding Earth in time-lapse videos from the International Space Station). The moon, also the largest in our Solar System, is also located within Jupiter’s strong magnetic field; this causes the aurorae to show a “rocking” motion.

From HubbleSite: "This is an illustration of the interior of Jupiter's largest moon, Ganymede. It is based on theoretical models, in-situ observations by NASA's Galileo orbiter, and Hubble Space Telescope observations of the moon's aurorae, which allows for a probe of the moon's interior. The cake-layering of the moon shows that ices and a saline ocean dominate the outer layers. A denser rock mantle lies deeper in the moon, and finally an iron core beneath that." Image Credit: NASA, ESA, and A. Feild (STScI)

From HubbleSite: “This is an illustration of the interior of Jupiter’s largest moon, Ganymede. It is based on theoretical models, in-situ observations by NASA’s Galileo orbiter, and Hubble Space Telescope observations of the moon’s aurorae, which allows for a probe of the moon’s interior. The cake-layering of the moon shows that ices and a saline ocean dominate the outer layers. A denser rock mantle lies deeper in the moon, and finally an iron core beneath that.” Image Credit: NASA, ESA, and A. Feild (STScI)

The Galileo space probe previously attempted to prove the theory of an underground ocean within Ganymede. However, according to NASA, “[The spacecraft] took brief ‘snapshot’ measurements of the magnetic field in 20-minute intervals, but its observations were too brief to distinctly catch the cyclical rocking of the ocean’s secondary magnetic field.” NASA stated that a group of scientists from Germany’s University of Cologne instead used HST to better observe this phenomenon. The team was led by Saur, who described the motivation to use Hubble’s capacity to view the ultraviolet spectrum in this unique manner:

“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,” he related.

NASA stated it’s theorized that the large ocean “fights” the magnetic field, causing the aurorae to rock by two degrees, as opposed to six degrees if no such ocean existed. In addition, the findings from the team show that the ocean is thought to be “ … 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.” The full report on these findings was published Thursday, March 12, in the Journal of Geophysical Research: Space Physics.

John Grunsfeld, NASA’s assistant administrator of its Science Mission Directorate, echoed Saur’s enthusiasm: “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,” he stated. Grunsfeld, a former astronaut who will soon be inducted into the U.S. Astronaut Hall of Fame, performed eight spacewalks during his spaceflight career over three missions in efforts to service HST.

From NASA/JPL: "The hemisphere of Ganymede that faces away from the Sun displays a great variety of terrain. In this Voyager 2 mosaic, photographed at a range of 300,000 kilometers, the ancient dark area of Regio Galileo lies at the upper left. Below it, the ray system is probably caused by water-ice, splashed out in a relatively recent impact." Image Credit: NASA/JPL

Ganymede has been capturing observers’ imaginations for decades. From NASA/JPL: “The hemisphere of Ganymede that faces away from the Sun displays a great variety of terrain. In this Voyager 2 mosaic, photographed at a range of 300,000 kilometers, the ancient dark area of Regio Galileo lies at the upper left. Below it, the ray system is probably caused by water-ice, splashed out in a relatively recent impact.” Image Credit: NASA/JPL

HST was deployed from Space Shuttle Discovery during STS-31 on April 25, 1990. A previous AmericaSpace article detailed some of the early challenges faced by the space telescope.

The author wrote: “However, shortly after [HST’s] deployment it was discovered that the telescope’s primary mirror contained a serious flaw that made it produce ‘nearsighted,’ distinctly out-of-focus images … But all was not lost. Two instruments were designed to help address the flaw. The Wide Field and Planetary Camera 2 (WFPC2) and the Corrective Optics Space Telescope Axial Replacement (COSTAR) system were designed to work together and jointly correct the abberation in Hubble’s primary mirror. By December 1993, these instruments were ready to do their work. In addition, other repairs were scheduled to lengthen the telescope’s operational life and replace failing components.” The space telescope was famously returned to health during the STS-61 (Endeavour) mission, which launched that month.

It is hoped HST will last through 2020, encompassing 30 years in orbit. At present time, the James Webb Space Telescope (JWST) is being manufactured, with its scientific “heart” recently undergoing a “deep freeze” test—JWST is meant to operate at one of the distant Lagrangian points, and will experience extremely cold temperatures. Like HST, JWST is also a cooperative project between NASA and the European Space Agency (ESA); it is scheduled to launch aboard an Ariane 5 launch vehicle from Europe’s Spaceport in Kourou, French Guiana, in 2018. While that telescope is being billed as Hubble’s successor, even at its ripe age HST still continues to deliver scientific evidence about our Solar System and Universe that stuns scientists and casual observers.

 

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2 comments to Hubble Shows Evidence of Large Underground Ocean on Ganymede

  • Gary Church

    The ocean moons of the gas giants are making Mars a very poor destination in comparison. Mars is a gimmick- mistakenly popularized as “just close enough” to get to on the cheap. There is no cheap.

    The same massively shielded, spinning, nuclear propelled spaceships required for any interplanetary travel are quite capable of bypassing the cold dim rock of Mars and reaching the dozens of moons in the outer solar system.

    Building these true spaceships requires first going to the Moon and exploiting lunar ice resources. The ice on the Moon should be the central focus of the entire Human Space Flight community.

    The Moon is the only place to acquire radiation shielding and assemble, test, and launch nuclear missions.

    It is perhaps time for NASA to renounce the “flexible path” and Mars as the “Horizon Goal.” Time to go back to the Moon.

  • […] Ganymede revealed tantalising hints of its own potential habitability to Hubble, when the latter uncovered evidence for the existence of a saltwater ocean below the moon’s surface. Such findings only bolster the case for the presence of potentially […]