Category Archives: Jupiter

Ganymede’s Aurorae Hint at an Ocean Ten Times Deeper than Earth’s

Illustration of Ganymede's auroral ovals, the stability of which hint at a global underground ocean. Credit: NASA, ESA, and G. Bacon (STScI).

Illustration of Ganymede’s auroral ovals, the stability of which hint at a global underground ocean. Credit: NASA, ESA, and G. Bacon (STScI).

It’s long been suspected that Jupiter’s giant moon Ganymede may harbor a subsurface ocean of liquid water beneath its icy yet hard-as-rock crust, and now some ingenious observations with the Hubble Space Telescope are making an even more convincing case for it!

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When a Comet Met Ganymede

Galileo image of a crater chain on Jupiter's moon Ganymede (NASA/JPL)

Galileo image of a crater chain on Jupiter’s moon Ganymede (NASA/JPL)

Captured by NASA’s Galileo spacecraft on April 5, 1997, this image shows Enki Catena, a 161.3-km (100-mile) long crater chain on the surface of Jupiter’s moon Ganymede. Named after the Sumerian god of fresh water, Enki Catena is thought to have been formed when a comet approached too close to Jupiter and was torn into 13 pieces, each impacting Ganymede in rapid succession… sort of a miniature version of what occurred in 1994 with comet Shoemaker-Levy 9.

Ganymede is not only Jupiter’s largest moon but also the largest moon in the Solar System. At 5,268 km (3,273 miles) across it is larger than Pluto and Mercury, and is the only moon that generates its own magnetosphere.

Launched in October 1989, Galileo arrived at Jupiter in December 1995 and orbited the giant planet 34 times before ending its mission with a dive into Jupiter’s atmosphere on September 21, 2003. Learn more about Galileo mission highlights here.

Source: CICLOPS

Eppur Si Muove: Galileo’s Big Night

Note: This is an edited repost of an article from 2014.
Jupiter and the fours "Galilean moons" Europa, Io, Callisto, and Ganymede. (Jan Sandberg/www.desert-astro.com)

Jupiter and the four “Galilean moons” Europa, Io, Callisto, and Ganymede. (Jan Sandberg/www.desert-astro.com)

405 years ago tonight, January 7, 1610, the Pisan astronomer Galileo Galilei looked up at a bright Jupiter at opposition through his handmade telescope and saw three little “stars” next to it, which piqued his natural scientific curiosity. He soon realized that these little objects weren’t stars at all but rather moons orbiting the giant planet (and, most importantly, not Earth). Further observations over the next few nights showed that the planet wasn’t moving relative to the little “stars” as it should if they were indeed background stars, and in fact the smaller bodies (of which he soon saw four) were moving along with Jupiter each in its own little orbit. This revelation helped change our entire view of the Solar System, causing no end of trouble for Galileo (as the Church didn’t appreciate data contradicting their conveniently Earth-centered Universe) but also opening the door for the discovery of many more moons around other planets.

Today Jupiter is now known to have at least 50 moons, with possibly as many as 67!

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Jupiter’s Moons Make Ghostly Auroral “Footprints”

UV image of Jupiter taken with the Hubble Space Telescope Imaging Spectrograph (STIS) on November 26, 1998. (NASA/ESA, John Clarke (University of Michigan))

Aurorae seen in a UV image of Jupiter taken with the Hubble Space Telescope Imaging Spectrograph (STIS) on November 26, 1998. (Credit: NASA and the Hubble Heritage Team)

We have all marveled at incredible photos and time-lapse videos of Earth’s auroral displays, captured by talented photographers that have braved the frigid nighttime temperatures of remote high-latitude locations as well as by those privileged few living in orbit aboard the International Space Station. But our planet isn’t the only one with curtains of light crowning its poles – aurorae have been observed on Jupiter, Saturn, Uranus, and Neptune as well (and Venus may even have them too.) While we know that these light shows are caused by interactions between atoms in planets’ upper atmospheres and charged particles from the Sun that get caught up in magnetic fields focusing out from around the poles, Jupiter in particular is known to have a peculiar additional type of auroral feature, created by the moons that orbit it.

The image above, captured by the Hubble Space Telescope Imaging Spectrograph (STIS) on November 26, 1998, shows Jupiter’s north polar region in ultraviolet light. The planet’s energetic aurorae can be seen wrapping around its pole in wavy circular arcs, just like Earth’s does. But there are also several bright spots that aren’t due to solar activity but are instead the “footprints” of three of its largest moons: Ganymede, Europa, and Io.

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An Ocean Beyond Earth: Europa Awaits

It’s no secret that Earth’s ocean is filled with life, much of it still a mystery or totally unknown to science. But what about the ocean on other worlds? I’m not talking about sci-fi planets or suspected alien Earths around other stars, but right here in our own solar system, where an ocean even deeper than ours lies hidden beneath a global shell of ice.

Scientists believe there is an ocean hidden beneath the surface of Jupiter’s moon Europa. In the video above, NASA-JPL astrobiologist Kevin Hand explains why scientists are so excited about the potential of this ice-covered world to answer one of humanity’s most profound questions: does life exist beyond Earth?

To learn more about Europa click here, and see the latest enhanced version of a Galileo image of Europa below:

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Dear Jupiter: Use More Sunscreen

Image of Jupiter's Great Red Spot from Voyager 1, 1979 data. Edited by Björn Jónsson.

Image of Jupiter’s Great Red Spot from Voyager 1, 1979 data. Edited by Björn Jónsson.

It’s the signature accessory of the largest planet in our solar system: Jupiter’s Great Red Spot, an enormous anticyclone over twice the width of our entire planet. Visible in even modest backyard telescopes, the GRS has been churning away for at least several hundred years. But, based on recent analysis of data gathered by the Cassini spacecraft during its pass by Jupiter in December 2000, the Great Red Spot’s rusty coloration may actually only be skin-deep – a “sunburn” created by interaction between Jupiter’s upper atmosphere and solar radiation.

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