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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.


Ganymede Gets a Little Geologic Love

The first geologic map (left) of Jupiter's moon Ganymede

The first geologic map of Jupiter’s moon Ganymede (left) and a composite surface map made from the best Voyager and Galileo images (right)

We don’t get to hear a lot about Ganymede these days, what with everyone paying so much attention to Titan and Enceladus and Europa and several other moons out there. Which is too bad because 1. Ganymede is plenty fascinating in its own right; and 2. it’s the LARGEST MOON IN THE SOLAR SYSTEM (and we shouldn’t forget it!) That’s why I was so happy to see this news come out today: geologists have created the first map of Ganymede that focuses exclusively on its complex geology, as observed close-up by the Voyager and Galileo spacecraft during their respective flybys. The resulting global map — which reminds me of some of the ornate illustrations that Giovanni Schiaparelli made of Mars in the 1880s — is a colorful layout of the many different terrains found across icy Ganymede, providing evidence of its complex history and a guide to future exploration missions.

Read more in my Discovery News article here.

Image credit: USGS Astrogeology Science Ctr/Wheaton/ASU/NASA/JPL-Caltech

OSIRIS-REx Captures a Picture of Jupiter from L4

Jupiter imaged by OSIRIS-REx on Feb. 12, 2017. The visible moons are Callisto, Io, and Ganymede. (NASA/Goddard/University of Arizona)

NASA’s OSIRIS-REx may be designed to study asteroids close up but recently it’s captured a view of something farther away and much, much larger: the giant planet Jupiter and three of its largest moons at a distance of over 400 million miles!

The image was taken on Feb. 12, 2017, when the spacecraft was 76 million miles (122 million km) away from Earth—near the Earth-Sun L4 point—and 418 million miles (673 million km) from Jupiter. It’s a combination of two images taken with the PolyCam instrument, OSIRIS-REx’s longest range camera, which will capture images of the asteroid Bennu from a distance of over a million miles.

Read the full article here: NASA’s OSIRIS-REx Takes Closer Image of Jupiter

Eppur Si Muove: Galileo’s Big Night, 407 Years Ago Today

Jupiter and its four largest "Galilean" moons photographed on April 16, 2016. © Jason Major

Jupiter and its four largest “Galilean” moons photographed on April 16, 2016. © Jason Major

407 years ago tonight, on January 7, 1610, the Pisan astronomer Galileo Galilei looked up at a brilliantly-shining Jupiter through his own handmade telescope and saw three bright little “stars” next to it, stirring his natural scientific curiosity. Further observations over the next several nights showed that the planet wasn’t moving relative to the little “stars” as it should if they were distant background stars, but rather the bright objects (of which he soon saw four) were moving along with Jupiter. Galileo correctly concluded that those little objects weren’t stars at all but rather moons that orbited the distant planet—and, most importantly, not the Earth. This cosmic revelation forced a change of the entire view of our solar system (causing no end of trouble for Galileo as the Church didn’t appreciate a challenge to their Earth-centered Universe) but also opened the door for the discovery of many more moons around other planets.

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