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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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E Pur Si Muove: Galileo’s Big Night

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

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

404 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 that orbited the giant planet (and not the Earth). Further observations over the next 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 a restructuring of their conveniently Earth-centered Universe) but also opening the door for the discovery of many more moons around other planets.

Drawings from Galileo's notebook

Drawings from Galileo’s notebook

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

As a result of his research and publications regarding the (actual) motions of bodies in the solar system, Galileo was eventually sentenced as a heretic by the Inquisition in Rome and spent the last 9 years of his life under house arrest. Still, his legacy of observation and science over dogma and established belief lives on to this day… in fact, if you go outside on a clear night now you can see a brightly shining Jupiter in the eastern sky, just as Galileo did 404 years ago. Take even a small telescope or pair of binoculars and you will easily see its four largest moons as pinpoints of light beside it. Thanks to Galileo and others like him, we now know what those are, and that there are countless other worlds and moons out there like them, just waiting for discovery.

Read more about Galileo here.

*E pur si muove – “and yet it moves” is a quote often attributed to Galileo, in that he muttered it as he “recanted” and accepted his punishment by the Roman court. But it is likely purely apocryphal, as there is no mention of it in records from the time.

Celebrate the Holidays with Cassini and Saturn

Saturn makes a beautifully-striped ornament in this natural-color image, showing its north polar hexagon jet stream and central vortex (Credit: NASA/JPL-Caltech/Space Science Institute)

Saturn makes a beautifully-striped ornament in this natural-color image, showing its north polar hexagon jet stream and central vortex (Credit: NASA/JPL-Caltech/Space Science Institute)

Cassini couldn’t make it to the mall this year to do any Christmas shopping but that’s ok: we all got something better in our stockings than anything store-bought! To celebrate the holidays the Cassini team has shared some truly incredible images of Saturn and some of its many moons for the world to “ooh” and “ahh” over. So relax, sit back and marvel at some sights from a wintry wonderland 900 million miles away…

Read the rest of this article here.

Dione to Join the List of Moons with Underground Oceans?

Angled sunlight brings Dione's "wispy lines" into relief

A slushy, icy ocean may be hiding beneath Dione’s cratered crust

Earth may display its seas on its surface for all the Universe to see, but further out in the Solar System liquid oceans are kept discreetly under wraps, hidden beneath cratered surfaces of ice and rock. And while Saturn’s moon Enceladus sprays its salty subsurface ocean out into space, other moons are less ostentatious — Europa, Ganymede, Titan… all are thought to have considerable underground oceans of liquid water, based on measurements of their mass, density, and shape.

Now, scientists are suggesting that Saturn’s 700-mile-wide moon Dione may also have a subsurface ocean… and may have even once exhibited icy geysers like its smaller sibling Enceladus.

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Europa Has Water and H2O Too

Chaos terrain on Europa suggests subsurface lakes. (NASA/JPL/Ted Stryk)

Reprocessed Galileo image of Europa by Ted Stryk (NASA/JPL/Ted Stryk)

According to research by NASA astronomers using the next-generation optics of the 10-meter Keck II telescope, Jupiter’s ice-encrusted moon Europa has hydrogen peroxide (aka H2O2)  across much of the surface of its leading hemisphere, a compound that could potentially provide energy for life if it has found its way into the moon’s subsurface ocean.

“Europa has the liquid water and elements, and we think that compounds like peroxide might be an important part of the energy requirement,” said JPL scientist Kevin Hand, the paper’s lead author. “The availability of oxidants like peroxide on Earth was a critical part of the rise of complex, multicellular life.”

Read my full article on Universe Today here.

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