View Full Version : Harry Potter and the Moons of Jupiter

Ron Baalke
July 2nd 03, 04:20 PM

Harry Potter and the Moons of Jupiter
NASA Science News
July 2, 2003

This week is your last good chance to see Jupiter's four largest moons
before school starts next fall.

Blistering-hot volcanoes that belch snow. Moons bigger than
planets. Icy worlds with vast underground oceans. All of these things can be
found in the latest Harry Potter novel. And according to NASA space probes,
they're all real.

It was late one night at Hogwarts when Harry, Ron and Hermione were doing
their homework: "a long and difficult essay about Jupiter's moons," but
Harry and Ron didn't have their facts straight.

"Harry, you must have misheard Professor Sinistra," says Hermione on page
300 of Harry Potter and the Order of the Phoenix. "Europa's covered in ice,
not mice!"

Correct. Jupiter's moon Europa is way too cold for mice: 260 F below zero.
Spacecraft have taken pictures of Europa's icy surface, and it looks totally

Underground, however, might be a different matter. Some scientists think the
ice on Europa hides the biggest ocean in the solar system--bigger than the
Pacific, Atlantic and Indian oceans combined. Here on Earth water and life
seem to go together. Could there be life in the waters of Europa? Microbes?
Alien fish? Swimming mice? No one knows--not even Hermione.

"And it's Io that's got the volcanoes," she says on page 295, correcting
Ron's essay.

Right again. Io is even weirder than Europa. Some people say Io, dotted with
volcanoes, looks like a pepperoni pizza, and that's about right. Io has more
pepperoni-colored volcanoes than Ron Weasley has freckles. At any given
moment, dozens of them might be active, spewing the hottest lava in the
solar system. The plumes rise 300 miles into space where it's so cold that
volcanic ash freezes before it falls back to the ground--sulfurous snow.
NASA's Galileo spacecraft has actually flown through some of these plumes
and survived.

"Jupiter's biggest moon is Ganymede, not Callisto," Hermione adds, pointing
over Ron's shoulder at another mistake.

Indeed, Ganymede is the largest moon in the whole solar system. It's
slightly wider than the planet Mercury and more than three-quarters the size
of the planet Mars. If it orbited the sun instead of Jupiter, Ganymede would
surely be considered a planet. Heavily-cratered Callisto is only a little
smaller than Ganymede and, like Europa, might be hiding a subterranean

These four wonderful moons, Io, Europa, Ganymede and Callisto are real. They
were discovered by Galileo Galilei in 1610 when he looked at Jupiter through
one of the first primitive telescopes. Galileo was amazed by the four little
stars he saw near the giant planet, and even more amazed when they moved
from night to night, orbiting Jupiter. Astronomers now call them the
Galilean satellites.

Almost everything known about the Galilean satellites--other than their
number, four, and the basic shapes and sizes of their orbits--comes from
NASA spacecraft, especially the two Voyagers, which flew by Jupiter in 1979,
and the Galileo space probe orbiting Jupiter now.

It's good to know that these missions have been closely followed at

This week you can see the Galilean satellites for yourself. If you live at
mid-northern latitudes, step outside around 9 p.m. and look west toward the
setting sun. The first bright star emerging from the twilight is Jupiter.
Point a telescope in that direction; a small one will do. (Remember, even
the cheapest department-store telescope is better than Galileo's 400
year-old spyglass.) The four moons will appear in the eyepiece as a line of
dim stars straddling the giant planet.

If you only see two or three moons, that's because one or two of them are
probably behind Jupiter. Look again later or perhaps tomorrow. The missing
moons will come out of hiding as they circle Jupiter.

Jupiter itself will look like a fat disk crossed by rust-colored cloud
belts. First-time observers often note that the planet seems squashed--wider
along the equator than between the poles. Is there something wrong with the
telescope? No. Jupiter really is flattened. Although Jupiter is 70 times
bigger around the middle than Earth, it spins more than twice as fast; a day
on Jupiter lasts only 9 hours and 55 minutes. This rapid spin is what gives
Jupiter its equatorial bulge.

Young wizards are advised not to wait too long to see these things because
Jupiter and its moons will soon disapparate! Or as a muggle astronomer would
say, they're about to disappear for a few months behind the sun. In fact,
this week is your last chance to see the moons of Jupiter before school
starts again in the fall.

So don't miss them. You do want to pass your O.W.L.s ... don't you?

July 2nd 03, 07:46 PM
On 2 Jul 2003 15:20:43 GMT, (Ron Baalke)

>Blistering-hot volcanoes that belch snow.

I've never heard of any volcano belching snow. At best volcano can send
up steam but not snow or water. AFAIK IO belches molten sulfur.
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Stephen Astro
July 3rd 03, 01:28 AM
Impmon > wrote in message >...
> On 2 Jul 2003 15:20:43 GMT, (Ron Baalke)
> typed:
> >Blistering-hot volcanoes that belch snow.
> I've never heard of any volcano belching snow. At best volcano can send
> up steam but not snow or water. AFAIK IO belches molten sulfur.

It might be 'snow' when it falls back.

Steve O.