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You’d expect the solar sys-
tem’s most distant planet,
which is some 30 times
farther from the Sun than
Earth, to be pretty chill.
But although aquamarine
Neptune is absolutely cold,
it’s definitely not calm.
Neptune sports the
strongest winds in the
solar system, which can
whip across the gaseous
planet at speeds up to
1,200 mph (2,000 km/h).
That’s about 1.5 times the
speed of sound! Plus, about
half the time, the world
hosts at least one giant anti-
cyclonic storm called a
great dark spot, which are
thought to take on a shad-
owy appearance because
their strong winds tear a
hole in Neptune’s methane-
laced cloud deck. However,unlike Jupiter’s seemingly
immortal Great Red Spot,
Neptune’s fierce storms
usually pop up and disap-
pear within just a few years.
Let’s not forget Triton,
Neptune’s largest satellite,
either. It’s the only large
moon in the solar system
that orbits in the opposite
direction of its host planet’s
spin. Scientists think Triton
might have this so-called
retrograde orbit because
it was captured from the
Kuiper Belt, a vast disk oficy remnants from the early
solar system, orbiting
beyond Neptune. But no
matter its origin, Triton is
a surprisingly active world.
Thanks to Voyager 2, we
know this frosty wonder-
land is home to a variety
of intriguing features: Its
frozen nitrogen crust is
adorned with rounded
mounds created by icy
lava flows, as well as vast,
smooth volcanic plains. It’s
also speckled by fewer cra-
ters than expected for an
object its age, suggesting
its surface is being rejuve-
nated. Voyager even found
that Triton hosts active ice
volcanoes that spew frozen
nitrogen as high as 5 miles
(8 km) above the moon’s
south pole.
I’ll leave you with one
final thought: In the
decades since Voyager 2
carried out the only mission
to the ice giants, scientists
have uncovered thousands
of exoplanets outside our
solar system. And despite
planetary formation models
suggesting ice giants should
be relatively rare, exoplan-
etary evidence suggests they
are surprisingly common.
So, although our ice giants
may seem too alien to mat-
ter, exploring them might
help us better understand
what it took to set the stage
for life here on Earth — or
even beyond.STATS
Mass: 17.15 Earth masses
Equatorial diameter:
30,800 miles (49,500 km)
Average temperature:
–330 F (–201 C)
Rotation period (day):
16 hours 7 minutes
Orbital period (year):
165 Earth years
Moons: At least 14 moonsNEPTUNE
Taken by Voyager 2 at a distance of
some 4.4 million miles (7.1 million
km), this view of Neptune features
a temporary great dark spot at
center (and a companion bright
smudge below that). First seen in
1989, this spot had disappeared by
the time Hubble observed the
world in 1994, though it did see a
similar feature in the ice giant’s
northern hemisphere. NASA/JPL-CALTECHVoyager 2 observed the surface of
Neptune’s moon Triton, which is
composed mainly of nitrogen ice,
as it flew by the world in 1989.
This contrast-enhanced map
approximates Triton’s true colors
and has a resolution of 1,970 feet
(600 m) per pixel. NASA/JPL-CALTECH/LPIHonorable mention:
PLUTO
BELOW: The western lobe of Pluto’s
“heart,” Sputnik Planitia, was imaged
by New Horizons during its flyby in- Thanks to the spacecraft,
astronomers now know the area is
a craterless region rich in slowly
shifting nitrogen, methane, and
carbon monoxide ices. NASA/JHU-APL/SWRI
Pluto, despite what the
International Astronomical
Union says, is still a planet
in the minds of many. And
whether it’s a planet or
dwarf planet, nearly all agree
Pluto is a fascinating world.
Covered in plains of nitro-
gen ice and textured with
mountain ranges of frozen
water, this demoted world
was closely studied less than
seven years ago by NASA’s
New Horizon spacecraft.STATS
Mass: 0.002 Earth masses
Diameter: 1,480 miles
(2,380 km)
Surface temperature:
–387 F (–233 C)
Rotation period (day):
About 6.4 Earth days
(retrograde)
Orbital period (year):
248 Ear th years
Moons: Charon, Hydra, Styx,
Kerberos, NixJake Parks is associate
editor of Astronomy.