The fantasy creations of the "Star Wars" universe are strikingly
similar to real planets in our own Milky Way galaxy. A super Earth in
deep freeze? Think ice-planet "Hoth." And that distant world with double
sunsets can't help but summon thoughts of sandy "Tatooine."
No indications of life have yet been detected on any of the nearly
2,000 scientifically confirmed exoplanets, so we don't know if any of
them are inhabited by Wookiees or mynocks, or play host to exotic alien
bar scenes (or even bacteria, for that matter).
Still, a quick spin around the real exoplanet universe offers tantalizing similarities to several Star Wars counterparts.
A more ancient Earth?
The most recently revealed exoplanet possessing Earth-like
properties, Kepler-452b, might make a good stand-in for Coruscant -- the
high-tech world seen in several Star Wars films whose surface is
encased in a single, globe-spanning city. Kepler-452b belongs to a star
system 1.5 billion years older than Earth's. That would give any
technologically adept species more than a billion-year jump ahead of us.
The denizens of Coruscant not only have an entirely engineered
planetary surface, but an engineered climate as well. On Kepler-452b,
conditions are growing markedly warmer as its star's energy output
increases, a symptom of advanced age. If this planet (which is 1.6 times
the size of Earth) were truly Earth-like, and if technological life
forms were present, some climate engineering might be needed there as
well.
City in the sky
Mining the atmospheres of giant gas planets is a staple of science
fiction. NASA, too, has examined the question, and found that gases such
as helium-3 and hydrogen could be extracted from the atmospheres of
Uranus and Neptune. Gas giants of all stripes populate the real
exoplanet universe; in "The Empire Strikes Back," a gas giant called
Bespin is home to a "Cloud City" actively involved in atmospheric
mining. The toadstool-shaped city provides apparent refuge for a fleeing
Princess Leia and company -- at least until Darth Vader wreaks his
usual havoc.
Many of the gas giants found so far by instruments such as NASA's
Kepler Space Telescope are so-called "hot Jupiters" -- star-hugging
behemoths far too thoroughly barbecued to be proper sites for floating
cities. One recent discovery, however, shows that gas "exogiants" can
orbit their stars at distances remarkably similar to those in our solar
system. An international astronomical team discovered a twin of our own Jupiter,
orbiting its star at about the same distance as Jupiter is from the
sun. The star, HIP 11915, is about the same age and composition as our
sun, raising the possibility that its entire planetary system might be
similar to ours. This not-so-hot Jupiter, about 186 light-years away
from Earth, was detected using the 11.8-foot (3.6-meter) telescope at La Silla Observatory in Chile.
Bespin's atmospheric layers include a band of breathable air, ideal
for floating cities. In our galaxy, emerging technology allows us to
read out the components of real exoplanet atmospheres -- including gas
giants (though so far none show signs of habitable layers). And tasting
the atmospheres of smaller, rocky, potentially habitable exoplanets soon
could be within reach. Astronomers using K2,
the second planet-finding mission of the Kepler space telescope,
recently detected three such planets orbiting a nearby dwarf star. The
starlight shining through the atmospheres of these planets could reveal
their composition in future observations.
Turn up the heat
The planet Mustafar, scene of an epic duel between Obi-Wan Kenobi and
Anakin Skywalker in "Revenge of the Sith," has a number of exoplanet
counterparts. These molten, lava-covered worlds, such as Kepler-10b and
Kepler-78b, are rocky planets in Earth's size range whose surfaces could
well be perpetual infernos. Kepler-78b, roughly 20 percent larger than
Earth, weighs in at twice Earth's mass; a comparable density means it
could be composed of rock and iron. That might make it, like Mustafar,
suitable for mining, although its extremely tight orbit around its
sun-like star, along with scorching temperatures, provides an unlikely
arena for industrial operations -- or for fencing with lightsabers.
Kepler-10b isn't much more pleasant. The first rocky world discovered
using the Kepler telescope, it also hugs its sun, some 20 times closer
than Mercury orbits ours. A balmy day on Kepler-10b means daytime highs
of more than 2,500 Fahrenheit (1,371 Celsius), even hotter than lava
flowing on Earth. The surface, free of any kind of atmosphere, might be
boiling with iron and silicates.
At 3,600 degrees Fahrenheit (1,982 Celsius), however, CoRoT-7b has
Kepler-10b beat. This well-grilled planet, discovered in 2010 with
France's CoRoT satellite, lies
some 480 light-years away, and has a diameter 70 percent larger than
Earth's, with nearly five times the mass. Possibly the boiled-down
remnant of a Saturn-sized planet, its orbit is so tight that its star
looms much larger in its sky than our sun appears to us, keeping its
sun-facing surface molten.
Deep freeze
The planet OGLE-2005-BLG-390, nicknamed "Hoth," is a cold super-Earth
that might be a failed Jupiter. Unable to grow large enough, it had to
settle for a mass five times that of Earth and a surface locked in the
deepest of deep freezes, with a surface temperature estimated at minus
364 degrees Fahrenheit (minus 220 Celsius). That most likely means no
"Hoth"-style tauntauns to ride, or even formidably fanged abominable
snowmen (aka "wampas"). Astronomers used an extraordinary planet-finding
technique known as microlensing to find this world in 2005, one of the
early demonstrations of this technique's ability to reveal exoplanets.
In microlensing, backlight from a distant star is used to reveal planets
around a star closer to us.
The planet lies toward the heart of the Milky Way, where a greater
density of stars makes microlensing events more likely. The one-time
event revealing the distant Hoth was captured by the Optical
Gravitational Lensing Experiment, or OGLE, and confirmed by other
instruments.
We won't have to travel 20,000 light years, however, to visit icy worlds. Saturn's smoggy moon, Titan, where the Cassini spacecraft's
Huygens probe landed in 2005, is pocked with methane lakes and socked
in permanently with thick, hydrocarbon haze. The freeze is so deep that
water ice is no different from rock. Another Saturn moon, Enceladus,
looks like a snowball but harbors a subsurface ocean much like Jupiter's
moon Europa, another ice ball with a likely ocean underneath. That
ocean would be warmed by tidal flexing as the little moon orbits
Jupiter.
Sunset? Make it a double
Luke Skywalker's home planet, Tatooine, is said to possess a harsh,
desert environment, swept by sandstorms as it roasts under the glare of
twin suns. Real exoplanets in the thrall of two or more suns are even
harsher. Kepler-16b was the Kepler telescope's first discovery of a
planet in a "circumbinary" orbit -- circling both stars, as opposed to
just one, in a double-star system. This planet, however, is likely cold,
about the size of Saturn, and gaseous, though partly composed of rock.
It lies outside its two stars' "habitable zone," where liquid water
could exist. And its stars are cooler than our sun, and probably render
the planet lifeless. Of course, we could look on the bright side (so to
speak). When the discovery was announced in 2011, Bill Borucki, the
now-retired NASA principal investigator for Kepler at Ames Research
Center, Moffett Field, California, said finding the new planet might
actually broaden the prospects for life in our galaxy. About half of all
stars belong to binary systems, so the fact that planets form around
these, as well as around single stars, can only increase the odds.
A more recently announced exoplanet, Kepler-453b, is also a
circumbinary and a gas giant, though its orbit within its star's
habitable zone means any moons it might have could be hospitable to
life. It was the tenth circumbinary planet discovered using the Kepler
telescope.
Ocean world
Kepler-22b, analog to the Star Wars planet Kamino (birthplace of the
army of clone soldiers)), is a super-Earth that could be covered in a
super ocean. Watery, storm-drenched Kamino makes its appearance in
"Attack of the Clones."
The jury is still out on Kepler-22b's true nature; at 2.4 times
Earth's radius, it might even be gaseous. But if the ocean world idea
turns out to be right, we can envision a physically plausible
Kamino-like planet, with the help of scientists at the Massachusetts
Institute of Technology in Cambridge. An ocean world tipped on its side
-- a bit like our solar system's ice giant, Uranus -- turns out to be
comfortably habitable based on recent computer modeling. Researchers
found that an exoplanet in Earth's size range, at a comparable distance
from its sun and covered in water, could have an average surface
temperature of about 60 degrees Fahrenheit (15.5 degrees Celsius).
Because of its radical tilt, its north and south poles would be
alternately bathed in sunlight and darkness, for half a year each, as
the planet circled its star.
Scientists previously thought such a planet would seesaw between
boiling and freezing, rendering it uninhabitable. But the MIT
scientists' three-dimensional model showed that the planet, even with a
relatively shallow ocean of about 160 feet (50 meters), would absorb
heat during its odd polar summer and release it in winter. That would
keep the overall climate mild and spring-like year round.
The shallow depth, by the way, would be ideal for Kamino-style ocean
platforms, allowing construction of covered cities at the ocean surface,
where armies of clones could march and drill in peace.
Fly me to the exomoon
Endor, the forested realm of the Ewoks, orbits a gas giant and was
introduced in "Return of the Jedi." Detection of exomoons -- that is,
moons circling distant planets -- is still in its infancy for scientists
here on Earth. A possible exomoon was observed in 2014 via
microlensing. It will remain forever unconfirmed, however, since each
microlensing event can be seen only once. If the exomoon is real, it
orbits a rogue planet, unattached to a star and wandering freely through
space. The planet might have hung on to its moon after somehow being
ejected during the early history of a forgotten planetary system. A team
of Japanese, New Zealand, and American astronomers analyzed data
gathered in 2011 with telescopes in New Zealand and Tasmania, and
suggested the possible exomoon. They said a small star accompanied by a
large planet also could have caused the same lensing effect.
More exomoons might soon be popping out from the depths of space. The
Harvard-based Hunt for Exomoons with Kepler, or HEK, has begun to scour
data from Kepler for signs of them. In early 2015, the researchers
examined about 60 Kepler planets and determined that existing technology
is sufficient to capture evidence of exomoons.
The hunt could have powerful implications in the search for life
beyond Earth. If exomoons are shown to be potentially habitable, it
would open another avenue for biology; habitable moons might even
outnumber habitable planets. Could they have bustling ecosystems, with
life forms even more exotic than Endor's living teddy bears, swinging
between trees Tarzan-style? Stay tuned.
Breaking up is hard to do
In “A New Hope,” Princess Leia’s home planet, Alderaan, is blown to
smithereens by the Empire’s Death Star as she watches in horror. Real
exoplanets also can experience extreme destruction. A white dwarf star
was caught in the act of devouring the last bits of a small planet in
2015, observed with the help of NASA's Chandra X-ray Observatory. White
dwarfs are super-dense stellar remnants about the size of Earth, but
with gravity more than 10,000 times that of our sun's surface. Tidal
forces could rip a planet caught in its pull to shreds.
Observers thought at first they were seeing a black hole in the act
of feeding inside a star cluster on the Milky Way's rim. X-ray
observations, however, matched theoretical models of a planet being torn
apart by a white dwarf.
A similar observation of a closer white dwarf was made by K2 in 2014.
In this case, a tiny rocky object, probably an asteroid, was being
vaporized into little more than a dusty ring as it whipped around the
star every 4.5 hours.
NASA's Spitzer Space Telescope also picked up signs of debris from a
likely asteroid collision in 2014. But rather than a sign of planetary
destruction, the colliding asteroids could be part of a construction
site. This young star -- about 1,200 light years away and only 35
million years old -- is surrounded by a ring of dust where such
collisions are frequent. The smashed and broken bits fuse into larger
and larger agglomerations, eventually forming full-sized planets.
Our own solar system might once have looked very similar, if anyone was watching.
NASA's Ames Research Center in Moffett Field, California, manages the
Kepler and K2 missions for NASA's Science Mission Directorate. NASA's
Jet Propulsion Laboratory in Pasadena, California, managed Kepler
mission development. Ball Aerospace & Technologies Corp. operates
the flight system with support from the Laboratory for Atmospheric and
Space Physics at the University of Colorado in Boulder.
JPL, a division of the California Institute of Technology in Pasadena, manages the Spitzer Space Telescope for NASA.
SOURCE - NASA
