Take Neptune for example. For many years, especially since 1989
when Voyager 2 flew past Neptune and measured its gravity field,
astronomers have known that the blue giant harbors a secret world
inside. Hidden deep below the azure cloud tops lies a rocky core not
much larger than Earth. Uranus has one, too! These “worlds within
worlds” could have exotic properties including scorching hot oceans and
diamond rain.
If only researchers could peel back the clouds for a closer look….
Astronomers using NASA’s Hubble Space Telescope have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b. The planet’s atmosphere is evaporating because of extreme irradiation from its parent star. Sciencecast Video
If only researchers could peel back the clouds for a closer look….
About 30 light years away, a Neptune-sized planetis having some of its layers peeled back.
Astronomers using NASA’s Hubble Space Telescope have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b.
“This cloud is spectacular,” says the study’s leader, David
Ehrenreich of the Observatory of the University of Geneva in
Switzerland. “The research team has nicknamed it ‘The Behemoth.’”
The planet’s atmosphere is evaporating because of extreme
irradiation from its parent star—a process that might have been even
more intense in the past.
“The parent star, which is a faint red dwarf, was once more
active,” says Ehrenreich. “This means that the planet’s atmosphere
evaporated faster during its first billion years of existence. Overall,
we estimate that the planet may have lost up to 10 percent of its
atmosphere.”
GJ 436b is considered to be a “Warm Neptune” because of its size
and because it is much closer to its parent star than Neptune is to our
own sun. Orbiting at a distance of less than 3 million miles, It whips
around the central red dwarf in just 2.6 Earth days. For comparison, the
Earth is 93 million miles from the sun and orbits it every 365.24 days.
Systems like GJ 436b could explain the existence of so-called “Hot Super-Earths.”
“Hot Super-Earths” are larger, hotter versions of our own planet.
Space telescopes such as NASA’s Kepler and the French led CoRoT have
discovered hundredsof them orbiting distant stars. The existence of The
Behemoth suggests that Hot Super-Earths could be the remnants of Warm
Neptunes that completely lost their gaseous atmospheres to evaporation.
Finding a cloud around GJ 436b required Hubble’s ultraviolet
vision. Earth’s atmosphere blocks most ultraviolet light so only a space
telescope like Hubble could make the crucial observations.
“You would not see The Behemoth in visible wavelengths because it
is optically transparent,” says Ehrenreich. On the other hand, it is
opaque to UV rays. “So when you turn the ultraviolet eye of Hubble onto
the system, it’s really kind of a transformation because the planet
turns into a monstrous thing.”
The ultraviolet technique could be a game-changer in exoplanet
studies, he adds. Ehrenreich expects that astronomers will find
thousands of Warm Neptunes and Super-Earths in the years ahead.
Astronomers will want to examine them for evidence of evaporation.
Moreover, the ultraviolet technique might be able to spot the signature
of oceans evaporating on Earth-like planets, shedding new light on
worlds akin to our own.
Maybe you can’t judge a book by its cover, but you can judge a planet by its Behemoth.
