Too bad it is not and
cannot be water but it is still an uncommon color taking special
conditions. In the meantime it has
gotten more press than I expected. It
reminds me that we were not sure what our color would be until the space age
let us know for sure.
The progress on planet
discovery has been breathtaking over the past decade and is accelerating. At least we now have the tools available to
plausibly recognize an Earth like planet if one is seen.
Anyway it is great
work.
Hubble telescope sees
true blue colour of nearby alien planet
Scott Sutherland Fri, 12 Jul, 2013
With
all the information astronomers have been able to gather about planets orbiting
other stars — their mass, the length of their year, their potential for harbouring life and even what's in their atmosphere — for the very first time,
they have figured out what colour a planet is, and it's turned out to be a
rather familiar shade of blue.
About
63 light years away, orbiting an orange dwarf star in thenorthern
constellation Vulpecula (the Fox), is a massive, scorching-hot gas
giant planet named HD 189733b. This 'hot Jupiter' orbits so close to its star
that its year lasts only around 2.2 of our Earth-days, and it's 'tidally-locked'
with its star, so that the same side of it faces the star at all times.
Temperatures on the 'day side' measure around 1,000 degrees Celsius, and those
on the 'night side' still reach around 500 degrees. It's estimated that this
temperature difference between the two sides of the planet whips up the
atmosphere into winds blowing over 7,000 km/h!
HD
189733b was discovered in 2005, using the 'transit
method', as astronomers in France saw the light from the star dim
repeatedly as the planet whizzed around it every 2 days or so. It was this same
transiting, or technically the exact opposite, that allowed them to figure out
what colour the planet is.
The
planet itself is far too close to the star to see directly. The light from the
star just completely washes out our view of everything close to it (thus the
'artist's conception' drawings). However, the light a telescope receives from
there includes both the light from the star and, at times, light reflected from
the planet's atmosphere. Using that, we can figure out the planet's colour.
So,
aiming the powerful Hubble Space Telescope at the star, astronomers
collected the light from this system. When the planet is on the same side of
the star as we are, we're not going to get much from it. When it swings around
the other side and is just about to duck behind the star, we have a brief
window of opportunity to pick up both the star's light and the reflected light
from the planet. When the planet disappears behind the star, we won't see the
reflected light, and then we'll pick it up again right after the planet emerges
from the other side of the star.
"We
saw the light becoming less bright in the blue, but not in the green or red.
Light was missing in the blue but not in the red when it was hidden," said
Prof. Frederic Pont, a member of the research team from the University of Exeter, according to a NASA statement. "This means that the object that
disappeared was blue."
This
video gives a very cool view of this hot planet, showing what it would look
like if we did a fly-by:
Earth
appears as a 'blue marble' or 'pale blue dot'
(depending on which spacecraft took the pictures), which is due to the water
that covers about 70% of the planet's surface. However, in the case of HD
189733b, the colour is not from a surface covered by water — it's far too hot
for that — but instead it's likely from an atmosphere that's filled with glass.
According
to NASA: "The cobalt blue color comes not from the
reflection of a tropical ocean as it does on Earth, but rather a hazy,
blow-torched atmosphere containing high clouds laced with silicate particles.
Silicates condensing in the heat could form very small drops of glass that
scatter blue light more than red light."
However,
as Prof. Pont mentions in a University of Exeter news release: "It's difficult
to know exactly what causes the colour of a planet's atmosphere, even for
planets in the Solar System, but these new observations add another piece to
the puzzle over the nature and atmosphere of HD 189733b. We are slowly painting
a more complete picture of this exotic planet."
Reading
about other planetary finds — like the three Kepler worlds announced back in April, and thethree potentially-habitable worlds orbiting nearby Gliese 667c —
I've always been impressed by the imagination and technical skills of the
artists at NASA's Ames Research Center and Caltech's Jet Propulsion Laboratory,
who try to give us an idea of what these planets may look like. However, while
my feelings towards those artists isn't going to be diminished by this new
discovery, this is still an amazing find.
"This
planet has been studied well in the past, both by ourselves and other
teams," Pont said in the news release. "But measuring its colour is a real
first — we can actually imagine what this planet would look like if we were
able to look at it directly."
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