Hubble Confirms Exoplanet Has a Blue Atmosphere

by Nancy Atkinson on July 11, 2013

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Artist’s impression of the deep blue planet HD 189733b. Credit: NASA/ESA.

Artist’s impression of the deep blue planet HD 189733b. Credit: NASA/ESA.

Since its discovery in 2005, exoplanet HD 189733b has been one of the most-observed planets orbiting another star, as its size, compact orbit, and proximity to Earth has made it a relatively easy target — as extrasolar planets go. From previous studies, astronomers thought the planet may have an enticing blue-sky atmosphere. Now, further examinations with the Hubble Space Telescope have confirmed this planet really does harbor an azure blue atmosphere, very similar to Earth’s ocean blue color.

But this is no ‘pale blue dot’ ocean world. It is a huge gas giant orbiting very close to its host star. It gets blasted with X-rays from its star — tens of thousands of times stronger than the Earth receives from the Sun — and endures wild temperature swings, reaching scorching temperatures of over 1,000 degrees Celsius. Astronomers say it likely rains glass – sideways — in howling 7,000 kilometer-per-hour winds.

Nope, not a place you’d want to visit.

But the new Hubble observations of its color are the first time an exoplanet’s color has been measured and confirmed. The astronomers measured how much light was reflected off the surface of HD 189733b — a property known as albedo.

“This planet has been studied well in the past, both by ourselves and other teams,” says Frédéric Pont of the University of Exeter, UK, co-author of a new paper. “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.”

HD 189733b is a Jupiter-sized extrasolar planet orbiting a yellow dwarf star that is in a binary system called HD 189733 in the constellation of Vulpecula, near the Dumbell Nebula, approximately 62 light years from Earth.

The planet’s blue atmosphere does not come from the reflection of a warm ocean, but is due to a hazy, turbulent atmosphere thought to be laced with silicate particles, which scatter blue light. Earlier observations using different methods have reported evidence for scattering of blue light on the planet, but these most recent Hubble observations give robust confirming evidence, the researchers said.

To make their measurements, the team used Hubble’s Space Telescope Imaging Spectrograph (STIS) to look at the system before, during, and after the planet passed behind its host star as it orbited. As it slipped behind its star, the light reflected from the planet was temporarily blocked from view, and the amount of light observed from the system dropped – not by much, about one part in 10,000 — but this was enough for STIS to determine the albedo.

“We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star,” explains Tom Evans of the University of Oxford, UK, first author of the paper. “From this, we can gather that the planet is blue, because the signal remained constant at the other colours we measured.”

Albedo is a measure of how much incident radiation is reflected. The greater the albedo, the greater the amount of light reflected. This value ranges from 0 to 1, with 1 being perfect reflectivity and 0 being a completely black surface. The Earth has an albedo of around 0.4.

According to the team’s paper, HD 189733b has an albedo of 0.4 ± 0.12.

The team says this determination will help in future studies of the atmospheres of other extra solar planets, as well as continuing the studies of one of the most-examined planets orbiting another star.

“It’s difficult to know exactly what causes the colour of a planet’s atmosphere, even for planets in the Solar System,” says Pont [5]. “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.”

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About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

umbrarchist July 11, 2013 at 4:13 PM

It is 63 light-years away. We can land robots on Mars with decent reliability. We can barely get out of the solar system but that takes 30 years. It is nice to know there are other planets rather than just speculate but otherwise until we can get to 20% of light speed, SO WHAT!?

Torbjörn Larsson July 11, 2013 at 7:43 PM

So very much what, if you are interested in science. Planet formation and astrobiology will both use these data.

So very much what, if you are interested in society. What advances science, advances society.

On the other hand, what would getting to “20% of light speed” accomplish? There are cheaper ways to send probes to nearby systems, for example.

umbrarchist July 12, 2013 at 1:28 AM

“On the other hand, what would getting “to 20% of” the universal speed
limit accomplish? There are cheaper ways to send probes to nearby
systems, for example.”

Now that is funny, care to explain it. 20% of light speed would mean 20 years to Alpha Centauri. Anything slower would take longer.

Kevin Frushour July 11, 2013 at 10:17 PM

FACT: We are all of finite lifetime.
FACT: We’re stuck in the era we’re born in.

Hey, I want all those things too – but our descendants won’t be able to enjoy them if we’re not here puttering about, building the foundation. Just be glad we weren’t born in a time when we couldn’t send probes to take pictures of nearby planets and speculating about them was a flight of fancy at best and a waste of time at worst. My space-interested ancestors would kill for some of the things I know now. You know more about our universe than Einstein, Copernicus, Galileo, Kepler, Hubble etc ever did.

umbrarchist July 12, 2013 at 1:24 AM

So we should have robots on the Moon prospecting for resources so we can launch from a low gravity well. The exo-planets aren’t going anywhere.

Jeffrey Scott Boerst July 12, 2013 at 7:40 AM

What ignorant comments you make. You are a troll.

umbrarchist July 12, 2013 at 4:14 PM

Yeah, not getting excited about planets vastly out of reach is so ignorant when we could have remote controlled robots on the Moon prospecting for usable material. Instead we use them to kill people on Earth. 200 years from now the exo-planets will still be out of reach and we will have a bigger list of them. YAWN!

elvigy July 11, 2013 at 5:17 PM

Awesome! It’s amazing that we can do this.

philw1776 July 11, 2013 at 6:19 PM

Amazing advances in space science. In the early 90s we knew of zero exoplanets. Now we’ve confirmed over a thousand and are taking spectra of tens revealing their chemical makeup. Totally revising our previous simplistic theories of planet formation. Kepler and ground based observations are revealing data on things we only dreamed of.

Kevin Frushour July 11, 2013 at 10:41 PM

“Nope, not a place you’d want to visit.”

So says you. With the proper safeguards, I’d be there in a heartbeat.

William Sparrow July 11, 2013 at 11:00 PM

And one heartbeat may be all you experience. Still, I’m with you, I’d be willing(lack of technological capabilities aside) to join you.

Peristroika July 12, 2013 at 12:39 AM

Yeah, I’d go. One of the systems with 5 worlds would be awesome. Spend the end of my life gathering new knowledge about a new solar system? You bet. And maybe, just for the icing on the cake, finally land on one…and take that first step.

Ken Lord July 12, 2013 at 7:29 PM

Proper safeguards = never landing on that planet, and probably getting no closer than many AU’s of that star.

Adam Singer July 12, 2013 at 10:59 AM

A planet that looks rather blue
And orbits another star, too?
The temperature’s high
And winds really fly
At least we have learned something new!

supershrimp July 12, 2013 at 12:35 PM

but why is blue if the atmosphere contains molten glass??? some weird chemistry because of star x-rays?

IVAN3MAN_AT_LARGE July 12, 2013 at 10:24 PM

At the 7th paragraph, it states: “The planet’s blue atmosphere does not come from the reflection of a warm ocean, but is due to a hazy, turbulent atmosphere thought to be laced with silicate particles, which scatter blue light. [...]“.

Tony Angel July 20, 2013 at 7:30 PM

Nice article but not all the facts are correct. It has been known that this exoplanet is blue for quite a few years. This was only a confirmation. From comments made by its discoverer, Professor Svetlana Berdiugina, when I was with her this past week, I think that she is a little put out that there seems to be no references to her teams work and papers. There are even artists impressions on the net from 2007 showing it as blue.

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