Astronomers Discover a Dark Alien World


An exoplanet has been discovered by astronomers that reflects less than one percent of the light it receives from its parent star. Less reflective than black acrylic paint, this planet is literally darker than coal!

TrES-2b is a Jupiter-sized gas giant orbiting the star GSC 03549-02811, about 750 light-years away in the direction of the constellation Draco. First discovered in 2006 by the Trans-Atlantic Exoplanet Survey (TrES), its unusual darkness has been identified by researchers led by David Kipping from the Harvard-Smithsonian Center for Astrophysics (CfA) and David Spiegel from Princeton University, using data from NASA’s Kepler spacecraft.

Kepler has located more than 1,200 planetary candidates in its field of view. Additional analysis will reveal whether any other unusually dark planets lurk in that data. (Image: NASA/Kepler mission/Wendy Stenzel)

The team monitored the brightness of the TrES-2 system as the planet orbited its star and detected a subtle dimming and brightening due to the planet’s changing phase. A more reflective planet would have shown larger brightness variations as its phase changed.

The dark exoplanet is tidally locked with its star and orbits it at a distance of only 5 million kilometers (3.1 million miles), keeping it heated to a scorching 1000º C (1,832º F). Too hot for the kinds of reflective ammonia clouds seen on Jupiter, TrES-2b is wrapped in an atmosphere containing light-absorbing chemicals like vaporized sodium and potassium, or gaseous titanium oxide. Still, this does not completely explain its extremely dark appearance.

“It’s not clear what is responsible for making this planet so extraordinarily dark,” stated co-author David Spiegel of Princeton University. “However, it’s not completely pitch black. It’s so hot that it emits a faint red glow, much like a burning ember or the coils on an electric stove.”

Regardless of its faint glow TrES-2b is still much darker than any planet or moon in our solar system.

The new work appears in a paper in the journal Monthly Notices of the Royal Astronomical Society. Read the news release here.


Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor and on Facebook for more astronomy news and images!

31 Replies to “Astronomers Discover a Dark Alien World”

  1. Nice article. Just a few points that I think need clarification and/or cleaned up in the article:

    TrES-2b was discovered in 2006. While the finding may be new, the planet is not.

    I believe David Kipping is with the Harvard Smithsonian Center for Astrophysics. Dave Spiegel is at Princeton.

  2. Ever stop and think about how lucky we are to be alive at a time when we can measure the albedo of an gas giant 750 light years away?

    When I was growing up, the word “exoplanet” didn’t exist. Now we may have discovered almost 2,000 of them. That just blows my mind.

    1. These are definitely strange and amazing times. And it’s only going to get more sci-fi when technology and humans start to merge. Perhaps some remnants of us will end up in new intelligent machines that explore the galaxy.

  3. Ever stop and think about how lucky we are to be alive at a time when we can measure the albedo of an gas giant 750 light years away?

    When I was growing up, the word “exoplanet” didn’t exist. Now we may have discovered almost 2,000 of them. That just blows my mind.

  4. What is meant by the planet changing phases? Is this like phase change in materials, or is this more like moon phases?

    If it’s the former, I want to hear more on that… Entire planets phase-changing?

    1. Definitely like the moon. As the planet goes around its star, it goes from “full planet” to “new planet” and the entire range between. The finding is that there’s surprisingly little change in brightness from one to the other due to the planet’s lack of reflectivity.

  5. What is meant by the planet changing phases? Is this like phase change in materials, or is this more like moon phases?

    If it’s the former, I want to hear more on that… Entire planets phase-changing?

  6. The proverbial dustball.

    Maybe the scifi enthusiasts got it wrong? It would be easier to make a “Dyson planet” to trap light energy (by atmosphere modification, say).

    1. @VakNee,

      Checking your profile of posts I see you use key phrases to post your advert sig for anon virtual privates networking. Begone please, and take your privates with you!


  7. um. If it reflect very little light. Then it will not be dark. It will be extremely bright. For a small thing like a piece of coal, we see black. For a whole planet taking a beating from a sun, this is going to be an extremely hot, bright planet. 1%, just that little, is more than enough to cause brightness from the energy of a star.

    1. The authors of the paper said it emits a “faint red glow” due to heating from the star.

      Also, if it reflects less than 1% of the light that hits it, that makes it at least 34 times darker than Jupiter.

  8. Its funny because in the 40s-60s scifi was huge…U look back and it wasn’t scuffed at….then it seems somewhere after Kennedy I guess we all lost perspective. Shut down, withdrew, and began to instead to criticize and deny possibility’s. I think its vital that our new perspective of the scale of things and more recent knowledge make it to the public consciousness.
    I mean now you have main stream scientist starting to say multi dimensions unarguably exist.
    We used to talk about space as in the universe and our solar system…Now its getting to become common knowledge that our galaxy alone would be the scale of what you would think a universe was being loosely described as. (A galaxy’s true scale and vastness has not been a standard knowledge or awareness among everyone) Its almost unarguable that at the center of our Galaxy alone there are things that have been around millions even billions of years longer then us. We live in the wilderness of our own galaxy. Galaxies themselves being as many as a grain of sand on all the beaches on Earth times a trillion. (uncountable I mean). And distances between these galaxies alone our unimaginable. It would take use thousands of years to even start to get a fraction across our own galaxy. (even at an advance speed I mean) Feels almost powerless because it would take millions of years to cross from one galaxy to another alone.
    Each Galaxy technically being an individual universe. Of which scientist are starting to think Real Universes themselves are galaxy like floating in an entirely other body.
    Anything anyone could ever want to know, or dream of is out there… almost depressing. Like you wake up and realize your a hamster in a glass box.

  9. The devils planet.This is where evil souls go and stay.Evil Souls that were abducted by aliens taken there.Trying to find a cure for their wrong doings.Souls are like magnets of the north and south poles fighting amongst each others.It does not settle down.

      1. the human soul is very real. you just call it by a different name.also, by your definition of “real” is very limited if you only go by what can be physically observed.

  10. Don’t ridicule me too much, but I have a question. Could someone explain to me how the reflectivity of the planet can cause an increase or decrease on the light the star puts out, as seen by TrES? It’s most likely my own ignorance, but I thought when utilizing the transit method, the result is ascertaining the radius of the planet? I’m assuming spectroscopy plays a significant role here? What else is at play? Thanks in advance.

    1. I’m not certain, as it’s new to me too, but I assume it goes like this:

      The planet is so close to the star that they are effectively the same point source of light when seen from Earth. When the planet passes in front of the star, it blocks a tiny bit of the light, so the point source appears darker (as you already know). But when the planet is elsewhere, the light it reflects adds to the brightness of the point source. As the planet moves and adopts different phases (like the Moon), the amount it contributes changes, and this can be measured.

  11. I don’t know if this makes sense or not, but I think it would be very interesting to work out the implications of this actually being a small black hole. The faint light emission might correspond to Hawking radiation from a steadily evaporating medium-small size black hole. The seasonal variation might be reflections off of an accretion disk, which might have a very limited surface area. I believe that the mass is determined from Doppler data from motion of the parent star, and the size of the planet is just estimated from its mass. The reflectivity is determined from light collected from the planet, but no image of the planet is actually resolved, it is way too far away for that. So I think it might be hard to disprove the black hole hypothesis.

  12. Okay I just looked up the temperature to mass relationship for black holes, and it looks like Hawking radiation could not account for this planet’s temperature, It would only be about 65 micro Kelvin. So the small black hole concept would only work if you could account for it’s brightness by the temperature of the in-falling matter just outside the event horizon. One would expect large redshifts in certain atomic transitions (seen in emission spectra), which could also cause confusion in the interpretation of chemical composition. Of course I have no idea if anything like this is present in the data they have collected, but it is interesting to think about.

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