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Exoplanets: Mapping a Distant Blue Dot

Glints of light off oceans or ice caps would be useful indeed as we try to figure out what we’re seeing on a distant terrestrial world. One day we’ll have the kind of instrumentation that can make direct observations of a planet like this, separating its light from that of its star. A ‘terrestrial planet finder’ mission that finds sun glints in its data would have identified a planet that could be suitable for life, one with large areas of water or ice.

Drake Deming (NASA GSFC) specializes in recognizing features like this in his work as deputy principal investigator for the Extrasolar Planet Observations and Characterization (EPOCH) study, a part of the extended mission of the Deep Impact spacecraft. EPOCH has produced two new videos showing bright flashes produced by sunlight as the Earth is seen to rotate from a distance of about eleven million miles. The idea is to produce a view of the Earth that can be studied in the same way a future planet-hunter spacecraft would study an exoplanet.

A tiny flash of light as a marker for life? It would hardly be proof, but such an event could be part of the constellation of confirming data involved in such a study. Deming has this to say on the subject:

“…these sun glints are important because, if we saw an extrasolar planet which had glints that popped up periodically, we would know that we were seeing lakes, oceans or other large bodies of liquid, such as water. And if we found large bodies of water on a distant planet, we would become much more optimistic about finding life.”

Image: A sun glint on Earth is captured (center of the black circle) in this image taken by NASA’s Deep Impact spacecraft as it looked at the north pole. The reddish area is North America, and the glint is coming from a body of water in California. Credit: Don Lindler, Sigma Space Corporation/GSFC.

Encouraging to planet hunters is the fact that the intensity of some glints was marked. Richard K. Barry at GSFC is leading the research into sun glints from the EPOCH results and creating a catalog that will relate each glint to a particular location on Earth. It’s clear from the EPOCH returns that sun glints appeared not only over calm areas of ocean but also over some land masses, surely caused by large inland lakes.

The videos EPOCH has provided are made from a compilation of green, blue and near-infrared images taken every fifteen minutes on a single day. Infrared is useful because it provides sharp contrast between land and water, with vegetation showing up better in the infrared than in visible light. That’s a useful fact not only for characterizing planets with water or ice, but also for looking at land masses, as Nicolas Cowan (University of Washington) explains:

“As Earth spins, different surface features rotate in and out of view, causing the color of the blue dot to change slightly from one hour to the next… [W]hen a large expanse of bare land, like the Sahara Desert, rotates into view, Earth gets a bit redder because continents reflect near infrared light relatively well.”

With over 400 extrasolar planets now identified, we have to consider the possibility that we’ll be inundated with terrestrial planet candidates as our observing tools improve. Narrowing down the field to those most likely to hold life will involve investigations like these, working with data from which sun glints can be extracted and, potentially, a rudimentary mapping of an exoplanet’s features could be begun, one that would at least point to the existence of oceans and continents.


Comments on this entry are closed.

  • Eniac January 13, 2010, 12:31

    If glints could be detected from extrasolar planets, I believe it would automatically enable high-resolution imaging of at least part of the planetary surface. As the planet turns, and goes through seasons, the spot where a glint would show up will scan over the planetary surface in a regular and predictable pattern. Observe long enough, and you get a map of the “glintiness” of that part of the surface that ever does get glints. The map will be high resolution, on the order of the size of a glint.

    The caveat is that the best way to detect a glint is to focus on the one known spot on the planet where it is expected. This is not possible with exoplanets, except perhaps using FOCAL. Polarization may be another way, but I doubt glints are bright enough to ever sort out from the rest of the planet’s reflected light, let alone the light of the parent star.

    Reading the mention of color variation as the Earth turns, I am wondering if you could use that for imaging even without glints. If you log the intensity and color of the planetary reflected light for a sufficiently long time, as the planet goes through its days and phases, you get the combined light of ever changing pieces of surface. Given enough observations, you might just be able to combine them and tomographically deconvolute the data into a surface map, similar to what is done in CAT and MRI imaging. Resolution would probably be worse than with glints, but detection far easier.

  • kurt9 January 13, 2010, 13:05

    I think you need a space-based platform like TPF or Darwin to actually image these exoplanets to detect oceans and what not. I don’t see that this can be done from Earth using current analytical techniques.

    If Kepler is successful (in finding lots of Earth-sized planets in the right orbits), it will increase scientific and political support for projects like TPF and Darwin, that will actually be able to characterize these planets with reasonable fidelity. If money is not available for TPF from the U.S. alone, then a deal with the Europeans and Asians to jointly fund one of these projects should be pursued.

  • andy January 13, 2010, 14:22

    Talking of observing conditions on extrasolar planets, in the news is the spectrum of the giant exoplanet HR 8799 c. Explaining the features of the spectrum will need much improved atmospheric models: apparently dust formation needs to be better handled.

  • Daniel January 13, 2010, 18:59

    talk about exoplanets…

    i was check the extrasolar planet encyclopaedia (EPE) ,and there is 5 extrasolar planet that NEVER been announced…

    this the scientific paper of 08/2009: http://exoplanets.org/papers/ms-1.pdf

    and this is extrasolar planet catalog in alphabetic order: http://exoplanet.eu/catalog-all.php?&munit=&runit=&punit=&mode=1&more=

    i send a e-mail for EPE, but they just told that the authors of this paper,don’t give the EPE the right of publicate this paper on the EPE

    this is strange because this planets it’s not secret, it’s already been announced since august of 2009 on the http://www.arXiv.org

    i don’t know, but for me, look like if something like that start happen in the EPE, that is the great reference in extrasolar planet of all.Now they could lose the credit of announce new exoplanets

  • Daniel January 13, 2010, 19:20

    oh yes the planet on this paper are: HD34445, HD126614, HD24496, HD13931,Gl 179

    there is one small note on the discussion on the end of this paper that talk about of the unannounced planetary system of Gl 179 a M dwarf star ,on a recently announced planet around HIP 794311 another M dwarf star with a gas giant planet see at:


    NOTE: i made a mistake this planets wasn’t announced http://www.arXiv.org but for the exoplanet.org at: http://exoplanets.org/papersframe.html


  • andy January 13, 2010, 19:23

    Daniel, both HD 179079 b and HD 73534 b (there appears to be a typo in the title of the paper you linked) are in the exoplanets list on EPE.

  • Bounty January 13, 2010, 19:53

    We also have Titan to help perfect our glint technique. https://centauri-dreams.org/?p=10752

  • drpayton January 14, 2010, 4:36

    TAU ZER0 FOUNDATION:! 500 Trillion watts….and we make more energy than we lose?… What is the difference? 5-3=N? Wouldn’t fussion create gravity? Doesn’t gravity travel at the speed of light? Equal and opposite reaction?…. I guess the first question is who am I to ask? I am a guy with a communication device that let’s me get RSS feeds all day from my front pocket. I read I listen and I contribute what little I am able, to a noble cause. We can choose robots as the next evolution of man or we can choose interstellar beings as our next step of evolution…Probes are cool but they are not man and they don’t even portray the nobility of man (if we are going let’s go!)….think positive…. I’m speaking from the perspective of a guy holding a good handheld com unit… Lol….all we need as a species is a reason to evolve. Fearless people, in the face of adversity, seem to always persevere …… We always seem to change when we need to… Contact lol. This is our choice no matter what. If we have a way to save a part of our humanity we should do whatever it takes to make sure that if this planet does suffer a total extinction. That we atleast have a way of sending an arc to an inhabitable planet. It is our duty to life… We could just as easily be the only life in our galaxy, as on the cusp of intergalactic freedom . It is our dutyas possibly the only sentients to populate the galaxy with the self aware. Seed the galaxy. Let’s not wait to determine if we are the only ones. That’s the nature of this world… Go forth and propogate! Send our dna to another inhabitable planet… Expect for it to take forever and make sure when it gets there that it at least interjects our species into the biosphere 50 times. Send more than one. We will find an inhabitable planet this year or next. Send us there… If in 500 years we send another that gets there faster, then that’s good but we need to start populating the stars. Project noah.

  • Daniel January 14, 2010, 9:35

    andy said:

    “Daniel, both HD 179079 b and HD 73534 b (there appears to be a typo in the title of the paper you linked) are in the exoplanets list on EPE.”

    sorry andy i put the wrong link here,now this is right link the say about planet around the stars HD34445, HD126614, HD24496, HD13931,Gl 179 that is NOT on EPE:


    at: http://exoplanets.org/papers/sixpack.pdf and you can check on extrasolar planet catalog in alphabetic order at: http://exoplanet.eu/catalog-all.php?&munit=&runit=&punit=&mode=1&more=

    sorry to give the wrong link i was too busy yesterday

    i hope everybody read now ;-)