‘Astro-comb’ Will Aid Search for Extra-terrestrial Planets

Article written: 8 May , 2009
Updated: 24 Dec , 2015


As the race ramps up to find Earth-like planets around other stars, lasers are a viable option.

That according to researchers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who have created an “astro-comb,” a sort of calibration tool based on wavelengths of light, to pick up minute variations in a star’s motion caused by orbiting planets.

In most cases, extrasolar planets can’t be seen directly—the glare of the nearby star is too great—but their influence can be discerned through spectroscopy, which analyzes the energy spectrum of the light coming from the star. Not only does spectroscopy reveal the identity of the atoms in the star (each element emits light at a certain characteristic frequency), it can also tell researchers how fast the star is moving away or toward Earth, courtesy of the Doppler effect, which occurs whenever a source of waves is itself in motion. By recording the change in the frequency of the waves coming from or bouncing off of an object, scientists can deduce the velocity of the object.

Though the planet might weigh millions of times less than the star, the star will be jerked around a tiny amount owing to the gravity interaction between star and planet. This jerking motion causes the star to move toward or away from Earth slightly in a way that depends on the planet’s mass and its nearness to the star. The better the spectroscopy used in this whole process, the better will be the identification of the planet in the first place and the better will be the determination of planetary properties.

Right now standard spectroscopy techniques can determine star movements to within a few meters per second. In tests, the Harvard researchers are now able to calculate star velocity shifts of less than 1 m (3.28 feet) per second, allowing them to more accurately pinpoint the planet’s location.

Smithsonian researcher David Phillips says that he and his colleagues expect to achieve even higher velocity resolution, which when applied to the activities of large telescopes presently under construction, would open new possibilities in astronomy and astro physics, including simpler detection of more Earth-like planets.

With this new approach, Harvard astronomers achieve their great improvement using a frequency comb as the basis for the astro-comb. A special laser system is used to emit light not at a single energy but a series of energies (or frequencies), evenly spaced across a wide range of values. A plot of these narrowly-confined energy components would look like the teeth of a comb, hence the name frequency comb. The energy of these comb-like laser pulses is known so well that they can be used to calibrate the energy of light coming in from the distant star. In effect, the frequency comb approach sharpens the spectroscopy process. The resultant astro-comb should enable a further expansion of extrasolar planetary detection.

The astro-comb method has been tried out on a medium-sized telescope in Arizona and will soon be installed on the much larger William Herschel Telescope, which resides on a mountaintop in the Canary Islands.

Preliminary results from the new technique were published in the April 3, 2008 issue of Nature. The Harvard group will present the most recent findings at the 2009 Conference on Lasers and Electro Optics/International Quantum Electronics Conference, May 31 to June 5 in Baltimore.

Source: Eurekalert

18 Responses

  1. nedwright says

    Does this need two bites of the PR apple? The same technique was pushed in April, see http://www.universetoday.com/2008/04/03/using-laser-combs-to-find-exoplanets/

    And the laser comb does not address the weak link in precision radial velocities which is getting the reference source and the celestial source to illuminate the spectrograph in exactly the same way. After, a thorium lamp has a large number of lines, so densely spaced reference lines have been available for half a century. But the iodine cell placed in the beam of light from the celestial source puts reference lines in the spectrum, and these absorption lines do illuminate the spectrograph in exactly the same way as the source.

  2. star-grazer west coast says

    I don’t doubt Earth-type planets and with a very good possibility , wth a good environment will eventually be found. It is fortunate for all, we will be too far-far-far from each other to interfer with each others cultures or germs

  3. h2owaves says

    this is great now we will have more help,poor little kepler won’t have to go at it alone.

  4. tacitus says

    It is fortunate for all, we will be too far-far-far from each other to interfer with each others cultures or germs

    Culturally, simple radio communications can overcome some of the barriers (albeit slowly and at long range). And simply knowing that we’re not the only intelligent life out there will definitely have some impact (though probably not a great deal).

    As for close enough contact to trade germs, well, yes, not in the next few centuries, probably not, but after that, who knows?

  5. star-grazer west coast says

    You’re correct ,there can be some impact but it may not a great deal as communications at best is perhaps centuries back and forth. Distance,IMHO, too many hazards to overcome, not being pessimistic, but realistically, outer space beyond the Suns’ protective heliosphere may be far more violent to living things then we can imagine.. Perhaps non-living robotic probes at best
    Even if we find something positive tomorrow at 50LY away, it would take a number of centuries before we even have a very slight idea what we are trying to say to each other. Perhaps by the next millinium, a probe can be sent. In a way, I may be too optomistic we will find something incredible, but pessimistic about being able to do much about it.

  6. Lawrence B. Crowell says

    To communicate with ETs might require some universal decryption system. I have been on a long program of understanding quantum gravity according to this. BTW, I worked on SIGINT stuff back in the 90s. So I am applying the sporadic groups (sphere packing) and algebraic variety methods in order to figure out how quantum gravity encrypts Q-bits. I suspect that to cypher ET communications similar mathematics will have to be applied.

    I really doubt interstellar visits are likely. At best we might send probes to some nearby stars. I published a book on this subject last year, Can Star Systems Be Explored? It is a way of discussing classical mechanics and relativity. When you start really running numbers on these things you find that starships might remain in the pages of science fiction.

    Lawrence B. Crowell

  7. Feenixx says

    I reckon the first human-populated starships…. whenever…. will be “burning bridges” missions – completely self-contained ecological systems, not designed to return. Just try and imagine: If they were traveling at relativistic speeds, if a few decades or a century had passed on board, what would they return to???
    This will probably be quite a while after launching many sophisticated robotic missions.
    I’m a great believer in robotic missions, even for exploring our own solar system. IMO, they are the way forward, for a number of practical reasons.
    Ouantum computing was mentioned for decrypting ET communications. Again, this will probably have to wait for a long time yet. The progress in quantum computing seems agonisingly slow. I make special effects for movies, simulating natural phenomena – I can see how juggling Q-bits would be a dream come true – but I doubt it’ll happen within my working life…. and if it did, I’d probably have to work with a quantum physicist. I find “Q-bit mathematics” hideously complicated.

  8. ukdave says

    Lawrence B. Crowell says :

    “… to figure out how quantum gravity encrypts Q-bits. I suspect that to cypher ET communications…”

    Is this because you believe that electromagnetic waves are too low tech for interstellar data transmission? Or is there another reason why ET might use Qbits for communication?

  9. Feenixx says

    I didn’t read Lawrence B. Crowell’s comment as “ET uses Q-bits to communicate”, but rather as “we need to apply Q-bit computing technology in order to attempt decrypting those communications” (which rules me out as ET radio operator).

    Now, the transmission technology, that’s a horse of a different colour. If I was a highly (technologically) advanced entity wanting to broadcast my presence, I might forget about transmitters and antennae and attempt to modulate the full EM spectrum of something a little more visible – say, a large star for communicating across a galaxy…. or a galaxy for communicating across the Universe.

  10. ukdave says


    “we need to apply Q-bit computing technology in order to attempt decrypting those communications”

    Once a Q-Bit is de-crypted – that’s it. It’s no longer Q-bit. The quantum decoherence breaks down and nothing more can be taken from it. Simultaneous calculations yes, data transmission (I think) impossible.

  11. Feenixx says

    we are talking circles around each other

    Consider a message from ET. It’s very alien. It means nothing to you.
    Now, digitise this message, converting it into a stream of bits (if it isn’t already a bit stream).
    Next, set about figuring out what it means.
    Your Cray, having to switch between all possible states it can assume, one at a time, could be at it a lifetime.
    A quantum computer, being able to handle superpositions of all possible states, is a better option.
    I reckon that’s what Lawrence B. Crowell meant – using a quantum computer to decrypt a message which is so alien that you may not even recognise it as a message.

  12. ukdave says

    Feenix –

    Ah – I see now where you’re going with this one!

    And perhaps you’re right – maybe this is what Lawrence was getting at. Mind you, the range of problems that you can be usefully directed at quantum computers is quite small – but who knows? Perhaps ET decryption is one of them.

  13. Feenixx says

    anything which require s a lot of “guessing” seems to be a candidate for quantum computing.
    “Cryptoanalysis” is one of the prime applications for quantum computing – apparently. I saw speed-ups by four orders of magnitude mentioned, over “classic” computing.

  14. Lawrence B. Crowell says

    The quantum computer will integrate a Golay code that is self dual. The duality in the Hamming measure captures the duality between a Hilbert space and its dual, eg bra vs kets.

    I am not sure of the practicality of a quantum computer. Environmental decoherence remains a bit of a problem. Yet the theoretical idea of a quantum computer does remain fascinating. The entire universe might ultimately be a grand quantum computer.

    Lawrence B. Crowell

  15. ukdave says

    I have to say Lawrence – your response is way over my head, but thanks anyway!

    (although your assertion that “Environmental decoherence remains a bit of a problem” might be under-stating the practical issues of environmental dechoherence by a few orders of magnitude!)


  16. Dark Gnat says

    For some reason, this reminds me of the “Comb the desert!” scene in Spaceballs.

  17. Damien says

    Feenixx Said: “I reckon the first human-populated starships…. whenever…. will be “burning bridges” missions – completely self-contained ecological systems, not designed to return. Just try and imagine: If they were traveling at relativistic speeds, if a few decades or a century had passed on board, what would they return to?”

    I have a more practical solution that would not require huge ecosystems and resources nor relativistic speeds. The only requirement would be a reasonably sophisticated robotic AI or two. The ship can travel for 100s of thousands of years or more if need be with the AIs running things. When they detect a habitable world say 20 years away, they can begin to unfreeze human sperm cells and eggs, fertilize the eggs and implant them into artificial wombs. At term, the infants would be raised by the AIs, taught about Earth, educated and trained to fly the ship, build structures and other survival skills. By the time they were grown up, they would have reached the planet and begin colonization.

    This way, you don’t need a huge biosphere and resources for a generational ship, you don’t need relativistic speeds and you don’t need to worry about ongoing psychological effects of endless space travel and any potential conflicts that no doubt would ensue.

  18. Lawrence B. Crowell says

    I seriously doubt these interstellar scenarios will happen. As technology grows our time frames of activities become compressed. In the ancient and medieval world structures which took over a century were built, cathedrals, monoliths, the Parthenon etc. In more recent time the projects we engage in last only a few years. Our economy runs on months and quarters. With communications the more advanced electronics becomes the more instant and compressed our communications become — text msg, twitter etc, and we are reducing language to a babble of acronyms that can be sent in microseconds.

    Interstellar flight and colonization of stars requires huge time frames. We are too time compressed for that to happen — even if it could happen.

    Lawrence B. Crowell

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