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posted by charon on Friday March 17, @08:04PM   Printer-friendly
from the a-lens-that-blinds-you dept.

The Sun could be used as a gravitational lens to magnify normally hard-to-image targets such as exoplanets. The catch? The equipment needs to be 550 AU away from the Sun:

Now Leon Alkalai from the Jet Propulsion Lab and his co-authors have picked up an earlier suggestion from Italian physicist Claudio Maccone to use our Sun, rather than a distant star, to create what might be the ultimate telescope based on the microlensing principle. Alkalai's team has investigated the viability of the method in detail as a breakthrough mission concept. They also presented their findings at NASA's recent Planetary Science Vision 2050 workshop in Washington, D.C.

To build such a "telescope," detecting instruments would be placed at a point in space where the Sun's gravity focuses lensed light from distant stars. Not only is the idea viable, according to the Alkalai team, it would produce images that separate the distant star from its exoplanet, a critical observation that is the goal of future space telescopes equipped with Starshades. And using the Sun as a lens would result in much greater magnification. Instead of a single pixel or two, astronomers would get images of 1,000 x 1,000 pixels from exoplanets 30 parsecs, or about 100 light years, away. That translates to a resolution of about 10 kilometers on the planet's surface, better than what the Hubble Space Telescope can see on Mars, which would allow us to make out continents and other surface features.

[...] There is a downside, however. The telescope's focal plane instruments would have to be at least 550 AU from the Sun (1 AU, or astronomical unit, is the distance from the Sun to Earth), which is well into interstellar space. The only spacecraft that has reached interstellar space so far is Voyager 1, which covered approximately 137 AUs in 39 years. So we would need a spacecraft that is at least 10 times faster, but Alkalai and his colleagues say this is within the reach of current technology.

Also at Engadget, MIT, and The New Yorker.

Mission to the Gravitational Focus of the Sun: A Critical Analysis


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  • (Score: 2) by Ken_g6 on Friday March 17, @08:15PM (13 children)

    by Ken_g6 (3706) on Friday March 17, @08:15PM (#480596)

    One of the big problems I see with this is that you can't easily point such a telescope at just any point in the sky. You have to place the telescope 550AU away from the sun, in the opposite direction of your target. So, practically, does that mean one telescope per target? Or would it be practical to move the telescope to another target within any reasonable period of time?

    • (Score: 1) by nitehawk214 on Friday March 17, @08:21PM (6 children)

      by nitehawk214 (1304) on Friday March 17, @08:21PM (#480599)

      The orbit of this thing will be thousands of years, so you are probably right. For comparison, Pluto is only 40ish AU away.

      --
      "Don't you ever miss the days when you used to be nostalgic?" -Loiosh
      • (Score: 4, Interesting) by Immerman on Friday March 17, @10:07PM (5 children)

        by Immerman (3985) on Friday March 17, @10:07PM (#480660)

        At that distance, orbiting starts to get a lot less relevant for anything not completely inert. Orbital speed is proportional to the inverse square root of the radius - Earth is orbiting at 30km/s and is 550 times closer to the sun, so the telescope would be orbiting at 30km/s * 1/(sqrt 550) = 1.3km/s Not nothing, but less than 1/4th the speed of the typical Mars lander on it's way to Mars.

        Of course its a *really* long way to the nearest gas station, so you're probably going to be relying on a nuclear powered photon rocket for propulsion, so it will likely take a *really* long time to make any significant change in where it's it's targeted. The solution would be to pick a direction rich in interesting things we'd like a radically better look at. I would guess someplace near the galactic core, just because that's the densest concentration of pretty much everything, so even minor changes in orientation would bring lots of new targets into view. Perhaps place it in an orbit that would cause its focus to slowly sweep across the galactic core over the course of the following century or whatever, with minor adjustments to get a good look at anything really interesting.

        • (Score: 0) by Anonymous Coward on Friday March 17, @10:36PM (4 children)

          by Anonymous Coward on Friday March 17, @10:36PM (#480667)

          At that distance, orbiting starts to get a lot less relevant for anything not completely inert.

          Orbiting is always relevant. There is no way you can change your velocity without changing your distance to the primary that's just how the universe works. Kepler's 2nd law will not be violated. There's only one speed that will keep you 550AU from the sun. Of course you can duck into a smaller orbit and push out again, but at a stupefyingly horrendous fuel cost. I don't think an ion/photon/VASIMR engine will even be able to give you the delta v you need and hauling any other sort of engine out that far would be amazingly expensive and of very limited use. It would be cheaper, as others suggested, to have several identical satellites in the same orbit imaging from different angles. Then it's just a case of waiting the necessary years for one of the satellites to be at the angle you wanted.

          (PS you might want to wait for night time too j/k)

          • (Score: 0) by Anonymous Coward on Saturday March 18, @12:11AM (2 children)

            by Anonymous Coward on Saturday March 18, @12:11AM (#480707)

            Thing is, this will be on an escape trajectory -- you have to exceed escape velocity to get there in any reasonable time, and there's no point slowing down to orbital velocity once you reach 550 AU. (Especially since 550 AU is the minimum distance, but at that point you're peering through the corona which limits observable frequencies; as you go farther out, the einstein ring gets bigger. 600-700 is a more practical figure.)

            So rather than thinking about orbits, think about dozens of km/s of radial velocity, and then superimposing whatever tangential velocity you like (subject to hauling the fuel with you) to navigate between targets. Unfortunately, fuel constraints basically mean we can pan between targets within a system well enough, but panning from one stellar system to another will either require impractical fuel supply or be impractically slow. (Roughly: 1 km/s starts panning at a rate of 1 arcminute per year, then another km/s to stop. That's around 700 AU, but of course the actual figures are a function of distance -- the further you go (and you're going further all the time) the harder it gets.)

            • (Score: 2) by Dunbal on Saturday March 18, @12:30AM (1 child)

              by Dunbal (3515) on Saturday March 18, @12:30AM (#480714)

              and there's no point slowing down to orbital velocity

              Except for the minor point of being able to keep and re-use your equipment for a bit longer than the time it takes to get from 550-700 AU or whatever the max feasible upper limit is...

              • (Score: 1, Interesting) by Anonymous Coward on Saturday March 18, @07:28AM

                by Anonymous Coward on Saturday March 18, @07:28AM (#480797)

                But there is no upper limit for the lensing mechanism, or at least none that matters in a practical sense. Just keep improving our end of the communications link to keep up with the increasing distance. In fact, not only does the Sun work better as you go out (because the Einstein ring gets out of the corona), but when you get far enough away (something like 6000 AU, IIRC), Jupiter becomes usable as a magnetic lens, too; while it has less power than the Sun, and the smaller Einstein ring will be harder to resolve, it has the helpful ability to sweep a relatively wide region of space for you every 12 years. And the optics keep working far beyond that; the only thing stopping us from using nearby stars as gravitational telescopes is the fact that none of them are pointed directly at anything interesting. (Moving 600 AU while using our sun as a gravity lens lets us look in any direction we choose; moving 600 AU while using, say, Barnard's Star as a lens only lets us realign by 10 arcminutes or so.)

                The real limit to the useful distance is the fuel requirements to realign the telescope, which get bigger with increasing distance; decelerating to orbit hardly solves that problem.

                (Another way of thinking about it is to note that, thanks to the rocket equation, it's cheaper to send one out on an escape trajectory, then send another when the first is about to run out of maneuvering fuel / get too far away, than to send the first one with enough fuel to slow down when it gets there.)

          • (Score: 2) by Immerman on Saturday March 18, @01:31AM

            by Immerman (3985) on Saturday March 18, @01:31AM (#480730)

            For long term stability, obviously. For more human timescales...not so much Consider:

            At 1AU, the acceleration by the sun is a paltry ~0.006 m/s/s
            At 550AU that falls to 0.006m/s/s *(1/550)^2 = 2x10^-8m/s/s

            So, if we brought it to a total, complete stop, and waited for it to fall back just 1AU (1.5x10^11m), to 549 AU from the sun, it would take about...
            Distance traveled = 1/2 a * t^2, or alternately t = sqrt(2d/a) = ~4x10^9 seconds, or 123 years.

            Plenty of time. And if instead of bringing it to a stop you left it coasting outward so that it would reach 700 AU or so before falling back - well the hardware would likely have stopped working long before it even reached the fallback point.

    • (Score: 2) by JoeMerchant on Friday March 17, @08:47PM (4 children)

      by JoeMerchant (3937) on Friday March 17, @08:47PM (#480616)

      Even at 550AU, it will need some orbital velocity or a constant fuel burn to stay in place, so it won't be targeting any one image for long. If it is in a circular orbit, that will be a period of millenia (Neptune orbits in 165 years at 30AU).

      More concerning to me is the unknown amount of dust, comets and other gunk out at 550AU that probably would mess up the images more than we would like.

      • (Score: 1) by khallow on Friday March 17, @09:19PM (1 child)

        by khallow (3766) Subscriber Badge on Friday March 17, @09:19PM (#480633) Journal

        Even at 550AU, it will need some orbital velocity or a constant fuel burn to stay in place, so it won't be targeting any one image for long. If it is in a circular orbit, that will be a period of millenia (Neptune orbits in 165 years at 30AU).

        I think it would make sense for a constant fuel burn approach, if we were trying to image a target of particularly high value, like a planet with an anomalous atmosphere or a Dyson sphere. One of the catches however, is that we might find a better way to image an object that doesn't require going 550 AU out. For example to get a resolution three orders of magnitude better than 'Hubble, we need a telescope with an effective base line of 8.4 km (1000 times longer than Hubble's diameter of 8.4 meters). It's a very hard problem, but a solvable one even on Earth (current max distances for Earth-side visual interferometry are about 100 meters IIRC).

        • (Score: 2) by Immerman on Friday March 17, @10:11PM

          by Immerman (3985) on Friday March 17, @10:11PM (#480662)

          I suspect building an 8.4km diameter optically perfect lens would be a lot more difficult than getting a telescope out to 550AU. Assuming your math is correct though, and the the Khallow Superscope would have a comparable resolving power, it would indeed be a lot more useful.

      • (Score: 0) by Anonymous Coward on Friday March 17, @10:40PM (1 child)

        by Anonymous Coward on Friday March 17, @10:40PM (#480670)

        a constant fuel burn to stay in place

        Explain this "stay in place" phenomenon please.

        • (Score: 0) by Anonymous Coward on Saturday March 18, @06:31AM

          by Anonymous Coward on Saturday March 18, @06:31AM (#480780)

          It would be "hovering" on a yuuuge scale

    • (Score: 3, Insightful) by istartedi on Friday March 17, @09:45PM

      by istartedi (123) on Friday March 17, @09:45PM (#480646)

      The "pointing mechanism" could be a "grand tour" of local interstellar space designed
      to pass through focal points of promising targets. I have no idea how good an exposure
      we would get at 10X Voyager speeds before moving out of the target zone. The math on
      this is beyond me...

  • (Score: 2) by Zz9zZ on Friday March 17, @08:25PM (3 children)

    by Zz9zZ (1348) on Friday March 17, @08:25PM (#480603)

    Until we have FTL this will never be done. It is a cool idea though!

    --
    ~Tilting at windmills~
    • (Score: 2) by takyon on Friday March 17, @09:57PM (2 children)

      by takyon (881) <takyonNO@SPAMsoylentnews.org> on Friday March 17, @09:57PM (#480650) Journal

      https://www.newscientist.com/article/2074961-how-planet-nine-may-have-been-exiled-to-solar-systems-edge/ [newscientist.com]

      We might even send a probe there one day. “It’s not as crazy as it sounds,” says Brown. “The way you do it is head straight for the sun, and as you swing around the sun and you’re getting this gravitational slingshot, you fire a whole bank of rocket engines.” Depending on the distance to Planet Nine, this could take anywhere from a few years to 20 years.

      "FTL" is NOT NEEDED to send a spacecraft hundreds of AU per decade.

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      [SIG] 04/14/2017: Soylent Upgrade v13 [soylentnews.org]
      • (Score: 2) by Zz9zZ on Friday March 17, @10:47PM (1 child)

        by Zz9zZ (1348) on Friday March 17, @10:47PM (#480676)

        Didn't say it couldn't be done, but I don't think anyone will unless it can be done with some microsatellite that is cheap enough. The cost to get it in place along with the limited targets it could observe make this a project that likely won't happen unless there is a specific target worth the effort. Say, some star system with signs of an advanced society.

        --
        ~Tilting at windmills~
        • (Score: 2) by Dunbal on Friday March 17, @10:56PM

          by Dunbal (3515) on Friday March 17, @10:56PM (#480685)

          Cons: Astoundingly expensive cost, multi-thousand year mission duration, with no guarantees of mission success
          Pros: Finding more rocks in space that are also impossibly far away.

  • (Score: 2) by bob_super on Friday March 17, @09:01PM

    by bob_super (1357) on Friday March 17, @09:01PM (#480623)

    You'd better be sure that the thing works before it gets there, because I ain't debugging it through a connection with 152.368 hours ping time.

  • (Score: 2) by wonkey_monkey on Friday March 17, @09:16PM (6 children)

    by wonkey_monkey (279) on Friday March 17, @09:16PM (#480631) Homepage

    So we would need a spacecraft that is at least 10 times faster

    Or you could just have some patience. Sheesh.

    --
    systemd is Roko's Basilisk
    • (Score: 2) by takyon on Friday March 17, @09:48PM (4 children)

      by takyon (881) <takyonNO@SPAMsoylentnews.org> on Friday March 17, @09:48PM (#480648) Journal

      If it is powered by an RTG, for example, the spacecraft has a certain life expectancy:

      https://en.wikipedia.org/wiki/New_Horizons#Power [wikipedia.org]

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      [SIG] 04/14/2017: Soylent Upgrade v13 [soylentnews.org]
      • (Score: 2) by mhajicek on Friday March 17, @09:58PM (3 children)

        by mhajicek (51) on Friday March 17, @09:58PM (#480651)

        True, but that life expectancy is determined largely by the isotope chosen. A low power rtg could last hundreds of years.

    • (Score: 2) by edIII on Friday March 17, @10:32PM

      by edIII (791) Subscriber Badge on Friday March 17, @10:32PM (#480666)

      Not really. The longer the duration of the mission, the greater the probability of failure. Extremely high latency comms combined with zero potential for physical maintenance means that the telescope needs extreme durability and suitable redundancy. If we can wait 200 years to see it in place, then send five of them to one location, and send 20 out in 4 different directions.

      Otherwise you've launched something with a high probability it will fail before it reaches its destination. Plus, ~200 years is a long damn time to get there and technology will have changed considerably making it obsolete.

  • (Score: 4, Funny) by Bot on Friday March 17, @10:04PM

    by Bot (3902) Subscriber Badge on Friday March 17, @10:04PM (#480657)

    Focal length: very good, but fixed
    Bokeh: way milky
    Notes: too much prone to flares, problematic in low/artificial light, limited mount options (space shuttle only, no Saturn V), good weather sealing, excellent factory support, awful portability, autofocus terribly slow, no flash sync, a bit pricey.
    Conclusion: not really a lens for newbies, but there are people who buy things like B/W leicas and hasselblads with a wooden grip, so this thing has a market.

  • (Score: 0) by Anonymous Coward on Saturday March 18, @12:20PM

    by Anonymous Coward on Saturday March 18, @12:20PM (#480822)

    Since Oracle bought Sun everything went closed and paywalled, I don't hope this to be the exception and thus will be charged wit astronomic prices. So I don't expect Sun Cloud will be a gravitant service in the market.

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