View Full Version : Proposed New Exoplanet Search Method

2011-Jan-26, 05:49 PM
I have a new exoplanet search method I would like to propose. I am not sure if this is the correct category to place it in. My method does not go against any mainstream science but rather just shows a new novel approach to detecting planets no one has thought of before.

My proposal is to use the Very Long Base Array (VLBA) of radio telescopes to find and detect exoplanets. The idea occurred to me when I was reading about the VLBA and its capabilities the other week. It has the ability to resolve down to 10 mircoarcseconds. This means in an image it takes, each pixel would represent 10 mircoarcseconds patch of sky. I was curious what size of objects this resolution could detect. I work in engineering and took drew up part of our solar system in AutoCAD (a computer aided drafting program) and copied it out to 4.3 light years (Alpha Centauri) and then to 10, 15, 20, etc. light years in increments of 5 out to 60 light years. What I found was that an earth sized planet would appear in 3 by 3 pixels in an image at 4.3 lights years and 2 by 2 pixels at 10 light years and at 15 ly it would be occupy 1 pixel in an image. An earth sized planet would be about 1/4 the width of a pixel at 60 ly. Depending on the sensitivity of the instruments this distance should still be detectable. I have attached a simple graph that shows the varying sizes of an earth sized planets at various distances.

My original thought was that we could use the Cosmic Microwave Background Radiation (CMDR) to silhouette exoplanets as they orbit their stars. I discussed my idea with Dr. Robert Nemeroff, one of the editors of the "Astronomy Picture of the Day" website. He pointed out that planets would be glowing highly in radio waves and microwaves either reflecting from their parent star or producing them themselves as gas giants do. I knew that they might reflect radio waves and microwaves from their stars, but only if the planet is not between us and its star.

I did some research and found that different types of planetary material will absorb different amounts of radio waves and microwaves. Rocky material has a dielectric constant of 2 – 8. The dielectric value of a material defines how much radio waves and microwaves they will absorb. Water on the other hand has a dielectric value that varies based on its temperature. At -30° C the value is 99, at 0° C the value is 88, at 20° C the value is 80 and at 80° C the value is 61. Given this, a water covered planet would reflect less energy than a rocky planet would. An ice covered planet would reflect even less energy than a water planet. So we are lucky in that the strength of the reflected radiation will tell is if the planet is covered in water or ice and approximately how much of the planet is covered.

Gas Giants and Their Moons:

With the extreme resolution of the VLBA we will be able to detect earth sized exomoons around gas giants belonging to the closer star systems as well. Below is a chart that shows estimated distances of an exomoon (in pixels) as it would be shown in an image. The actual distance used to estimate the below image pixel spacing is based on a gas giant the size of Jupiter with a moon at the equivalent distance that Europa orbits Jupiter. The image size of a Jupiter sized gas giant is also shown for comparison. With luck we will find some exomoons belonging to gas giants in the goldilocks zones.

Parent Star Europa Equivalent Jupiter Gas
Distance Distance Giant Size
4.3 ly 300 pixels 74 pixels
10 ly 134 pixels 31 pixels
15 ly 88 pixels 20 pixels
20 ly 66 pixels 15 pixels
25 ly 52 pixels 12 pixels
30 ly 43 pixels 10 pixels
35 ly 37 pixels 9 pixels
40 ly 33 pixels 8 pixels
45 ly 29 pixels 7 pixels
50 ly 26 pixels 6 pixels
55 ly 24 pixels 5 pixels
60 ly 22 pixels 5 pixels
(Note: values were determined using CAD)

Because I am basically an amateur astronomer, I don't have access to the VLBA but I was hoping that some astronomers reading this post that would work in the exoplanet field or know of any, would be able to take this new exoplanet detection method and test use it. I was thinking that the first star system to be searched should be Gliese 581 to verify its method as well as verify the Gleise581g and its other planets. A couple other systems (23 Librae b and HD 69830) have been found to have gas giants in the habitable zones as well and should be checked out in follow up sessions with the VLBA to detect any habitable exomoons.

Please feel free to comment on my proposal, I appreciate feedback.
Thanks Chad

2011-Jan-26, 06:06 PM
Welcome to the BAUT forums, chadwick2424. I've moved your thread from the ATM forum to the Astronomy forum.

2011-Jan-26, 06:50 PM
I don't think you would be able to resolve anything at 1 pixel. Testing the current VLBA on the nearest systems (< 10ly) might be a good proof of concept, but it seems like you would need a LOT more resolution to be useful.

Also, it would only seem to work on radio sources.

edit: added a more realistic pixel mapping!

2011-Jan-26, 07:06 PM
With direct interferometric detection, it's not just the resolution that matters, but photon sensitivity. Interferometry works well with bright objects like stars and circumstellar disks, but probably couldn't detect planets (yet) as you describe. Interferometric images aren't really images in the traditional sense, but reconstructions. You can "image" a contact binary for example, but if one component was far under-luminous, it wouldn't show up, even with the same physical size.

Followup: My understanding of interferometry isn't as robust as I'd like so if something in my post is wrong, please point it out.


A nearby companion star, with approximately the mass of our Sun, could be the reason for such a disc around HD 62623. This companion, though not directly detected due to its brightness being thousands of times lower than the primary star, is betrayed by a central cavity between the gas disk and the central star.

2011-Jan-26, 09:03 PM
Going a little further with Hungry4Info's thoughts: The radio brightness of such an object would be pretty low... AND it would be very close to something pretty bright (the star's corona). However, the same principle will also work with some large (perhaps space-based) optical interferometry system in the future. The downside to that would be the limitation of how many simultaneous systems you could examine at once... a small number, and the equipment will be pricey.

2011-Jan-26, 09:03 PM
It's a good idea, in theory. In practice, planets -- especially small, rocky planets -- around other stars just don't emit radio waves strongly enough to be detected by the VLA or other interferometers.

John Jaksich
2011-Jan-26, 09:07 PM
Definitely---do not pack-up your ideas---but as was pointed out----some of the basic ideas of interferometrry---have not presented themselves to you---(i.e. sources or ideas).

I am sorry to say that you may need to go a few steps further (and perform more literature searches on radar-image interferometry).

Either the engineering aspects have not caught up with the science --or the science is not quite there yet. As Dr. Nemeroff pointed out, you have a problem of a very intense black body that would blot out (any typical signature of "quantum" spectrum).

In a last ditch effort I might have a suggestion or two---(1) try to contact some of the individuals at the SETI@Home project ----I am sure they may have some good suggestions and you may end up solving some of their problems in return.

(2) There is a rather new technique called "spec(k)led" spectroscopy---it may be a way to adopt to your VBLA methodololgy.

Rest assured that there are others here who will help you---I find your ideas original.

Good luck and welcome to BAUTforum.

2011-Jan-27, 11:01 AM
You seem to have been pipped at the post:-
Radio Interferometric Planet Search (http://astro.berkeley.edu/~gbower/RIPL/)
Radio search for magnetised extrasolar planets (http://radio.astro.gla.ac.uk/exoplanets/)

Well, these are astrometric searches rather than imaging. Apparently a program is being looked at for SKA as well, whenever it gets built. It will be interesting to see what kind of imaging can be done with that. RIPL is targeting nearby M type stars so it wouldn't surprise me if Gliese 581 is being looked at.

Slightly related question.. can you do nulling interferometry at radio wavelengths?

2011-Jan-27, 01:45 PM
it wouldn't surprise me if Gliese 581 is being looked at.
The planets at Gliese 581 have very small astrometric amplitudes.
GJ 581 b → 0.10 ľas
GJ 581 c → 0.06 ľas
GJ 581 d → 0.18 ľas
GJ 581 e → 0.01 ľas
GJ 581 f → 0.79 ľas (existence disputed)
GJ 581 g → 0.07 ľas (existence disputed)

In comparison, an Earth-mass planet in a 1 AU orbit around a solar-mass star 10 pc away has an astrometric amplitude of 0.3 ľas.
The VLBA's accuracy of 100 ľas, as quoted by your link, makes it clear that it is ill-equipped to detect any of the reported planets to Gliese 581.

2011-Jan-27, 03:50 PM
The planets at Gliese 581 have very small astrometric amplitudes.
GJ 581 b → 0.10 ľas
GJ 581 c → 0.06 ľas
GJ 581 d → 0.18 ľas
GJ 581 e → 0.01 ľas
GJ 581 f → 0.79 ľas (existence disputed)
GJ 581 g → 0.07 ľas (existence disputed)

In comparison, an Earth-mass planet in a 1 AU orbit around a solar-mass star 10 pc away has an astrometric amplitude of 0.3 ľas.
The VLBA's accuracy of 100 ľas, as quoted by your link, makes it clear that it is ill-equipped to detect any of the reported planets to Gliese 581.

Only a couple of orders of mag out! :) I hadn't appreciated just how small the orbits were for Gliese 581. Even SKA would struggle to resolve some of those.

2011-Jan-27, 08:06 PM
Here is another proposal to use the VLBA to detect exoplanets: http://arxiv.org/abs/0704.0238

2011-Jan-27, 09:38 PM
I think the original poster supposed to radio-search for planets by sending microwaves and waiting for them to come back, just like it happens for radars and aircrafts.

Hence, I think it would never work: even if we had enough energy to send in the space, we should wait some dozens of years to detect distant planets!

2011-Feb-01, 05:28 PM
Hi Jumpjack, That's definately NOT what I was thinking. no one wants to sit around and wait 10 to 40 years for radar returns that will be so miniscule that they would be completely undectible. We would be luck to see one photo return in that type of method.

2011-Feb-01, 06:37 PM
The major issues are that (if I understand properly) this idea relies first on the planets having a lower microwave surface brightness than the CMBR, and second on the detection being sensitive enough to detect the CMBR in each numerical pixel above the noise. Almost anything has a higher surface brightness than the CMBR, not least because it's bathed in CBR photons (the only exception I know of is formaldehyde in molecular clouds as observed in a few structurally interesting transition wavelengths). And VLBI has the worst surface-brightness sensitivity of any technique I can think of - it's fabulous for astrometry and structure, but the radio emission has to be pretty bright to make it work. (Albeit "bright" is much looser than it used to be, with new calibration and fringe-finding methods).

2011-Feb-03, 08:58 PM
I checked out the link to arxiv.org and sure enough they are proposing the exact same thing I am except they have got alot more detail in their paper. Basically the limitation at this point is how sensitive is the electronic equipment used for measuring the incoming radio and mircowaves. But their paper says that planned upgrades in the future should be able to detect planets smaller than jupiter.

Well, I gave it a try, Thanks everyone for your comments.