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Old 7th April 2018, 09:14 AM   #1
Fudbucker
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Possible to Resolve Planets in Andromeda Galaxy?

How big would a telescope need to be to spot planets in the Andromeda Galaxy? Is it even theoretically possible?
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Old 7th April 2018, 09:18 AM   #2
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Originally Posted by Fudbucker View Post
How big would a telescope need to be to spot planets in the Andromeda Galaxy? Is it even theoretically possible?
Only through lensing, I would think:

https://newatlas.com/extragalactic-exoplanets/53244/
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Old 7th April 2018, 10:07 AM   #3
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If they build my 1km wide replica of the Death Star only with a relescope in place of a superlaser they might see those planets.
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Old 7th April 2018, 11:30 AM   #4
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Are there enough photons coming from those planets and reaching here to make it possible?
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Old 7th April 2018, 11:42 AM   #5
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Originally Posted by Fudbucker View Post
How big would a telescope need to be to spot planets in the Andromeda Galaxy? Is it even theoretically possible?
Second question first: most definitely!

You can do some simple calculations yourself: what is the angle subtended by a disk of diameter 10k km (say), at a distance ~the same as that to M31? At a wavelength of 500nm (say), what is the diameter of a telescope mirror needed to barely resolve such an angle? A 10k km planet located at 10 au (say) from a B star in M31 would appear to have what V band magnitude (assume an albedo of 50%)? And so on ...

Of course, the telescope may be in orbit, or the surface of the Moon; "spot" may mean "observe as it transits its homesun"; and so on ....
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Old 7th April 2018, 03:35 PM   #6
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Originally Posted by Belz... View Post
If they build my 1km wide replica of the Death Star only with a relescope in place of a superlaser they might see those planets.
They might, but what is a relescope?????
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Old 7th April 2018, 03:37 PM   #7
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Originally Posted by Fudbucker View Post
Are there enough photons coming from those planets and reaching here to make it possible?
Not to mention how far have they spread out due to various fields and solids they are likely to have passed through or been blocked by???
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Old 8th April 2018, 05:47 AM   #8
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By my rough calculations, if you had a large telescope somewhere in the Andromeda galaxy and you were trying to image Jupiter (and assuming Jupiter is close to "full" at the time but not obscured by the sun), your telescope would intercept approximately one photon from Jupiter per hour, per square kilometer of telescope aperture.

So, not impossible, but very very difficult!
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Old 8th April 2018, 06:52 AM   #9
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Originally Posted by fuelair View Post
Not to mention how far have they spread out due to various fields and solids they are likely to have passed through or been blocked by???
Photons are massless point particles. They don't spread out from contact with other things. ETA: Maybe you're thinking of marshmallows. Or tennis balls.

Last edited by theprestige; 8th April 2018 at 07:46 AM.
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Old 8th April 2018, 08:26 AM   #10
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Originally Posted by theprestige View Post
Photons are massless point particles. They don't spread out from contact with other things. ETA: Maybe you're thinking of marshmallows. Or tennis balls.
I got hit by two last week, it didn't even sting.
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Old 8th April 2018, 11:03 AM   #11
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They do diffract and reflect though.
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Old 9th April 2018, 12:41 AM   #12
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Originally Posted by theprestige View Post
Photons are massless point particles. They don't spread out from contact with other things. ETA: Maybe you're thinking of marshmallows. Or tennis balls.
It's not a simple "pont particle" (in fact, a photon is not a "point particle" in any meaningful sense that I know of) once you get to field-theoretical descriptions. Photons are quantized solutions to Maxwell's equations; excitations of the EM field. Photon number is not a conserved quantity, so a single photon can absolutely "spread" (scatter) through interaction with other objects.
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Old 9th April 2018, 10:05 AM   #13
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Originally Posted by Fudbucker View Post
How big would a telescope need to be to spot planets in the Andromeda Galaxy? Is it even theoretically possible?
My guess is that a really wide interferometer could...
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Old 9th April 2018, 10:30 AM   #14
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If they're in DNS, sure. But they're probably not in DNS.
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Old 9th April 2018, 10:51 AM   #15
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As far as I understand, most of the extrasolar planets discovered in our galaxy to date have been identified by detecting the very slight changes in light caused by the plants eclipsing their star during their orbits (transit photometry). Resolving planets as separate light sources by "direct" imaging (usually using large telescope arrays) has been much, much more limited.

Given that, I would presume that detecting planets in Andromeda by transit photometry (etc.) would require only that individual stars be resolved and that their light output could be very accurately measured over multiple days. But I also presume there must be technical difficulties in this context because I have not read about this being done.

Experts here?
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Old 9th April 2018, 11:58 AM   #16
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Originally Posted by Giordano View Post
As far as I understand, most of the extrasolar planets discovered in our galaxy to date have been identified by detecting the very slight changes in light caused by the plants eclipsing their star during their orbits (transit photometry). Resolving planets as separate light sources by "direct" imaging (usually using large telescope arrays) has been much, much more limited.

Given that, I would presume that detecting planets in Andromeda by transit photometry (etc.) would require only that individual stars be resolved and that their light output could be very accurately measured over multiple days. But I also presume there must be technical difficulties in this context because I have not read about this being done.

Experts here?
Not an expert.

If the Hubble - which can easily resolve individual stars in M31 - were to stare at it continuously for a year, there's no doubt it would identify thousands of M31 candidate exoplanets. If three+ 10m class ground-based (preferably at ~4+km altitude) telescopes, spaced appropriately in the northern hemisphere, equipped with the very best in adaptive optics, were to conduct a coordinated campaign over two+ years, ditto (though likely hundreds rather than thousands).

Converting "candidate" status to "almost certain" would take comparably enormous amounts of time on the very best facilities we currently have.

Anyone have a cool $10+bn to spend for a dedicated facility?

Didn't think so.

Guys, this is not rocket astronomy, merely time and money (and dedication); the basic physics was established well over a century ago, and most of the engineering within the last two decades (at the most).

Now, about detecting exoplanets in a galaxy at z~5 ....
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Old 9th April 2018, 02:06 PM   #17
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Originally Posted by fuelair View Post
They do diffract and reflect though.
and get absorbed. <snip>



Edited by Loss Leader:  Edited for Rule 11.
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Old 9th April 2018, 03:20 PM   #18
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Originally Posted by Wolrab View Post
I got hit by two last week, it didn't even sting.
I'm about half non-ginger Irish... I can tolerate a good ten or twelve on any given day.

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Old 15th April 2018, 08:41 PM   #19
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Originally Posted by Fudbucker View Post
How big would a telescope need to be to spot planets in the Andromeda Galaxy? Is it even theoretically possible?

We had a similar thread around 10 years ago except it was about whether or not it was possible to have a visible spectrum image of a planet around another star in our galaxy:

http://www.internationalskeptics.com...d.php?t=123523


Which is theoretically possible but it would require a collection area of several square km (even more if not space based). So... technology that is probably a good 100 years away.
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