Author Topic: Project Blue to image a planet in the Alpha Centauri system  (Read 10481 times)

Offline Star One

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Project Blue to image a planet in the Alpha Centauri system
« Reply #20 on: 11/16/2016 06:52 AM »
There have been other kickstarters successful at that six figure level of fund raising. Not such raising this kind of figure but exceeding it.

https://www.entrepreneur.com/article/235313
« Last Edit: 11/16/2016 06:52 AM by Star One »

Offline IainMcClatchie

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #21 on: 11/16/2016 08:10 AM »
The major specific I recall is that they want to build a telescope sized like a fridge with a mirror 45-50 centimeters across.  On top of that, they did specify it would be imaging in the visible light.

....I suppose the question is, with essentially unlimited viewing time (the advantage of a private 'scope versus Hubble or Webb) and apparently a handful of 21st-Century tricks, can a telescope only half-a-meter wide indeed image something around either Alpha Centauri A and B?

Well, it's not going to image any such planet.

An Earth-sized (12700 km diameter) planet around Alpha Centauri A (4.37 light-years) is 3e-10 radians across.  To resolve that with 550 nm (green) light, you'd need an aperture 2.2 km in diameter.  That will make the planet fill one pixel.  This is obviously not the way to go.

Instead, they've figured out how to block most of the light from one point source so that another extremely close and faint point source, 4000 times too close to resolve, can be detected.  With just one reading in the visible band, they can say something about size.  If they can get a spectrum, maybe in the 700 to 950 nm band which is detectable by off-the-shelf CMOS imagers, then they might be able to say something about water.  If they'd use a MWIR detector (still off-the-shelf, but a smaller shelf) then they could see the 2.7 micron absorption band for water and say something more definitive.

MWIR 2.7 microns doesn't require cooled optics, although for the light levels they might get, maybe it does.

Offline Hungry4info3

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #22 on: 11/16/2016 09:17 PM »
Yes, a small telescope can image a planet at Alpha Centauri.
http://www.centauri-dreams.org/?p=34560

An Earth-sized (12700 km diameter) planet around Alpha Centauri A (4.37 light-years) is 3e-10 radians across.  To resolve that with 550 nm (green) light, you'd need an aperture 2.2 km in diameter.  That will make the planet fill one pixel.  This is obviously not the way to go.

Why do we need the planet to fill a pixel for useful science? We certainly haven't needed to meet this requirement for the dozens of other exoplanets that have been imaged.

Offline baldusi

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #23 on: 11/16/2016 11:01 PM »
A 50cm mirror won't resolve a planet, but can easily treat it as a point source. I did the math a while ago, and each pixel was quite smaller than an AU. So as point source you could do direct imaging. Yes, you won't resolve a continent, but any spectral analysis could be done, and it's apparent movement could be done. Even the doppler shift taken. And if you have two years of observations you could do a very good orbit determination.

Offline redliox

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #24 on: 11/18/2016 07:52 PM »
A 50cm mirror won't resolve a planet, but can easily treat it as a point source. I did the math a while ago, and each pixel was quite smaller than an AU. So as point source you could do direct imaging. Yes, you won't resolve a continent, but any spectral analysis could be done, and it's apparent movement could be done. Even the doppler shift taken. And if you have two years of observations you could do a very good orbit determination.

Right!  There's a huge amount of significant science that can still be done such as:
1) Establishing temperature range
2) Presence of water
3) Atmospheric Composition

The Kepler telescope didn't produce vibrant images of its exoplanets, but it virtually single-highhandedly nailed down a factor in the Drake Equation.  We now know that planets are extremely common and aren't uncommon in habitable zones.  We may not get fancy images of Alpha Centauri's planets but we would get revelations about sunlike stars and the prospects of humanity's likely future destination.
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Offline as58

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #25 on: 11/18/2016 11:29 PM »
A 50cm mirror won't resolve a planet, but can easily treat it as a point source. I did the math a while ago, and each pixel was quite smaller than an AU. So as point source you could do direct imaging. Yes, you won't resolve a continent, but any spectral analysis could be done, and it's apparent movement could be done. Even the doppler shift taken. And if you have two years of observations you could do a very good orbit determination.

Not by this project. There's very little information available, but I haven't seen anything about spectroscopy. It seems that all the project hopes to do is image the planet. (I'm not sure if imaging is really the right word when the signal from a possible planet is dug out of two years of data.) Honestly, to me this seems scientifically kinda pointless, but it could be good test bed for advanced coronagraphic techniques.

Offline IainMcClatchie

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #26 on: 11/18/2016 11:40 PM »
A 50cm mirror won't resolve a planet, but can easily treat it as a point source. I did the math a while ago, and each pixel was quite smaller than an AU. So as point source you could do direct imaging. Yes, you won't resolve a continent, but any spectral analysis could be done, and it's apparent movement could be done. Even the doppler shift taken. And if you have two years of observations you could do a very good orbit determination.

1 AU at 4.3 light years is 3.7 microradians.  A 50 cm aperture with 550 nm light will resolve two peaks 1.3 microradians apart.  You can theoretically resolve the sun and a little dot next to it.

The problem is that the Sun (3.8e26 watts) is a couple billion times brighter than, say, the Earth (1.7e17).  The ratio is better is the visible band, but it's still large.  The sensor itself has a dynamic range limitation of a few thousand to one, but this can be worked around.  The tricky bit is that the optical system itself has dynamic range limitations.  Apparently these folks have figured out how to reject most of the light from Alpha Centauri A and B so that their telescope can see a potential planet.  I'm sure that's possible, but I haven't seen an explanation of how.

Offline as58

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #27 on: 11/18/2016 11:56 PM »
1 AU at 4.3 light years is 3.7 microradians.  A 50 cm aperture with 550 nm light will resolve two peaks 1.3 microradians apart.  You can theoretically resolve the sun and a little dot next to it.

The problem is that the Sun (3.8e26 watts) is a couple billion times brighter than, say, the Earth (1.7e17).  The ratio is better is the visible band, but it's still large.  The sensor itself has a dynamic range limitation of a few thousand to one, but this can be worked around.  The tricky bit is that the optical system itself has dynamic range limitations.  Apparently these folks have figured out how to reject most of the light from Alpha Centauri A and B so that their telescope can see a potential planet.  I'm sure that's possible, but I haven't seen an explanation of how.

I think the contrast ratio is even a bit worse in the visible, about 1e-10. It increases to ~1e-7 at 10 um,  but of course then you'd need an aperture more than ten times as large for the same resolution.

I haven't seen anything about technical details, but there are some coronagraph designs that have IWA of less than 2*lambda/D, (which would be just enough) and, with aggressive post processing, possibly good enough starlight suppression. But I think this is right at the limit of what can be done with a 50 cm telescope.

Offline redliox

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #28 on: 11/21/2016 07:07 PM »
Keeping an eye out on how Project Blue's kickstarter's doing.  Not wholly promising: only about 8% funded with 29 days to go.  Possibly still a shot, but if this doesn't work they might need to take a more academic route with funding from agencies.
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Offline Star One

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #29 on: 11/22/2016 12:04 AM »
Keeping an eye out on how Project Blue's kickstarter's doing.  Not wholly promising: only about 8% funded with 29 days to go.  Possibly still a shot, but if this doesn't work they might need to take a more academic route with funding from agencies.
Of course it will not work as if anyone is going to fund it up to such a high amount when it isn't a gadget or computer game. The only chance they have as if it catches the eye of a few passing millionaires with money to spend.
« Last Edit: 11/22/2016 12:05 AM by Star One »

Offline Star One

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #30 on: 11/24/2016 07:30 PM »
Alpha Centauri is now officially called
Rigil Kentaurus.

Quote
Among the names formally approved by the WGSN are Proxima Centauri (for the nearest star to the Sun and host star of the nearest known exoplanet), Rigil Kentaurus (the ancient name for Alpha Centauri and names for dozens of bright stars commonly used for astronavigation. Among the stars with newly approved names that have recently been reported to host extrasolar planet candidates are: Algieba (Gamma1 Leonis), Hamal (Alpha Arietis), and Muscida (Omicron Ursae Majoris).

http://astronomynow.com/2016/11/24/international-astronomical-union-formally-approves-227-star-names/

Offline redliox

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #31 on: 11/24/2016 10:36 PM »
Alpha Centauri is now officially called
Rigil Kentaurus.

Quote
Among the names formally approved by the WGSN are Proxima Centauri (for the nearest star to the Sun and host star of the nearest known exoplanet), Rigil Kentaurus (the ancient name for Alpha Centauri and names for dozens of bright stars commonly used for astronavigation. Among the stars with newly approved names that have recently been reported to host extrasolar planet candidates are: Algieba (Gamma1 Leonis), Hamal (Alpha Arietis), and Muscida (Omicron Ursae Majoris).

http://astronomynow.com/2016/11/24/international-astronomical-union-formally-approves-227-star-names/

Ironically Proxima Centauri keeps the same name.  It would have made more sense to renamed Alpha Centauri to Rigil Centauri likewise.
« Last Edit: 11/24/2016 11:43 PM by redliox »
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Offline as58

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #32 on: 11/25/2016 05:51 AM »
Ironically Proxima Centauri keeps the same name.  It would have made more sense to renamed Alpha Centauri to Rigil Centauri likewise.

Proxima Centauri didn't 'keep the same name'; that name wasn't officially recognised by IAU before. Alpha Centauri wasn't renamed, it just now also has an official proper name in addition to its Bayer designation and other catalogue names. This IAU decision changes pretty much nothing. Everyone, including professional astronomers, was already using name Proxima Centauri and l believe Alpha Centauri will continue to be used more commonly than Rigil Kentaurusi. I'm not sure why IAU set up a working group to start giving proper names to stars (in most cases, just making traditional names official). Maybe it is a reaction to all kinds of 'name a star for a fee' schemes.
« Last Edit: 11/25/2016 04:36 PM by as58 »

Offline Ben the Space Brit

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #33 on: 11/25/2016 08:28 AM »
Personally, thanks to Sid Meier, I think of A-Cent A as 'Apollo' and A-Cent B as 'Hercules'. I can't personally foresee any point in the future when A-Cent B isn't 'Proxima', no matter what the various governing bodies say.
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Offline redliox

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #34 on: 11/25/2016 02:36 PM »
Personally, thanks to Sid Meier, I think of A-Cent A as 'Apollo' and A-Cent B as 'Hercules'. I can't personally foresee any point in the future when A-Cent B isn't 'Proxima', no matter what the various governing bodies say.

Can kind of relate since I played that game too.  ;)

I can understand Apollo, so he was a deity related to the sun although I dunno Hercules is star/sun worthy (outside of his actual constellation); however I have to admit Hercules (or Herakles) does have ties to centaur myths; there aren't too many well-known centaur names alas.
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Offline as58

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #35 on: 11/25/2016 04:35 PM »
Personally, thanks to Sid Meier, I think of A-Cent A as 'Apollo' and A-Cent B as 'Hercules'. I can't personally foresee any point in the future when A-Cent B isn't 'Proxima', no matter what the various governing bodies say.

Not exactly sure if I understand you correctly, but Alpha Centauri B is not the same star as Proxima Centauri. Proxima Centauri is (probably) the third star of the Alpha Centauri system, so it's Alpha Centauri C (though that name is very rarely used). Alpha Centauri A is Rigil Kentaurus (yes, different spelling). Alpha Centauri B has no proper name, neither official nor (at least to my knowledge) unofficial.

Offline Ben the Space Brit

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #36 on: 11/25/2016 09:01 PM »
Sorry, I mistyped; it should have been "I can't personally foresee any point in the future when A-Cent C isn't 'Proxima', no matter what the various governing bodies say."

As for the selection of the name 'Hercules', Mr Meier's justification was that the close binary orbit of the A and B elements of Alpha Centauri would rule out a large planetary system and certainly any large objects significantly outside the orbit of the Earth-like Chiron around A-Cent A. Because Hercules in Greek mythology eradicated the Centaurs, Meier proposed the name for A-Cent B as it was 'the slayer of the Centaurs', the force that prevented A-Cent A from having more than a fairly small planetary system.
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Offline CuddlyRocket

Alpha Centauri is now officially called
Rigil Kentaurus.

Not quite. The IAU Working Group on Star Names approved the name Rigil Kentaurus for Alpha Centauri A. It had previously approved the name Proxima Centauri for Alpha Centauri C. It has yet to approve a name for Alpha Centauri B. Both the bulletins announcing the approvals and the IAU's Catalog of Star Names specifically specifies the letters in these two cases.

The WGSN only names individual stars, whether or not they are part of a multiple star system. It will get round to naming the other components as some future date (it made an exception for Proxima Centauri as the star was just about to hit the headlines due to the discovery of the orbiting planet) and might later consider naming multiple star systems. Note that the IAU does not regard 'Alpha Centauri' as a name but as a designation.

I'm not sure why IAU set up a working group to start giving proper names to stars (in most cases, just making traditional names official). Maybe it is a reaction to all kinds of 'name a star for a fee' schemes.

Partly. But it was also a result of the NameExoWorlds process where the public was invited to name exoplanets and their host stars where the latter didn't already have a name. They didn't want to approve a star name that was already the name of a star and realised that there was no recognised list of such names. Also, it's an opportunity for public outreach once the more famous stars have been dealt with and a way of being more inclusive in regard to other cultures.

Offline Star One

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #38 on: 11/27/2016 06:19 PM »
Alpha Centauri is now officially called
Rigil Kentaurus.

Not quite. The IAU Working Group on Star Names approved the name Rigil Kentaurus for Alpha Centauri A. It had previously approved the name Proxima Centauri for Alpha Centauri C. It has yet to approve a name for Alpha Centauri B. Both the bulletins announcing the approvals and the IAU's Catalog of Star Names specifically specifies the letters in these two cases.

The WGSN only names individual stars, whether or not they are part of a multiple star system. It will get round to naming the other components as some future date (it made an exception for Proxima Centauri as the star was just about to hit the headlines due to the discovery of the orbiting planet) and might later consider naming multiple star systems. Note that the IAU does not regard 'Alpha Centauri' as a name but as a designation.

I'm not sure why IAU set up a working group to start giving proper names to stars (in most cases, just making traditional names official). Maybe it is a reaction to all kinds of 'name a star for a fee' schemes.

Partly. But it was also a result of the NameExoWorlds process where the public was invited to name exoplanets and their host stars where the latter didn't already have a name. They didn't want to approve a star name that was already the name of a star and realised that there was no recognised list of such names. Also, it's an opportunity for public outreach once the more famous stars have been dealt with and a way of being more inclusive in regard to other cultures.

Thank you for that. Why didn't they name all three stars in the system at once as it seems illogical not to do so? Also what is likely to be the name for Alpha Centauri B?

Offline as58

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Re: Project Blue to image a planet in the Alpha Centauri system
« Reply #39 on: 11/27/2016 06:44 PM »
Thank you for that. Why didn't they name all three stars in the system at once as it seems illogical not to do so? Also what is likely to be the name for Alpha Centauri B?

Alpha Centauri B has never had a proper name (or more accurately, originally Rigil Kentaurus was the name of both A and B because to naked eye they appear as a single star). So IAU would probably have to come up with something new, which is obviously more complicated than just making an old name official.