zoom in on close planetary systems

[achihod]

Hey Everybody,

Every now and then I see articles stating that scientists found earth like exoplanets orbiting stars in distances of hundreds or thousands of light years from us. How come we can find stars so far away or have hubble take pictures of distant stars and galaxies but have yet to find out whether proxima centaury b is tidally locked or not, has a habitable climate or not, whether there are more planets orbiting alpha centaury and so on. if we can look so far how come we can't zoom in to relatively close planetary systems such as these to have a clearer view of their planets' surface and to confirm or deny data ?

if we can look so far away how come we can't zoom in to see if there is rivers, structures, etc. on a planets that not thousands of light years away but only 4.3-4.4 ly away ?

thanks a lot

Achihod

 

[COLGeek]

The discovery of exoplanets is generally not accomplished with optical means (like via a visual image from a telescope). We simply don't have the means to zoom in on planets as you suggest.

Methods of detecting exoplanets - Wikipedia

en.wikipedia.org

 

[achihod]

Thanks a lot for your reply COLGeek.
that's right, discovery of exoplanets is made with transit calculations and such methods
But the hubble telescope took visual images of stars and galaxies many light years away didn't it? So I was thinking whether it could take closer images of closer objects

 

[COLGeek]

Thanks a lot for your reply COLGeek.
that's right, discovery of exoplanets is made with transit calculations and such methods
But the hubble telescope took visual images of stars and galaxies many light years away didn't it? So I was thinking whether it could take closer images of closer objects

Even "close" is a relative term in regards to objects that are light-years away. Hubble is not capable of such a feat.

 

[Catastrophe]

The detail (separation between two points) depends on the aperture of your telescope which is effectively.

QUOTE
A useful rule of thumb is that the maximum magnification your telescope can handle is around 50 times the telescope's aperture in inches. Any higher and the image gets too dim and blurry. So, a 6 inch scope can magnify up to 300x, while an 8 inch scope can magnify 400x.
QUOTE

Imagine you have two dots at a certain distance. Looking at them, the distance between them can be used as a test for your eye. You will not see them beyond a certain distance.
Increasing the width of your objective lens collects light from a wider area. As the quote shows, the larger the aperture (width) the smaller the separation you are able to discern. Imagine one mm viewed at 1000 light years. You can keep increasing the aperture but there will come a point where the width of your lens might need to be the distance from here to the Moon. In other words there is a practical limit to the smallness of the separation you can detect as distance increases.

 

[rod]

"if we can look so far away how come we can't zoom in to see if there is rivers, structures, etc. on a planets that not thousands of light years away but only 4.3-4.4 ly away ?"

My observation - good question. Consider that 4.3 ly distance is 40.618E+12 km from Earth. An exoplanet at 1 AU distance from its parent star is 0.76" from the host star and only thousands of km in diameter compared to 150E+6 km size for 1 AU, so the exoplanet will be a very small angular size to resolve. There are a number of exoplanets reported now as imaged but not surface details though. http://www.sciencedaily.com/releases/2011/10/111006173612.htm, and https://phys.org/news/2017-02-dedicated-planet-imager-eyes-worlds.html

This exoplanet site shows 49 are imaged now, https://exoplanetarchive.ipac.caltech.edu/index.html

This exoplanet site lists 139 imaged, http://exoplanet.eu/

 

[Catastrophe]

Rod, am I not correct in stating that one needs larger apertures to detect smaller details. Hence to see road signs on an inhabited exoplanet (or microbes) would require a very large aperture telescope?

 

[rod]

Rod, am I not correct in stating that one needs larger apertures to detect smaller details. Hence to see road signs on an inhabited exoplanet (or microbes) would require a very large aperture telescope?

Yes Catastrophe, as a general statement about telescopes and angular resolution. My example used the specifics of the question and provided specifics. Another good example. Apollo 11 and other landing sites on the Moon and equipment left behind. When the Moon is 385,000 km distance, a telescope with large aperture and great resolution could see a crater 1.87 meters in diameter, that is 1E-3" size, assuming that kind of resolution was possible and imaged clearly. 1E-3" resolution looking at an exoplanet 41E+12 km distance, could see an object just less than 199,000 km in diameter or about 123500 miles across.

 

[Helio]

Perhaps something roughly correct could add to the above.
6 lyrs distance
60 km diameter aperture
600 km pixel size

But the mammoth aperture size required could be reduced to obtain near-equal resolution by combining one or more other apertures to form an interferometer. The dim light we receive from an exoplanet, however, would still require large apertures to get enough lift to be useful.

It's amazing that we have imaged some exoplanets directly. We have been talking about how hard asteroids are to see and these are right on our door step, figuratively speaking. We also have never imaged a single Oort Cloud object, and these are in our back yard. Yet we can see exoplanets that are much farther. The reason is that the ones we can see are highly illuminated thanks to their proximity to their bright host star, which makes up for the vast distance their light must travel to reach us.

 

[Catastrophe]

Is it possible to have multiple smaller apertures (how many) over the 60 km diameter aperture which would be requires?

 

[Helio]

Is it possible to have multiple smaller apertures (how many) over the 60 km diameter aperture which would be requires?

Yes, but the engineering challenges I expect would be enormous.

If two, say, Hubble Telescopes were separated by 60km but, somehow, perfectly tied together to allow their light to be properly combined, then they would have the resolution stated. At least that's my understanding but I hesitate because you don't see this mentioned since the challenge is beyond today's technology, perhaps. The twin large telescopes in Hawaii (Keck) can work as an interferometer so it can be done, but it's worth noting they don't use it very often, I think.

But, astronomers are very clever. They can "see" things in greater detail than we might expect. For instance, when a planet is behind their star the only light we observe will be that of the star. When the planet is elongated in its orbit, say quarter phase, then its illuminated light is added to the starlight. Astronomers can subtract the starlight from that signal and reveal the illuminated light, So, that spectrum can at least give us the color of the planet. Further, the planet is rotating, so we can see color changes that also reveal more of the planet.

[In my amateur quest to determine our Sun's true color -- falsifying the yellow hypothesis -- I presented an instrument that would produce the actual color of any object if we know it's spectrum. The spectrum is easily reproduced from a known light source and using a mask to compensate for spectral intensities. The trick is recombining this light into a spot for the eye to behold. One astronomer coined this part of it a "scrambler". I began making it with small light fibers but when I discovered how simple the answer was for the Sun's color, I lost interest.

I call it the Asterochromograph. ]

A similar technique is used during transit when the spectral light subtraction is used to determine the spectrum of just the atmosphere of the exoplanet during transit.

 

[dfjchem721]

The twin large telescopes in Hawaii (Keck) can work as an interferometer so it can be done, but it's worth noting they don't use it very often, I think.

This is correct about the Kecks. They are two ten meter telescopes connected by an interferometer which is supposed to combine the two images and eliminate distortions to create an "effective" aperture that is ca. the distance between the two scopes. The below was stolen from WIki*:

"Keck Interferometer

The Interferometer allowed the light from both Keck telescopes to be combined into an 85-metre (279 ft) baseline, near infrared, optical interferometer. This long baseline gave the interferometer an effective angular resolution of 5 milliarcseconds (mas) at 2.2 µm, and 24 mas at 10 µm. Several back-end instruments allowed the interferometer to operate in a variety of modes, operating in H, K, and L-band near infrared, as well as nulling interferometry. As of mid-2012 the Keck Interferometer has been discontinued for lack of funding. The instrument is currently in mothballed status and could be reactivated if funding permits."

* https://en.wikipedia.org/wiki/W._M._Keck_Observatory

 

[Helio]

Thanks! I will assume our atmosphere limits resolution to make the work “too much squeeze for the juice” as I heard a lady entrepreneur once state years ago.

 

[rod]

FYI, here is another example for angular resolution and what it would take to resolve an object at 10 pc distance from Earth. You need 0.93048 mas resolution and very good here to see the disk image of the Sun at 10 pc. A telescope or combination of telescopes like that could see an object about 1.74 meters in diameter on the Moon when it is 385,000 km away. Those exoplanet imaging telescopes should provide some excellent views of the Apollo 11 and other sites landing equipment