Can long exposure techniques be used to capture detailed images of planets?

[nosacz666]

I have this little idea for science-fiction story. It would be about the community of scientists, who investigate from the surface of the Earth the history of various planet. Alas, I came across serious technical problems. Do you think it could be possible to somehow extract information from beams of star light? Or to build lenses powerful enough to observe planet as if under the microscope? The problem is, however I will resolve this, I need a solid physics explanation. Could you help me?

 

[jedishrfu]

Isn't this like monitoring the television and radio broadcasts from some planet? As long as they are strong enough to override background signals then they could be decoded.

So while you might not be able to see into the planets full history or resolve details on the planet sufficiently you could see the TV shows they make and maybe discern their history from a historical show that they produced...

Of course, you could factor in time travel on our planet, go back in time and see the earlier signals transmitted by the planet of interest and do similar things...

Using this approach of decoding their programs becomes like an archeological operation where you're interpreting things you don't quite understand and so you could have debate between your charaters here as to what you're actually seeing...

 

[nosacz666]

Oh, that's brilliant! Thank's, jedishrfu =]

 

[Borek]

Watching their TV will be still a matter of the resolution. λ/D and so on.

Unless each their TV station will operate at a different frequency.

To get an idea about orders of magnitude involved, you should be able to easily calculate radius of the antenna required to watch TV emitted by a TV station on the Earth sized planet orbiting Alpha Centauri. Assume there are only two TV stations, located at poles. Basically this is just a plug and chug, all information (distances, wavelengths) easy to google.

Actually if you ever calculate it, post the result, that would be an interesting information.

 

[Vanadium 50]

Looking at a planet from great distances suffers from two problems - the resolution, as Borek points out, and simple light collection. The only science fiction author I know who took this problem seriously was Charles Sheffield in his Heritage Universe, which is littered with artifacts from an ancient civilization called the Builders.

Here is Wikipedia's description of one of those artifacts, Lens:

Lens is what its name implies, but on an extremely massive scale. Lens is a focusing region of space 0.23 light-years across with no apparent thickness. It has a 0.22 light-years effective aperture and 427 light-years focal length. Through it, planetary objects have been observed in galaxies more than 100 million parsecs away. It is not known how Lens is constructed. It is not made of any particles known by science and it is not a form of space-time singularity.

It is perhaps worth noting that Sheffield describes what his artifact does in great deal, and says nothing about how it works. This is in contrast to many people who post in this section, looking for explanations on how some plot element might work.

 

[Ryan_m_b]

I've read SF novels that involved this sort of thing. A prominent one that springs to mind is Alistair Reynold's Blue Remembered Earth (and to a lesser extent its sequel). The book features a device called the Occulus Array which consists of thousands of interferometers that are placed in orbits on the outskirts of the solar system. In the book the array is used to study all sorts of things including the surface of distant exo planets. I think I right in saying that this set up would be equivalent to a solar system sized telescope but perhaps a more knowledgeable person could jump into clarify.

 

[D H]

I think I right in saying that this set up would be equivalent to a solar system sized telescope but perhaps a more knowledgeable person could jump into clarify.

It would be more or less equivalent in terms of angular resolution to a solar system sized telescope. It would not be anywhere close to a solar system sized telescope in terms of light gathering power.

 

[Ryan_m_b]

It would be more or less equivalent in terms of angular resolution to a solar system sized telescope. It would not be anywhere close to a solar system sized telescope in terms of light gathering power.

That makes sense. Does this mean there's a hard limit on what it would be able to detect or could such an array go for a long exposure time like a camera?

 

[Borek]

This is exactly the same as with taking normal pictures with any camera. Long exposition and moving elements are blurred.

 

[Ryan_m_b]

This is exactly the same as with taking normal pictures with any camera. Long exposition and moving elements are blurred.

Quite true on the blurring, I once took some long exposure shots of the moon and saw this affect. I assume that it is possible in principle to feed the data into some software that could correct for this? Given an object that's rotating and moving at a fixed rate it would seem like something easy to work out.