If we can't go to other solar systems, can we bring them to us?

Factual Questions
1

Of course I don’t mean literally put an exoplanet in orbit around Earth, what I mean is, what are the theoretical limits on how much we can learn about exoplanets from the comfort of Earth or near Earth orbit? Right now we can detect them, and apparently we can even figure out their rough size, orbital period, and even some characteristics of their atmosphere and density. With foreseeable technological improvements, what else can we learn about planets outside our solar system? For example:

  1. Is it possible to find evidence of life? Doesn’t life as we know it alter the atmosphere significantly, even without technology?

  2. What would it take to actually get a photo of an exoplanet as good as a Hubble photo of Saturn? Is it even possible?

  3. Could there ever be a way to get precise measurements of the properties of exoplanets without sending probes?

  4. Could the surface of an exoplanet be mapped from light years away?

  5. Are there any NASA projects designed to move beyond Kepler and learn even more about other solar systems?

2

Here is a recent proposal for using the sun as a gravitational lens. And here is one about hairy balls.

3

Wow, if that thing can get pictures THAT detailed with current tech, that sounds like an incredible project. Imagine if we could get an actual image of a planet like the one pictures, with continents and oceans? And I assume at that level of sharpness we can see life too!

4

I’ve read the suggestion (here, for instance) of locating observatories on the moon. No atmosphere, and if you locate one on the far side, no radio interference.

5

I don’t know enough to comment on the scientific validity of the theory but I know that I’ve heard the suggestion than placing another Hubble type instrament as close as the orbit of Saturn would provide enough of a stereo imaging effect to hugely improve our ability to discern such information.

Could be complete bollocks for all I know.

6

There is no practical reason to opeate observatories on the far side of the Moon. Setting aside the issue of the fine electrostatic dust which contaminates everything by levating and stubbornly adhering to every availble surface, an observatory fixed to the lunar surface would be subject to both the rotation of the Moon (meaning it will be facing in some sunward aspect for half of the Moon’s rotational period) and tidal vibrations. We have solar orbiting observatories in which the optics can be pointed in any arbitrary direction and maintained to a high degree of precision which can work without propellant as long as the satellite has power and working momemtum wheels.

As for the question of the o.p., there are physical limits to the degree of imagine that can be done of planetary objects at interstellar distances, but we aren’t even approaching those limits yet. Right now we are restricted by the size of observatories that can be carried by satellite launch vehicles into orbit, but larger and more capable vehicles and inflatable/deployable optical collectors could easily improve that by an order of magnitude, and multiple satellites in an interferometer array could improve that still, potentialy to the physical limits of available light to collect. Mapping a world in detail even at the distance of Alpha Centuari is probably beyond feasibility, but we can certainly get some good estimates of the composition of planetary atmopheres by looking at the spectra as it passes in front of its star(s), and seeing free oxidizing species in the atmosphere, while not definitive, would suggest some non-equilibrium thermodynamics processes suggestive of life.

Using instruments with different spectral and resolution capabilities will help in detecting exoplanets and investigating their properties with the ultimate intent of sending some kind of flyby probe when (and if, fingers crossed) propulsion capability would allow for it to be sent in a reasonable timeframe to expect it would still be operational when reaching another star system. Sending a crewed vehicle is well beyond any plausible propulsion and habitation technology at this point, and may always remain so, but advances in technology may allow us to explore other worlds via proxy, while we may still potentially explore and exploit the vast resources within our own solar system.

Stranger

7

Keep in mind that telescope would have to be placed around 550 AU out, which is a mite far.

8

I see that in 40 years, Voyager 1 has only travelled 145 AU out. Does this plan include a way to get out that far in less than 180 years?

9

This?

10

They mean that 70s idea where they use nuclear explosions to propel spacecraft? I was hoping better ideas were on the horizon.

11

No bombs required. A thermal rocket basically takes an inert propellant, heats it up, and blasts the hot propellant out backwards. In the case of nuclear thermal propulsion, the heat source is a nuclear reactor.

12

Oh. What’s the top speed on that given current tech?

13

New Worlds Mission is one of many concept studies to image an exoplanet. Though by “imaging” they mean isolating it as a distinct point and measuring its spectrum. The concepts are fairly modest, designed to be launched by existing launchers.

To actually resolve surface features on an exoplanet, you will need a bigger telescope. To resolve a planet 15 light-years away at the same resolution Hubble images Saturn, you need a 230-meter aperture telescope, or an optical interferometer with elements spaced up to 230 meters apart. (By the way, you can’t make an interferometer with just 2 telescopes linked together, you need many telescopes arrayed in 2 dimensions.) And probably an external starshade (see above link).

14

And maybe even read their license plates!

15

That actually sounds surprisingly doable. As successul as Hubble was, why not just try to build the biggest telescope feasible?

16

We already have propulsion technology to send probes out further than the Voyagers. The New Horizons probe, which went past Pluto and other Kuiper Belt objects, is traveling much faster than the Voyagers, and will pass them as the most distant man-made object in the not-too-distant future. It costs more than a gravity-assist mostly-ballistic trajectory, of course, but it’s still well within the range of affordability. There’d be problems communicating with something that far out, but that’s still a problem that can be solved by throwing money at it.

17

Thank you for your reply. I’m excited at the idea of what we can learn from solar orbiting observatories.

18

Will… break for… zlorp?

19

Another fly in the ointment for the gravity lens telescope idea: with probes like New Horizons and the Voyagers, most of the delta vee comes early on from the initial launch and planetary slingshots, after that mostly doing minor corrections to their aim and crusing forwards. But this telescope would have to speed out towards the necessary position and then some point along the way begin slowing itself down so that it isn’t an interstellar probe, and shape it’s orbit into a reasonably round one instead of a cometary one, requiring it to carry a fuckton more fuel and reaction mass.

20

Excellent question. There have been many directly imaged extrasolar planets, but thus far technology doesn’t permit showing surface detail: List of directly imaged exoplanets - Wikipedia

In theory a space-based free-flying interferometer could be any size needed. Smaller ones have been proposed which would have milli-arcsecond resolution, which is about 50 times better than Hubble Space Telescope.

None of those seriously proposed would show fine detail on an extra-solar planet, however they might show an almost-featureless planetary disc. But the spectrographic data would be substantial – you could probably tell many things about the atmospheric composition.

Imagine if you wanted to visually see detail roughly equal to this photo of Jupiter at 1 arc-second angular resolution: http://www.ianmorison.com/wp-content/uploads/2018/05/J50.jpg

The angular diameter of Jupiter from earth is about 50 arc-sec, so the above image had angular resolution of about 1/50th the diameter to show that detail.

Jupiter is 86,000 mi in diameter, so the above image can resolve about 1/50th of that or features 1,700 mi wide. What telescope (or space interferometer) diameter would be needed to resolve something 1,700 mi wide at a distance of 4.4 light years? IOW if you wanted to see a Jupiter-size planet with that much detail around the closest star.

Plugging those numbers into this calculator says angular resolution of 1.5E-5 arc sec is needed: Angular Size Calculator

Plugging 1.5E-5 arc sec and 500 nm light wavelength into this calculator gives 10,000 meter diameter: Angular Resolution Calculator

So in theory it would take a free-flying space optical interferometer about 10 km in diameter to image a Jupiter-size planet at Alpha Centauri at the above-shown quality. To have major scientific value, it wouldn’t need to have such resolution; if it was 1/5 that size it would probably be very informative.

That is only a crude resolution & diameter calculation. There would also be issues with glare from the star the extrasolar planet orbits and probably many other factors. However those are all probably solvable. You could possibly build such a device for less money than sending a small “fly by” interstellar probe to one destination, and such a device could observe continuously many such extrasolar planets.

Proposed “Darwin” space-based interferometer: Darwin (spacecraft) - Wikipedia

“The Future of Space-Based Interferometry”: https://www.noao.edu/meetings/interferometry/workshop-files/Carpenter-Space-comp.pdf