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Would it be possible to see electric lights on distant planets using current telescopes?

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    $\begingroup$ While detecting and resolving an artificial light itself may not be an option soon, an unusually skewed spectrum of a planet may be easier to detect. On the other hand, in the last years we almost abandoned sodium and mercury lamps that would create a distinct signature for our fellow alien astronomers. Modern LEDs become more and more "natural". $\endgroup$
    – fraxinus
    Dec 19, 2022 at 21:09

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No. There are very few exoplanets that can even be imaged as "dots". There are none that can be resolved as discs and it would be well beyond current technology to see lights on the surface of an Earth-like planet.

Most exoplanets are only known from periodic dimming of a star as the planet passes in front of its star, or wobbles in a star's motion, as the planet's gravity causes the star to move forward and back.

We could see lights on Mars, if they existed as they do on Earth, but they don't.

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    $\begingroup$ This answer is focused on direct imaging and ignores the possibility of spectroscopic information. We’re not able to directly image the atmosphere of any exoplanet either, yet we can detect their absorptive spectroscopic influence. Theoretically characteristic emissive spectroscopic information from very large-scale illumination could similarly be detected. $\endgroup$
    – Michael MacAskill
    Dec 20, 2022 at 23:00
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    $\begingroup$ @MichaelMacAskill My answer stands, If you feel you can add something please write your own answer. $\endgroup$
    – James K
    Dec 20, 2022 at 23:33
  • $\begingroup$ You don't need to resolve a planet as a disk to observe light emitted from it. After all, you can't resolve most stars into disks, but you can see their light without even using a telescope. $\endgroup$
    – John
    Jan 1 at 4:39
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I did a few rough calculations.

Let's assume a neighbor system (4 light years), and a population of 1 billion people each transmitting 1000W of light into the night sky.

Then on Earth, a 100 square meters telescope would receive about 2 photons per minute from the electric lights. This is far beyond current technology, especially as there are much, much brighter sources in very close vicinity.

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    $\begingroup$ To add to this: Currently planned telescopes (such as Roman) might be able to achieve a contrast of a few parts per billion at Jupiter-like distances from a star. 1e9 people putting out 1e3 watts per person is still a contrast of 1:1e15 against our sun. $\endgroup$
    – Izzy
    Dec 19, 2022 at 23:16
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No, at least not with currently deployed telescopes. However, it is theoretically possible with current (or near future) technology. We could potentially image the lights of an exoplanet using a Solar Gravitational Lens (SGL), as is currently under consideration by the NASA Institute for Advanced Concepts as a "Phase II" program. "Phase II" is described as signifying that NASA has:

determined that much of the foundational technology exists or is in intermediate levels of readiness due to the proliferation of government and commercial smallsat programs.

The technique works the same as we normally observe gravitational lensing. That is, the light of a distant object is concentrated in a narrow region of space called a focal line by a massive object between the observer and the lensed object. This lensing dramatically increases the resolution and apparent brightness of the observed object, enabling us to see things that are too far away or too dim for us to directly observe with conventional telescopes.

A SGL mission would send probes so that they place the Sun between the probe and the exoplanet. By blocking out the light of the sun, the probe could observe the Einstein Ring of the exoplanet surrounding the Sun. This ring could be reconstructed into a traditional image to view the surface of the exoplanet, such as this simulated image. Simulated exoplanet image

At this resolution (estimated by NASA as being up to ~25 km-scale surface resolution for an Earth sized exoplanet at 30 pc), it would be possible to directly observe lights of an advanced alien civilization.

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    $\begingroup$ Of course, it takes a long time with current technology to get to the SGL focal distance of ~547.6 AU, especially if you want to remain there (and not just do a flyby). In comparison, Voyager 1 is currently ~158.5 AU from the Sun. voyager.jpl.nasa.gov/mission/status $\endgroup$
    – PM 2Ring
    Dec 19, 2022 at 19:09
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    $\begingroup$ Per the wikipedia page to which you linked, the SGL was granted a NIAC Phase III award, confirmed here. That's still a smallish amount of money ($2 million), maybe 3 or 4 people at JPL working full time for two years. $\endgroup$
    – David Hammen
    Dec 19, 2022 at 21:35
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    $\begingroup$ Another problem is that this telescope would basically point in a single direction for all its operative lifetime, and then need to work with that. Changing the view direction would take as long time as setting up a new telescope. So this would only be able to investigate one single solar system... you better select one where you have good reason to believe it has life on it! $\endgroup$
    – leftaroundabout
    Dec 20, 2022 at 13:14
  • $\begingroup$ Can't they intercept photons closer to Earth by by using a circular array of detectors to intercept photons . $\endgroup$
    – user48394
    Dec 20, 2022 at 18:47
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    $\begingroup$ @DaveTheWave Not really. The converging light rays form a cone 547.6 AU long, with the Sun's disk as the base of the cone, and the apex of the cone at the SGL point. If you want to collect photons at half that distance, your circular collector has a diameter of half the Sun's diameter. That's rather large, and the photons are very diffuse, making them hard to detect. $\endgroup$
    – PM 2Ring
    Dec 20, 2022 at 20:33
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Here there was only sludge, microbial mats and goop for 1.5 billion years, then it was filaments, small specs and sludge for 1.5 billion years, and there has been light for 50 years, and even those look like a volcano or a reflection of moons and stars onto clouds or ice.

i.e. Venus because of it's clouds reflects more than 4 times as much incoming light than the moon, and more than twice of the Earth's.

So astronomers want to detect chemicals rather than lights, we don't know what alien light bulbs use for chemistry, however we can measure high oxygen content on another planet, which means photosynthesis. Planet Rarth's oxygen started rising about 1000 million years ago at the same time as life-form size was rising.

https://astronomy.swin.edu.au/cosmos/a/Albedo

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We need hypersensitive instruments for that.

Freeman Dyson postulated an industrial society could be detected on Infrared. Like Earth looking for heat islands in urban areas.

Another would periodic spikes in infrared waves from stars because society was tapping its power.

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TL;DR:

We could detect but it really depends on the distance you're talking about

Long answer:

Not using current technology (if the distance is huge). The Solar Gravitational lensing mission could do detect city lights from exoplanets but a mass (like a galaxy, neutron star and blackhole) would be required (which also most probably would be available).

If the distance is too far away according to the inverse square law the light's intensity would get smaller to a limit where we can't really detect it.

Because of the Doppler shift it would be tougher because the redshift created from the effect would be huge if the distance is huge as per Hubble law but that is kind of manageable because we even have radio telescopes. But one of the most powerful telescopes we have ever made the JWST has the mid-infrared ranges ( 5-28.5 μm) but doppler shift could extend even farther as per the distance so it's a catch 22 situation if we want to see large distances then we would have encounter more redshift too.

We wouldn't see the lights if the planet/asteroid is in the zone of avoidance

Also since different elements (in the Periodic table) in Bulbs emit different Wavelengths of light we're not sure which wavelength to focus on like Argon, Xenon, Incandescent (Tungsten)!

The amount of light emmited is based on the energy usage given by the Karshadev scale

Hope it helps, Thanks

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