Lasers on earth visible from Mars

In summary, the conversation discusses the visibility of a laser beam from Mars and the amount of power it would require. It is mentioned that the human eye cannot resolve the Earth's disk from Mars, so the laser would need to be focused in order to be seen. The estimated power needed ranges from a regular laser pointer to a naval anti-missile experimental laser. It is also mentioned that direct propulsion with light pressure would require a large amount of power.
  • #1
andrewbee
Hi,

I read something interesting about some amateur astronomers lasing the ISS with a blue-light laser, and the astronauts were able to spot it.

How powerful would a laser have to be to be seen by the human eye from Mars? It would be shone from the dark side of Earth of course. Are we talking one (or several) guide star lasers from the big observatories? Metal-cutting beams (c. 50w)? Naval anti-missile experimental lasers (c. 100 kw)?

Any input appreciated.

Thanks
 
Physics news on Phys.org
  • #2
The human eye cannot resolve the disk of Earth from Mars, so you always have much more sunlight than laser light.
Even if we neglect this and just take the minimal distance (~55 million km), it depends on the focus of the laser beam: If you use a telescope (in the "wrong" direction of light) to focus the beam, the power can be reduced significantly compared to a regular laser.

Edit: For a laser pointer of 1mW, I calculated 4000km as lower bound on the visibility range a while ago. 10000 times this distance would need 100 million times the power, or 100kW, assuming the focussing remains the same.
 
Last edited:
  • #3
That's really helpful,thanks. Did you make any assumptions about whether it was red, green or blue light?
 
  • #4
700nm -> red
A shorter wavelength could improve the visibility limit a bit, but it also gives a lower number of photons per power, and it is harder to create.
 
  • #5
mfb said:
For a laser pointer of 1mW, I calculated 4000km as lower bound on the visibility range a while ago. 10000 times this distance would need 100 million times the power, or 100kW, assuming the focussing remains the same.

That's surprising.

One of my favorite novels is https://www.amazon.com/dp/0974776963/?tag=pfamazon01-20, in which they propel a spaceship to Earth by the power of a laser shined from Alpha Centauri. If it takes 100kW just to be able to see it on Mars, it must take petawatts to propel a ship to the nearest star.

https://www.amazon.com/dp/0671741926/?tag=pfamazon01-20 is another novel that did a similar thing.
 
Last edited by a moderator:
  • #6
Well, such a system would have a much better focus than a laser pointer. If you use something like the E-ELT (40m-mirror, currently under construction), a strong laser pointer could be sufficient to be visible from Mars. The laser spot would have a diameter of a few kilometers there.

Direct propulsion with light pressure requires insane amounts of power - about 1 gigawatt (or 1 big powerplant) per 6N (enough to hold a mass 600g on earth), even if the whole laser hits the spacecraft .
 

FAQ: Lasers on earth visible from Mars

1. How far away can a laser on Earth be seen from Mars?

The distance at which a laser on Earth can be seen from Mars depends on several factors, including the strength and wavelength of the laser, atmospheric conditions on both planets, and the location of the observer on Mars. However, on average, a laser with a power of 1 watt and a wavelength of 532 nanometers could be seen from about 30-50 kilometers away on Mars.

2. What type of laser would be visible from Mars?

Lasers that emit visible light in the red or green spectrum would be most visible from Mars. This includes lasers with wavelengths of 532 nanometers (green) and 650 nanometers (red). However, other factors such as atmospheric conditions can also affect the visibility of the laser.

3. Can a laser on Earth be used to send messages to Mars?

Yes, it is possible to use a laser on Earth to send messages to Mars. This process, known as optical communication, has been successfully tested by NASA and other space agencies. However, it requires precise alignment between the Earth and Mars and specialized equipment on both ends.

4. How powerful would a laser need to be to be seen from Mars?

The power of a laser needed to be seen from Mars depends on the factors mentioned in the first question. However, in general, a laser with a power of at least 1 watt would have a good chance of being seen from Mars.

5. What is the purpose of having lasers visible from Mars?

The visibility of lasers from Mars has various potential applications, including communication, navigation, and even search for extraterrestrial life. Additionally, it can serve as a way to study the atmosphere and weather patterns on both planets.

Similar threads

Back
Top