There are 3 areas of scientific concern here:
Laser Light: How Much Hits Mars?Using 3.5W blue & 1W red (& IR) lasers, even with Mars at a lowly 17 deg alt in the sky, we were able to rain 4.4 Quadrillion photons per second down onto the surface of Mars. This was at the recent opposition of Mars [closest approach]. That’s about 2mW [energy-intensity in joules per sec] hitting Mars. So 122 Million photons per Sq Km [of ‘effective’ surface area] are smashing into Mars.
Physical/Chemical Effect On MarsJust Google “Terraforming Mars”: Wikipedia also gives a reasonable summary. A constant theme is the early need to increase atmospheric pressure. CO2 sublimation from the poles is described as a means to effect a greenhouse reaction. Water realease would also help. All that is needed is light/heat. Well, at a lesser scale, that is exactly what we are doing… We are applying light/heat to Mars.
Biological effect On MarsScientists still believe there might be very primitive life on Mars. If there is, it is probably photosynthetic and, like some plants, might prefer blue/red laser light to sunlight. Our laser light may also encourage growth of ‘dark plants’ which could enhance any greenhouse effect, plus produce O2. It is also thought that high energy blue-UV light probably first sparked life… So, might we do that for Mars?!
We used this simplified equation for air mass [Earth]:
We calculate incident sunlight intensity using:
So we also used it for laser light intensity leaving the Earth’s atmosphere.
3.5W & 1W strong blue & red lasers:
<3mm initial beam diameter; divergence < 2.5 mRad (Full Angle), wavelength 450nm
100mW red ‘nano’ laser:
<4mm initial beam diameter; divergence <0.5mRad, wavelength 650nm
Calculate energy of a photon:
Planet’s effective Surface Area:
SA = π r2
So can 122 blue photons per sq m actually sublimate CO2 into atmosphere? Yes, if already on the ‘cusp’.
Can these photons provide energy to photosynthetic life? Absolutely, it is a very efficient process of energy transfer.
Could it break chemical bonds and start life?… possibly!
Is it measurable? Yes, if you had a sensitive detector on Mars [this is additional to sunlight and background radiation].
Earth’s air mass is a significant impediment, especially when Mars is “low in the sky”. Below 10 deg alt the calculations become unreliable. So we try to laser Mars when it is well above this angle.
The equation used does not discriminate between different wavelengths (hence colors) of light. The air mass (molecules) scatters more blue light photons than longer wavelength red photons (hence blue skies and orange-red sunsets). At low angles (laser light must travel further through air mass) This “Rayleigh Scattering” is significant at low altitudes, hence we routinely deploy powerful red lasers (100mW and 1W) if the target planet is <20deg in the sky. Above this angle we routinely employ strong blue lasers (1W-3.5W). So the estimate of 4.4 Quadrillion photons per second smashing into Mars is an average approximation when using red or blue lasers (under-estimate for red and over estimate for blue).
Because of this issue, from 2017 until early 2019 we used high energy Infra-red lasers (2W PLE-Pro 808nm IR “JetLaser”) with <2mRad beam divergence). This required use of a night-vision IR headset (“Yukon Spartan”). Although we could target Mars effectively, avoid light polution and (less) danger to aircrew, it was a tricky process and difficult to ensure laser protection for the left eye. Nevertheless, we persevered with this whenever Mars was <20deg until sudden laser failure in Feb 2019. Since then we have returned to red and blue visible light lasers (green “EVO” laser only for programmable morse code messaging: “we claim peaceful possession of Planet Mars.”
Note: there is minimal Rayleigh scattering on Mars (v sparse atmosphere), but there is some “Mie Scattering” by dust particles. Red light suffers more deflections but we have not included this factor in our calculations (so our estimates will be off the mark during one of Mars’ frequent dust storms).
Mars moves through space at ~54,000 mph (86,700 kph) so has progressed more than 26000 miles (~42000 km) in 30 minutes. That’s 6 times the diameter of Mars. For the purpose of laser targeting, it is the velocity of Mars (speed & direction) which is important. Note that special relativity applies. The velocity of the laser light source (Earths orbital & rotational velocities) does not matter.
Light time from Earth to Mars varies from 3 to 22 minutes. We dont do much laser application once the light time exceeds 15 minutes. The laser is precisely aligned to the telescope. We always keep Mars in the high-power field of view (FOV), but depending on the relevant light time, we can slightly adjust the firing position in anticipation of Mars’ progression. The requirement is minimal/none when Mars is close at opposition (3 minutes light time each way) but we must anticipate Mars movement over 20 minutes when the Earth-Mars light-time is 10 minutes. Although our powerful lasers comprise tightly collimated beams, the inevitable divergence is such that even when Mars is close at opposition, the beam width is more than 30 times the diameter of Mars. We dont miss our target.