Grail Mission to the Moon: Does Light Exert Pressure?

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SUMMARY

The forum discussion centers on the concept of radiation pressure exerted by sunlight, particularly in the context of the Grail mission to the Moon. It confirms that photons, despite being massless, carry momentum and can exert pressure, a phenomenon known as radiation pressure. The discussion highlights the significance of solar pressure in satellite operations, particularly when maneuvering old satellites out of the geosynchronous belt. The area to mass ratio of an object, such as the Moon, plays a crucial role in the impact of solar radiation pressure, which is minimal due to its low ratio.

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  • Understanding of electromagnetic radiation and photons
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  • Familiarity with satellite dynamics and geosynchronous orbits
  • Basic principles of momentum and energy in physics
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RJ Emery
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In a NY Times article about the Grail mission to the moon (see http://tinyurl.com/84dc5ew), the last paragraph states:

But if part of the core is still molten, as is currently thought, the sloshing will delay the deformation to slightly after the closest approach. The effect is so tiny that the scientists will first have to account for effects like the pressure of light from the Sun pushing on the Moon.​

Does light (photons) exert a pressure?

Sunlight consists of much more than pure light (photons). It is a stream of particles which have mass that can understandably exert a pressure. Therefore, is the writer mistaken?
 
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RJ Emery said:
Does light (photons) exert a pressure?
Sure. See: Radiation pressure

Despite being massless, photons carry momentum and energy and can exert pressure.
 
RJ Emery said:
Does light (photons) exert a pressure?

Sunlight consists of much more than pure light (photons). It is a stream of particles which have mass that can understandably exert a pressure. Therefore, is the writer mistaken?

As Doc Al said - yes it does.

And sunlight consists of only the electromagnetic radiation (i.e - photons).

The Sun does emit a lot more than just sunlight - i.e. the solar particles in the solar wind, etc. - but those would be considered separately in their own right.

Solar pressure is significant enough that one has to take it into consideration when pushing an old satellite out of the geosynchronous belt to make room a new satellite. It may be small, but it's one of the few perturbations that doesn't eventually cancel itself out, meaning the orbits of old dead satellites can become more elliptical, bringing the old dead satellite back into the geo belt at perigee.

The affect of solar radiation pressure depends on the area to mass ratio of the object. Because of the solar arrays, satellites have a relatively high area to mass ratio. The Moon would have a very small area to mass ratio, meaning they're accounting for very small effects, indeed!
 

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