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The amount of light that an object reflects is called its albedo; a scale of 0-1, 0 being a black body ad 1 reflecting all light. This question is probably going to be closed [It is "subjective" ?? No idea how] so I may as well be brief.

In the 1990's some scientists were suggesting that if you changed the albedo of an asteroid then it could be hotter on one side. That would change the curve of orbit. I have heard nothing since about this idea. I imagine that various ways would exist such as spraying the asteroid with paint or putting a solar panel on it. Is this possible? [I would ask if anyone is trying to do it but the rules of stack overflow say I can only ask one question.]

Snack_Food_Termite
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  • If you appended the line "so would changing its albedo take it off a collision course", and maybe say with what, it would clarify your question a great deal. – TimWescott Nov 21 '19 at 20:33
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    What is your question? Are you asking if it is possible to change the albedo? Or are you asking if it is possible to change the orbit because of heating? – JohnHoltz Nov 22 '19 at 02:09

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Yes, in theory, it is possible to use albedo modification as a way to influence the orbital parameters of a body through solar pressure. This is the same principle used in solar sails, a propulsion method that relies on radiation pressure from the Sun to propel space probes and even adjust their attitude. The theoretical basis has been known since the late 19th century, the principle was experimentally demonstrated in 1899 by Lebedev and successfully deployed on a spacecraft in 2010 by the IKAROS mission.

It can be applied to asteroids by simply making them more reflective, which will increase the effects of solar pressure. Over enough time, the minute but constant acceleration will add up to significant changes in their trajectory. If the aim is to avoid a planetary impact, it might not even be necessary to coat a specific side of the asteroid.

Here is a Master's Thesis on the related subject of designing a payload that can acomplish said albedo modification. From the abstract:

The development of the Surface Albedo Treatment System (SATS) onboard a spacecraft mission to the near earth asteroid (NEA) Apophis in 2012 is an innovative concept of deflecting NEAs from possible impact with the Earth through altering the Yarkovsky effect, a non-secular force in the solar system due to uneven surface thermal emission most profoundly affecting small rotating bodies subjected to sunlight. Though this force is small, its magnitude can be dramatic if extended over a period of time and if it uses the close approach of an asteroid near Earth to magnify the perturbation.

The payload dispenses colored powder called albedo changing particles (ACPs) onto the surface changing its albedo and indirectly the surface temperature which changes the Yarkovsky effect. This study gives an in-depth description of both computational and experimental parts of the design of this system with primary focus on initial ground test setup. The initial experiments proposed to design the SATS is outlined in detail and justified by the mission criterion of interest as well as modeling the actual dispersal on the surface.

AEhere supports Monica
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  • That is awesome! Wish that I could give you bonus points! I am not an engineer. I have wondered about this since I heard it somewhere 20 years ago. – Snack_Food_Termite Nov 22 '19 at 08:56
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    I'm glad you found it useful! You can read about solar sails as a propulsion method if you want to know more. I have not looked too deep into this topic so you can feasibly find better technical papers out there, but the basic idea is sound. – AEhere supports Monica Nov 22 '19 at 09:06