If a typical marshmallow weighs 20 grams, then from E = mc^2 you get an energy of 20 x (3x10^10) x (3 x 10^10) = 2 x 10^22 ergs. I believe this is about equal to the yield of 5 - 10 hydrogen fusion bombs. The answer is, no, such an impact would not have any measurable effect on the Earth's orbit.