10e-3 m/s^2 is hard to believe, as the lander would have to be ~250m away from t...

10e-3 m/s^2 is hard to believe, as the lander would have to be ~250m away from the center of mass [1]. More likely it is 2500m away from the center of mass, giving 6.67e-11 * 1.0e13 / 2500 ^ 2 = 0.0001 m/s^2, so about 1 gram.

[1] I can't find a reliable estimate of the surface gravity online, but the mass estimate at http://blogs.esa.int/rosetta/2014/08/21/determining-the-mass... seems accurate.