Aspace probe lands on the surface of a spherical asteroid 250 miles in a diamterer andmeasures the strenght of its gravitational fiels strength to be 4.95 x 10^-11. what is the mass of the asteroid?

I'm thinking it's 2 you are asked to explain the earth's magnetic field. which is the best reply? 1. the earth's magnetic south is similar to the north pole of a magnet. 2. the earth's core has a strong magnetic charge similar to the south pole of a magnet. 3. the earth's geomagnetic south is similar to the south pole of a magnet. 4. the earth's magnetic charge is not centered at either pole; it varies based on location.