How big would a asteroid need to be to heat Mars back up?

No.11837598 ViewReplyOriginalReport
Wish list would be:
1. Heat surface temp to earth like levels
2. Melt and spin the core to produce earth like magnetic field, and produce volcanoes to release water/gas.
3. Bonus would be knock it into a closer orbit to the sun
4. Not blow the planet to dust
Could it be possible for us to alter the orbit of an asteroid to make the collision happen?