Mars is called the red planet.The reddish color is due to the rust on its surface this rust is iron oxide. Iron oxide (rust) is formed due to the reaction between iron and water.But there is no water in mars!.So scientists proposed that there was water billions of years ago that combined with martian rocks rich in iron to form iron oxide.
The Earth has its own magnetic field , it acts like there is huge bar magnet buried inside,but this bar magnet is not on the earth rotational axis it is shifted by some angle.The south of the bar magnet is on the magnetic north and the south polarity is on the magnetic north(image).As opposite polarities attract the magnetic needle (north) is attracted to the south polarity in the magnetic north.That’s why the needle always points north.If you want to know “why earth has magnetic field?”go to letter E.