How close does Mars pass by Earth in miles and how years between the near passing?
Mars and Earth pass each other every 2 years and 2 months, which is called a Mars Opposition. The first source can give you information about the orbit of mars and what angle of rotation will bring the two the closest (for mars the perihelic position brings Earth and Mars about 56 million km away from each other). The next passing will be March 3, 2012. The snopes link addresses a false email that has been circulating about the Mars Oppositions. Maybe you received that email, check it out if your interested.
