About 140 million miles away from Earth, the most relatable planet in the solar system orbits the sun. Mars, popularly known as the Red Planet, is the fourth planet from the sun, after Mercury, Venus, and Earth. We know more about Mars than any other planet but our own. That knowledge has been gained over centuries and has grown exponentially in recent years with the successful landings on Mars of the Curiosity and Perseverance rovers in 2012 and 2021 respectively. Today we celebrate those and other accomplishments on Red Planet Day, which coincides with the launch of Mariner 4, the first probe sent to Mars, on this day in 1964.