Earth and Mars, like all the other planets in the solar system, orbit the sun in elliptical orbits. Because our planet is closer to the sun than Mars, it races along its orbit more quickly. Earth makes two trips around the sun in about the same amount of time it takes Mars to make one trip. Earth has been racing toward Mars for months, gaining on the Red Planet by more than 200,000 miles each day. We will finally catch up to Mars and pass relatively close to it on April 8. Astronomers call this close approach "opposition."
During opposition the sun, Earth and Mars are lined up in a straight line with Earth in the middle. Mars will be at its biggest and brightest in two years when it arrives at opposition in April.
NASA has been sending space probes off to Mars to take advantage of its close alignment with Earth during opposition. The Mars Odyssey orbiting spacecraft was launched in 2001 and studied the composition of the Martian surface. In 2003, when Earth and Mars were only 34.6 million miles apart, the closest they have been in 60,000 years, NASA sent the twin Mars Exploration Rovers Spirit and Opportunity to the Red Planet. Opportunity celebrated its 10th year of exploration on the Martian surface last month. In 2005, NASA sent the Mars Reconnaissance Orbiter to Mars. In 2007, the Phoenix Polar Lander was sent to the icy northern pole of Mars to analyze samples of soil and ice.
The Mars Science Laboratory, Curiosity, was launched in 2011 to take advantage of our last close encounter with Mars. The rover is investigating Mars' past or present ability to sustain microbial life. Last year, NASA sent the MAVEN orbiter to Mars in hopes of discovering how Mars went from wet and warm to a bitter cold and dry world.