Approaching Mars

Earth and Mars will have a breathtaking close encounter in October 2005.

By the time you finish reading this sentence, you'll be 25 miles closer to the planet Mars.

Earth is racing toward Mars at a speed of 23,500 mph, which means the red planet is getting bigger and brighter by the minute. In October, when the two planets are closest together, Mars will outshine everything in the night sky except Venus and the Moon. (You're another 50 miles closer: keep reading!)

It's only June now, but Mars is already eye-catching. You can see it early in the morning, rising before the sun in the eastern sky, shining almost twice as bright as a 1st-magnitude star. A sky map, below, shows where you could have found Mars on Tuesday morning, May 31st, when it appeared beautifully close to the Moon.

Why are we rushing toward Mars? It's simple orbital mechanics. Think of Earth and Mars as two runners on a circular race track, with lanes corresponding to planetary orbits. Earth, running fast on the inside lane, circles the course in 12 months. Mars, plodding along an outside lane, takes twice as long to go around. Every two years, approximately, Earth catches Mars from behind and laps it.

The Moon and Mars on May 31st 2005

That's where we are now, approaching Mars from behind. Relative speed: 23,500 mph.

We won't actually lap Mars until autumn, October 31st at 0319 Universal Time, to be exact. Only 43 million miles (69 million km) will separate us from Mars, then, compared to an average distance of about 140 million miles (225 million kilometers). It's a great time to send spacecraft there.

The orbits of Earth and Mars.

Mindful of that, NASA plans to launch the Mars Reconnaissance Orbiter (MRO) on August 10th, 2005. Because it takes 6+ months to reach Mars, the best time to start the trip is a month or so before closest approach - thus, August. MRO will arrive in March 2006, enter orbit, and begin a 2-year mission to map the red planet in greater detail than ever before.