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

by Dr Tony Phillips

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.

The spacecraft's high-resolution cameras will be able to discern objects, such as rocks and rovers and crashed Mars landers, less than 1 meter across. A radar sounder will probe for underground water while spectrometers map the distribution of surface minerals. Other instruments will monitor the atmosphere, teaching researchers back on Earth how to forecast martian weather. These are key elements in NASA's plan to eventually send humans to Mars.

The Mars rovers Spirit and Opportunity are already there. They arrived in January 2004 on the heels of another Earth-Mars close encounter in 2003. (Remember, this happens every two years.) The two robots were supposed to stop working months after they landed, worn down by wind, stuck in sand, or exhausted by too little solar power. Credit NASA engineering: Spirit and Opportunity are still rolling and, if they hold true to form, they'll be "alive" to see Mars Reconnaissance Orbiter when it gets there, a tiny point of light in the martian night sky, mapping the red planet for explorers of the future.

Back on Earth people are going to enjoy watching Mars swell and brighten in the months ahead. By mid-summer, amateur astronomers with backyard telescopes will be able to spot polar ice caps and dust storms and strange dark markings. By autumn, even the least attentive of your neighbors will be remarking on "that bright red thing in the sky."

Mark October 31st as the best day of all: Mars will rise at sunset, hang overhead at midnight, and "blaze forth against the dark background of space with a splendour that outshines Sirius and rivals the giant Jupiter himself." That's how astronomer Percival Lowell described a similar close encounter in the 19th century.

Can't wait? Don't. You can see Mars any clear morning this summer. You missed Tuesday morning, May 31st as Mars and the fat crescent Moon had a pleasing close encounter in the dawn sky. Rising in the east around 4:30 AM. A sight guaranteed to wake you up! But don't worry! There will be other opportunities. How about trying tonight for instance?

More good news by the way... you're now 1000 miles closer to the planet Mars.