Astronomers Ready for Close Encounter of a Mars Kind

John Roach
for National Geographic News

August 12, 2003

On August 27, the orbits of Earth and Mars will bring the two planets the closest they have been in nearly 60,000 years. For the weeks surrounding this celestial event, the red planet will be the brightest star in the night sky.

Precisely 34,646,418 miles (55,758,006 kilometers) will separate Earth and Mars during the event. Mars won't approach the Earth as closely again for another 284 years, at which time it will approach even closer, according to astronomers.

Mars rises in the southeastern sky progressively earlier each night in August and September. By late August, Mars will be visible after 9 or 10 p.m. local time. As the night progresses, the planet climbs higher and shifts to the south.

The planet will look like a "very bright red star" said Robert Zubrin, president of the Indian Hills, Colorado-based Mars Society. Most people should be able to see it, even from the most light-polluted cities.

Close Orbits

To explain why Mars and Earth are so cozy at this point in time, Zubrin likened the orbits of the planets around the Sun to the minute and hour hands on a clock.

"Sometimes they are close to each other, and sometimes not," he said. "On a clock, the two hands make a close pass about once an hour. Earth and Mars make a close pass every 26 months. But since Earth's orbit is almost circular and Mars's is somewhat elliptical, some passes are closer than others. This one is the best."

Myles Standish, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena, California, likens the phenomenon to two race cars, Earth and Mars, speeding around two race tracks with Earth orbiting the inside track.

Neither track is perfectly circular. But there is one place where the tracks are closest together. When Mars and Earth happen to reach that place simultaneously, it makes for an unusually close approach.

"It gets more complicated, because the race tracks are changing shape and size, and they are rotating, changing their orientation," said Standish. "So this place where the two tracks are closest together changes."

Standish added that over the past 60,000 years the point of the shortest distance between Mars's and Earth's orbits has been decreasing and will continue to do so for the next several hundred years.

Mars Observations

Astronomers refer to Mars's position on August 27 as "perihelic opposition," which means that the planet is at a point in its orbit when it is both closest to the Sun and to the Earth.

An amateur astronomer with a good telescope should be able to spot features on Mars, including the South Polar Cap, which will be shrinking in the warmth of the late southern hemisphere Martian spring. Zubrin noted that continental-scale color variations will also be discernable.

Bright yellow areas on Mars indicate deserts covered by fine, windblown dust. The planet's dark markings are areas of bare rock or darker dust.

According to The Planetary Society, it is best to wait a few hours while Mars rises above the horizon before viewing it through a telescope. (To view objects on the horizon, sky watchers must peer through more pollution, haze, and other atmospheric turbulence. Less turbulence is encountered when viewing objects higher in the sky.)

Roy Britt, a science writer for the Web site Space.com, said that Mars is currently so bright that with a little concentration an amateur observer should be able to see the planet after the sun rises. "This might present their first opportunity to make a daytime planet sighting. It's something they won't forget," he said in a statement.

Exploring Mars

The close approach of Mars later this month happens to coincide with a wave of interest in the red planet by the space-science community. There are currently five spacecraft from various nations en route to Mars to study the planet's geology and probe for signs of life.

Zubrin, of the Mars Society, said that the coincidence of the close approach of Mars to Earth and the bevy of new spacecraft bound for the planet occurred because the close approach falls near the launch window for spacecraft, which opens for a few months every 26 months.

"This May to June was a good time to launch," he said.

According to Standish, the spacecraft would have all been launched to the red planet even if the close approach was not taking place. "There is a continuing high level of interest in Mars and the technology for exploring it is available," he said.

Scientists are interested in Mars because it is the most Earth-like planet in the solar system. It has mountains and valleys, polar ice caps, and dry river beds. Scientists are particularly keen to discern whether water, a key ingredient for life, exists or existed in the past on Mars.