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Asteroid Tags Along With Earth Path Brings Object Under Influence Of Planet’s Gravity

Thu., June 12, 1997

Earth has a newly recognized celestial companion, a sort of vagabond little brother to the moon, a Canadian astronomer reports.

The object is a small asteroid, about 2-1/2 miles wide, with an unusual wandering solar orbit. The orbital path brings the object, known formally as asteroid 3753, so under the influence of Earth’s gravity that it qualifies as a natural companion like the moon, says Paul Wiegert, a postdoctoral fellow at Canada’s York University.

The astronomer reports on the six-month computer analysis uncovering the previously unknown link between the object and Earth in today’s edition of Nature, the British science journal. Another astronomer discovered the asteroid in 1986 at an Australian observatory.

“So far as we know, it’s unique,” Wiegert said of the asteroid in a telephone interview. “There may be others, but this is the first one we know of.”

The object travels in what astronomers call a horseshoe pattern that spirals forward along the solar orbital path of Earth. At its farthest point from the sun, the asteroid comes close to Mars. Its closest solar pass approaches Mercury.

The origin and composition of the asteroid are a mystery.

The object belongs to a class of small “near-Earth” asteroids. Like 3753, many of these objects cross Earth’s orbital path, posing a threat of collision. But Earth’s gravitational forces so strongly push and pull on 3753 at various junctures that the potential for an impact with it are very small, Wiegert said.

The closest 3753 comes to Earth is 9 million to 10 million miles, once every 385 years. The last such passing was about a century ago, according to the analysis by Wiegert and his colleagues.

“It’s hard to tell exactly what we will learn about this,” Wiegert said of the implications of the findings for the larger architecture of the solar system. “It’s a very intriguing piece of the puzzle. It’s so unexpected that the implications of it are still being analyzed.

“But it’s a very important clue to how the solar system formed and how it evolved,” he said.

Potentially fragments of planets, asteroids have long intrigued astronomers.

Recently, they have become destinations of camera-equipped planetary probes. In the future, they could become bases for explorers venturing out into the solar system as well as a source of mineral deposits mined for use on Earth.

Earth’s newly discovered companion is too faint to become the focus of romantic lore like the moon.

“Certainly, astronomers with ground-based telescopes will want to take a look at it and maybe with small spacecraft,” Wiegert said.


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