Picture of Palomar observatory at night.

Inside the hunt for mysterious ‘twilight’ asteroids

A group of space rocks stays mostly inside the orbit of Earth, making them difficult to pick out in the glare of the sun—and potentially a threat to our planet.

The Zwicky Transient Facility's 605-megapixel field camera, fitted to a 48-inch telescope at Palomar Observatory, California, surveys the entire visible sky each night. Recently it discovered the first known asteroid to live entirely inside the orbit of Venus.
Photograph by Bill Ross, Getty Images

A mysterious group of asteroids grazes the heart of the solar system, hiding in sunlight and occasionally swooping close to a rocky planet. Perhaps the best known of these oddballs is a cosmic rock discovered only two years ago known as ꞌAylóꞌchaxnim, which means “Venus girl” in the language of California’s indigenous Pauma people.

As the only known asteroid that lives entirely within the orbit of Venus, ꞌAylóꞌchaxnim represents a largely unseen population of space rocks–one that could threaten life as we know it.

Astronomers estimate they’ve found the majority of the potentially hazardous asteroids that mainly exist beyond our home world’s orbit. But spotting inner asteroids is tricky because from Earth’s perspective, they live their lives sheathed in sunbeams, tucked behind a curtain of sunlight that telescopes can’t pierce. Yet in recent years, astronomers have begun to pluck these rocks from the glare by searching for their faintly glowing signatures as the sun rests just below the horizon.

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