Scientists Discover the Closest Known Asteroid to the Sun

Scientists have discovered a rare asteroid that orbits closer to the Sun than any known object of its kind.

2019 AQ3 measures about one mile (1.4 kilometers) in diameter and makes a circuit around the Sun in just 165 days—the shortest year of any catalogued asteroid. The asteroid was detected by the Zwicky Transient Facility (ZTF) near San Diego on January 4, 2019.

"We have found an extraordinary object whose orbit barely strays beyond Venus's orbit—that's a big deal," Quanzhi Ye, a postdoctoral scholar at Caltech who spotted the object, said in a statement.

2019 AQ3 belongs to an ultra-rare class called the Atira asteroids (also known as Apohele asteroids) that orbit closer to the Sun than Earth. Of the roughly 800,000 asteroids catalogued by scientists, the vast majority are located farther from the Sun than Earth. Millions of these space rocks are distributed in the asteroid belt between the orbits of Mars and Jupiter.

The first Atira asteroid was discovered in 2003, and a total of 19 of these rocks have been spotted since, including 2019 AQ3.

That small number doesn’t necessarily mean Atiras are uncommon, just that they are hard to detect against the Sun’s blinding glare. “There might be many more undiscovered asteroids out there like it," Ye said.

The find could help scientists pinpoint objects that are potentially hazardous to Earth in the inner solar system. Currently, we are defenseless against any hazardous asteroids on collision courses with Earth, but at least we’re working on technologies that can hopefully deflect dangerous objects. But if we can’t even see the asteroids through the Sun’s intense brightness, we could be caught by surprise.

Fortunately, 2019 AQ3 poses no threat to Earth. Its orbit is strangely tilted relative to the plane of the solar system, guiding it inside Mercury’s orbit at its closest point and just beyond Venus’s orbit at its farthest.

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