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Astronomers Spot First Asteroid Nearer to the Sun Than Venus

Such “intervenusian” rocks are both rare and difficult to detect

An image of asteroid 2020 AV2, taken on January 8, 2020 by the Elena robotic unit part of the Virtual Telescope Project (Gianluca Masi, Virtual Telescope Project)
smithsonianmag.com

By and large, asteroids have a tough time getting much closer to the sun than the approximate orbit of Earth. That’s what makes 2020 AV2 so special. This intrepid asteroid, first detected on January 4 by researchers at the Palomar Observatory in California, is now officially the first of its kind known to revolve around the sun within the orbit of Venus.

In other words, the space nugget is “intervenusian,” Gianluca Masi, director of the Virtual Telescope Project, who observed the asteroid on January 8, tells Laura Geggel at Live Science.

2020 AV2’s tight-knight tango with the sun also earns the asteroid a few more noteworthy titles. Apart from Mercury, no other natural object in our solar system is known to have a smaller aphelion—the point at which an orbiting body is farthest from the sun. Capable of completing a lap around its star in just 151 days, the space rock also has the shortest known orbital period of any asteroid documented thus far, Masi writes in a statement.

Nearly 1 million asteroids hail from the mid-to-outer reaches of our solar system, each a pint-sized relic left over from around the time the planets first formed. Most orbit the sun in the aptly named asteroid belt, which lies roughly between Mars and Jupiter, and are kept in check by the latter’s gravitational pull.

Occasionally, however, unusual cosmic events, such as encounters with a planet’s gravity, can jettison asteroids away from this belt and toward the sun. If the rock survives the trip, and manages to secure a stable orbit, it may find itself taking shorter trips around our star than Earth does—a trait that earns it the rare title of Atira asteroid. The Atira club is an exclusive one, with only 21 known members; 2020 AV2 essentially started a party for one, which is now known as a Vatira asteroid, with an added “V” for “Venus."

Compounding these sun-hugging asteroids’ relative rarity is the fact that they’re also very difficult to spot. Because Atiras spend so much of their time close to the sun, astronomers can only detect them during fleeting periods of twilight. But the Palomar Observatory’s survey camera, Zwicky Transient Facility, managed to spy 2020 AV2—its third Atira so far—while scouring the sky earlier this year.

Researchers don’t yet know how or when 2020 AV2 wound up in its intimate orbit, or if more asteroids like it exist, Caltech astronomer George Helou says in a statement. But “getting past the orbit of Venus must have been challenging,” he adds. Eventually, 2020 AV2 will probably crash land onto the surface of Venus or Mars, tragically capping its sun-adjacent sojourn. Though Helou notes that a gravitational encounter with one of the two planets could also fling the asteroid away from the sun—a journey that would, perhaps fittingly, send it back in the direction of home.

About Katherine J. Wu
Katherine J. Wu

Katherine J. Wu is a Boston-based science journalist and Story Collider senior producer. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University. Previously, she served as a Digital Editor at NOVA Next and was Smithsonian magazine's 2018 AAAS Mass Media Fellow.

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