First Asteroid Found Inside Orbit of Venus

A rare asteroid orbiting snugly within the inner confines of our solar system has been discovered by Caltech's Zwicky Transient Facility, or ZTF, a survey camera based at Palomar Observatory. The newfound body, named 2020 AV2, is the first asteroid found to orbit entirely within the orbit of Venus.

"Getting past the orbit of Venus must have been challenging," says George Helou, executive director of the IPAC astronomy center at Caltech and a ZTF co-investigator, who explains that the asteroid must have migrated in toward Venus from farther out in the solar system. "The only way it will ever get out of its orbit is if it gets flung out via a gravitational encounter with Mercury or Venus, but more likely it will end up crashing on one of those two planets."

2020 AV2 belongs to a small class of asteroids known as Atiras, which are bodies with orbits that fall within the orbit of Earth. More specifically, it is the first "Vatira" asteroid, with the "V" standing for Venus. Vatira asteroids, which were only hypothesized until now, have orbits that fall entirely inside the orbit of Venus.

The ZTF camera is particularly adept at finding asteroids because it scans the entire sky rapidly and thus can catch the asteroids during their short-lived appearances in the night sky. Because Vatiras orbit so close to our sun, they are only visible at dusk or dawn.

2020 AV2 is the third Atira discovered by ZTF as part of its Twilight program developed by Wing-Huen Ip of the National Central University in Taiwan, and Quanzhi Ye, formerly of Caltech and now at the University of Maryland. The asteroid, which was initially designated ZTF09k5, was first flagged as a candidate on January 4, 2020, by Bryce Bolin, a postdoctoral scholar at Caltech. Soon thereafter, an alert was posted by the Minor Planet Center, the official organization for cataloging small solar system bodies such as asteroids, and this piqued the interest of the astronomical community. Several telescopes around the globe followed up on the target, helping to pin down the body's unusual orbit and narrow down estimates of its size.

The asteroid spans about 1 to 3 kilometers and has an elongated orbit tilted about 15 degrees relative to the plane of our solar system. During its 151-day orbit around the sun, it always travels interior to Venus, but at its closest approach to the sun, it comes very close to the orbit of Mercury.

"An encounter with a planet probably flung the asteroid into Venus's orbit," explains Tom Prince, the Ira S. Bowen Professor of Physics at Caltech and a senior research scientist at JPL, which Caltech manages for NASA, as well as a co-investigator of ZTF. "It's the opposite of what happens when a space mission swings by a planet for a gravity boost. Instead of gaining energy from a planet, it loses it."

Members of the ZTF team says they look forward to hunting for more Vatira asteroids in the future. "We have no idea how many more there are like this or if it's unique," says Helou.

ZTF is funded by the National Science Foundation and an international collaboration of partners. Additional support comes from Caltech and the Heising-Simons Foundation. ZTF data are processed and archived by IPAC. NASA supports ZTF's search for near-Earth objects through the Near-Earth Object Observations program.