Space rocks are supposed to hang out in the Asteroid Belt between Mars and Jupiter where millions of them spin around the sun in orbits dictated by gravitational forces. But a newly-observed asteroid cataloged as 2020 AV2 is a maverick because its orbit lies completely within that of the planet Venus, closer to the sun than Earth.
Another name for asteroid is minor planet. These smaller orbital bodies have diameters (widths) ranging from 480 miles (775 km) to under one mile (1.6 km). In addition to the main asteroid belt between Mars and Jupiter, a cluster of asteroids known as the Trojans follow the same orbit as Jupiter’s.
Then there are the Near-Earth asteroids (NEAs) such as 2003 SD220 that came as close as 1.8 million miles to Earth, its closest approach in more than 400 years. 2003 SD220 will make an even closer approach in 2070.
Atira asteroids are a small group of known asteroids with orbits completely within that of our own planet. Only about 20 of these unusual objects have been logged – out of the nearly one million asteroids identified in Earth’s Solar System.
On June 10, 2019, an astronomer at the California Institute of Technology, captured images of a small Atira asteroid half a mile across named 2019 LF6 that goes once around the sun in 151 days. The CalTech astronomer was visiting as a research assistant from the University of Maryland and said:
“You don’t find kilometer-sized asteroids very often these days. Thirty years ago, people started organizing methodical asteroid searches, finding larger objects first, but now that most of them have been found, the bigger ones are rare birds.”
The Maryland astronomer states on his website:
“Hi there! My name is Quanzhi, you can call me QZ.”
He then explains that “my name should really be written as Ye Quanzhi, where Ye (pronounced as ‘Yeh’) is my surname and Quanzhi (pronounced as Ch’üan Chih) is my first name.”
QZ and his colleagues have just netted the rarest of the rare birds: an asteroid that orbits inside the elliptical path of inner planet Venus, the second planet from the Sun named after the Roman goddess of love and beauty.
The team of astronomers from Zwicky Transient Facility (ZTF) at Caltech first observed the new Atira asteroid 2020 AV2 and brought the space oddity to the world’s attention on January 16, 2020. The Zwicky camera is attached to a telescope at Palomar Observatory in Southern California and scans the entire sky quickly. This makes the equipment ideal for observing asteroids during their brief nocturnal appearances.
QZ called this recent find “a very exciting discovery” and repeated the odds of successfully locating an NRA:
“Astronomers have been systematically searching the skies for small bodies since the 1970s and ’80s, and there’s not much uncharted frontier left in the inner solar system. Asteroids with orbits interior to Venus’s orbit are challenging to observe, and I’m thrilled we finally found this one.”
2020 AV2 is the first Vatira ever spotted. The letter ‘v’ added before ‘Atira’ signifies that the asteroid’s orbit falls entirely inside the orbit of Venus. Up until now, Vatiras were hypothesized based on orbital mathematics. Now, we know they exist.
Vatiras (and the planet Venus) have orbits so close to our sun that they are can only be seen from Earth at dusk or dawn, making viewing hours quite limited. This makes finding them even harder.
Tom Prince, a co-investigator of ZTF as well as the Ira S. Bowen Professor of Physics at Caltech and a senior research scientist at the NASA Jet Propulsion Laboratory, speculated on how the first identified Vatira came to be where it is:
“An encounter with a planet probably flung the asteroid into Venus’ orbit. 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.”
George Helou, executive director of the IPAC astronomy center at Caltech and a ZTF co-investigator agreed that “Getting past the orbit of Venus must have been challenging.”
Helou thinks that 2020 AV2 is destined to remain as an earthly NRA unless one of two things happens:
“The only the 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.”
Ye and Wing-Huen Ip of the National Central University in Taiwan have found three 2020 Atira asteroids before the end of January under the Twilight program both developed. They were tipped off on January 4 by Bryce Bolin, a postdoctoral scholar at Caltech, who first announced that the unusual space rock might turn out to be the first validated Vatira.
The elongated orbit of 2020 AV2 is tilted about 15 degrees relative to the plane of our solar system. When closest to the sun, the Near-Earth asteroid passes very close to the orbit of Mercury, the innermost planet in our solar system.
Sky geeks can find out more about the singular 2020 AV2 by watching this video.
ZTF astronomers are now encouraged by their success to seek and capture images of more Vatira asteroids. Ye enthused:
“Now we finally found the tip of the iceberg. Who wouldn’t wonder what’s underneath it?”