A newfound asteroid has the shortest orbit known for an asteroid. Astronomers call it 2019 LF6. A year there lasts only 151 days.
A team of astronomers led by Quanzhi Ye from Caltech University has recently found an asteroid that swings out beyond Venus and, at times, comes closer in than Mercury.
Asteroids whose orbits fall entirely within Earth’s are known as Atira asteroids. We have detected only 20 such asteroids until now and 2019 LF6 is one of them.
The team found this asteroid using the Zwicky Transient Facility (ZTF) at the Palomar Observatory in California.
The asteroid is about a kilometer in size.
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“You don’t find kilometer-size asteroids very often these days,” says Quanzhi Ye, a postdoctoral scholar at Caltech who discovered 2019 LF6 and works with Tom Prince, the Ira S. Bowen Professor of Physics at Caltech and a senior research scientist at JPL, and George Helou, the executive director of IPAC, an astronomy center at Caltech.
“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,” he says. “LF6 is very unusual both in orbit and in size—its unique orbit explains why such a large asteroid eluded several decades of careful searches.”
Atira asteroids are very hard to find because they are very close to the Sun. So, the only times we can observe them from Earth are very soon after sunset or just before sunrise.
“We only have about 20 to 30 minutes before sunrise or after sunset to find these asteroids,” says Ye.
However, it’s likely ZTF will find more.
Zwicky Transient Facility (ZTF)
The ZTF is a 123-centimeter telescope with a state-of-the-art 600-megapixel camera on it. The telescope and camera have a wide field of view, so each image covers a staggering 47 square degrees. That’s over 200 times the area of the full Moon on the sky. It can image the entire northern hemisphere sky in just three nights, seeing objects a little fainter than 20th magnitude.
To find the Atira asteroids, the ZTF team has been carrying out a dedicated observing campaign. They named this campaign “Twilight” after the time of day best suited for discovering the objects.
“Both of the large Atira asteroids that were found by ZTF orbit well outside the plane of the solar system,” says Prince. “This suggests that sometime in the past they were flung out of the plane of the solar system because they came too close to Venus or Mercury,” says Prince.
ZTF has already found around 100 near-Earth asteroids and about 2,000 asteroids orbiting in the Main Belt between Mars and Jupiter.