Hop Aboard 2019 LF6, The Asteroid With The Shortest Year Known

Watch 2019 LF6 orbit the sun in this animation. The asteroid orbits completely within Earth’s orbit, circling the sun every 151 days, a record. The asteroid follows the white loop. Mercury’s orbit is pink, Venus purple and the Earth blue. NASA / JPL-Caltech

A newly discovered, kilometer-sized asteroid orbits the sun entirely inside Earth’s orbit. Named 2019 LF6 it takes just five months (151 days) to complete its orbit, the shortest known of any asteroid. 2019 LF6 belongs to the Atira asteroid family, a select group of 20 asteroids (to date) that all orbit interior to Earth’s orbit.

Always hidden in the glow of twilight due to its proximity to the sun, finding the asteroid was no easy task. Its discoverer, Quanzhi Ye, who works out of Caltech, used the Zwicky Transient Facility, or ZTF, a state-of-the-art camera at the Palomar Observatory that scans the skies every night for things that flicker or move. Astronomers call them transient objects; they include supernovae, flickering stars and asteroids on the move. ZTF scans the sky quickly, making it ideal for finding Atira asteroids, which because they appear so close to the sun, are only visible briefly during twilight.

Asteroid 2019 LF6 travels across the sky in images captured by ZTF on June 10. The movie has been sped-up — the actual time elapsed is 13 minutes. ZTF/Caltech Optical Observatories

“We only have about 20 to 30 minutes before sunrise or after sunset to find these asteroids,” said Ye in a press release. It’s incredible it was found at all given how faint it was at discovery — 19th magnitude — well beyond visibility in amateur-sized telescopes.

As 2019 LF6 plies its orbit, it can swing within 29.7 million miles (47.8 million km) of the sun, which is closer than Mercury’s average solar distance. At those times, a person standing on the asteroid’s rocky surface would see the sun appear nearly 3 times larger (1.5°) and more than 6 times brighter than the view from Earth.

At the far end of its orbit, the asteroid reaches a little beyond Venus at a distance of 73.8 million miles. From that vantage point, the sun would shrink to 0.7° or 20 percent larger than the Earth view. How nuts it would be to watch the sun’s apparent size and brightness vary like every 5 months.

In addition to the two Atira objects, ZTF has so far found around 100 near-Earth asteroids and about 2,000 asteroids orbiting in the main belt between Mars and Jupiter. There are undoubtedly many more Atira asteroids hidden in the solar glare, the reason NASA is considering a spacecraft called NEOCam (Near-Earth Object Camera) that would search for asteroids from orbit above the glow of the atmosphere.

NEOCam would spot them by detecting the heat they radiate. Being close to the sun Atira asteroids are warmer than other asteroids and give off gobs of infrared light. In case you’re wondering whether there’s any chance asteroids in the family could impact the Earth in the future, it’s possible. Although they orbit closer to the sun that our planet and never cross its path, the gravity of Mercury and Venus could potentially “perturb” an object’s orbit and change it into an Earth-crossing one.

Life has so many ifs, doesn’t it? And a few whens, too.

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