Astronomers spot asteroid with shortest year known

Animated diagram of orbits of inner planets & fast elongated orbit of asteroid.
The orbit of asteroid 2019 LF6 (white) falls entirely within the orbit of Earth (blue). Image via NASA/JPL-Caltech.

On July 8, 2019, Caltech astronomers announced their discovery of an unusual asteroid with the shortest year known for any asteroid. The rocky body, dubbed 2019 LF6, is about half a mile (1 km) in size and circles the sun roughly every 151 days.

2019 LF6 is one of only 20 known Atira asteroids, which are objects whose orbits fall entirely within Earth’s path around the sun. That is, their orbit has an aphelion (farthest point from the sun) smaller than Earth’s perihelion (nearest point to the sun). In its orbit, 2019 LF6 swings out beyond Venus and, at times, comes closer to the sun than Mercury, which circles the sun every 88 days.

Quanzhi Ye, a postdoctoral scholar at Caltech, discovered 2019 LF6. He said in a statement:

You don’t find kilometer-size 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. 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.

Animated star photo with white dots, one of which is moving.
Asteroid 2019 LF6 is seen here traveling across the sky in images captured on June 10, 2019. The movie has been sped up: the actual time elapsed is 13 minutes. Image via ZTF/Caltech Optical Observatories.

2019 LF6 was discovered via the Zwicky Transient Facility, or ZTF, a state-of-the-art camera at California’s Palomar Observatory that scans the skies every night for transient objects, such as exploding and flashing stars and moving asteroids. Because ZTF scans the sky so rapidly, it is well-suited for finding Atira asteroids, which have short observing windows. Ye said:

We only have about 20 to 30 minutes before sunrise or after sunset to find these asteroids.

The ZTF team has discovered one other Atira asteroid so far, named 2019 AQ3. Before the astronomers spotted 2019 LF6, 2019 AQ3 had the shortest known year of any asteroid, orbiting the sun roughly every 165 days. Tom Prince is a physics professor at Caltech and a senior research scientist at JPL. Prince said:

Both of the large Atira asteroids that were found by ZTF orbit well outside the plane of the solar system. 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.

Bottom line: Asteroid 2019 LF6 orbits the sun roughly every 151 days, the shortest year yet known for an asteroid.

Via Caltech

July 12, 2019

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