A near-Earth asteroid designated 2017 HG4 flew past Earth at a distance of 0.61 LD (~234 240 km / 145 550 miles) on April 22, 2017, four days before it was discovered. This makes it the 20th known asteroid to fly past Earth within 1 lunar distance since January 9, 2017 (according to data available September 20, 2017).
2017 HG4 belongs to the Aten group of asteroids, defined by having a semi-major axis of less than one astronomical unit, roughly an average distance from the Earth to the Sun. They also have an aphelion (furthest distance from the Sun) greater than 0.983 AU.
The estimated size of this object is between 7.8 and 17 m (25 - 55 feet) and it flew past us at a speed (relative to the Earth) of 4.02 km/s at 06:25 UTC. It was first observed at Pan-STARRS 1, Haleakala on April 26, 2017.
The next close approach of this object will take place at 10:17 UTC on April 16, 2021 (+/- 15:52 hours).
As of April 24, 2017, there are 16 162 known near-Earth objects, 16 056 are asteroids. Of those, 1 176 belong to the Aten group of asteroids. Since the start of the year, we discovered 52 Atens.
2017 HG4 is the 20th known near-Earth asteroid to flyby Earth within 1 lunar distance (~384 000 km / 238 606 miles) since the start of the year, according to data available at CNEOS on September 20, 2017. Another near-Earth asteroid, designated 2017 HV2, flew past Earth at a distance of 0.33 LD (~126 720 km / 78 740 miles) a day after HG4, on April 23, 2017.
Featured image: The green line indicates the object's apparent motion relative to the Earth, and the bright green marks are the object's location at approximately one hour intervals. The Moon's orbit is gray. The blue arrow points in the direction of Earth's motion and the yellow arrow points toward the Sun. Credit: Minor Planet Center.