2022 WJ1

2022 WJ₁
	Orbit before impact
Discovery
Discovered by	David Rankin; (Mt. Lemmon Srvy)
Discovery site	Mt. Lemmon Obs.
Discovery date	19 November 2022
Designations
MPC designation	2022 WJ1
Alternative designations	C8FF042
Minor planet category	NEO · Apollo
Orbital characteristics
	Epoch 9 August 2022 (JD 2459800.5)
	Uncertainty parameter 6
Observation arc	3.04 hours
Aphelion	2.817 AU
Perihelion	0.928 AU
Semi-major axis	1.872 AU
Eccentricity	0.5043
Orbital period (sidereal)	2.56 yr (935.9 days)
Mean anomaly	310.198°
Mean motion	0° 23m 4.778s / day
Inclination	2.582°
Longitude of ascending node	56.748°
Time of perihelion	May 2020 (last perihelion); 16 December 2022 (would have been)
Argument of perihelion	35.034°
Earth MOID	0.000256 AU (38,300 km; 0.100 LD)
Jupiter MOID	2.418 AU
Physical characteristics
Mean diameter	<1 m
Apparent magnitude	≈31 @ 0.2 AU; ≈15 (before entering Earth's shadow)
Absolute magnitude (H)	33.554±0.363

2022 WJ₁, formerly designated C8FF042, was a small, harmless ≈1-metre near-Earth asteroid or meteoroid that impacted Earth's atmosphere on 19 November 2022 at 08:27 UT in Southern Ontario, Canada, above the Golden Horseshoe region, southwest of Toronto.^[4]^[8]^[9] Meteorites were detected by weather radar during dark flight.

Discovery

The asteroid was discovered three hours before impact by David Rankin at Mount Lemmon Observatory, during routine observations for the Mount Lemmon Survey.^[2] The first image was taken at 04:53 UT when the asteroid was 0.000859 AU (128.5 thousand km; 79.8 thousand mi; 0.334 LD) from Earth.^[10] Using the first four images of the asteroid, Scout estimated a 25% chance of an Earth impact.^[11] The next four images raised the chance to 50%. Within about an hour, further observations raised the chance of impact to 100%. The final observation was from Mauna Kea, 32 minutes before impact, just before it entered Earth's shadow.^[12] The asteroid brightened to about apparent magnitude 15 (about the brightness of Pluto) before disappearing into Earth's shadow.^[1]

It is the sixth successfully-predicted asteroid impact.^[8]^[c] With an absolute magnitude of 33.6, it is the smallest asteroid discovered while it was in space.^[13]

Impact

A meteorite fall was presumed to have occurred along the south shores of Lake Ontario, from east of Grimsby to Niagara-on-the-Lake with most meteorites landing in the water.^[14] Larger fragments would have fallen farther to the east.^[14] During dark flight, weather radar signatures appeared from an altitude of ~15 km down to 850 metres.^[14] Meteorites should have a fresh black fusion crust.^[15] Most findable fragments would likely be around 5 grams and the size of a nickel. The main mass might be the size of a soccer ball and be located between Port Weller and Virgil.^[15]

There was also an observed ordinary chondrite meteorite fall in Grimsby at 01:03 UT 26 September 2009 with 13 recovered meteorites totaling 215 grams (the main mass was 69 grams).^[16] The 2009 fall has a strewn field of 8 km x 4 km.^[16]

The Minor Planet Center noted that Earth's atmosphere was impacted above Brantford 70 km from Grimsby.^[2] The resulting sonic boom was mostly heard in Hamilton while the fireball was visible to observers in the Greater Toronto Area and as far as the U.S. states of Maryland, Ohio, Pennsylvania, and New York.^[17]

Simulated final trajectory estimate from JPL Horizons with 1 minute markers CST (UT-6hr) and lines down to surface.	View from sunlit side of Earth. Without Earth's gravity, 2022 WJ₁'s trajectory would have missed Earth. Red markers show inside Earth's shadow.

Orbit

The Apollo asteroid was inbound approaching a mid-December perihelion (closest approach to the Sun) when it impacted Earth.^[5] Even at opposition on 15 October 2022 when 2022 WJ₁ was 0.2 AU (30 million km; 78 LD) from Earth, it had an unobservable apparent magnitude of 31 which is about 600 times too faint to be detected by even the most sensitive automated allsky surveys.^[7]^[d]

2022 WJ₁ orbited from inside Earth's orbit with perihelion at 0.92 AU to the middle of the asteroid belt at 2.8 AU.^[5]

Notes

^ Earth MOID as defined for 9 August 2022 roughly 100 days before Earth approach.
^ An absolute magnitude of 33.6 and assumed albedo of 0.14 gives a diameter of 0.7 meters.
^ The other five predicted impactors are: 2008 TC3, 2014 AA, 2018 LA, 2019 MO, and 2022 EB5.
^ Math: $({\sqrt[{5}]{100}})^{31-24}\approx 630$