2011 ES4

2011 ES₄
Discovery
Discovered by	MLS
Discovery site	Mount Lemmon Obs.
Discovery date	2 March 2011; (first observation only)
Designations
MPC designation	2011 ES4
Alternative designations	P1154IU (NEOCP 2020)
Minor planet category	Apollo; NEO;
Orbital characteristics
	Epoch 31 May 2020 (JD 2459000.5)
	Uncertainty parameter 1
Observation arc	9.54 yr (3,485 days)
Aphelion	1.3548 AU
Perihelion	0.8260 AU
Semi-major axis	1.0904 AU
Eccentricity	0.24248
Orbital period (sidereal)	1.14 yr (415.9 days)
Mean anomaly	337.252°
Inclination	3.3735°
Longitude of ascending node	339.890°
Argument of perihelion	273.568°
Earth MOID	0.000630 AU (94,200 km)
Jupiter MOID	3.681 AU
Physical characteristics
Mean diameter	22–49 m (CNEOS); ~25 m (82 ft);
Absolute magnitude (H)	25.4

2011 ES₄ (also written 2011 ES4) is an Apollo near-Earth asteroid roughly 22–49 meters (72–160 feet) in diameter. It was first observed on 2 March 2011 when the asteroid was about 0.054 AU (8,100,000 km; 5,000,000 mi) from Earth and had a solar elongation of 159 degrees. It passed closest approach to Earth on 13 March 2011.^[3] Before the 2020 approach, the asteroid had a short observation arc of 4 days and had not been observed since March 2011. The asteroid was expected to pass within 1 lunar distance of Earth in early September 2020, but did not. There was no risk of a 2020 impact because the line of variation (LOV) did not pass through where Earth would be, and the closest possible 2020 Earth approach was about 0.00047 AU (70,000 km; 44,000 mi).^[3] One line of variation showed the asteroid passing closest to Earth on 5 September 2020 at 0.06 AU (9,000,000 km; 5,600,000 mi) with a magnitude of 23, which would place it near the limiting magnitude of even the best automated astronomical surveys.^[5]

2011 ES₄ was recovered as P1154IU^[6]^[2] on 5 September 2020 at apparent magnitude 18.^[7] It passed 0.009886 AU (3.847 LD; 1,478,900 km; 919,000 mi) from Earth on 2 September 2020.^[3] With the observation arc being extended to 9 years, it was removed from the Sentry Risk Table on 6 September 2020.

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