(285263) 1998 QE2

(285263) 1998 QE₂

First radar images of 1998 QE2 taken at Goldstone on 30 May 2013
Discovery[1][2][3]
Discovered by	LINEAR
Discovery site	Lincoln Lab's ETS
Discovery date	19 August 1998
Designations
MPC designation	(285263) 1998 QE2
Alternative designations	1998 QE2
Minor planet category	Amor NEO PHA[1][2]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	19.24 yr (7,029 days)
Aphelion	3.8092 AU
Perihelion	1.0377 AU
Semi-major axis	2.4234 AU
Eccentricity	0.5718
Orbital period (sidereal)	3.77 yr (1,378 days)
Mean anomaly	49.758°
Mean motion	0° 15m 40.32s / day
Inclination	12.859°
Longitude of ascending node	250.14°
Argument of perihelion	345.65°
Known satellites	1[4][a]
Earth MOID	0.0345 AU (13.4 LD)
TJupiter	3.239
Physical characteristics
Mean diameter	1.08 km (calculated)[5] 2.7 km[a] 2.75 km[6] 3.2±0.3 km[4][7]
Synodic rotation period	2.726±0.001 h[8] 4 h (upper limit)[a] 4.749±0.001 h[b] 4.751±0.002 h[9] 5.39±0.02 h[10]
Geometric albedo	0.06[6] 0.20 (assumed)[5]
Spectral type	S (assumed)[5]
Absolute magnitude (H)	16.4[6] 16.98±0.02[10] 17.2[5] 17.3[1]

(285263) 1998 QE₂, provisional designation 1998 QE₂, is a dark asteroid and synchronous binary system, classified as near-Earth object and potentially hazardous asteroid of the Amor group, approximately 3 kilometers in diameter.^[7] It was discovered on 19 August 1998, by astronomers of the LINEAR program at Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States.^[2] Its sub-kilometer minor-planet moon was discovered by radar on 30 May 2013.^[4][a]

As an Amor asteroid the orbit of 1998 QE₂ is entirely beyond Earth's orbit. The asteroid orbits the Sun at a distance of 1.0–3.8 AU once every 3 years and 9 months (1,378 days; semi-major axis of 2.42 AU). Its orbit has an eccentricity of 0.57 and an inclination of 13° with respect to the ecliptic. The Earth minimum orbit intersection distance with the orbit of the asteroid is 0.035 AU (5,200,000 km; 3,300,000 mi), which translates into 13.4 lunar distances. As with many members of the Amor group, this asteroid has an aphelion beyond the orbit of Mars (at 1.66 AU) which also makes it a Mars-crosser.^[1]

The sooty surface of 1998 QE₂ suggested that it might have previously been a comet that experienced a close encounter with the Sun.^[11] However, the Tisserand parameter with respect to Jupiter (T_J=3.2) does not make it obvious whether 1998 QE₂ was ever a comet, since cometary T_J values are typically below 3.^[6]

On 31 May 2013, 1998 QE₂ approached within 0.039 AU (5,800,000 km; 3,600,000 mi) (15 lunar distances) of Earth at 20:59 UT (4:59 pm EDT).^[12] This was the closest approach the asteroid will make to Earth for at least the next two centuries.^[13] It is a very strong radar target for Goldstone from May 30 to June 9 and will be one for Arecibo from June 6 to June 12.^[6] At its closest approach the asteroid had an apparent magnitude of 11 and therefore required a small telescope to be seen.^[6]

Integrating the orbital solution shows the asteroid passed 0.08 AU (12,000,000 km; 7,400,000 mi) from Earth on 8 June 1975^[12] with an apparent magnitude of about 13.9.^[14] The next notable close approach will be 27 May 2221, when the asteroid will pass Earth at a distance of 0.038 AU (5,700,000 km; 3,500,000 mi).^[6]

Goldstone radar observations on 29 May 2013 discovered that 1998 QE₂ is orbited by a minor-planet moon approximately 600–800 meters in diameter.^[4][15][a] In radar images, the satellite appears brighter than 1998 QE₂ because it is rotating significantly more slowly, which compresses the radar return of the satellite along the Doppler axis. This makes the satellite appear narrow and bright compared to 1998 QE₂.^[16] The satellite orbits the primary every 32 hours with a maximum separation of 6.4 kilometers (4.0 mi).^[17] Once the satellite's orbit is well determined, astronomers and astrophysicists will be able to determine the mass and density of 1998 QE₂.

The surface of 1998 QE₂ is covered with a sooty substance, making it optically dark with a geometric albedo of 0.06,^[6] meaning it absorbs 94% of the light that hits it, which is indicative for a carbonaceous surface of a C-type asteroid. The asteroid is covered with craters and is dark, red, and primitive.^[18]

With a diameter between 2.7 and 3.2 kilometers, 1998 QE₂ is one of largest known potentially hazardous asteroid (see PHA-list).^[19] Conversely, the Collaborative Asteroid Lightcurve Link assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 1.08 kilometers based on an absolute magnitude of 17.2.^[5]

• 
  Orbit of 1998 QE₂ on 31 May 2013
• 
  and 2 June 2013^[1]

• NASA Radar Reveals Asteroid Has Its Own Moon at NASA
• Animation of binary asteroid 1998 QE2 derived from radar data
• Arecibo Radar Sees Asteroid 1998 QE2 and Moon Archived 23 September 2015 at the Wayback Machine (15 June 2013)
• Asteroid Lightcurve Database (LCDB), query form (info Archived 16 December 2017 at the Wayback Machine)
• Asteroids with Satellites, Robert Johnston, johnstonsarchive.net
• (285263) 1998 QE2 at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• (285263) 1998 QE2 at ESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• (285263) 1998 QE2 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters