_1996_HW1_image_3D.png) Shape model of1996 HW1 | |
| Discovery[1][2] | |
|---|---|
| Discovered by | Tom Gehrels |
| Discovery site | Steward Observatory |
| Discovery date | 23 April 1996 |
| Designations | |
| (8567) 1996 HW1 | |
| NEO · Amor | |
| Orbital characteristics[3] | |
| Epoch 21 November 2025 (JD 2461000.5) | |
| Uncertainty parameter 0 | |
| Aphelion | 2.96437AU |
| Perihelion | 1.12697 AU |
| 2.04567 AU | |
| Eccentricity | 0.44909 |
| 2.92592 y (1068.69 d) | |
| 314.321° | |
| 0.33686° / d | |
| Inclination | 8.44896° |
| 177.0929° | |
| 177.282° | |
| Earth MOID | 0.12152 AU |
| TJupiter | 3.652 |
| Physical characteristics | |
| Dimensions | 3.78±0.19 ×1.64±0.16 ×1.49±0.22 km[4]: 226 [a] |
| 2.02 km[4]: 226 | |
| Volume | 4.34±1.09 km3[4]: 226 [b] |
| 8.76243±0.00004 h[4]: 226 | |
| 281±5°[4]: 226 | |
| −31±5°[4]: 226 | |
| 0.156[3] | |
| Sq-type[5]: 7 | |
| 15.36[3] | |
(8567) 1996 HW1 is anear-Earth asteroid (NEA) located in theinner Solar System. It was discovered on 23 April 1996 by astronomerTom Gehrels atSteward Observatory. It is acontact binary asteroid, with two lobes separated by a distinct "neck"; altogether, the asteroid is on average 2 kilometres (1.2 mi) in diameter. It has arotation period of 8.76 hours, which is likely gradually slowing because of theYORP effect.
1996 HW1 was discovered on 23 April 1996 by astronomerTom Gehrels, who was working as a part of theSpacewatch survey atSteward Observatory, Arizona, United States.[2] The asteroid was assigned theprovisional designation1996 HW1 by theMinor Planet Center (MPC), and its discovery was published in a Minor Planet Circular on 2 May 1996.[6]: 115 Once its orbit was sufficiently determined, it was numbered (8567) by the MPC on 11 April 1998.[7]: 56 As of 2025[update], it remains unnamed.[3]
1996 HW1 orbits the Sun at an average distance—itssemi-major axis—of 2.05astronomical units (AU), with anorbital period of 2.93 years. It is classified as anear-Earth asteroid; because its orbit lies entirely outsideEarth's orbit, it is also classified as anAmor asteroid.[3][8] Along its orbit, its distance from the Sun varies between 1.13 AU atperihelion to 2.96 AU ataphelion due to itsorbital eccentricity of 0.45. Its orbit isinclined by 8.45° with respect to theecliptic plane.[3]
1996 HW1 is acontact binary object with dimensions of 3.78 by 1.64 by 1.49 kilometres (2.35 by 1.02 by 0.93 mi)[4]: 217 and an equivalent mean diameter of 2.02 kilometres (1.26 mi).[4]: 226 Its two lobes have an estimated mass ratio of 2:1, and are separated by a prominent neck.[4]: 223, 217
Spectroscopic observations of1996 HW1 show that it isclassified as anSq-type asteroid, with spectral properties betweenS-type asteroids andQ-type asteroids.[5]: 7 It has ageometric albedo of 0.156,[3] though itsvisible light albedo is higher at approximately 0.33.[9]: 231 Its spectrum is significantly reddened, indicating that its surface has undergone appreciablespace weathering.[5]: 7
1996 HW1 has a siderealrotation period of 8.76 hours, spinning in aretrograde direction with poleecliptic coordinates of (281°, –31°). Its spin properties were derived from itslightcurve, or variations in its observed brightness, which was additionally supported byradar observations.[4]: 212 Assuming a bulk density of 2.0 g/cm3, the asteroid is spinning slower than its minimum energy state of 7.4 hours, placing its neck under compressive andshear stress. A lower assumed density of 1.43 g/cm3 makes its observed rotation period its minimum energy state, but such a density requires an improbableporosity of 58%.[4]: 222
1996 HW1's spin is likely being slowed by theYORP effect, where irregularly shaped asteroids experience a torque by emitting thermal radiation.1996 HW1's faster rotation period in the past suggests that its two lobes originally may have been separated as abinary system. The YORP effect slowly removesangular momentum from binary asteroids, though how quickly this leads to the two components merging depends on the mass ratio. Given the mass ratio of1996 HW1's two lobes, they could have merged in a span of 1 million years (Myr), within the typical 10 Myr dynamical lifetimes of NEAs.[4]: 222–223
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