 1989 ML photographed by theCanada–France–Hawaii Telescope in December 2015 | |
| Discovery[1] | |
|---|---|
| Discovered by | E. F. Helin,J. Alu |
| Discovery site | Palomar Observatory,United States |
| Discovery date | 29 June 1989 |
| Designations | |
| MPO 244277, 1992 WA | |
| Orbital characteristics[2] | |
| Epoch 21 November 2025 (JD 2461000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 12250 days (33.54 yr) |
| Aphelion | 1.4470 AU (216.47 Gm) |
| Perihelion | 1.0985 AU (164.33 Gm) |
| 1.2728 AU (190.41 Gm) | |
| Eccentricity | 0.1369 |
| 1.436yr (524.518d) | |
Averageorbital speed | 26.28 km/s |
| 121.513° | |
| 0° 41m 11.911s / day | |
| Inclination | 4.379° |
| 104.272° | |
| 183.625° | |
| Earth MOID | 0.08233 AU |
| Physical characteristics | |
| Dimensions | 0.276±0.037 km[3] |
| 19.228 h (0.8012 d)[4] | |
| 0.37±0.15[3] | |
| X-type[5]: 142 E-type[3] | |
| 19.45 (JPL)[2] | |
(10302) 1989 ML is an unnamednear-Earth asteroid located in theinner Solar System. It is relatively small, estimated to be around 300 metres (980 ft) in diameter. AnAmor asteroid, it orbits betweenEarth andMars. It is anX-type asteroid, so its precise surface composition is yet unknown, though telescopic observations indicate it may be relatively enriched iniron. It was discovered byEleanor F. Helin andJeff T. Alu atPalomar Observatory on 29 June 1989. 1989 ML was the former backup target forJapan'sHayabusa mission, but launch delays meant that the rendezvous had to be cancelled.
1989 ML is classified as anear-Earth object (NEO) and anAmor asteroid,[1] meaning that its orbit never crosses theEarth's.[6]: 489 It has asemi-major axis of 1.273astronomical units (AU), completing an orbit around theSun every 1.436 years (524.518 days). It has a moderatelyelliptical orbit with anorbital eccentricity of 0.137, with its distance from the Sun varying from 1.0985 AU to 1.273 AU. 1989 ML has a relatively loworbital inclination of 4.379° with respect to theecliptic plane.[2] Its proximity to Earth means that 1989 ML's orbit is strongly perturbed and chaotic; theLyapunov time of its orbit is roughly 1,000 years.[7]
In 2007, a team of astronomers led by Michael Mueller used observations from theSpitzer Space Telescope to estimate 1989 ML's physical properties. Adopting anabsolute magnitude value of19.5±0.3, Mueller et al. derived a diameter of 0.246 ± 0.037 kilometres (0.153 ± 0.023 mi).[3] Analysis of 1989 ML'slightcurve, or fluctuations in its observed brightness, indicate that it rotates once every 19.228 hours and has atumbling rotation.[4] The high amplitude of its lightcurve implies that it may be very elongated, with its longest axis being at least 2.2 times longer than its intermediate axis.[8]
Spectroscopic observations conducted by Palomar Observatory in 1999 revealed that 1989 ML has a relatively flat (or neutral) spectrum. As a result, a definitive interpretation of its surface composition could not be made, though its spectrum was noted to resemble dark, impact-shockedchondrites.[5]: 144 Due to its neutral spectrum, 1989 ML was classified as anXc-type asteroid under the Bus classification scheme, suggesting that it belongs to theE-type,M-type, orP-type classifications under theTholen classification scheme.[3][9]: 31 These asteroid types are spectrally degenerate, meaning that they can only be distinguished from each other byalbedo.[10] E-type asteroids have relatively high geometric albedos of 0.3–0.6; M-type asteroids have moderate albedos of 0.1–0.2; and P-type asteroids have dark albedos below 0.1, appearing to be rich inorganic compounds.[3]
Mueller et al. estimated 1989 ML's geometric albedo to be0.37±0.15, suggesting an E-type classification and ruling out a P-type classification. 1989 ML's optical andnear-infrared colors were additionally compared to other asteroids, demonstrating that they differed from the color data of M-type and P-type asteroids. They also differed from the colors of the E-type asteroids64 Angelina and3103 Eger, but agreed with the color of44 Nysa, another E-type asteroid. Nysa-type spectra are consistent withsilicate mineralogy enriched in iron, whilst Angelina-type spectra are consistent with silicates containingsulfides, indicating that 1989 ML is relatively enriched in iron.[3]
1989 ML is an attractive target forspacecraft exploration due to its relative accessibility from Earth. It was considered as a backup target ofJAXA'ssample-return missionHayabusa (then MUSES-C), with the primary target being4660 Nereus. However, both targets had to be given up due to launch delays.[5]: 140, 143 Hayabusa would instead go on to rendezvous with25143 Itokawa in 2005.[11] 1989 ML was also considered by theEuropean Space Agency as a candidate target for theDon Quijote mission concept to study the effects ofimpacting a spacecraft into an asteroid; however, they too changed to other targets.[12]
