 | |
| Discovery[1] | |
|---|---|
| Discovered by | James Craig Watson |
| Discovery date | 25 November 1872 |
| Designations | |
| (128) Nemesis | |
| Pronunciation | /ˈnɛmɪsɪs/[2] |
Named after | Nemesis |
| A872 WA;1952 HW1 | |
| main-belt[1][3] · Nemesis | |
| Adjectives | Nemesian/nəˈmiːʒ(i)ən/[4][5] |
| Orbital characteristics[3] | |
| Epoch 23 March 2018 (JD 2458200.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 144.93yr (52,934 d) |
| Aphelion | 3.10 AU (463.69 Gm) |
| Perihelion | 2.40 AU (359.00 Gm) |
| 2.75 AU (411.35 Gm) | |
| Eccentricity | 0.1272 |
| 4.56 years (1,665 d) | |
| 345.49° | |
| 0° 12m 58.32s / day | |
| Inclination | 6.2453° |
| 76.243° | |
| 303.82° | |
| Physical characteristics | |
| 163±5 km[6] 162.5±1.3 km[7] 184.2±5.2 km[8] | |
| Flattening | 0.17[a] |
| Mass | (3.4±1.7)×1018 kg[6] (6.0±2.6)×1018 kg[8] |
Meandensity | 1.5±0.8 g/cm3[6] 1.82±0.79 g/cm3[8] |
| 77.81 h (3.242 d)[9] 38.9325 h (1.62219 d)[3] | |
| 0.067 (calculated)[6] 0.067±0.005[3] | |
| Tholen =C[3] SMASS =C[3] | |
| 7.70[3] | |
128 Nemesis is a large 180 kmmain-beltasteroid, ofcarbonaceous composition. It rotates rather slowly, taking about 78 hours to complete one rotation.[3][9] Nemesis is the largest member of the Nemesian asteroid family bearing its name. It was discovered byJ. C. Watson on 25 November 1872,[3] and named afterNemesis, the goddess of retribution inGreek mythology.
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This object is orbiting theSun with aperiod of 4.56 years and aneccentricity (ovalness) of 0.13. Theorbital plane isinclined by 6.2° to theplane of the ecliptic. It is categorized as aC-type asteroid,[10] indicating a primitivecarbonaceous composition. Based onIRAS data Nemesis is about 188 km in diameter and is around the 33rd largestmain-belt asteroid,[11] whileWISE measurements yield a size of ~163 km.[7] The 77.81‑hour[12]rotation period is the second longest for an asteroid more than 150 km in diameter.[13]
Between 2005 and 2021, Nemesis has been observed tooccult eight stars.
