| Minorplanet: | yes |
| Background: |
|
| 101 Helena | |
| Discovered: | 15 August 1868 |
| Mpc Name: | (101) Helena |
| Alt Names: | A868 PA |
| Pronounced: | [1] |
| Epoch: | 31 July 2016 (JD 2457600.5) |
| Semimajor: | 2.5848AU |
| Perihelion: | 2.22353AU |
| Aphelion: | 2.94606abbr=onNaNabbr=on |
| Eccentricity: | 0.13977 |
| Period: | 4.16 yr (1517.9 d) |
| Inclination: | 10.1976° |
| Asc Node: | 343.419° |
| Arg Peri: | 348.030° |
| Avg Speed: | 18.44 km/s |
| Mass: | 3.0 kg |
| Density: | 2.0 g/cm3 |
| Surface Grav: | 0.0184 m/s2 |
| Escape Velocity: | 0.0348 km/s |
| Rotation: | 23.08abbr=onNaNabbr=on |
| Abs Magnitude: | 8.33 |
| Mean Motion: | / day |
| Observation Arc: | 145.07 yr (52986 d) |
| Uncertainty: | 0 |
| Moid: | 1.21369AU |
| Jupiter Moid: | 2.4117AU |
| Tisserand: | 3.387 |
101 Helena is a large, rocky main-belt asteroid. It was discovered by Canadian-American astronomer J. C. Watson on August 15, 1868, and was named after Helen of Troy in Greek mythology.
This object is orbiting the Sun with a period of 4.16 years and an eccentricity of 0.14. Its orbital plane is inclined by 10.2° to the plane of the ecliptic. Radar observations were made of this object on Oct 7 and 19, 2001 from the Arecibo Observatory. Analysis of the data gave an estimated ellipsoidal diameter of 71×63×63 ± 16% km. The mean diameter estimated from IRAS infrared measurements is 66 km, in agreement with the radar findings. It is classified as an S-type asteroid in the Tholen system, suggesting a predominantly silicate composition. 101 Helena is spinning on its axis with a period of 23 hours.