Alexhelios
| (216) Cleopatra I (Alexhelios) | |
|---|---|
| Provisional or systematic name | S / 2008 (216) 1 |
| Central body | (216) Cleopatra |
| Properties of the orbit | |
| Major semi-axis | 678 ± 13 km |
| Periapsis | 678 ± 13 km |
| Apoapsis | 678 ± 13 km |
| eccentricity | 0.00 |
| Orbit inclination | 51.0 ± 2.0 ° |
| Orbital time | 2.32 ± 0.02 d |
| Physical Properties | |
| Albedo | ≈ 0.1164 ± 0.0040 |
| Medium diameter | 8.9 ± 1.6 km |
| surface | 249 km 2 |
| Medium density | ≈ 3.6 ± 0.4 g / cm 3 |
| discovery | |
| Explorer |
|
| Date of discovery | September 19, 2008 |
| Remarks | Larger moon of the Cleopatra system |
Alexhelios is the outer and larger of the two moons of the main belt asteroid (216) Cleopatra . Its mean diameter is around 8.9 kilometers, which is about 1/14 of Cleopatra's mean diameter.
Discovery and naming
Alexhelios was discovered on images from September 19, 2008 by Franck Marchis, Pascal Descamps, Jérôme Berthier and JP Emery using adaptive optics at the 10 m Keck II telescope on Mauna Kea in Hawaii on the same day shortly before Cleoselene . Cleopatra was at a convenient distance of 1.23 AU from Earth at this time . As early as 1993, a search for companions with the Hubble space telescope was unsuccessful, but Cleopatra was 2.38 AU away at the time. The discovery was announced on September 24, 2008; the moon was given the provisional designation S / 2008 (216) 1 .
The Cleopatra system is after (87) Sylvia , (45) Eugenia and (3749) Balam the fourth asteroid multiple system discovered in the main belt and the sixth overall.
On February 18, 2011, both moons were officially named after the two children of Cleopatra and Marcus Antonius , Cleopatra Selene II and Alexander Helios . In Greek mythology , Selene represents the moon and Helios the sun .
Track properties
Alexhelios orbits Cleopatra on a prograde , elliptical orbit at a mean distance of around 678 kilometers from its center (around 11.2 Cleopatra radii). The eccentricity of the orbit is practically circular at 0.00, the orbit inclination is about 51 °. The orbit of the inner moon Cleoselene is on average about 224 km from the orbit of Alexhelios.
Alexhelios orbits Cleopatra in 2 days and 7.7 hours, which corresponds to about 736.6 orbits in one Cleopatra year (about 4.67 earth years).
Physical Properties
size
Alexhelios has a diameter of 8.9 km, based on the assumed equal reflectivity of 11.6% corresponding to Cleopatra . The surface is therefore relatively dark.
Assuming an average diameter of 8.9 km, the surface area is around 249 km 2 , which is slightly less than the area of the Swiss canton of Nidwalden .
Provisions of the diameter for Alexhelios
| year | Dimensions km | source |
|---|---|---|
| 2008 | 5.0 | Marchis et al. |
| 2010 | 8.9 ± 1.6 | Descamps et al. |
The most precise determination is marked in bold .
internal structure
Since Alexhelios is probably made of the same material as Cleopatra, the density is estimated at 3.6 g / cm 3 , as with Cleopatra . It can therefore be assumed that Alexhelios is porous inside and, like the mother body, belongs to the Rubble Piles .
The mean surface temperature is around 166 K (−107 ° C).
According to calculations, Cleopatra's strange shape, its rotation and the moon Alexhelios were formed by an oblique impact about 100 million years ago. Accordingly, the increased rotation caused by the impact pulled the mother asteroid into the elongated shape observed today and caused Alexhelios to break off. The breaking off of Cleoselene apparently occurred much later, this event is believed to have occurred 10 million years ago.
See also
Web links
- Two Companions Found Near Dog-Bone Asteroid Discovery Report with picture of Cleopatra, Cleoselene and Alexhelios
- A dog-bone-shaped asteroid's two moons: Cleopatra, Cleoselene, and Alexhelios With animation of Cleopatra, Cleoselene and Alexhelios (English)
Individual evidence
- ^ Daniel WE Green: IAUC No. 8980: S / 2008 (216) 1 and S / 2008 (216) 2 Discovery Publication (September 2008). Retrieved September 11, 2017 .
- ↑ a b Pascal Descamps et al .: Triplicity and Physical Characteristics of Asteroid (216) Cleopatra (PDF). Retrieved September 11, 2017 .
- ^ Franck Marchis et al .: Two Companions Found Near Dog-Bone Asteroid (2006). (No longer available online.) Archived from the original on September 11, 2017 ; accessed on September 11, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
