Hydra (moon)
| Hydra | |
|---|---|
|
|
| Hydra captured by the New Horizons spacecraft on July 14, 2015 | |
| Provisional or systematic name | S / 2005 P 1 Pluto III |
| Central body | Pluto |
| Properties of the orbit | |
| Major semi-axis | (64,780 ± 88) km |
| Periapsis | 64,443 km |
| Apoapsis | 65,117 km |
| eccentricity | 0.0052 ± 0.0011 |
| Orbit inclination | 0.25 ° ± 0.11 (equatorial plane) ° |
| Orbital time | 38.2065 ± 0.0014 d |
| Mean orbital velocity | 0.1233 km / s |
| Physical Properties | |
| Albedo | 0.04-0.35 |
| Apparent brightness | 22.96 ± 0.15 mag |
| Dimensions | 55 × 40 km |
| Dimensions | 5 · 10 16 - 2 · 10 18 kg |
| Acceleration of gravity on the surface | ≈ 0 m / s 2 |
| Escape speed | ≈ 0 m / s |
| Surface temperature | −240–−218 ° C / 33–55 K |
| discovery | |
| Explorer |
Research team from the |
| Date of discovery | June 15, 2005 |
Hydra is the outermost and second largest of the five known moons of the dwarf planet Pluto .
Discovery and naming
Hydra was discovered on June 15, 2005 along with another Pluto moon, Nix , by the Pluto Companion Search Team in images taken by the Hubble Space Telescope on May 15 and 18, 2005; two members of the team: Max J. Mutchler (June 15) and Andrew J. Steffl (August 15) discovered both independently. On the recordings, Hydra was 1.85 arc seconds away from Pluto. When both moons were subsequently localized on images from November 2002, the discovery was announced on October 31, 2005. The moon was initially given the provisional designation S / 2005 P 1 . The actual existence of the two celestial bodies was confirmed by further observations of the Pluto system on February 22, 2006.
On June 21, 2006, the moon was officially named by the International Astronomical Union (IAU) after Hydra (Greek for "water snake"), the nine-headed sea monster from Greek mythology . If it lost a head, two new ones grew in its place. The hydra was considered the daughter of Echidna and Typhon and the sister of Kerberos , Chimaira and the Sphinx .
In addition, the names Nix and Hydra correspond to the initials of the New Horizons space probe , which explored the system in July 2015.
Track properties
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Hydra orbits the common center of gravity of the Pluto-Charon system in a prograde , slightly elliptical orbit at an average distance of 62,745 km (64,780 km distance from Pluto's center, approx. 56.18 Pluto radii). The orbit eccentricity is 0.0052, the orbit is inclined 0.25 ° to the equator of Pluto . The orbit is the most eccentric in the Pluto system.
The orbit of the next inner moon Kerberos has a radius about 7,000 km smaller; Nix and Charon orbit Pluto in even tighter orbits.
Hydra orbits Pluto in 38 days, 4 hours 57 minutes and 21.6 seconds, which corresponds to around 2371.7 orbits in a Pluto year (around 248.09 earth years).
The orbital period is close to a 1: 6 orbit resonance with Charon, with a deviation of 0.3%. Whether this is a real resonance can only be reliably determined with a more precise orbit determination, in particular the determination of the precession rate . If there is no real resonance, there is a hypothesis that such a near-resonance comes from the outward migration of Charon. It is therefore maintained by the periodic local fluctuation of 5% in the gravitational field strength due to the orbit of Pluto and Charon around each other.
However, Hydra's rotation is not predictable and its orbital plane is not the same as that of Charon.
Physical Properties
The dimensions of the moon are 55 × 40 km. Before the flyby through New Horizons in 2015, the exact value could not be determined because the reflectivity ( albedo ) of the surface was not known.
Hydra is 25% brighter than Nix. The Hubble recordings from 2002 to 2003 implied that Nix is the bigger moon. During the Hubble observations, which were specially tuned to observe the faint moons between 2005 and 2006, Hydra again turned out to be the brighter moon. In spectral examinations, in contrast to the reddish Pluto, Hydra showed itself in a similarly neutral gray color as Charon and Nix.
Hydra, analogous to the theory of the formation of the Earth's moon , is probably the product of the great collision of a predecessor of Pluto with another Pluto-sized body of the Kuiper belt , which formed the moon Charon. In the process, debris got into outer orbits around Pluto, which formed the moon Hydra.
exploration
After being discovered in the summer of 2005 by images from the Hubble Space Telescope , the two newly discovered moons were observed in September 2005 by the Keck and Gemini observatories in Hawaii and by the ESO-VLT telescope in Chile to confirm the discovery however, it failed because the conditions for an observation of the Pluto system at that time were not favorable. On October 24th, Marc W. Buie and Eliot F. Young were able to make out the moons in the 2002 images.
The New Horizons spacecraft, launched in 2006, passed Charon and Pluto on July 14, 2015. Since the discovery of Hydra and Nix as well as the fourth moon Kerberos had not yet been confirmed when the probe was launched, they were not included in the mission. However, Hydra and Nix were subsequently added to the observation program. Positions and paths should be recorded more precisely.
See also
Individual evidence
- ↑ a b "New Horizons captures two of Pluto's smaller moons" , accessed on July 22, 2015 at 12:40 am
- ↑ http://www.raumfahrer.net/news/astronomie/04062015210943.shtml Ralph-Mirko Richter: At least two of Pluto's smaller moons are tumbling , in Raumfahrer.net, Date: June 4, 2015, Accessed: June 7, 2015.
Web links
- IAUC 8625: S / 2005 P 1 and S / 2005 P 2 October 31, 2005 (discovery)
- IAUC 8676: S / 2005 P 1 and S / 2005 P 2 February 22, 2006 (confirmation)
- IAUC 8686: S / 2005 P 1 and S / 2005 P 2 March 9, 2006 (observation details )
- IAUC 8723: Satellites of Pluto June 21, 2006 (designation)
- Wm. Robert Johnston: (134340) Pluto, Charon, Nix, and Hydra
- Background Information Regarding Our Two Newly Discovered Satellites of Pluto - Website of the Explorers
- NASA's Hubble Reveals Possible New Moons Around Pluto (English)
- NASA press release on the discovery (English)
- Hubble Confirms New Moons of Pluto (English)
- Product Naming (English)
- Die Entdecker: New Constraints on Additional Satellites of the Pluto System Astronomical Journal, 2005 (English)
- Die Entdecker: Orbits and photometry of Pluto's satellites: Charon, S / 2005 P1 and S / 2005 P2 Astronomical Journal, 2005 (English)