Nunam (moon)

from Wikipedia, the free encyclopedia
(79360) Sila I (Nunam)
Provisional or systematic name S / 2005 (79360) 1
Central body (79360) Sila
Properties of the orbit
Major semi-axis 2,777 ± 19 km
Periapsis 2,721 km
Apoapsis 2,833 km
eccentricity 0.020 ± 0.015
Orbit inclination 103.51 ± 0.39 °
Orbital time 12.50995 ± 0.00036 d
Physical Properties
Albedo 0.117 ± 0.035 / 0.024 (system)
Apparent brightness 6.3 (absolute) likes
Medium diameter 236 ± 28 km
Dimensions 1.084 ± 0.022  ·  10 19 (system) kg
Medium density 0.72 + 0.37 / -0.23 (system) g / cm 3
Surface temperature −231 ° C (~ 42) K
discovery
Explorer
  • Denise C. Stephens
  • Keith S. Noll
Date of discovery October 22, 2002

Nunam is the smaller component of the Cubewano - double system (79360) Sila -Nunam . Its mean diameter is 236 kilometers, which is around 95% of the parent asteroid . This asteroid is the first to be officially classified as a moon and as part of a dual system.

Discovery and naming

Nunam was discovered on October 22, 2002 by Denise C. Stephens and Keith S. Noll while observing Sila with the Hubble Space Telescope . Both components of the system could be recognized as clearly separated by the recordings. The discovery was announced on October 5, 2005, the moon was given the provisional designation S / 2005 (79360) 1 .

On January 9, 2012, Nunam and Sila received the official name, named after Inuit gods. Sila ("spirit") is the Inuit god of heaven, weather and life force. Nunam is the earth goddess, in some traditions as Sila's wife. Nunam created the land animals and, in some traditions, the Inuit people . In other traditions, it was Sila who created the first humans out of damp sand. Sila breathed life into the Inuit.

Track properties

Orbit5.gif

Nunam and Sila orbit the common barycentre on a prograde , slightly elliptical orbit at a distance between 2721 km and 2833 km from each other (major orbit half-axis 2777 km, this corresponds to 22.4 Sila and 23.5 nunam radii. This results in an average distance between the two Surfaces of about 2535 km, assuming a round shape of both bodies.) The orbit eccentricity is 0.02, the orbit is 103.51 ° inclined to the ecliptic .

Nunam and Sila orbit the barycentre in 12 days, 12 hours and 14.3 minutes, which corresponds to 8522.97 orbits ("months") in a Sila Nunam year (291.91 earth years).

Physical Properties

internal structure

The extremely low system density of 0.72 g / cm³, which is far below that of water, indicates that water ice must predominate on both bodies, which is not sufficient to explain the low density, since even pure ice with 0.91 g / cm³ is even denser. It can therefore be assumed that both bodies must have cavities inside. (→ Rubble Piles )

surface

In visible light, Sila and Nunam are very red and have a flat spectrum with no near-infrared features that shows no water ice absorptions, which is similar to the spectrum of Ixion . It appears that the surfaces of both components have been renewed by ejecta from impacts on the other body. The surface temperature should be around −231 ° C (42 K ).

Is Nunam a Cubewano?

The questions of a not entirely clear classification of an entire system

Nunam is 236 km in diameter, which is about 95% of the main body. For this reason the system (79360) Sila-Nunam as a whole - a novelty in history - was officially named as a double asteroid system for the first time . Of course, the question arises as to when a system is to be designated as an official dual system, as there is still no official definition for this from the IAU . During the 2006 discussions about the status of Pluto and Charon , it was decided not to call this a double (dwarf planet) system, Charon has officially remained a moon - although the common barycentre lies outside the main body of Pluto, which is basically the main question: where the barycenter must be located so that a companion has the same status as its main body. The smaller component Menoetius of the Patroclus -Menoetius system, for example, which also has 92.8% of the diameter of Patroclus, is officially classified as a moon like Charon.

Nunam is now classified as a natural satellite (moon) of Sila (S / 2005 (79360) 1) and as part of the system (79360) Sila-Nunam (whose "moon name" appears for the first time - as a further novelty - in the system name), whereby Nunam is basically "upgraded" because no body in the solar system has had this status in the history of planetary research. A number of other important unanswered questions arise from these and the following circumstances: Is Nunam also a Cubewano ? Since Sila officially has this classification and Sila-Nunam is officially classified as a system, Nunam would have to be part of the "Double Cubewano" Sila-Nunam, and thus be a Cubewano (or "Classic KBO") itself. In this case it would also be an asteroid and thus the first “lunar asteroid” (or as the technical name for it would be, asteroid moons are assigned, over 220 are already known) in the solar system and would itself have an asteroid numbering, which in turn would be called , it would theoretically have to be renumbered - which can of course be ruled out, since the whole system already has a number. Therefore, Nunam as an individual body would have to receive the number (79360) itself, which can also be ruled out, since asteroid numbers are never assigned twice. At most there was still the possibility of him by analogy with the double stars , (79360) B Nunam or (79360) Sila Nunam B to call.

From these considerations and ambiguities, Nunam can now summarize the following classification options:

  • Nunam is the satellite (79360) Sila I - Nunam (S / 2005 (79360) 1) - it should officially be the moon
  • Nunam is part of the system as a satellite (79360) Sila-Nunam I - Nunam - as the moon of the whole system it should also officially have
  • Nunam is the satellite (79360) Sila I - Nunam (S / 2005 (79360) 1) and an asteroid , TNO and CKBO (Cubewano)
  • Nunam is part of the system as a satellite (79360) Sila-Nunam I - Nunam and an asteroid , TNO and CKBO (Cubewano)
  • Nunam is not part of the system (79360) B Nunam as it is not a real satellite
  • As not a real satellite, Nunam is part of the system (79360) Sila-Nunam B

Other questions that arise from this

On the basis of these facts, the designation of the Sila-Nunam system turns out to be a curiosity, and it raises the fundamental question of what should happen to the dual systems in the long term. Nunam is a classic example of a need for action on the part of the IAU with regard to the classification of objects, especially in the outer solar system. The following specific fundamental questions should be clarified:

  • Where must the barycentre be located or by how many percent would the "secondary" have to be smaller in order to no longer be considered a system component or from when would a moon become a "system component" (official double asteroid )? A definition according to the two most logical variants - barycentre outside the surface of the main body or double-bound rotation (which, however, is usually very difficult to determine) or even both - would affect a whole series of TNO and other objects in the solar system, such as most likely the - already named - systems Antiope / S / 2000 (90) 1 ( outer main belt , sometimes also called Antiope A and B), Patroclus / Menoetius ( L 5 -Jupiter Trojans ), Borasisi / Pabu , Logos / Zoe ( CKBOs ), Ceto / Phorcys ( centaurs ) - and especially the dwarf planet Pluto with its moon Charon and many other named and unnamed asteroids. A third definition according to a percentage of the size ratio, e.g. B. cautious 90% would already include the two mentioned first, one from 50% would include all - including a "double dwarf planet system" Pluto-Charon, which demonstrably also fulfills the above two criteria.
  • What happens to the individual objects in the case of a system classification? Are they more or less upgraded as a system component or do they even lose their status because they are no longer listed individually? This question is scientifically though insignificantly, but plays an important role in the assessment and perception of celestial bodies, especially since this particular point ultimately classifications and names one does not seem insignificant impact exercises, as in 2006, especially in the up -Pluto debate was felt .
  • What is the most correct (and also most sensible) system name for a "secondary" in a system like Sila-Nunam, and do the already officially named dual system components also receive an additional system name such as Patroclus-Menoetius? And can a "primary" like Sila be officially designated without an addition, ie 79360 Sila-Nunam (1997 CS29) (official) and 79360 Sila (1997 CS29) ?
  • It is needed for the centaur subclasses, for example, as there are some who are also TNO (Ceto / Phorcys), and some who do not move beyond the orbit of Neptune, such as. B. Hidalgo , Sedna is an “IOO” (Inner Oort Cloud Object), “OKBO” (Outer KBO), “OSDO” (Outer SDO), “ODO” (Outer Detached Object) etc., when will other dwarf planet candidates be classified as such and other questions of this kind.

exploration

After its discovery, Nunam (and Sila) could be dated back to 1997 on photos and therefore the orbit of the system is now relatively well known. In total, the asteroid has been observed by various telescopes such as the Hubble Space Telescope and also earth-based telescopes, a total of 219 times within 15 years. (As of Sept. 2012)

See also

Web links

Individual evidence

  1. ↑ DC Stephens, KS Noll: discovery publication , arxiv : astro-ph / 0510130 .
  2. ^ DL Rabinowitz et al .: Evidence for Recent Resurfacing of the Binary Kuiper Belt Object 1997 CS29 , bibcode : 2009DPS .... 41.6509R
  3. ^ IAU (MPC) List Of Transneptunian Objects
  4. ↑ JPL Small-Body Database Browser: (79360) Sila-Nunam