Paha (moon)

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(47171) Lempo I (Paha)
Provisional or systematic name S / 2001 (47171) 1
Central body (47171) Lempo
Properties of the orbit
Major semi-axis 7411 ± 12 km
Periapsis unknown
Apoapsis unknown
Orbital time 50.302 ± 0.001 d
Physical Properties
Albedo 0.079 + 00.013- 00.011
Medium diameter 132.0 + 08.0- 09.0 km
Dimensions 7.5 x 10 17 kg
surface 55,000 km 2
Medium density 0.64 + 00.15- 00.11g / cm 3
Surface temperature 44–45 (−229 to −228 ° C) K
discovery
Explorer

Chadwick A. Trujillo
Michael E. Brown

Date of discovery December 8, 2001
Remarks Smallest component of the (47171) Lempo triple system

Paha (systematic name S / 2001 (47171) 1 ) is a moon of Plutino (47171) Lempo , which consists of two main bodies. The whole system is the first known multiple asteroid system in the Kuiper Belt .

Discovery and naming

Paha was discovered on December 8, 2001 by astronomers Chadwick A. Trujillo and Michael E. Brown through observations of the system with the Hubble Space Telescope . The discovery was announced on January 10, 2002; the moon was given the provisional designation S / 2001 (47171) 1 .

On October 5, 2017, the Minor Planet Center announced the name Paha . Paha is - like Hiisi - one of the helpers of the god Lempo from Finnish mythology . The other two components of the system have been named after Lempo and Hiisi.

Since the companion's discovery, the designation "(47171) 1999 TC 36 " has officially been used for the largest component of the system (A 1 ), while the designation S / 2007 (47171) 1 for the smaller component (A 2 ) and for the more distant moon S / 2001 (47171) 1 was applicable. But the name is often used for the whole system. Unofficially, the moon is therefore sometimes referred to as "(47171) 1999 TC 36 B" or simply "B" .

The Lempo system has been observed through several space-based and earth-based telescopes. In December 2017, there were a total of 331 observations over a period of 43 years.

properties

Orbit

Paha orbits the common center of gravity of the system in an orbit at a distance of 7411 km (about 54.5 A 1 or 59.1 A 2 radii). The orbital eccentricity and inclination are not yet determined.

The orbit time of Paha is 50 days, 7 hours and 15 minutes. Its orbit is well within the Hill radius of 590,000 km, but also well outside of the synchronous orbit.

size

The most precise determination of the diameter ( geometric mean ) Pahas is 132 km, based on the estimated density of 0.64 g / cm³ and the corresponding assumed equal reflectivity of 7.9%. The moon thus has around half the diameter of the main body (48.6%) and the companion (52.6%). The size ratio is therefore roughly 2: 2: 1, which is unique in the solar system.

Assuming an average diameter of 132 km, the surface area is almost 55,000 km², which is just about the size of Croatia .

Provisions of the diameter for Paha
year Dimensions km source
2009 135.0 + 022.0- 018.0 Benecchi et al. a.
2010 139.0 + 022.0- 018.0 Benecchi et al. a.
2012 132.0 + 08.0- 09.0 Mommert et al. a.
The most precise determination is marked in bold .

internal structure

The unusually low mean density of 0.64 g / cm³ is an indication that it is not a compact body, but that the object should be a rubble pile , an accumulation of dust and rocks, which is interspersed with cavities. The porosity is estimated to be up to 68%.

Paha's mass could be calculated to be 7.5 · 10 17 ; the total mass of the system is about 1.3 ∙ 10 19 .

The mean surface temperature is 44–45  K (−229 to −228 ° C).

Emergence

So far, there are two hypotheses about the origin of the triple system. Either it came about as a result of a major collision, after which the entire system was re-formed from the accretion disk that had arisen, or the third component was gravitationally captured by the already existing double asteroid. The similar sizes and masses of the A 1 and A 2 components favor the latter hypothesis.

See also

Web links

Individual evidence

  1. ^ Daniel WE Green: IAUC No. 7787: S / 2001 (47171) 1 Discovery Publication (Jan. 10, 2002). Retrieved September 17, 2017 .
  2. ^ Daniel WE Green: IAUC No. 7807: S / 2001 (47171) 1 confirmation of discovery (January 24, 2002). Retrieved September 17, 2017 .
  3. ↑ MPC / MPO / MPS archives . Minor Planet Center. Retrieved December 15, 2017.
  4. ↑ JPL: 47171 Lempo (1999 TC 36 ) at the JPL. Retrieved December 14, 2017 .
  5. ↑ SD Benecchi et al .: (47171) 1999 TC36, A Transneptunian Triple (September 2009) (PDF). Retrieved September 17, 2017 .
  6. ↑ SD Benecchi et al .: (47171) 1999 TC 36 , A transneptunian triple (June 2010). Retrieved September 17, 2017 .
  7. ↑ M. Mommert, AW Harris, C. Kiss, A. Pál, P. Santos-Sanz, J. Stansberry, A. Delsanti, E. Vilenius, TG Müller, N. Peixinho, E. Lellouch, N. Szalai, F. Henry, R. Duffard, S. Fornasier, P. Hartogh, M. Mueller, JL Ortiz, S. Protopapa, M. Rengel, A. Thirouin: “TNOs are Cool”: A survey of the trans-Neptunian region. V. Physical characterization of 18 Plutinos using Herschel-PACS observations . In: Astronomy and Astrophysics . 541, no.A93 , May 4, 2012. arxiv : 1202.3657 . bibcode : 2012A & A ... 541A..93M . doi : 10.1051 / 0004-6361 / 201118562 .