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47171 Lempo

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Lead content

History ✓

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Discovery ✓

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Lempo was discovered with the 0.9-meter WIYN telescope (left) at Kitt Peak

The Lempo system was discovered on 1 October 1999 by American astronomers Eric Rubenstein and Louis-Gregory Strolger during an observing run for their Nearby Galaxies Supernova Search (NGSS) project at the Kitt Peak National Observatory in Arizona. Initiated in 1998, the NGSS project was a three-year-long CCD-based survey of galaxies along the celestial equator to search for nearby, low-redshift supernovae. The Kitt Peak Observatory's WIYN 0.9-meter telescope was used for wide-field imaging of this region, which coincided with the ecliptic plane where Kuiper belt objects (KBOs) including Lempo were likely to occur. Lempo was identified by Rubenstein as a relatively bright, slow-moving object in the constellation Cetus on images taken by Strolger on 1 October 1999. At an apparent magnitude of 20, its exceptional brightness for a suspected KBO warranted follow-up observations to confirm the object.

Lempo was observed by Rubenstein and Strolger for three consecutive days after its discovery. The object was also found in images taken by Strolger on 30 September 1999, one day prior to its discovery. The discovery was then announced by the Minor Planet Center on 21 December 1999 and the object was given the provisional designation 1999 TC36. The provisional designation indicates that Lempo was the 903rd minor planet discovered in the first half of October 1999. By 2002, additional observations have extended Lempo's observation arc to over two years, sufficient to determine an accurate orbit. Lempo was consequently given the permanent minor planet number 47171 by the Minor Planet Center on 21 September 2002. As of 2020, over 500 total observations of Lempo have been obtained within an observation arc of over 45 years. The earliest known observations of Lempo have been identified in precovery images dating back to 18 June 1974, as photographic plates of the Siding Spring Observatory's Digitized Sky Survey from June 1974 and May and September 1976.

Name ✓

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Name origin, meaning, and date (MPC 2017)

Trinary system

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Size comparison of the Lempo system's components
Orbit diagram of the Lempo triple system

Lempo is a hierarchical triple (or trinary) system consisting of a central primary, which is itself a binary system of two similarly-sized components (Lempo and Hiisi), and a small satellite on a wide and eccentric circumbinary orbit (Paha). The structure of the hierarchy is discerned by denoting the apparent Lempo–Hiisi primary with the letter A and the smaller, outer companion Paha with the letter B; the individual primary components Lempo and Hiisi are distinguished as A1 and A2, respectively.[1] The three components ordered from largest to smallest are Lempo, Hiisi, and Paha.[2]

Assuming spherical shapes with a uniform bulk density for all components, the system mass estimated based on the motion of Paha is (12.75±0.06)×1018 kg.[1][3] The orbital motion of the Lempo–Hiisi components gives somewhat a higher estimated mass of (14.20±0.05)×1018 kg. This discrepancy is probably related to unaccounted gravitational interactions of the components in a complex triple system.[1]

Lempo is one of the only three trans-Neptunian multiple systems with more than two components; the other two are the dwarf planets Pluto and Haumea.[1] The binary Kuiper belt object 385446 Manwë is suspected to have once been a hierarchical triple system similar to Lempo, but the orbit of its inner binary evolved by tides and became a contact binary.[4]

Paha

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Paha
Hubble timelapse of Paha orbiting Lempo–Hiisi from 2003–2006
Discovery[5]
Discovered byChadwick A. Trujillo
Michael E. Brown
Discovery date8 December 2001
Designations
(47171) Lempo I [6]
Pronunciation/ˈpɑːhɑː/
S/2001 (1999 TC36) 1 [7]
S/2001 (47171) 1
Orbital characteristics[8]
Epoch 24 May 2006 12:00 UT
(JD 2453880.0)
7411±12 km
Eccentricity0.2949±0.0009
50.302±0.001 d
Inclination79.3°±0.2°[a]
325.2°±0.1°
292.1°±0.2°
Satellite of47171 Lempo
Physical characteristics
132+8
−9 km[9]
Mass7.67×1017 kg[3]
Mean density
0.64 g/cm3 (system)[9]
0.079+0.013
−0.011 (system)[9]
V−I=1.120±0.050[10]
22.6[11]
(Δmag 2.24±0.03)[1]

Paha, officially designated (47171) Lempo I Paha,[6] is the smaller, outer component of the Lempo triple system. It was discovered on 8 December 2001 by astronomers Chadwick Trujillo and Michael Brown using the Hubble Space Telescope's Space Telescope Imaging Spectrograph to survey for binary trans-Neptunian objects.[12] The discovery was reported in an IAU Circular notice published by the International Astronomical Union 10 January 2002.[5]

The discovery observations of the apparent Lempo–Paha binary were taken on 8 and 9 December, which had measured apparent separations of 0.365″±0.001″ and 0.370″±0.001″, respectively. The pair exhibited a large flux difference of 2.21±0.01 magnitudes in the unfiltered images.[5] Following the discovery announcement, Franck Marchis and colleagues reanalyzed archival 4 October 2001 observations of Lempo from the Lick Observatory's Shane telescope adaptive optics system and identified a clear detection of Paha.[13] They reported an apparent separation of 0.246″±0.017″ and flux difference of 1.89±0.14 magnitudes in a follow-up IAU Circular published on 24 January 2002.[14]

Paha previously had the temporary provisional designation S/2001 (1999 TC36) 1 before it was changed to S/2001 (47171) 1 after Lempo was numbered.[7] Being the smaller, outer component on a circumbinary orbit around the central Lempo–Hiisi binary, it was sometimes designated "component B" in scientific literature.[1] It received its permanent satellite designation and name alongside Lempo and Hiisi on 5 October 2017.[15]

Characteristics

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Size, density, mass, etc.

In unfiltered visual wavelengths, Paha appears 2.2 magnitudes dimmer than the primary on average, corresponding to an individual apparent magnitude of 22.6.[11]

Circumbinary orbit, chaos, etc.

Keplerian orbit fit suggests mutual events occuring between Paha and Lempo–Hiisi around 2069, but mutual perturbations may shift the timing on the order of a decade.

Hiisi

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Hiisi
Hubble images of the Lempo-Hiisi system, with the two components marked "1" and "2"
Discovery[16][1]
Discovered bySeth Jacobson
Jean-Luc Margot
Susan D. Benecchi et al.
Discovery dateOctober 2007
Designations
(47171) Lempo II [6]
Pronunciation/ˈpɑːhɑː/
Orbital characteristics[8]
Epoch 24 May 2006 12:00 UT
(JD 2453880.0)
867±11 km
Eccentricity0.101±0.006
1.9068±0.0001 d
Inclination88.9°±0.6°[a]
330.0°±1.0°
47.7°±6.3°
Satellite of47171 Lempo
Physical characteristics
251+16
−17 km[9]
Mass5.273×1018 kg[3]
Mean density
0.64 g/cm3 (system)[9]
45.763±0.002 h (assumed)[1]
0.079+0.013
−0.011 (system)[9]
V−I=1.19±0.01[1]
20.2[11]
(Δmag 0.17)[1]

Hiisi, officially designated (47171) Lempo II Hiisi,[17] is the inner, second-largest component of the Lempo triple system. Together with the primary component Lempo, it forms the central binary Lempo–Hiisi which the outer component Paha revolves around. The existence of a third, inner component (or second companion) in the Lempo system was first hypothesized in 2006 by John Stansberry and collaborators, who noted that the primary seemed to have an unusually low density.[18] Further evidence to the existence of an inner component was posited by Seth Jacobson and Jean-Luc Margot in October 2007, who noticed a distinct elongation of the primary in Hubble images.[16] The binarity of the Lempo primary was eventually confirmed in a more extensive analysis of Hubble images by Susan Benecchi and collaborators in 2009.[1][6]

Due to complex discovery circumstances involving different independent groups of researchers,[19] Hiisi did not have a formal provisional designation signifying the year of its first observation or discovery.[17] Instead, it was unofficially designated "component A2" in scientific literature for being the smaller component of the central Lempo–Hiisi binary.[1] It eventually received its permanent satellite designation and name while the larger, first component A1 maintained the name Lempo on 5 October 2017.[15]

Characteristics

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Comparison of mean separation distances and diameters of trans-Neptunian close binaries including Lempo–Hiisi

The separation between the two components is only about half the diffraction limit of Hubble, making it impossible to fully resolve the system. Instead, it appears elongated in Hubble images, revealing its binary nature.

The separation between the two components is only about half the diffraction limit of Hubble, making it impossible to fully resolve the system. Instead, it appears elongated in Hubble images, revealing its binary nature.[1] This central pair has a semi-major axis of around 867 km and a period of about 1.9 days.[1] Assuming equal albedos of about 0.079, Lempo and Hiisi are approximately 272+17
−19 km and 251+16
−17 km in diameter, respectively.[9] The earlier discovered satellite Paha orbits the barycenter of the Lempo–Hiisi system.

Keplerian orbit fit suggests mutual events around 2075, but mutual perturbations may shift the timing on the order of a decade.

System dynamics

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The orbital dynamics of the Lempo system are highly complex and could not be modelled with solely Keplerian dynamics.[1][3] Many crucial parameters such as initial spin states and shapes of the individual components are unknown and thus could not adequately model the dynamics of the Lempo system as a three-body problem without leading to significantly chaotic behavior. In a 2018 dynamical study, Alexandre Correia found that simulated models using realistically assumed spin states and shapes failed to explain the presently eccentric mutual orbit of the inner Lempo–Hiisi binary, even with the inclusion of eccentricity-damping tidal forces. Correia concluded that the present orbits, spin states and shapes of all components of the Lempo system needed to be remeasured to a greater precision before a more sophisticated model could be developed.[3]

Origin

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Formation hypotheses

Physical characteristics

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Introduce the system absolute magnitude and (erroneous) dwarf planet candidate prior to discovery of its components. Mention effective diameter as a single object. (single paragraph)

Spectra and surface

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Surface composition, albedo, color, and spectroscopy/photometry studies

Internal structure

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Density, mass, and internal structure of the components.

Orbit

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Heliocentric orbit from JPL-SSD and Buie

Exploration

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Mention New Horizons 2 and other exploration proposals from Zangari et al. (2018)

References

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References

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External links


Lempo resources

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Discovery

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Trinary system

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System dynamics

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Formation

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Photometry and size/density

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Rotation(?)

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Spectra and surface

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  1. ^ a b c d e f g h i j k l m n o Cite error: The named reference Benecchi2010 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference johnston was invoked but never defined (see the help page).
  3. ^ a b c d e Cite error: The named reference Correia2018 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Brunini2020 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference IAUC7787 was invoked but never defined (see the help page).
  6. ^ a b c d Cite error: The named reference MPC-object was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference johnston-moonslist was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Benecchi was invoked but never defined (see the help page).
  9. ^ a b c d e f g Cite error: The named reference TNOsCool5 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Hainaut2012 was invoked but never defined (see the help page).
  11. ^ a b c Cite error: The named reference Grundy was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference HST-9110 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Marchis was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference IAUC7807 was invoked but never defined (see the help page).
  15. ^ a b Cite error: The named reference MPC106502 was invoked but never defined (see the help page).
  16. ^ a b Cite error: The named reference Jacobson2007 was invoked but never defined (see the help page).
  17. ^ a b Cite error: The named reference johnston-binastnames was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference Stansberry2006 was invoked but never defined (see the help page).
  19. ^ Cite error: The named reference johnston-asteroidmoonsall was invoked but never defined (see the help page).


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