Contact binary (small Solar System body)

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A contact binary is a small Solar System body, such as a minor planet or comet, that is composed of two bodies that have gravitated toward each other until they touch, resulting in a bilobated, peanut-like overall shape. Contact binaries are distinct from true binary systems such as binary asteroids where both components are separated. The term is also used for stellar contact binaries.

An example of a contact binary is the Kuiper belt object 486958 Arrokoth, which was imaged by the New Horizons spacecraft during its flyby in January 2019.[1]

History

The existence of contact binary asteroids was first speculated by

Lagrange points, which allowed for low-speed collisions between planetesimals to take place and form contact binaries.[6]: 1915  The hypothesis of Hektor's contact binary nature contributed to the growing evidence of the existence of binary asteroids and asteroid satellites, which were not discovered until the Galileo spacecraft's flyby of 243 Ida and Dactyl 1993.[4]
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Until 1989, contact binary asteroids have only been inferred from the high-amplitude U-shape of their light curves. The first visually confirmed contact binary was the

radar imaging by the Arecibo Observatory and Goldstone Solar System Radar in August 1989.[7] These radar observations were led by Steven J. Ostro and his team of radar astronomers, who published the results in 1990.[7] In 1994, Ostro and his colleague R. Scott Hudson developed and published a three-dimensional shape model of Castalia reconstructed from the 1989 radar images, providing the first radar shape model of a contact binary asteroid.[8]

In 1992, the

2001 QG298 with the University of Hawaiʻi's 2.24-m telescope at Mauna Kea, as part of a survey dedicated to measuring the light curves of KBOs.[9] With their results published in 2004, they discovered that 2001 QG298 exhibits a large, U-shaped light curve amplitude characteristic of contact binaries, providing the first evidence of contact binary KBOs.[9] Sheppard and Jewitt identified additional contact binary candidates from other KBOs known to exhibit large light curve amplitudes, hinting that contact binaries are abundant in the Kuiper belt.[9]

The contact binary nature of comets was first suspected after the

Jupiter family comet 103P/Hartley in 2010 also revealed a thick-necked, peanut-shaped nucleus similar to 19P/Borelly. By that time, half of the comets that have been imaged in detail were known to be bilobate, which implied that contact binaries in the comet population are similarly abundant as contact binaries in other minor planet populations.[11]
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Formation and evolution

Generally, contact binary objects in the Solar System form when two objects collide at speeds slow enough that their shapes do not become disrupted. However, the mechanisms leading to this differ depending on the size and orbital location of the object.

Near-Earth asteroids

Collisional fragments[13]: 218 

Due to their close proximity to the Sun, the evolution of near-Earth asteroid (NEA) shapes and binary systems is dominated by the uneven reflection of sunlight off their surfaces, which causes gradual orbital acceleration by the

Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect
.

High-mass ratio and doubly-synchronous binary systems such as 69230 Hermes are plausible sources for contact binaries in the NEA population, since they are subject to the binary YORP effect, which acts over timescales of 1,000–10,000 years to either contract the components' orbits until they contact, or expand their orbits until they become gravitationally detached asteroid pairs.[14]: 166–167 [15]: 430  The origin of contact binaries from doubly-synchronous binaries in the NEA population is evident from the fact that very few doubly-synchronous binary NEAs are known, whereas contact binary NEAs are much more common.[14]: 167  For doubly-synchronous binary systems with 1 km (0.62 mi)-diameter components, the tangential and radial impact velocities when they collide are less than 50 mm/s (2.0 in/s), which are low enough to not disrupt the shapes of the two bodies.[14]: 167 

In 2007, Daniel J. Scheeres proposed that contact binary asteroids in the NEA population can undergo rotational fissioning after being rotationally accelerated by the YORP effect.[16] Depending on the relative sizes and shapes of the fissioned components, there are three possible evolutionary pathways for contact binary NEAs.[16]: 384  Firstly, if the primary component is elongated and dominates the mass of the system, the secondary will either escape the system or collide with the primary since the orbits of the fissioned components are unstable.[16]: 384  Secondly, if the primary component is elongated and accounts for roughly half of the system's mass, the secondary can temporarily orbit the primary before it will collide with the primary, reforming the contact binary but with a different distribution of the system mass.[16]: 384  Thirdly, if the primary is spheroidal and dominates the mass of the system, the fissioned components can remain in long-lasting orbits as a stable binary system.[16]: 384  As shown by these cases, it is unlikely that fissioned contact binaries can form stable binaries.[17]: L58 

In 2011, Seth A. Jacobson and Scheeres expanded upon their 2007 theory of binary fission and proposed that NEAs can go through repeated cycles of fissioning and reimpacting through the YORP effect.[14]: 167 

Trans-Neptunian objects

In the trans-Neptunian region and especially the Kuiper belt, binary systems are thought to have formed from the direct collapse of gas and dust from the surrounding protoplanetary nebula due to streaming instability. Through impacts and gravitational perturbations by the outer planets, the mutual orbits of binary trans-Neptunian objects contract and eventually destabilize to form contact binaries.[18]: 59 

Geophysical properties

Impacts on one of the lobes of contact binary rubble pile asteroids do not cause significant disruption to the asteroid as the shockwave produced by the impact is damped by the asteroid's rubble pile structure and then blocked by the discontinuity between the two lobes.[19]

Occurrence

Near-Earth asteroids

In 2022, Anne Virkki and colleagues published an analysis of 191 near-Earth asteroids (NEAs) that were observed by the Arecibo Observatory radar from December 2017–2019. From this sample, they found that 10 out of the 33 (~30%) NEAs larger than 200 m (660 ft) in diameter were contact binaries, which is double the previously estimated percentage of 14% for contact binaries of this diameter in the NEA population.[20]: 24  Although the sample size is small and therefore not statistically significant, it could imply that contact binaries could be more common than previously thought.[20]: 24 

Kuiper belt

In 2015–2019, Audrey Thirouin and Scott Sheppard performed a survey of KBOs from the

H ≥ 6) are contact binaries consisting of nearly equal-mass components,[22]: 12  whereas at least 10–25% of the population of cold classical KBOs of the same size range are contact binaries.[21]: 16  The differing contact binary fractions of these two populations imply they underwent different formation and evolution mechanisms.[21]
: 17 

Thirouin and Sheppard continued their survey of KBOs in 2019–2021, focusing on the twotino population in the 1:2 orbital resonance with Neptune.[23]: 2–3  They found that 7–14% of twotinos are contact binaries, which is relatively low albeit similar to the contact binary fraction of the cold classical population.[23]: 9  Thirouin and Sheppard noted that the twotinos' contact binary fraction is consistent with predictions by David Nesvorný and David Vokrouhlický in 2019, who suggested that 10–30% of dynamically excited and resonant Kuiper belt populations are contact binaries.[23]: 9 [18]: 59 

486958 Arrokoth is the first confirmed example of a contact binary KBO, seen through stellar occultations in 2018 and spacecraft imaging in 2019.

A stellar occultation by the KBO 19521 Chaos on 29 March 2023 revealed that it had an apparently bilobate shape 380 km (240 mi) across, which could potentially make it the largest known contact binary object in the Solar System.[24] However, the bilobate shape seen in the occultation could well be two binary components transiting each other during the event; this is supported by the smaller-than-expected size of Chaos measured in the occultation.[25]

Comets

Irregular moons

The Cassini spacecraft observed several irregular moons of Saturn at various phase angles while in it was orbit around Saturn from 2004–2017, which allowed for the determination of rotation periods and shapes of the Saturnian irregular moons. In 2018–2019, researchers Tilmann Denk and Stefan Mottola investigated Cassini's irregular moon observations and found that Kiviuq, Erriapus, Bestla, and Bebhionn exhibited exceptionally large light curve amplitudes that may indicate contact binary shapes, or potentially binary (or subsatellite) systems.[26]: 422  In particular, the light curve amplitude of Kiviuq is the largest of the irregular moons observed by Cassini, which makes it the most likely candidate for a contact binary or binary moon.[26]: 422 [27]: 101  Considering that the irregular moons have most likely undergone or were formed by disruptive collisions in the past, it is possible that the fragments of disrupted irregular moons could remain gravitationally bound in orbit around each other, forming a binary system that would eventually become a contact binary.[26]: 421 

Examples

distant minor planets, the icy Kuiper belt object Arrokoth was confirmed to be a contact binary when the New Horizons spacecraft flew past in 2019.[1] The small main-belt asteroid 152830 Dinkinesh was confirmed to have the first known contact binary satellite after the Lucy probe flew by it on November 1, 2023.[31]

See also

References

  1. ^ a b "Ultima Thule is first contact binary to be explored by a spacecraft". UPI. Retrieved 21 September 2019.
  2. Bibcode:1971NASSP.267..155C. Archived from the original on 10 March 2022. Retrieved 11 November 2023.{{cite conference}}: CS1 maint: bot: original URL status unknown (link
    )
  3. ^
    Bibcode:1978BAAS...10..597H
    .
  4. ^
    doi:10.1016/0019-1035(80)90147-5
    .
  5. doi:10.1126/science.207.4434.976
    .
  6. Bibcode:1979LPSC...10.1897H
    .
  7. ^
    S2CID 119245876
    .
  8. doi:10.1126/science.263.5149.940
    .
  9. ^
    S2CID 119486610
    .
  10. doi:10.1016/j.icarus.2003.05.001
    .
  11. ^
    doi:10.1088/2041-8205/734/1/L2
    . L2.
  12. ^
    doi:10.1016/j.icarus.2009.12.026
    .
  13. doi:10.1006/icar.1996.0046
    .
  14. ^
    S2CID 119245876
    .
  15. doi:10.1016/j.icarus.2005.02.001
    .
  16. ^
    doi:10.1016/j.icarus.2007.02.015
    .
  17. doi:10.1086/516572
    .
  18. ^
    doi:10.1016/j.icarus.2019.04.030
    .
  19. doi:10.1038/30911
    .
  20. ^
    doi:10.3847/PSJ/ac8b72
    . 222.
  21. ^
    doi:10.3847/1538-3881/ab18a9
    . 228.
  22. doi:10.3847/1538-3881/aac0ff
    . 248.
  23. ^
    doi:10.3847/PSJ/ac7ab8
    . 178.
  24. ^ Leiva, Rodrigo (22 September 2023). "A stellar occultation by Chaos 2023-09-28 07:14 UTC: a possible contact binary and search for a satellite". groups.io. Archived from the original on 11 November 2023. Retrieved 10 November 2023.
  25. Bibcode:2023pses.conf80462G
    . 80462.
  26. ^
    ISBN 9780816537488
    .
  27. S2CID 127269198
    .
  28. ^ Quick Rosetta update: Churyumov-Gerasimenko is a contact binary!
  29. ^ Success! A final flawless burn. Rosetta now in tandem with its comet
  30. ^ The formation mechanism of 4179 Toutatis' elongated bi-lobed structure in a close Earth encounter scenario
  31. ^ Kretske, Katherine. "NASA's Lucy Surprises Again, Observes 1st-ever Contact Binary Orbiting Asteroid - NASA Science". science.nasa.gov. Retrieved 9 November 2023.
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