Radiation astronomy/Kuiper belts

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Known objects in the Kuiper belt, are derived from data from the Minor Planet Center. Credit: WilyD.

The Kuiper belt is a region of the solar system extending from the orbit of Neptune (at 30 AU to approximately 60 AU from the Sun.[1] It consists mainly of small bodies.

"[B]roadband optical photometry of Centaurs and Kuiper Belt objects from the Keck 10 m, the University of Hawaii 2.2 m, and the Cerro Tololo InterAmerican (CTIO) 1.5 m telescopes [shows] a wide dispersion in the optical colors of the objects, indicating nonuniform surface properties. The color dispersion [may] be understood in the context of the expected steady reddening due to bombardment by the ubiquitous flux of cosmic rays."[2]

In the image at right, objects in the main part of the Kuiper belt are coloured green, while scattered objects are coloured orange. The four outer planets are blue. Neptune's few known trojans are yellow, while Jupiter's are pink. The scattered objects between Jupiter's orbit and the Kuiper belt are known as centaurs. The scale is in astronomical units. The pronounced gap at the bottom is due to difficulties in detection against the background of the plane of the Milky Way.


Axes list distances in AU, projected onto the ecliptic, with ecliptic longitude zero being to the right, along the "x" axis).

Positions are accurate for January 1st, 2000 (J2000 epoch) with some caveats:

For planets, positions should be exact.

For minor bodies, positions are extrapolated from other epochs assuming purely Keplerian motion. As all data is from an epoch between 1993 and 2007, this should be a reasonable approximation.

Data from the Minor Planet Center[3] or Murray and Dermott[4] as needed.

Radial "spokes" of higher density in this image, or gaps in particular directions are due to observational bias (i.e. where objects were searched for), rather than any real physical structure. The pronounced gap at the bottom is due to obscuration by the band of the Milky Way.


"These authors proposed that the whole-disk surface colors of KBOs could be the result of the competition between the effects of irradiation of surface organics by cosmic-rays and the global resurfacing due to impacts. [...] When these high-energy protons collide with an icy target, they penetrate very [deep] under the surface."[5]


"The depth of the absorption bands and the continuum reflectance of [Kuiper Belt Object] 1996 TO66 suggest the presence of a black- to slightly blue-colored, spectrally featureless particulate material as a minority component mixed with the water ice."[6]

Ultima Thule[edit]

Ultima Thule is a contact binary object, composed of two individual objects fused together. Credit: Alan Stern, New Horizons, NASA.{{fairuse}}
Polar view is of 2014 MU69. Credit: Johns Hopkins University Applied Physics Laboratory.{{free media}}

Greyscale view of 2014 MU69 on the right was taken by the Ralph, or Multispectral Visible Imaging Camera (MVIC) aboard New Horizons on 1 January 2019, from a distance of 6,700 kilometres (4,200 mi).[7]

"Obtained with the wide-angle Multicolor Visible Imaging Camera (MVIC) component of New Horizons' Ralph instrument, this image was taken when the KBO was 4,200 miles (6,700 kilometers) from the spacecraft, at 05:26 UT (12:26 a.m. EST) on Jan. 1."[7]

The contact binary object is made up of two lobes named "Ultima" (right) and "Thule" (left).[7]

Its axis of rotation is located near the bright "neck" of the object and spins clockwise from this viewpoint.[8]}}

"This movie shows the propeller-like rotation of Ultima Thule in the seven hours between 20:00 UT (3 p.m. ET) on Dec. 31, 2018, and 05:01 UT (12:01 a.m.) on Jan. 1, 2019."[8]

The image on the left is a composite of two photographs taken respectively by the Long Range Reconnaissance Imager (LORRI) and the Ralph (MVIC) instruments aboard New Horizons on 1 January 2019. The spacecraft was 137,000 kilometres (85,000 mi) away from 2014 MU69 when this image was taken.[9]

This image was "taken at a distance of 85,000 miles (137,000 kilometers) at 4:08 Universal Time on January 1, 2019, [...] is an enhanced color image taken by the Multispectral Visible Imaging Camera (MVIC)) [...]."[9]

Kilometre-sized Kuiper belt objects[edit]

Enlargement (b) of the light curves (a) with error bars representing the detector readout noise and target shot noise overlaid with the best-fit theoretical light curve (black line). Credit: Ko Arimatsu, K. Tsumura, F. Usui, Y. Shinnaka, K. Ichikawa, T. Ootsubo, T. Kotani, T. Wada, K. Nagase and J. Watanabe.{{fairuse}}

"Kuiper belt objects (KBOs) [have a] size distribution of kilometre-sized (radius = 1–10 km). [...] These kilometre-sized KBOs are extremely faint, and it is impossible to detect them directly. Instead, the monitoring of stellar occultation events is one possible way to discover these small KBOs6,7,8,9. [This is] the first detection of a single occultation event candidate by a KBO with a radius of ~1.3 km, which was simultaneously provided by two low-cost small telescopes coupled with commercial complementary metal–oxide–semiconductor cameras. [The] surface number density of KBOs with radii exceeding ~1.2 km is ~6 × 105 deg−2. This surface number density favours a theoretical size distribution model with an excess signature at a radius of 1–2 km (ref. 5). If this is a true KBO detection, this implies that planetesimals before their runaway growth phase grew into kilometre-sized objects in the primordial outer Solar System and remain as a major population in the present-day Kuiper belt."[10]

Regarding the two graphs in the right image: "Light curves of the occultation event candidate obtained with the two OASES observation systems. a, Light curves of an occulted star as a function of the time offset t from the central time of the occultation event candidate obtained with OASES-01 (blue line) and OASES-02 (red line), respectively, normalized to average fluxes. The equatorial coordinates of the occulted star are right ascension = 18 h 29 m 02.7 s and declination = −23° 02′ 34.6′′, while the ecliptic coordinates are λ = 276.7° and β = +0.2°. The Gaia G band magnitude31 of the star is 12.1. The central time of the occultation candidate is estimated to be 12 h 56 m 05.283 s ut on 28 June 2016. The signal-to-noise ratios derived from the light curves of OASES-01 and OASES-02 are 4.9 and 5.4, respectively. [...] b, Enlargement of the light curves with error bars representing the detector readout noise and target shot noise overlaid with the best-fit theoretical light curve (black line). The main noise source is the detector readout noise, and typical error bar sizes are ~0.21 and ~0.17 for OASES-01 and OASES-02, respectively. [These] error sizes are comparable to actual standard deviations of the light curves (0.20 and 0.18 for OASES-01 and OASES-02, respectively). Open blue and red circles correspond to the theoretical light curve integrated over each bin (15.4 Hz interval). Note that the timings of the OASES-01 and OASES-02 exposures are not synchronized. Assuming that the spherical occulting object lies on a circular KBO orbit with an inclination of 0.2°, the best-fit KBO radius, impact parameter and distance yield 1.3-0.10.8 km, 0.6-0.31.4 km and 33-3+17 au, respectively. The best-fit χ2 value from the fit is 7.0, with 12 d.f."[10]

Scattered disks[edit]

The diagram shows scattered disc objects out to 100 AU. Credit: Eurocommuter.

Scattered Disk Objects (up to 100 AU): Kuiper Belt objects are shown in grey, resonant objects within the Scattered Disk are shown in green.

The position of an object represents

  • its orbit’s semi-major axis a in AU and the orbital period in years (horizontal axis)
  • its orbit’s inclination i in degrees (vertical axis).

The size of the circle illustrates the object’s size relative to others. For a few large objects, the diameter drawn represents the best current estimates. For all others, the circles represent the absolute magnitude of the object.

The eccentricity of the orbit is shown indirectly by a segment extending from the left (perihelion) to the aphelion to the right. In other words, the segment illustrates the variations of the object's distance from the Sun. Objects with nearly circular orbits will show short segments while highly elliptical orbits will be represented by long segments.

Main resonances with Neptune are marked with vertical bars; 1:1 marks the position of Neptune’s orbit (and its Trojan asteroids), 2:3 marks the orbit of Pluto (and plutinos) etc.

Oort clouds[edit]

An artist's rendering is of the Oort cloud and the Kuiper belt (inset). Credit: NASA.{{free media}}

The Oort cloud or the Öpik–Oort cloud[11] is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun.[12] This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance.[13]

See also[edit]


  1. Alan Stern; Colwell, Joshua E. (1997). "Collisional Erosion in the Primordial Edgeworth-Kuiper Belt and the Generation of the 30–50 AU Kuiper Gap". The Astrophysical Journal 490 (2): 879–882. doi:10.1086/304912. 
  2. Jane Luu and David Jewitt (November 1996). "Color Diversity among the Centaurs and Kuiper Belt Objects". The Astronomical Journal 112 (5): 2310-8. http://adsabs.harvard.edu/full/1996AJ....112.2310L. Retrieved 2013-11-05. 
  3. The MPC Orbit (MPCORB) Database.
  4. Carl D. Murray and Stanley F. Dermott (1999). Solar System Dynamics. Cambridge University Press. ISBN 0 521 57295.9 Check |isbn= value: invalid character (help).
  5. R Gil-Hutton (January 2002). "Color diversity among Kuiper belt objects: The collisional resurfacing model revisited". Planetary and Space Science 50 (1): 57-62. http://www.sciencedirect.com/science/article/pii/S0032063301000733. Retrieved 2014-01-23. 
  6. Robert H. Brown, Dale P. Cruikshank, and Yvonne Pendleton (July 1, 1999). "Water Ice on Kuiper Belt Object 1996 TO66". The Astrophysical Journal 519 (1): L101-4. doi:10.1086/312098. http://iopscience.iop.org/1538-4357/519/1/L101/fulltext/. Retrieved 2013-06-01. 
  7. 7.0 7.1 7.2 Johns Hopkins University Applied Physics Laboratory (24 January 2019). "New Horizons' Newest and Best-Yet View of Ultima Thule". Retrieved 24 January 2019.
  8. 8.0 8.1 Johns Hopkins University Applied Physics Laboratory (15 January 2019). "New Movie Shows Ultima Thule from an Approaching New Horizons". Retrieved 16 January 2019.
  9. 9.0 9.1 Johns Hopkins University Applied Physics Laboratory (1 January 2019). "First color image of Ultima Thule". Retrieved 2 January 2019.
  10. 10.0 10.1 Ko Arimatsu, K. Tsumura, F. Usui, Y. Shinnaka, K. Ichikawa, T. Ootsubo, T. Kotani, T. Wada, K. Nagase and J. Watanabe (28 January 2019). "A kilometre-sized Kuiper belt object discovered by stellar occultation using amateur telescopes". Nature Astronomy. doi:10.1038/s41550-018-0685-8. https://www.nature.com/articles/s41550-018-0685-8. Retrieved 30 January 2019. 
  11. Fred Lawrence Whipple, G. Turner, J. A. M. McDonnell, M. K. Wallis (1987-09-30). "A Review of Cometary Sciences". Philosophical Transactions of the Royal Society A (Royal Society Publishing) 323 (1572): 339–347 [341]. doi:10.1098/rsta.1987.0090. http://rsta.royalsocietypublishing.org/content/323/1572/339.short. 
  12. Alessandro Morbidelli (2006). Origin and dynamical evolution of comets and their reservoirs of water ammonia and methane. arXiv:astro-ph/0512256.
  13. Kuiper Belt & Oort Cloud. NASA. Retrieved 2011-08-08.

External links[edit]