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3 Juno

392px-Juno 4 wavelengths

Juno seen at four wavelengths. A large crater appears dark at 934 nm.


3 Juno (jew'-noe (key)) was the third asteroid to be discovered and is one of the largest main belt asteroids, being the heaviest of the stony S-type. It was discovered on September 1, 1804 by German astronomer Karl L. Harding, using a humble 2-inch telescope. It was named after the mythological figure Juno, the highest Roman goddess. The adjectival form of the name is Junonian.

Characteristics

Moon and Asteroids 1 to 10 at 10 km per px

Size comparison: the first 10 asteroids profiled against Earth's Moon. Juno is third from the left.

Juno is one of the largest asteroids, containing approximately 1.0% the mass of the entire asteroid belt. In a ranking by size, it is in the lower teens. It vies with 15 Eunomia for the honour of being the largest of the stony S-type asteroids, although the newest estimates put Juno in second place. Amongst S-types it is unusually reflective, which may be indicative of different surface properties. It is the main body in the Juno family.

Juno rotates in a prograde direction, with the north pole pointing towards ecliptic coordinates (β, λ) = (27°, 103°) with a 10° uncertainty[1]. This gives an axial tilt of 51°.

Spectroscopic studies of the Junonian surface permit the conclusion that Juno could be the body of origin of ordinary chondrites, a common group of stony meteorites composed of iron-containing silicates such as olivine and pyroxene[2]. The maximum temperature on the surface, when the sun is overhead, was measured at about 293 K on October 2, 2001. Taking into account also the heliocentric distance at the time, gives an estimated maximum of 301 K (+28°C) at perihelion [3].

Infrared images reveal that it possesses an approximately 100 km wide crater or ejecta feature, the result of a geologically young impact[4].

Observations

Juno was the first asteroid for which an occultation was observed. It passed in front of a dim star (SAO 112328) on February 19, 1958. Since then, several occultations by Juno have been observed, the most fruitful being on December 11, 1979, which was registered by 18 observers.[5]

Radio signals from spacecraft in orbit around Mars and on its surface have been used to estimate the mass of Juno from the tiny perturbations induced by it onto the motion of Mars.[6] Juno's orbit appears to have changed slightly around 1839, very likely due to perturbations from a passing asteroid, whose identity has not been determined. An alternate but less likely explanation is an impact by a sizeable body.[7]

In 1996, Juno was imaged by the Hooker Telescope at Mount Wilson Observatory at visible and near-IR wavelengths, using adaptive optics. The images spanned a whole rotation period and revealed an irregular shape and a dark albedo feature, interpreted as a fresh impact site.[4]

Animation
Juno mpl anim
Juno moving across background stars.
Star field
3Juno-LB1-apmag
Juno during opposition in 2009.

Aspects

Stationary,
retrograde
Opposition Distance to
Earth (AU)
Maximum
brightness (mag)
Stationary,
prograde
Conjunction
to Sun
November 2, 2005 December 9, 2005 1.06025 7.5 January 16, 2006 February 24, 2005
February 19, 2007 April 10, 2007 2.13320 9.7 June 5, 2007 September 2, 2006
April 18, 2008 June 12, 2008 2.28071 10.1 August 10, 2008 November 14, 2007
August 15, 2009 September 21, 2009 1.18972 7.6 October 31, 2009 January 18, 2009
January 24, 2011 March 13, 2011 1.78236 8.9 May 1, 2011 July 10, 2010
March 27, 2012 May 20, 2012 2.37727 10.2 July 20, 2012 October 23, 2011
June 14, 2013 August 4, 2013 1.67506 8.9 September 21, 2013 December 23, 2012
December 17, 2014 February 1, 2015 1.33782 8.2 March 12, 2015 April 13, 2014
March 7, 2016 April 28, 2016 2.30641 10.0 June 27, 2016 September 28, 2015
May 9, 2017 July 3, 2017 2.07904 9.7 August 27, 2017 November 30, 2016
October 20, 2018 November 22, 2018 1.03276 7.4 December 31, 2018 February 16, 2018
February 14, 2020 April 4, 2020 2.07425 9.6 May 29, 2020 August 25, 2019
April 14, 2021 June 8, 2021 2.31368 10.1 August 6, 2021 November 9, 2020

References

  1. M. Kaasalainen et al Models of Twenty asteroids from photometric data, Icarus, Vol. 159, p. 369 (2002).
  2. M. J. Gaffey Mineralogical variations within the S-type asteroid class, icarus, Vol. 106, pp. 573 (1993).
  3. L. F. Lim et al Thermal infrared (8-13μm) spectra of 29 asteroids: the Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) Survey, Icarus, Vol. 173, pp. 385 (2005).
  4. 4.0 4.1 Mt Wilson Observatory S. Baliunas et al Multispectral analysis of asteroid 3 Juno taken with the 100-inch telescope at Mount Wilson Observatory, Icarus, Vol. 163, pp 135 (2003).
  5. Millis, R. L., Wasserman, L. H.; Bowell, E.; Franz, O. G.; White, N. M.; Lockwood, G. W.; Nye, R.; Bertram, R.; Klemola, A.; Dunham, E.; Morrison, D. (February 1981). "The diameter of Juno from its occultation of AG+0°1022". Astronomical Journal 86: 306–313. DOI:10.1086/112889.
  6. Pitjeva, E. V. (2004). "Estimations of masses of the largest asteroids and the main asteroid belt from ranging to planets, Mars orbiters and landers". 35th COSPAR Scientific Assembly. Held 18–25 July 2004, in Paris, France, 2014.
  7. Hilton, James L. (February 1999). "US Naval Observatory Ephemerides of the Largest Asteroids". Astronomical Journal 117 (2): 1077–1086. DOI:10.1086/300728. Retrieved on 2012-04-15.

External links

See also


Minor planets
Previous minor planet 3 Juno Next minor planet
List of asteroids
The minor planets
Vulcanoids | Near-Earth asteroids | Main belt | Jupiter Trojans | Centaurs | Damocloids | Comets | Trans-Neptunians (Kuiper belt · Scattered disc · Oort cloud)
For other objects and regions, see: asteroid groups and families, binary asteroids, asteroid moons and the Solar system
For a complete listing, see: List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.

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