3 Juno
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Template:Minor Planet
| density=3.4 g/cm³
| gravity=0.12 m/s²
| escape_velocity=0.18 km/s
| rotation=0.3004 d
| spectral_class=S-type asteroid
| abs_mag=5.33
| albedo=0.238Template:Ref
| temperature=~163 K
max: 301 K (+28° C)[5]}}
3 Juno (jew'-noh) was the third asteroid to be discovered and is one of the largest main belt asteroids. 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.
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Characteristics
Image:Moon and Asteroids 1 to 10 at 10 km per px.png Juno is close to being the seventh largest asteroid (it cannot currently be ranked relative to 52 Europa), with a mass approximately 1.0% the mass of the entire asteroid belt. It is the main body in the Juno family. Amongst the stony S-type asteroids, it is unusually reflective, which may be indicative of different surface properties.
Juno rotates in a prograde direction, with the north pole pointing towards ecliptic coordinates (β, λ) = (27°, 103°) with a 10° uncertaintyTemplate:Ref. 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 pyroxeneTemplate:Ref. 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 Template:Ref.
Infrared images reveal that it possesses an approximately 100 km wide crater or ejecta feature, the result of a geologically young impactTemplate:Ref.
Observations
Some notable observation milestones for Juno include:
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 observersTemplate:Ref.
Radar signals from spacecraft in orbit around Mars and/or on its surface have been used to estimate the mass of Juno from the tiny perturbations induced by it onto the motion of Mars.
A study by James L. Hilton (1999) suggests that Juno's orbit changed (slightly) around 1839Template:Ref, "very likely" due to perturbations from a passing asteroid, whose identity has not been determined yet. An alternate yet unlikely explanation is an impact by a sizeable body.
In 1996, Juno was imaged by the Hooker Telescope at Mount Wilson Observatory, using adaptive optics. The images spanned a whole rotation period and revealed an irregular (lumpy) shape with a dark feature, interpreted as a fresh impact site.
Aspects
A table with the aspects (opposition, conjunction to sun, etc.) of 3 Juno from 2005 to 2020.
Notes
- Template:Note E. V. Pitjeva, Estimations of Masses of the Largest Asteroids and the Main Asteroid Belt From Ranging to Planets, Mars Orbiters And Landers Solar System Resarch, Vol. 39 pp. 176 (2005).
- Template:Note Supplemental IRAS Minor Planet Survey
- Template:Note M. Kaasalainen et al Models of Twenty asteroids from photometric data, Icarus, Vol. 159, p. 369 (2002).
- Template:Note M. J. Gaffey Mineralogical variations within the S-type asteroid class, icarus, Vol. 106, pp. 573 (1993).
- Template:Note 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).
- Template:Note 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).
- Template:Note L. Millis et al The diameter of Juno from its occultation of AG+0°1022, The Astronomical Journal, Vol. 86, pp. 306 (1981).</div>
- Template:Note James L. Hilton, U.S. Naval Observatory Ephemerides of the Largest Asteroids The Astronomical Journal, Vol. 117 pp. 1077 (1999)
External links
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