Asteroid Juno: An Underestimated Giant of the Solar System

Scientific Summary

Juno (3 Juno), discovered in 1804 by Karl Harding, is one of the largest S-type asteroids in the main belt. Its irregular dimensions of 320 × 267 × 200 km (mean diameter ~234 km) reveal a massive body composed of silicates and metals, representative of the rocky materials of the protoplanetary disk. Juno's surface is marked by a huge impact crater, probably resulting from a violent collision. Through its composition, size and traces of visible cataclysmic events, Juno constitutes a fossil of the primitive Solar System. It illuminates the diversity of materials present in the protoplanetary disk and the processes that prevented the formation of a planet between Mars and Jupiter, a region disturbed by the gravity of the latter.

What is asteroid Juno and what is its scientific importance in the main belt?

Juno, officially designated 3 Juno, is the third asteroid discovered (1804) and one of the largest in the main belt, with an average diameter of about 234 km and irregular dimensions of 320 × 267 × 200 km. Astronoo's article presents it as an "underestimated giant", whose study is crucial for several reasons. Firstly, its S-type classification indicates a composition of silicates and metals, making it a witness to the diversity of materials present in the protoplanetary disk. Secondly, Juno has a remarkable feature: a huge impact crater, probably caused by a collision with another body. The study of this structure, although its exact dimensions remain to be specified, offers a window into the violent collision history that shaped not only asteroids but also planets. Finally, its rapid rotation (7.2 hours) and its orbit (2.67 AU, period of 4.36 years) make it a dynamically interesting object. The article emphasizes that Juno, like other large listed asteroids (Ceres, Pallas, Vesta), is a fossil of the formation of the Solar System, because the main belt represents a region where planet formation was prevented by Jupiter's gravitational perturbations.

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Asteroid Juno: a large asteroid

Juno, officially designated 3 Juno, is one of the largest asteroids in the main belt. Discovered in 1804 by German astronomer Karl Harding, Juno is the third asteroid to have been identified, after Ceres and Pallas.

Orbit and rotation

Asteroid Juno orbits the Sun at an average distance of 2.67 astronomical units, with an orbital period of about 4.36 Earth years. Its rotation is rapid, with a period of only 7.2 hours, which is relatively short for an asteroid of this size.

Scientific importance

Juno is of great interest to astronomers due to its composition and size. Studies of this asteroid can provide valuable information on the formation and evolution of the solar system. In addition, its surface shows signs of impact craters, which can help understand the collision history in the asteroid belt.

Table of the largest asteroids

The 25 largest asteroids in the main belt
Rank	Name	Number	Mean diameter	Spectral type	Year of discovery
1	Ceres	1	940 km	C (dwarf planet)	1801
2	Vesta	4	525 km	V	1807
3	Pallas	2	512 km	B	1802
4	Hygiea	10	430 km	C	1849
5	Interamnia	704	326 km	F	1910
6	Europa	52	315 km	C	1858
7	Davida	511	289 km	C	1903
8	Sylvia	87	286 km	X	1866
9	Hektor	624	250 km	D (Jovian Trojan)	1907
10	Euphrosyne	31	248 km	C	1854
11	Juno	3	240 km	S	1804
12	Psyche	16	226 km	M	1852
13	Cybele	65	222 km	X	1861
14	Thisbe	88	218 km	B	1852
15	Camilla	107	215 km	C	1868
16	Herculina	532	212 km	S	1872
17	Doris	48	210 km	C	1857
18	Iris	7	200 km	S	1847
19	Patientia	451	198 km	C	1899
20	Amphitrite	29	195 km	S	1854
21	Lutetia	21	190 km	M	1852
22	Bamberga	324	185 km	C	1892
23	Egeria	13	180 km	G	1850
24	Electra	130	178 km	G	1873
25	Eunomia	15	175 km	S	1851

References

NASA/JPL, Small-Body Database: 3 Juno, ssd.jpl.nasa.gov/sbdb.cgi?sstr=3 (new window)
IAU Minor Planet Center, 3 Juno — Observations and Ephemerides, minorplanetcenter.net (new window)
Carry, B. (2012), Density of asteroids, Planetary and Space Science 73, 98–118, DOI: 10.1016/j.pss.2012.03.009 (new window)
DeMeo, F. E. & Carry, B. (2014), Solar System evolution from compositional mapping of the asteroid belt, Nature 505, 629–634, DOI: 10.1038/nature12908 (new window)
Kaasalainen, M. et al. (2002), Models of twenty asteroids from photometric data, Icarus 159, 369–395, DOI: 10.1006/icar.2002.6907 (new window)
Warner, B. D., Harris, A. W., & Pravec, P. (2009), The asteroid lightcurve database, Icarus 202, 134–146, DOI: 10.1016/j.icarus.2009.02.019 (new window)
Johnston’s Archive, Asteroid dimensions and physical data, johnstonsarchive.net/astro/asteroidmoons.html (new window)
Wikipedia (EN), 3 Juno, en.wikipedia.org/wiki/3_Juno (new window)

FAQ: Everything you need to know about asteroid Juno (3 Juno)

What is asteroid Juno and when was it discovered?

Juno, officially designated 3 Juno, is a large main-belt asteroid. It was discovered in 1804 by German astronomer Karl Harding, making it the third asteroid identified in history, after Ceres (1801) and Pallas (1802).

What are the main physical characteristics of Juno?

Juno is an S-type asteroid, composed primarily of silicates and metals. Its shape is irregular with dimensions of about 320 × 267 × 200 kilometers (mean diameter 234 km). Its rotation period is very rapid, about 7.2 hours, and it orbits the Sun at an average distance of 2.67 astronomical units (AU), with an orbital period of 4.36 Earth years.

Why is Juno a scientifically important object?

Juno is important for several reasons:

Its size and composition (S-type) make it a major representative of the rocky-metallic materials of the main belt.
It has a huge impact crater, the study of which helps to understand the collision history in the Solar System and their effects on the internal structure of asteroids.
Like other large asteroids, it is a fossil from the era of Solar System formation, providing clues about primitive processes.

What is known about the large crater on Juno?

The article mentions the presence of a huge impact crater on Juno's surface, the result of a violent collision with another body. Although the exact dimensions of the crater are not precisely known, it could cover a significant portion of the surface. Its analysis, via telescope data, makes it possible to estimate the energy of the impact and study the asteroid's internal structure.

What is Juno's position in the main asteroid belt?

Juno is located in the main belt, a region situated between the orbits of Mars and Jupiter (between 300 and 600 million kilometers from the Sun). This zone contains several hundred thousand objects, which could not form a planet because of Jupiter's gravitational perturbations. Juno is one of the largest members of this belt.

Where does Juno rank in terms of size among the largest asteroids?

According to the table provided in the article, Juno (3 Juno) is the 12th largest asteroid on the list presented, with dimensions of 320 × 267 × 200 km. It is preceded by giants like Ceres (974.6 km), Pallas, Vesta, Hygiea, and others, but remains a major object in the main belt.