121 Hermione
121 Hermione is a large, dark main-belt asteroid named after a figure from Greek mythology and notable for its irregular shape, carbon-rich surface, and small natural satellite.
121 Hermione is a large asteroid in the outer part of the main asteroid belt, orbiting the Sun between Mars and Jupiter. It belongs to the numbered minor planets and was the 121st such body to receive a permanent number. Hermione is generally described as a dark, carbon-rich asteroid, meaning it reflects little sunlight and is thought to preserve material similar to some of the Solar System's early primitive matter.
The asteroid was discovered in 1872 by the American astronomer James Craig Watson and was named after Hermione of Greek mythology, the daughter of Menelaus and Helen. Like many nineteenth-century asteroid names, it follows the custom of drawing from classical myth. Over time, observations of its brightness and outline showed that Hermione is not close to spherical. Instead, it has an irregular, elongated form that has sometimes been compared to a contact-binary or heavily lopsided body.
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Physical characteristics
Hermione is one of the larger dark asteroids known, with a diameter on the order of a few hundred kilometers. Its surface appears very dark, consistent with carbonaceous material. Studies of its changing light curve, together with direct imaging from large telescopes, have helped astronomers model its three-dimensional shape. Those results suggest a body that may be fractured or loosely assembled rather than a single solid rock.
An important development came when a small moon was discovered orbiting Hermione in the early 2000s. The presence of this satellite made the system especially valuable, because the moon's orbit allows astronomers to estimate Hermione's mass. When that mass is compared with its size, the resulting density has been taken as evidence that the asteroid may contain substantial empty space inside, a trait often associated with a rubble-pile structure created by ancient impacts and reassembly.
Why it matters
- It is a major example of a large, low-albedo main-belt asteroid.
- Its irregular shape helps researchers study how collisions alter asteroid bodies.
- Its moon provides a way to measure mass more directly than for many solitary asteroids.
- The system contributes to broader work on asteroid composition, density, and internal structure.
Hermione is not among the brightest asteroids for casual observers, but it has scientific importance because it connects several themes in planetary science: primitive composition, impact history, and binary formation. As telescope imaging and orbit modeling have improved, 121 Hermione has become a useful case for understanding how large asteroids evolve over billions of years in the crowded environment of the main belt.
Related articles
Author
AlegsaOnline.com 121 Hermione Leandro Alegsa
URL: https://en.alegsaonline.com/art/111142
Sources
- adsabs.harvard.edu : "Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey"
- adsabs.harvard.edu : "Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit"
- cfa-www.harvard.edu : "IAUC 7980"
- astron.berkeley.edu : 121 Hermione and S/2002 (121) 1
- cfa-www.harvard.edu : Discovery Circumstances: Numbered Minor Planets
- cfa-www.harvard.edu : IAUC 8264
- psi.edu : Supplemental IRAS minor planet survey
- psi.edu : PDS node taxonomy database