22 Kalliope
A large M-type asteroid with a moon, Linus.
22 Kalliope is a large asteroid in the main belt, discovered by J. R. Hind on 16 November 1852. Its name comes from Calliope, the Greek Muse of epic poetry. The asteroid has a small moon called Linus.
Kalliope is somewhat elongated and slightly asymmetric, with a diameter of about 166 km. This measurement, taken from observations of mutual eclipses between Kalliope and Linus using the VLT at the European Southern Observatory, is 8% smaller than earlier estimates from IRAS. Its spectrum is M-type, suggesting a surface that may partly consist of iron–nickel metal. The asteroid’s density is roughly 3.4 g/cm³. Because Kalliope is likely a rubble pile with a possible porosity of 20–40%, the material density would be between 4.2 and 5.8 g/cm³, indicating a mix of metal and silicates. However, spectroscopic studies show evidence of hydrated minerals and silicates, pointing to a stony surface composition. Its low radar albedo also argues against a purely metallic surface.
Lightcurve analysis places Kalliope’s pole near ecliptic coordinates (β, λ) = (−23°, 20°) with a 10° uncertainty, giving it an axial tilt of 103° and a slightly retrograde rotation. Between 2004 and 2021, the asteroid was observed to occult fifteen stars. In 2022, it was found to belong to an asteroid family that formed about 900 million years ago; its moon Linus may have formed at the same time.
Kalliope’s only known natural satellite, Linus, is about 28 km in diameter—large enough to be a notable asteroid on its own. It orbits roughly 1100 km from Kalliope’s center, or about 13.2 Kalliope radii. Linus was discovered on 29 August 2001 by Jean-Luc Margot and Michael E. Brown; another team led by William Merline independently detected the moon three days later.
On 7 November 2006, the first stellar occultation by an asteroid’s satellite (Linus) was successfully observed by a group of Japanese observers. The prediction had been made just one day earlier by Berthier et al., based on over five years of regular observations of the Kalliope binary system using adaptive optics on ground-based telescopes. The observed chords of Linus allowed an estimate of its size at 20–28 km.
- Discovery date
- 16 November 1852
- Discoverer
- J. R. Hind
- Diameter
- approximately 166 km
- Density
- about 3.4 g/cm3
- Axial tilt
- 103°
- Moon name
- Linus
- Moon diameter
- about 28 km
Lore & Background
22 Kalliope is somewhat elongated, approximately 166 km in diameter, and slightly asymmetric, as evidenced by resolved images taken with the VLT at the European Southern Observatory. This diameter, measured by observing mutual eclipses of Kalliope and Linus, is 8% smaller than that calculated from IRAS observations. Its spectrum is M-type, indicating a surface that may be partially composed of iron–nickel metal, but spectroscopic studies have shown evidence of hydrated minerals and silicates, suggesting a stony surface composition. The asteroid's density is about 3.4 g/cm3, and since it is likely a rubble pile with a possible porosity of 20–40%, the material density is 4.2–5.8 g/cm3, meaning Kalliope is probably made of a mixture of metal with silicates. It also has a low radar albedo, inconsistent with a purely metallic surface. Lightcurve analysis indicates that Kalliope's pole most likely points towards ecliptic coordinates (β, λ) = (−23°, 20°) with a 10° uncertainty, giving it an axial tilt of 103°, and its rotation is slightly retrograde. Between 2004 and 2021, 22 Kalliope has been observed to occult fifteen stars. In 2022, it was discovered that 22 Kalliope is part of an asteroid family that formed about 900 million years ago, and its moon, Linus, may have been formed at the same time.
Reader's Guide
22 Kalliope is significant as a large M-type asteroid that challenges simple compositional models. Its surface shows signs of both metal and hydrated silicates, and its low radar albedo contradicts a purely metallic interpretation, suggesting a complex history. The asteroid's moon, Linus, discovered on 29 August 2001 by Jean-Luc Margot and Michael E. Brown, is about 28 km in diameter and orbits about 1100 km from Kalliope's center. The first stellar occultation by an asteroid's satellite was observed for Linus on 7 November 2006, allowing its size to be estimated at 20–28 km. Kalliope's membership in an asteroid family that formed about 900 million years ago, with Linus possibly forming at the same time, provides insight into the evolution of binary asteroids. Its density and inferred porosity indicate it is a rubble pile, likely a mixture of metal and silicates, making it a key object for understanding the internal structure and composition of M-type asteroids.
Frequently Asked Questions
Who discovered 22 Kalliope and when?
J. R. Hind identified this main-belt asteroid on 16 November 1852, making it one of the earlier large asteroids catalogued in the nineteenth century.
Where does the name 22 Kalliope come from?
It is named after Calliope, the Greek Muse presiding over epic poetry, following the long tradition of giving asteroids the names of figures from classical mythology.
What is 22 Kalliope made of and how dense is it?
Its M-type spectral signature points to a surface that likely contains significant iron–nickel metal, and its bulk density of roughly 3.4 g/cm³ is consistent with a substantial metallic core component.
Does 22 Kalliope have a moon?
Yes — it hosts a small satellite called Linus, and the mutual eclipses between the two bodies have been used to refine measurements of Kalliope's true size.
What shape and size is 22 Kalliope?
Kalliope is noticeably elongated and slightly lopsided, spanning about 166 km across, and it tumbles with a pronounced axial tilt of roughly 103°, giving it a distinctive rolling rotation.
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