Linus (moon)
Large moon of asteroid 22 Kalliope, discovered in 2001.
Linus, also known as (22) Kalliope I, is a moon that circles the large M-type asteroid 22 Kalliope. Astronomers Jean-Luc Margot and Michael E. Brown spotted it on August 29, 2001, using the Keck telescope in Hawaii; a separate team confirmed the detection a few days later with the Canada-France-Hawaii Telescope, both instruments located on Mauna Kea. Initially given the provisional designation S/2001 (22) 1, it was named in July 2003 after the International Astronomical Union approved a proposal from the discovery paper. The name references the mythological Linus, son of the muse Calliope and credited with inventing melody and rhythm, but also honors Linus Torvalds, creator of the Linux operating system kernel, and Linus van Pelt from the *Peanuts* comic strip.
With a diameter estimated at 28 ± 2 km (17 ± 1 mi), Linus is exceptionally large for an asteroid moon—large enough to be a notable asteroid in its own right. In the main belt, only the smaller components of the double asteroids 617 Patroclus and 90 Antiope are known to be larger. Its orbit precesses rapidly, completing a cycle every few years, likely due to Kalliope’s non-spherical shape. Observations show that Linus’s brightness varies significantly, hinting that the moon itself may be elongated. It probably formed from impact debris after a collision with Kalliope, or as a fragment captured following the breakup of a parent asteroid, sometimes called proto-Kalliope.
- discovered
- August 29, 2001
- discoverers
- Jean-Luc Margot and Michael E. Brown
- diameter
- 28 ± 2 km
- parent_asteroid
- 22 Kalliope
- provisional_designation
- S/2001 (22) 1
- named_after
- Linus (mythological son of Calliope), Linus Torvalds, and Linus van Pelt
Lore & Background
Linus was discovered on August 29, 2001, by astronomers Jean-Luc Margot and Michael E. Brown using the Keck telescope on Mauna Kea in Hawaii. A separate team also detected the moon on September 2, 2001, using the Canada-France-Hawaii Telescope, also on Mauna Kea. It received the provisional designation S/2001 (22) 1 until its naming was approved by the International Astronomical Union in July 2003.
The naming proposal, which appeared in the discovery paper, referred to the mythological Linus, son of the muse Calliope and inventor of melody and rhythm. However, the name was also intended to honor Linus Torvalds, inventor of the Linux operating system kernel, and Linus van Pelt, a character in the Peanuts comic strip.
Linus' orbit precesses rapidly, completing one cycle in several years, primarily due to the non-spherical shape of Kalliope. Its brightness varies appreciably between observations, suggesting an elongated shape. The moon may have formed from impact ejecta from a collision with Kalliope or from a fragment captured after the disruption of a parent asteroid.
Reader's Guide
Linus is significant as one of the largest known asteroid moons in the main belt, with only the smaller components of double asteroids 617 Patroclus and 90 Antiope being larger. Its discovery and study have provided insights into the properties of the M-type asteroid 22 Kalliope, including its low density and non-spherical shape, which influence Linus' rapid orbital precession. The moon's variable brightness suggests an elongated shape, and its origin remains uncertain—either from impact ejecta or from a captured fragment of a disrupted parent body. The naming of Linus is notable for its triple homage: to a mythological figure, to a computer scientist, and to a comic strip character, reflecting a blend of classical and modern cultural references. As a relatively large moon, Linus helps astronomers understand the formation and evolution of binary asteroid systems in the main belt.
Did You Know?
- Linus has an estimated diameter of 28 ± 2 km, making it very large compared to most asteroid moons.
- Its name honors both the mythological Linus and Linus Torvalds, inventor of the Linux kernel.
- Linus' orbit precesses rapidly due to the non-spherical shape of its parent asteroid, 22 Kalliope.
- The moon was independently detected by two teams using telescopes on Mauna Kea in 2001.
More in Discoveries by Michael E. Brown 1-24
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