Pasiphaë group

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The Pasiphaë group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Pasiphaë and are thought of have a common origin.

Their semi-major axes (distances from Jupiter) range between 22.8 and 24.1 million km (the same range as the Carme group), their inclinations between 144.5° and 158.3°, and their eccentricities between 0.25 and 0.43.

This diagram illustrates the largest irregular satellites of Jupiter. Among the Pasiphaë group, Sinope and Pasiphaë itself are labelled. An object's position on the horizontal axis indicates its distance from Jupiter. The vertical axis indicates its inclination. Eccentricity is indicated by yellow bars illustrating the object's maximum and minumum distances from Jupiter. Circles illustrate an object's size in comparison to the others.

Core members of the group include (from the largest to the smallest):^[1]

• Pasiphae
• Sinope, two-thirds the size of Pasiphaë
• Callirrhoe
• Megaclite
• Autonoe
• Eurydome
• Sponde

The International Astronomical Union (IAU) reserves names ending in -e for all retrograde moons, including this group's members.

[edit] Origin

The Pasiphaë group is believed to have been formed when Jupiter captured an asteroid which subsequently broke up after a collision. The original asteroid was not disturbed heavily: the original body is calculated to have been 60 km in diameter, about the same size as Pasiphaë; Pasiphaë retains 99% of the original body's mass. However, if Sinope belongs to the group, the ratio is much smaller, 87%.^[2]

Unlike the Carme and Ananke groups, the theory of a single impact origin for the Pasiphaë group is not accepted by all studies. This is because the Pasiphaë group, while similar in semi-major axis is more widely dispersed in inclination ¹ . However, Secular resonances, known for both Pasiphae and Sinope, could shape the orbits and provide the explanation for the post-collision dispersal of the orbital elements.^[3] Alternatively, Sinope might be not a part of the remnants of the same collision and captured independently instead.^[4]

The differences of colour between the objects (grey for Pasiphaë, light red for Callirrhoe and Megaclite) also suggest that the group could have a more complex origin than a single collision.^[4]

This diagram compares the orbital elements and relative sizes of the core members of the Pasiphaë group. The horizontal axis illustrates their average distance from Jupiter, the vertical axis their orbital inclination, and the circles their relative sizes.

This diagram compares the wide dispersion of the Pasiphaë group (red) with the more compact Ananke (blue) and Carme (green) groups.

¹ Nesvorny 2003, concurring on Ananke and Carme groups, lists only Megaclithe for Pasiphae

[edit] References

1. ^ Scott S. Sheppard, David C. Jewitt, Carolyn Porco Jupiter's outer satellites and Trojans, In: Jupiter. The planet, satellites and magnetosphere. Edited by Fran Bagenal, Timothy E. Dowling, William B. McKinnon. Cambridge planetary science, Vol. 1, Cambridge, UK: Cambridge University Press, ISBN 0-521-81808-7, 2004, p. 263 - 280 Full text(pdf).
2. ^ Sheppard, Scott S.; Jewitt, David C. (May 5, 2003). "An abundant population of small irregular satellites around Jupiter". Nature 423: 261–263. DOI:doi:10.1038/nature01584.  However, Nesvorny 2003, while concurring on the Ananke and Carme groups, lists only Megaclithe for Pasiphaë's group
3. ^ David Nesvorný, Cristian Beaugé, and Luke Dones Collisional Origin of Families of Irregular Satellites, The Astronomical Journal, 127 (2004), pp. 1768–1783 Full text.
4. ^ ^{a b} Grav, Tommy; Holman, Matthew J.; Gladman, Brett J.; Aksnes, Kaare Photometric survey of the irregular satellites, Icarus, 166,(2003), pp. 33-45. Preprint