148780 Altjira (provisional designation ) appears to be a triple or contact binary double classical Kuiper belt object.Johnston's Archive on (148780) Altjira Retrieved 2011-11-29 The secondary is large compared to the primary, approximately of the primary vs. to the secondary. The lightcurve is quite flat (), which is indicative of a "quasi-spherical body with a homogeneous surface". The system mass is .
In 2008, Altjira was named after the Arrernte creation deity, Altjira (Alchera).
Physical characteristics Altjira is a binary system consisting of two bodies of nearly equal size, making it a true synchronous binary rather than a typical primary-satellite system.
Size and dimensions Observations using thermal modeling indicate that the Altjira system has a combined effective diameter of approximately . The primary body has an estimated diameter of 246 (+38/−139) km, while the secondary body (the companion) possesses a radius of roughly 111 km (a diameter of ~222 km).
Density and porosity The bulk density of Altjira is exceptionally low, estimated at roughly (300 kg/m3). This makes Altjira one of the least dense known large Kuiper belt objects (KBOs). Such an incredibly low density implies that the interiors of both bodies are highly porous, resembling loose "rubble piles" rather than solid ice or rock.
Albedo and color Altjira has a relatively high geometric albedo, measured at . It exhibits a very red surface color in the visible spectrum, which is a typical trait among cold classical Kuiper belt objects.
Satellite
Altjira's companion was discovered on 6 August 2006, from images taken by the Hubble Space Telescope. The companion has no official designation. The secondary's orbit has the following parameters: semi-major-axis, ; period, ; eccentricity, ; and inclination, (retrograde). There is indirect evidence that Altjira may be an unresolved hierarchical triple system.
See also 47171 Lempo – the first and only confirmed hierarchical triple system in the Kuiper belt 58534 Logos – a contact binary and potential triple system in the cold classical Kuiper belt
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