A giant crater on 90 Antiope?

Abstract

Mutual event observations between the two components of 90 Antiope were carried out in 2007-2008. The pole position was refined to λ 0 = 199.5±0.5° and β 0 = 39.8±5° in J2000 ecliptic coordinates, leaving intact the physical solution for the components, assimilated to two perfect Roche ellipsoids, and derived after the 2005 mutual event season (Descamps et al., 2007). Furthermore, a large-scale geological depression, located on one of the components, was introduced to better match the observed lightcurves. This vast geological feature of about 68 km in diameter, which could be postulated as a bowl-shaped impact crater, is indeed responsible of the photometric asymmetries seen on the "shoulders" of the lightcurves. The bulk density was then recomputed to 1.28 ±0.04 gcm -3 to take into account this large-scale non-convexity. This giant crater could be the aftermath of a tremendous collision of a 100-km sized proto-Antiope with another Themis family member. This statement is supported by the fact that Antiope is sufficiently porous (~50%) to survive such an impact without being wholly destroyed. This violent shock would have then imparted enough angular momentum for fissioning of proto-Antiope into two equisized bodies. We calculated that the impactor must have a diameter greater than ~17 km, for an impact velocity ranging between 1 and 4 km/s. With such a projectile, this event has a substantial 50 % probability to have occurred over the age of the Themis family.

Simultaneous spectroscopic and photometric observations of binary asteroids

“…This might indicate a common origin for the two components, a conclusion that is consistent with a recent study by Descamps et al 2009.…”

The large crater on the small Asteroid (2867) Steins

“…However, some fine details of the light curves in that work were not fully explained and another extended observing campaign was carried out by Descamps et al, 2009. In this more recent work, the shapes of the components have been corrected to fully explain the data.…”

“…The new data more fully constrain the tri-axial sizes of the 2 bodies (Table 2) and reveal a large geological feature, diameter 68 km on one of them. This was described by Descamps et al, 2009, as an impact crater, although given that it has not been directly imaged this is contentious. Further, given the nature of the observations and analysis method it is not possible to determine which of the pair contains the crater.…”

“…Expressed as a fraction of the mean radii of the two components, this putative crater has D/R between 1.54 and 1.62 (in Descamps et al, 2009 the putative crater diameter was given with respect to the mean diameter as ~0.7, which is equivalent to D/R~1.4).…”

“…There is also the recent report of a newly detected large depression on (90) Antiope (a binary asteroid with components of 86 and 91 km diameter) found by observing its light curves. The structure in the light curves has been interpreted as arising due to a bowl shaped depression on the surface of one component and it has been suggested that this may be a crater (Descamps et al, 2009). …”