Context : Asteroid ( 7 ) Iris is an ideal target for disk-resolved imaging owing to its brightness ( V \sim 7–8 ) and large angular size of 0.33″ during its apparitions .
Iris is believed to belong to the category of large unfragmented asteroids that avoided internal differentiation , implying that its current shape and topography may record the first few 100 Myr of the solar system ’ s collisional evolution .

Aims : We recovered information about the shape and surface topography of Iris from disk-resolved VLT/SPHERE/ZIMPOL images acquired in the frame of our ESO large program .

Methods : We used the All-Data Asteroid Modeling ( ADAM ) shape reconstruction algorithm to model the 3D shape of Iris , using optical disk-integrated data and disk-resolved images from SPHERE and earlier AO systems as inputs .
We analyzed the SPHERE images and our model to infer the asteroid ’ s global shape and the morphology of its main craters .

Results : We present the 3D shape , volume-equivalent diameter D _ { { eq } } =214 \pm 5 km , and bulk density \rho =2.7 \pm 0.3 g ⋅ cm ^ { -3 } of Iris .
Its shape appears to be consistent with that of an oblate spheroid with a large equatorial excavation .
We identified eight putative surface features 20–40 km in diameter detected at several epochs , which we interpret as impact craters , and several additional crater candidates .
Craters on Iris have depth-to-diameter ratios that are similar to those of analogous 10 km craters on Vesta .

Conclusions : The bulk density of Iris is consistent with that of its meteoritic analog based on spectroscopic observations , namely LL ordinary chondrites .
Considering the absence of a collisional family related to Iris and the number of large craters on its surface , we suggest that its equatorial depression may be the remnant of an ancient ( at least 3 Gyr ) impact .
Iris ’ s shape further opens the possibility that large planetesimals formed as almost perfect oblate spheroids .
Finally , we attribute the difference in crater morphology between Iris and Vesta to their different surface gravities , and the absence of a substantial impact-induced regolith on Iris .