7 Iris

Iris is an S-type asteroid. Its surface likely exhibits albedo differences, with possibly a large bright area in the northern hemisphere.[9] Overall the surface is very bright and is probably a mixture nickel-iron metals and magnesium- and iron-silicates. Its spectrum is similar to that of L and LL chondrites with corrections for space weathering,[10] so it may be an important contributor of these meteorites. Planetary dynamics also indicates that it should be a significant source of meteorites.[11]

Among the S-type asteroids, Iris ranks fifth in geometric mean diameter after Eunomia, Juno, Amphitrite and Herculina.

Star rich field showing asteroid Iris (apmag 10.1)

Iris's bright surface and small distance from the Sun make it the fourth-brightest object in the asteroid belt after Vesta, Ceres, and Pallas. It has a mean opposition magnitude of +7.8, comparable to that of Neptune, and can easily be seen with binoculars at most oppositions. At typical oppositions it marginally outshines the larger though darker Pallas.[12] But at rare oppositions near perihelion Iris can reach a magnitude of +6.7 (last time on October 31, 2017 reaching a magnitude of +6.9),[7] which is as bright as Ceres ever gets.

A study by Hanus et al. using data from the VLT's SPHERE instrument names eight craters, and seven recurring features who remain nameless due to a lack of consistency and their occurrence on the edge of Iris. The tentative naming scheme is that of colors in Latin. It is unknown whether these names are accepted by the IAU. All 8 features are craters, the remaining 7 features are unknown, and are named A through G.[13]

Lightcurve analysis indicates a somewhat angular shape and that Iris's pole points towards the ecliptic coordinates (β, λ) = (10°, 20°) with a 10° uncertainty.[6] This gives an axial tilt of 85°, so that on almost a whole hemisphere of Iris, the sun does not set during summer, and does not rise during winter. On an airless body this gives rise to very large temperature differences.