Dear ARPS Member,

Our observing campaign to study the unusual asteroid (846) Lipperta has now finished. It has lasted 130 days in all and the results are rather unexpected.

The vast majority of asteroids rotate once every 4-40 hours but it seems that Lipperta stands apart in that it looks to be one of, if not THE slowest rotator amongst ALL the small solar system bodies currently known.

Bob Buchheim and Gordon Gartrelle first discovered its exceptional slow rotation in 2010-2011 (Minor Planet Bulletin 38, 151-153 (2011)). Their incomplete lightcurve strongly suggested Lipperta takes a full 68 days to spin once.

As you can see from the attached, we have sort of confirmed Bob and Gordon's discovery, but with certain provisos.

The lightcurve does not repeat itself exactly, i.e. within the uncertainty limits of the photometry. This could be a consequence of the change in the aspect of the asteroid as seen from Earth over a 4-month timespan. Alternatively, but less likely, is the possibility that the object may be showing comet-like activity that changes its apparent brightness by approx. 5% or so. Cometary activity has been recently claimed for this object by Ferrin et al. Thirdly, there may be an extremely slow rotation about its non-principal spin axis. My feeling is that the first explanation is the most probable although this has yet to be checked out.

Richard Miles
2017 June 22