# A dearth of small members in the Haumea family revealed by OSSOS

## Abstract

While collisional families are common in the asteroid belt, only one is known in the Kuiper belt, linked to the dwarf planet Haumea. The characterization of Haumea’s family helps to constrain its origin and, more generally, the collisional history of the Kuiper belt. However, the size distribution of the Haumea family is difficult to constrain from the known sample, which is affected by discovery biases. Here, we use the Outer Solar System Origins Survey (OSSOS) Ensemble to look for Haumea family members. In this OSSOS XVI study we report the detection of three candidates with small ejection velocities relative to the family formation centre. The largest discovery, 2013 UQ15, is conclusively a Haumea family member, with a low ejection velocity and neutral surface colours. Although the OSSOS Ensemble is sensitive to Haumea family members to a limiting absolute magnitude (Hr) of 9.5 (inferred diameter of ~90 km), the smallest candidate is significantly larger, Hr = 7.9. The Haumea family members larger than 20 km in diameter must be characterized by a shallow H-distribution slope in order to produce only these three large detections. This shallow size distribution suggests that the family formed in a graze-and-merge scenario, not a catastrophic collision.

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## Data availability

The data that support the plots within this paper are available from the corresponding author upon reasonable request.

## Code availability

The survey simulator is available publicly from the OSSOS webpages: http://www.ossos-survey.org/simulator.html. A detailed description of usage is available29.

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## Acknowledgements

This work is based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France–Hawaii Telescope (CFHT) that is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii. We recognize and acknowledge the very significant cultural role of the summit of Maunakea. We are most fortunate to have the opportunity to conduct observations from this mountain. B.C.N.P., D.R. and S.M. acknowledge support from a BYU Mentored Environment Grant.

## Author information

R.E.P. tested the models using the survey simulator, determined the mass and population estimate, and wrote most of the paper draft. B.C.N.P. generated the orbital distribution models used, and S.M., D.R. and B.C.N.P. classified the objects as Haumea family member candidates. M.A. assisted with the mass estimate and generating the approximate Pan-STARRS1 survey simulator blocks. M.A., M.T.B., Y.-T.C., B.J.G., J.J.K., S.G. and K.V. did the object detections and survey characterization for the OSSOS survey.

Correspondence to Rosemary E. Pike.

## Ethics declarations

### Competing interests

The authors declare no competing interests.