A planetesimal orbiting within the debris disc around a white dwarf star.

Acknowledgments: This work is based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in La Palma, Canary Islands. This work has made use of data from the European Space Agency (ESA) mission Gaia (www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium [(DPAC), www.cosmos.esa.int/web/gaia/dpac/consortium]. Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Based on observations made with European Southern Observatory (ESO) Telescopes at the La Silla Paranal Observatory under program IDs: 595.C-0650. Funding: This research has been carried out with telescope time awarded by the CCI International Time Programme. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC grant agreement 320964 (WDTracer). T.R.M. acknowledges support from STFC (ST/P000495/1). J.D.L acknowledges the funding support of the Natural Sciences and Engineering Research Council of Canada. D.V. acknowledges the support of the STFC via an Ernest Rutherford Fellowship (grant ST/P003850/1). M.R.S. is thankful for support from Fondecyt (1141269). A.J.M. and M.B.D. acknowledge the support of KAW project grant 2014.0017. A.J.M. also acknowledges the support of VR grant 2017-04945. O.T. was partially supported by a Leverhulme Trust Research Project Grant. F.M. acknowledges support from the Royal Society Dorothy Hodgkin Fellowship. P.R.-G. acknowledges support provided by the Spanish Ministry of Economy, Industry and Competitiveness through grant AYA-2017-83383-P, which is partly funded by the European Regional Development Fund of the European Union. This research was supported by the Jet Propulsion Laboratory through the California Institute of Tec