The activity of comet C/2007 D1 (LINEAR) at 9.7 AU from the Sun

Aims. We report on the unusual distant activity of the dynamically new comet C/2007 D1 (LINEAR), observed at r(h) = 9.7 AU postperihelion. This comet is particularly interesting because of its quite large perihelion distance (r(q) = 8.8 AU). Methods. We analyse V and R band images taken at the TNG telescope to characterise the dust coma of the comet and investigate its photometry, colours, and dust production. Results. The colour of the dust is redder than the Sun (V - R = 0.505 +/- 0.093 at the photometric aperture of radius 2.2"). The Af rho value is measured to be 1983 +/- 81 cm for an aperture of radius = 2.2 ''. An upper limit to the cometary nucleus radius of a(N) <= 18 km is derived. A dust mass-loss rate of dM(d)/dt = 5.3 x 10(2) kg s(-1) is measured, which implies that C/2007 D1 (LINEAR) is a very active comet despite its quite large perihelion distance.