Colour, albedo and nucleus size of Halley's comet

Halley's comet (1982 i) is now bright enough for broadband photometry by large infrared telescopes^1-3. We report here on photometry of the comet in the B (0.44 µm), J (0.55 µm), V (1.25 µm) and K (2.2 µm) broadband filters during a time when the coma was very weak and presumed to contribute negligibly to the broadband photometry. The V - J and J - K colours suggest that the colour of the nucleus of Halley's comet is similar to that of the D-type asteroids, which in turn suggests that the surface of the nucleus is of albedo < 0.1.