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Indirect detections of massive — presumably Jupiter-like — planets orbiting nearby Sun-like stars have recently been reported1,2. Rocky, Earth-like planets are much more difficult to detect, but clues to their possible existence can nevertheless be obtained from observations of the circumstellar debris disks of dust from which they form. The presence of such disks has been inferred3 from excess far-infrared emission but, with the exception of beta Pictoris4, it has proved difficult to image these structures directly as starlight dominates the faint light scattered by the dust5. A more promising approach is to attempt to image the thermal emission from the dust grains at submillimetre wavelengths6,7. Here we present images of such emission around Fomalhaut, beta Pictoris and Vega. For each star, dust emission is detected from regions comparable in size to the Sun's Kuiper belt of comets. The total dust mass surrounding each star is only a few lunar masses, so any Earth-like planets present must already have formed. The presence of the central cavity, approximately the size of Neptune's orbit, that we detect in the emission from Fomalhaut may indeed be the signature of such planets.

The magnitude and timescale of variations in the luminosity of quasars provide crucial constraints on the mechanism of emission and the physical size of the emitting region. We have observed variations by a factor of two in the infrared flux from the bright quasar 3C273 on a timescale as short as one day. Variations of this magnitude, over such short periods, are unprecedented. In February 1988, the behaviour of the source changed from having a stable infrared flux and slow optical variations (on timescales of weeks or months) to a state characterized by recurrent infrared and optical flaring. The optical variations were of several per cent per day, changing from increase to decrease approximately every week. The amplitude of the repeated optical flares was 30–40%. The data are consistent with re-injection/acceleration of electrons followed by rapid cooling. The inferred magnetic field is 0.7 gauss and the data are marginally consistent with no relativistic beaming.