The discovery of a faint glow of scattered sunlight from the dust trail ofthe Leonid parent comet 55p/Tempel-Tuttle

A meteoric cloud is the faint glow of sunlight scattered by small meteoroid s in the dust trail along the orbit of a comet as seen by an earthbound obs erver. While these clouds were previously only known from anecdotes of past meteor storms, we now report the detection of a meteoric cloud by modern t echniques in the direction of the dust trail of comet 55P/Tempel-Tuttle, th e parent of the Leonid meteor stream. Our photometric observations, perform ed on Mauna Kea, Hawaii, reveal the cloud as a local enhancement in sky bri ghtness during the Leonid shower in 1998. The radius of the trail, deduced from the spatial extent of the cloud, is approximately 0.01 AU and is consi stent with the spatial extent mapped out by historic accounts of meteor sto rms. The brightness of the cloud is approximately similar to 2%-3% of the b ackground zodiacal light and cannot be explained by simple model calculatio ns based on the zenith hourly rate and population index of the meteor strea m in 1998. If the typical size of cloud particles is 10 mu m and the albedo is 0.1, the brightness translates into a number density of 1.2 x 10(-10) m (-3). The meteoroid cloud would be the product of the whole dust trail and not only the part that was crossed in 1998.