Several searches for near-Earth objects have recently been initiated, as a
result of increased awareness of the hazard of impacts on the Earth. These
programs mainly search for asteroids, so amateur astronomers can still cont
ribute to the discovery of comets, especially out of the orbital plane of t
he Solar System. An ideal way to search for comets would be to use a spaceb
orne instrument capable of imaging the whole sky on a daily basis in a syst
ematic and repeatable way. Such an instrument already exists on the solar o
bservatory SOHO; it operates at the Lyman-alpha wavelength of neutral hydro
gen, which is the main component of the emission cloud of a comet. Here we
report the discovery, using archival data from this satellite, of a hithert
o unnoticed comet which reached a perihelion of 1.546 a.u. on 26 June 1997.
We derive the water production rate of the comet as a function of time and
rnd that it increases after perihelion, like that of comet Halley.