Debate has raged for decades over whether there is lightning on Venus. From the Venera and Pioneer Venus missions in the 1970s there seemed to be evidence in favour of it, and similarly from Galileo in 1990. But during two flybys, in 1998 and 1999, Cassini found nothing. New data from the European Space Agency's Venus Express offer the latest proof that the cloudy skies of Venus are indeed riven by electromagnetic discharges.

Among a clutch of mission papers now published in Nature, C. T. Russell et al. report the detection of whistler-mode waves, propagating from the planet's atmosphere to its ionosphere (Nature 450, 661–662; 2007). The waves are nearly circularly polarized, are at frequencies close to 100 Hz and appear in bursts lasting between 0.25 and 5 seconds — exactly as would be expected, say the authors, of lightning in venusian clouds.

Venus Express arrived at the planet in April 2006, after a 153-day journey from Earth. Russell and colleagues' evidence is derived from 37 orbits made during May and June 2006. Extrapolating the rate of lightning observed using the magnetometer on board Venus Express to a rate experienced across the whole planetary surface suggests that lightning is triggered half as often on Venus as on Earth (only about 50 times per second). Nevertheless, its very presence is tantalizing: the high temperatures around the lightning discharge make possible some chemical processes that might not otherwise occur.

The mission is scheduled to last until May 2009, at which point Venus Express will have been in orbit for roughly four venusian sidereal days.