A polar vortex in 3-D at Venus' south pole, as seen by the VIRTIS instrument on board ESA's Venus Express.
Credit: ESA / VIRTIS-VenusX / INAF-IASF /Obs. de Paris-LESIA (G. Piccioni, IASF-INAF)
Venus is more Earth-like than previously thought—including lightning where theory held that none could exist.
Venus is the world closest to Earth in terms of size, mass, distance and chemical makeup, but while Earth is a haven for life, Venus is typically described as hellish, with a crushing atmosphere holding choking clouds of sulfuric acid over a rocky desert surface hot enough to melt lead.
The Venus Express mission that the European Space Agency launched in 2005 is now shedding light not just how Venus became the daunting world it is, but also how it still remains somewhat Earth-like.
The spacecraft intriguingly found evidence of lightning on the planet, even though none should exist. The clouds of Venus are like smog clouds on Earth, which do not generate lightning here.
The probe did not actually see visible flashes in Venus' sky, but it did spot "whistlers"—low-frequency radio waves that last for a split-second and are thought to come from electrical discharges.
"We consider this the first definitive evidence of abundant lightning on Venus," said researcher David Grinspoon. "So how much lightning is there? If the high latitudes are typical, we can extrapolate to the planet as a whole there are about 50 lightning flashes per second, about half the rate on Earth, but it's possibly higher."
Just as lightning alters chemistry on Earth—creating ozone and smog components such as nitrogen oxides—so too do researchers expect lightning to have profound effects on Venus. "New models of Venus' atmosphere and climate need to include this new fact," Grinspoon said.
Venus Express also focused on vast rotating vortexes of clouds at Venus' poles. These vortexes are reminiscent of vortexes that appear over the poles on Earth in the winter of each hemisphere. Although the vortexes on Venus are larger and more energetic than Earth's, in many respects they are quite similar, researchers said.
The space mission also shed light on how Earth-like Venus was. For instance, Venus may have had Earth-like oceans in its distant past, but its searing hot surface cannot sustain water now. Although vast volumes of water vapor are not now seen in Venus' atmosphere, new findings suggest how a great deal of water may have been lost.
Venus does not have a strong magnetic field as Earth does, meaning that sunlight could then have broken up the water into hydrogen and oxygen that then easily escaped the planet's atmosphere. Scientists had seen hydrogen leaving from Venus, but now they also have seen oxygen depart.
"Learning about the escape rates of hydrogen and oxygen will help us reconstruct how much water Venus had in the past," Grinspoon said. "Venus may have lost at least up to an Earth's ocean's worth of water."
The scientists discussed their findings in a teleconference with reporters today and detail the work in the Nov. 29 issue of the journal Nature.