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.
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