Lightning in the atmosphere of Venus is either ubiquitous, rare, or
non-existent, depending on
how one interprets diverse observations. Quantifying when and where, or
even if lightning
occurs would provide novel information about Venus’s atmospheric
dynamics and chemistry.
Lightning is also a potential risk to future missions, which could float
in the cloud layers (~50–
70 km above the surface) for up to an Earth-year. Over decades,
spacecraft and ground-based
telescopes have searched for lightning at Venus using many instruments,
magnetometers, radios, and optical cameras. Two optical surveys (from
the Akatsuki orbiter and
the 61-inch telescope on Mt. Bigelow, Arizona) observed several flashes
at 777 nm (the
unresolved triplet emission lines of excited atomic oxygen) that have
been attributed to lightning.
This conclusion is based, in part, on the statistical unlikelihood of so
many meteors producing
such energetic flashes, based in turn on the presumption that a low
fraction (< 1%) of a meteor’s
optical energy is emitted at 777 nm. We use observations of terrestrial
meteors and analogue
experiments to show that a much higher conversion factor
(~5–10%) should be expected.
Therefore, we calculate that smaller, more numerous meteors could have
caused the observed
flashes. Lightning is likely too rare to pose a hazard to missions that
pass through or dwell in the
clouds of Venus. Likewise, small meteors burn up at altitudes of
~100 km, roughly twice as high
above the surface as the clouds, and also would not pose a hazard.