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\begin{document}

\title{The Venus Life Equation}



\author[1]{Noam Izenberg}%
\author[2]{Diana M. Gentry}%
\author[2]{David L. Smith}%
\author[2]{Penelope J. Boston}%
\author[3]{David Grinspoon}%
\author[4]{Grzegorz Slowik}%
\author[5]{Mark Bullock}%
\author[6]{Martha Gilmore}%
\affil[1]{JHU Applied Physics Laboratory}%
\affil[2]{ARC}%
\affil[3]{PSI}%
\affil[4]{Univ. Zielona Góra}%
\affil[5]{Sci. Tech. Corp.}%
\affil[6]{Wesleyan University}%


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  \date{May 14, 2024}


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\begin{abstract}
Does life currently exist, or did life once exist, on other worlds in
our solar system? The proximity of the rocky planets of our solar
system, Venus and Mars, make them obvious targets for the first attempts
to answer these questions via direct exploration, with concomitant
implications for, and input to, how we think of exoplanets. Given the
limited resources we have to explore our neighbors in space, an
ecological assessment (based on terrestrial ecosystem principles) might
help us target our search and methodology. Studies of extreme life on
Earth consistently reveal adaptability. Mars has been the target of many
life-related investigations {[}1, many others{]}. Venus has not, yet
there may be compelling reasons to think about extant life on the second
planet {[}2{]}, and lessons to learn there about searching for life
elsewhere in the solar system and beyond. The Venus Life Equation: Venus
may have been habitable for billions of years its history and may still
be habitable today. Our current state of knowledge of the past climate
of Venus suggests that the planet may have had an extended period --
perhaps 1-2 billion years -- where a water ocean and a land ocean
interface could have existed on the surface, in conditions possibly
resembling those of Archaean Earth {[}3{]}. At present, Venus' surface
is not hospitable to life as we know it, but there is a zone of the
Venus middle atmosphere, \textasciitilde{}55 km altitude, just above the
sulfuric acid cloud layer, where the combination of pressure,
temperature, and gas-mix are more Earth-like than anywhere else in the
solar system {[}2, 4{]}. The question of whether life could have -- or
could still -- exist on the Earth's closest neighbor is more open today
than it's ever been. Here we approach the question of present-day life
on Venus in a manner analogous to the Drake Equation {[}5{]}, treating
the possibility of current Venus life as an exercise in informal
probability -- seeking qualitatively the likelihood or chance of the
answer being nonzero.The working version of the Venus Life Equation is
expressed as: L = O * R * A where L is the likelihood (zero to 1) of
there being life on Venus in the present-day, O (origination) is the
chance life ever began and ``broke out'' on Venus, R (robustness) is the
potential current and historical size of diversity of the Venus
biosphere, A (acceptability) is the chance that conditions amenable to
live persisted spatially and temporally to the present. The Venus Life
Equation is a work-in-progress as a pre-decadal White Paper {[}6{]} and
its variables are currently being refined. {[}1{]} McKay 1997, Springer,
Dordrecht, 1997. 263-289. {[}2{]} Limaye et al. 2018 Astrobiology,
18(9), 1181-1198. {[}3{]} Way et al. 2016 JGR 43(16) 8376-8383. {[}4{]}
Schulz-Makuch et al. 2004 Astrobiology 4, 11-18. {[}5{]} Burchell 2006,
Int. J. Astrobio, 5(3) 243-250. {[}6{]} Izenberg et al. 2020,
https://is.gd/vd4JE7 (location of Latest version of Venus Life Equation
White Paper).%
\end{abstract}%



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