This document assesses the probability of finding life or remnants of life on Venus. While Venus' current surface conditions of extreme heat and acid rain make life unlikely, the planet may have been habitable in the past. Venus shares characteristics with Earth that could support life, such as carbon, water, nitrogen and oxygen in its atmosphere. Life may have originated on Venus or been transferred there from Earth via meteorites. While surface life seems impossible, atmospheric conditions could allow for life similar to extremophiles on Earth. Anthropic activity is a possible explanation for chemical imbalances in Venus' atmosphere, suggesting life may exist there. In conclusion, finding life on Venus is possible based on the planet's history and chemistry, though current evidence

1. Kieran Jeffs 26028042 Life in the Cosmos
Assess the probability of finding life, or the
remains of life, on Venus
With no magnetic field, sulphuric acid rain and a blisteringly hot surface temperature, the question of whether or
not the solar system’s hottest planet will prove to harbour life seems a simple one to answer. Whilst such
conditions appear to make the prospect of Venusian life laughably unlikely, evidence from extremophiles here on
Earth as well as the more hospitable conditions on Venus in the past mean there is an argument to be had. In
addition, Venus shares many of the characteristics that have helped life develop on Earth. It, too, is a rocky planet,
and can also rely on the meteor deflecting services of Jupiter’s massive gravitational pull. A clearer picture of
whether or not Venus is compatible with life can be revealed by determining whether or not it has the ingredients
that made life possible on Earth, such as carbon and liquid water, and by seeing if the difficulties thrown up by the
planet’s harsh environment are surmountable. Doing so shows that the prospect of finding life, or its remains, on
the second planet from the sun is not as fanciful as it at first appears, and can in fact be considered a tentative
possibility.
The first and most obvious question to ask when considering if life is possible on Venus is whether or not it has the
necessary chemical ingredients. From this perspective Venus’s surface temperature and pressure, in excess of
700K and 90 atmospheres respectively, create immediate difficulty by removing the possibility of liquid water
existing on the planet’s surface [1]. This would be lethal to all equivalent forms of life on Earth’s surface, for whom
liquid water plays a fundamental role as a solvent which cells can use to transport various life-essential molecules
[2]. It has, however, been speculated that water’s biological niche could be filled by other chemicals. Carbon
dioxide is a supercritical fluid (which can dissolve molecules like a liquid) under Venus’s surface conditions, and
could potentially be used as a biosolvent there [3]. Supercritical CO2, and several other chemicals [4], could
therefore potentially replace water, although many are inferior on account of being unable to dissolve as many
molecules as effectively [4]. The speculative nature of non-water-based biochemistry also means that it should be
considered only as a possibility, not a catch all solution to problems for surface life. Non-surface life, on the other
hand, is a firmer proposition as conditions in the upper atmosphere allow for the limited presence of water vapour
[5], and so for the potential development of more familiar life. Water aside, the most important chemical
ingredient for Earth’s life is carbon. On Earth, carbon is used in all organisms on account of its ability to bond with
hydrogen, nitrogen and oxygen to form organic molecules, and the way in which it can form complex molecule
chains through bonding with itself [6]. Other elements such as silicon have been proposed as realistic alternatives
that could replace carbon on the surface [7], but current understanding is insufficient to make this more than
another speculative possibility. A more attractive proposition is again the planet’s upper reaches, as 96.5% of the
atmosphere of Venus consists of stable carbon dioxide (fig. 1) [8]. Whilst it may appear that such an
overwhelmingly CO2 environment is itself a fatal impediment to lifeforms, it has been shown that this is not the
case; both bacteria and certain types of algae are capable of surviving under similar conditions [9]. With carbon
and water discussed, the two most significant ingredients left to address when considering Earthlike life are
nitrogen and oxygen, both of which are also present in the Venusian atmosphere [10]. There are a variety of other
chemical components utilized by Earthlike life which it would be beyond the scope of this essay to address, except
to say that the more important ones (such as phosphorus and assorted cations) are present in Venus’s atmosphere

2. Kieran Jeffs 26028042 Life in the Cosmos
and that, whilst the scarcity of certain components might limit the quantity of life, the present materials would be
sufficient to cater for at least some Earthlike organisms [12]. Even so, it should be reasserted that complete,
unquestioning chauvinism towards the biological chemistry on Earth should be approached with caution, as there
is no absolute need for any particular element or compound that we see in Earth’s organisms to be necessary for
those on Venus [13].
Liquid water was a necessary component for the formation of life on Earth in another regard; it provided a place
for organic molecules spontaneously generated in the air to accumulate and eventually form living organisms (the
primordial soup) [14]. Fortunately, Earthlike habitable conditions may have existed on Venus for some time before
the planet reached its current temperature, having fallen victim to a runaway greenhouse effect [15]. The exact
duration of this period is unknown, but it lies in the range of 600 million to 2 billion years and it is therefore
possible that life had enough time to take hold [16]. Consequently, Organisms which evolved in a primordial soup
like that on Earth before adapting to the changing conditions could exist, in addition to those who evolved more
recently in a soup of supercritical CO2 or similar. Moreover, even if the habitable window was too brief to allow for
the spontaneous formation of life (abiogenesis) on Venus, it is still possible that life could have been transferred to
there from space (panspermia) [17]. It has been shown that organisms are capable of surviving the vacuum of
space long enough to travel between Earth and Venus, and so the idea of meteoric ejecta from the Earth bringing
organisms to Venus is a noteworthy alternative to abiogenesis [18]. The meteorite that contributed to the downfall
of the dinosaurs ejected around half of its mass back into space following impact, of which 0.1% reached Venus;
sufficiently large for the transfer of life [19]. It was demonstrated in 2001 that bacterial spores were capable of
surviving a simulation of this process, from impact to ejection to re-entry [20]. It seems therefore that the chances
of life starting on Venus are, at worst, no less favourable than on Earth.
Should the lack of liquid water be overcome, the temperature and pressure on Venus’s surface would still inhibit
the development of Earthlike life on several fronts. Firstly, and most simply, these temperatures would be
sufficient to kill any form of life on Earth, indeed being above the temperature used for medical sterilization [21].
No known form of life on Earth is capable of withstanding these temperatures for an extended period of time, with
even the hardiest of extremophiles such as the Tardigrade capable of enduring only a little over 420K [22]. It is
arguable, however, that this is not necessarily the death knell for any hope of life on Venus’s surface. One could
assert that the reason no Terrestrial life is capable of withstanding such conditions is because there is no
Figure 1. Graphical representation of Venus’s atmospheric composition. Notable features are the
overwhelming dominance of CO2, the significant quantity of SO2 (sulphuric acid) and the presence of H2O
(water droplets) [11].

3. Kieran Jeffs 26028042 Life in the Cosmos
evolutionary necessity to do so under Earth’s milder environment. Furthermore, Terrestrial life has shown itself to
be capable of adapting to thrive in extreme temperature environments, such as the thermophilic bacteria which
have been observed to exist in the planet’s boiling springs [23]. Whilst these organisms are fairly simple and can
still only withstand temperatures of around 350K, it can be contended that this is simply because that is the
benchmark needed to survive in their particular environment. The significant point remains that life can
demonstrably adapt to survive in high temperature environments, and so life on Venus’s surface would only need
to extend upon what has already been shown to be possible. Indeed, from a thermodynamic perspective, there is
no way in which Earth’s temperature is more preferable to Venus’s for life and, whilst the exact chemistry such a
lifeform would use is unknown, this is primarily a result of lack of research rather than lack of possibility [24].
Furthermore, Earth’s high pressure environment dwelling extremophiles (Piezophiles) have been able to develop
techniques to overcome the difficulties that Venus’s pressure would bring. For example, high pressure ocean
dwelling organisms have developed novel ways of transporting material through the cell membrane, which
becomes increasingly impermeable to vital nutrients in such environments [25]. Piezophiles on Earth have been
discovered to thrive at pressures in excess of 380 atmospheres, with some species of bacteria capable of surviving
at over 1000 atmospheres; comfortably higher than the surface pressure of Venus (fig 2.) [26]. One can therefore
see that pressure alone is unlikely to be responsible for any lack of life on Venus’s surface. Temperature and the
aforementioned lack of liquid water provide far sterner opposition though and, whilst they should not be seen as
sufficiently strong evidence to abandon all hope of discovering surface organisms, it is a wise course of action to
search for life further afield, such as in the planet’s atmosphere.
Although it would take a remarkable series of evolutionary quirks for a species, having arisen in Venus’s habitable
period, to adapt to the increasing temperature, pressure and desiccation on the surface, conditions in the upper
reaches of Venus’s atmosphere could provide a far more hospitable environment [29]. Although the region is
Figure 2. Growth rates of various bacteria classes at different pressures. One can see that Earth’s Piezophiles
and Obligatory Piezophiles (those which require high pressure environments rather than merely tolerating
them) can comfortably withstand the pressure of the Venusian surface [27].

4. Kieran Jeffs 26028042 Life in the Cosmos
highly acidic, temperatures 51km-62km out from the Venusian surface occupy a substantially more hospitable
range of 253K-338K; similar to conditions where organisms can thrive in Earth’s atmosphere (fig 3.) [30]. The
pressure here is also far more forgiving, being equal to 1 bar 50km above the surface [5]. From experience on
Earth, we know that it is possible for organisms to survive in the upper atmosphere, where various experiments
have found photosynthetic bacteria living in substantial quantities [31]. Venus also has several advantages to the
Earth in this regard, having a more stable cloud structure and plentiful sources of energy [32]. All that would be
required for this is that Earthlike conditions persisted on Venus long enough for surface life to spread to the
atmosphere as it has on Earth, which is plausible given what we know of the planet’s history [32], or that life was
transferred there later by panspermia. The remaining obstacle to this theory is therefore the acidic environment
which any potential organism would have to adapt to. Fortunately, we again have evidence that it is possible for
life to survive under such circumstances. Acidithiobacillus Thiooxidans, a species of extremophile bacteria that
occupies the ceilings of caves, not only survives under high PH environments but in fact derives its energy through
a chemosynthetic process involving sulphur compounds [33]. Such organisms would therefore be well suited to
conditions in Venus’s atmosphere, and we have extremophiles on Earth capable of living under similar PH levels to
those on Venus [32]. Earth’s history provides us with further clues about life’s capacity to adapt in this manner.
During what is known as the Great Oxygenation Event some 2.3 billion years ago, Earth’s saturated oxygen sinks
were unable to absorb any more of the huge quantity of oxygen that was being produced by the photosynthesis of
certain bacteria (fig. 4) [34]. This led to a catastrophic alteration of Earth’s atmosphere, which rapidly went from
having negligible levels of oxygen to having levels comparable to today [35]. The damage oxygen caused to cell
components such as nucleic acids, proteins and lipids led to the extinction of most of the planet’s anaerobic
organisms [36]. Despite this event, however, life persisted (and indeed diversified [36]) and we now inhabit a
planet occupied primarily by organisms to which oxygen is not toxic, using antioxidants to either prevent the
formation of reactive oxygen species or to remove such species before they can cause cell damage [37]. The mere
existence of oxygen-tolerant organisms and extremophiles such as AT suggests that life finds a way, even in the
Figure 3. Pressure, temperature and composition of Venus’s atmosphere at various altitudes. There is a range
from 51km to 62km where pressure and temperature are similar to what might be encountered on Earth [28].

5. Kieran Jeffs 26028042 Life in the Cosmos
face of initially poisonous chemicals. Given the discussed period of Earthlike conditions on Venus and the fact that
the obstacles in its still temperate atmosphere seem to be surmountable, one can see atmospheric conditions as a
strong argument in favour of the idea that life may someday be found on Earth’s sister planet. A variety of NASA
missions to Venus have revealed potential evidence for this, finding trace elements in Venus’s atmosphere that are
not in equilibrium with each other [10]. The primary factor which leads to a lack of equilibrium in Earth’s
atmosphere is biological activity, and it has been suggested that biological activity may therefore be behind the
disequilibrium present in the atmosphere of Venus [39]. In addition to this there are a myriad of other anomalies
such as the presence of carbonyl sulphide, which is so difficult to produce inorganically that it is often taken as an
unambiguous indicator of biological activity, the unexpected scarcity of carbon monoxide and the simultaneous
presence of both hydrogen sulphide and sulphur dioxide, which react with each other and as such are somewhat
perplexing to find together [40]. Volcanism is a possible alternative source for carbonyl sulphide, and, whilst the
other anomalies can also be accounted for inorganically, their presence does not get much less puzzling [40]. As
such it is not unduly bold to cite these anomalies as evidence for life in Venus’s atmosphere.
Continuing with the assumption that any life present on Venus will be in its atmosphere, and is capable of handling
all the previously discussed hazards, the fact that Venus lacks a magnetosphere and orbits closer to the sun
suggests organisms would still encounter high levels of solar ultraviolet radiation and cosmic rays, both of which
are damaging to organic molecules [41]. A speculative Venusian organism could not rely on the in-built magnetic
field which shields Earth’s life from radiation, but it could garner some protection from what is known as Venus’s
induced magnetosphere [42]. Venus’s ionosphere separates its atmosphere from outer space, and the Sun’s
magnetic field wraps around Venus in a manner akin to the movement of water around an island in a river [42].
The combination of this and the limited cloud cover available would afford atmospheric organisms sufficient
protection to prevent their being wiped out by high energy cosmic rays and extreme solar particle events, with
radiation dosages during even the most extreme historical examples being insufficient to propose a significant
survival challenge [43]. With cosmic rays and solar events manageable, UV radiation becomes the more pressing
Figure 4: Change in the composition of Earth’s atmosphere over time. Following the saturation of Earth’s
oxygen sinks over 2 billion years ago, the atmospheric oxygen concentration climbs to heights fatal to much of
Earth’s life before the GOE [38].

6. Kieran Jeffs 26028042 Life in the Cosmos
threat, especially considering its ability to significantly damage DNA [44]. Ironically, the previously discussed
sulphuric acid clouds may actually be life’s saving grace in this instance. It has been proposed that Venusian
organisms may be able to use sulphur compounds as a kind of UV sunscreen, protecting them from the worst of
the UV radiation’s damage [45]. It is even possible that, far from being threatened by it, organisms in the Venusian
atmosphere in fact derive their energy from UV radiation, using sulphur compounds as a means of converting UV
to lower frequencies possible for use in photosynthesis [46]. Dark streaks in UV images taken of Venus hint at a
presence in the atmosphere absorbing UV radiation, and this could be accounted for by the proposed organic
activity (figure 5) [46]. As such, it seems that radiation levels are not a fatal blow to hopes of finding existing
Venusian life, and may in fact be responsible for it. Considering previous factors discussed in this essay this is not
necessarily surprising; often it seems that what proves lethal for one organism is essential to another organism
which has had time to adapt.
In conclusion, the proposition that life or the remains of life will someday be found on the planet Venus is a
realistic, but not certain, possibility. Even from a chauvinistic, Earth-biology based perspective, Venus undeniably
has all the prerequisite chemicals to harbour life as we know it. Extremes of pressure, temperature and acidity on
the surface are admittedly harsh challenges, but still surmountable with an optimistic view of life’s capacity to
adapt. Even with the surface dismissed as inhospitable, the sternest sceptic would be hard pressed to deny that
there is little threat to survival in the atmosphere that one or another Earthbound lifeform has not already
mastered. Despite this evidence, to lean towards denying the possibility of life presently existing on Venus is at
least understandable, primarily on account of the innumerable factors that are necessarily too speculative or left
to chance. However, the position that Venus could definitively never at any point have supported life, despite
having had up to 2 billion years of Earthlike conditions, borders on indefensible. It takes little imagination to see
how life could have taken seed on Venus to begin with either, be that through abiogenesis during the period
where it experienced Earthlike conditions, or through panspermia via a meteorite from Earth or elsewhere.
However, it should be noted that astrobiology is a field in its infancy. Our current knowledge of what conditions
Figure 5. UV image of Venus. The dark regions show where something is absorbing the UV radiation [47], [48].

7. Kieran Jeffs 26028042 Life in the Cosmos
life can survive under are unavoidably speculative, and it is for this reason that determining the feasibility of life on
Venus by inserting Earth’s organisms into similar conditions gives a pessimistic prediction at best. To illustrate,
consider that the overwhelming majority of Earth’s life does not live in the previously discussed boiling springs,
and indeed would be obliterated if it did, yet still we find organisms which have been able to adapt to these
conditions. If there were no boiling springs on Earth we would not have organisms which could survive in them,
but in that scenario would it be reasonable to take their absence as evidence that such life was impossible? It is
apparent that this is not the case, and by the same token it is short-sighted to assume that life absolutely cannot
exist in any Venusian environment, however harsh. Simply put, life on Venus appears difficult for terrestrial
organisms because no terrestrial organism has been forced to meet the same challenge that any Venusian species
would; a gradual transition from Earthlike conditions to the stable yet unforgiving conditions that exist on Venus
today. If they did, it would not be irrational to assume that some would adapt and survive in the same way that life
has conquered seemingly every inhospitable niche of our own planet, from deep ocean volcanic vents to boiling
springs, and from sulphuric acid cave networks to the atmosphere itself. And, when even a pessimistic, Earth-
centric evaluation of Venus’s hospitability suggests that it may be able to support life, it is not bold for
astrobiologists to some day dream of finding it there.
Word count minus figures and references: 2998

8. Kieran Jeffs 26028042 Life in the Cosmos
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