I’ve maintained for years that the first discovery of life beyond Earth, assuming we make one, will be in an extrasolar planetary system, through close and eventually unambiguous analysis of an exoplanet’s atmosphere. But Alex Tolley has other thoughts. In the essay below, he looks at a privately funded plan to send multiple probes into the clouds of Venus in search of organisms that can survive the dire conditions there. And while missions this close to home don’t usually occupy us because of Centauri Dreams’ deep space focus, Venus is emerging as a prominent exception, given recent findings about anomalous chemistry in its atmosphere. Are the clouds of Venus concealing an ecosystem this close to home?
by Alex Tolley
The discovery of phosphine (PH3), an almost unambiguous biosignature on Earth, in the clouds of Venus in 2021 increased interest in reinvestigating the planet’s clouds for life, a scientific goal that had been on hiatus since the last atmospheric entry and lander vehicle mission, Vega-2 in 1984. While the recent primary target for life discovery has been Mars, whether extinct, or extant in the subsurface, it has taken nearly half a century since the Viking landers to once again look directly for Martian life with the Perseverance rover.
However, if the PH3 discovery is real (and it is supported by a reanalysis of the Pioneer Venus probe data), then maybe we have been looking at the wrong planet. The temperate zone in the Venusian clouds is the nearest habitable zone to Earth. If life does exist there [see Figure 1] despite the presence of concentrated sulfuric acid (H2SO4), then it is likely to be in this temperate zone layer, having evolved to live in such conditions.
Figure 1. Schematic of Venus’ atmosphere. The cloud cover on Venus is permanent and continuous, with the middle and lower cloud layers at temperatures that are suitable for life. The clouds extend from altitudes of approximately 48 km to 70 km. Credit: J Petkowska.
But why launch a private mission, rather than leave it to a well-funded, national one?
National space agencies haven’t been totally idle. There are four planned missions, two by NASA (DAVINCI+, VERITAS), one by ESA (EnVision) to investigate Venus, all due to be launched around 2030, as well a Russian one (Venera-D) to be launched at the same time:
VERITAS and DAVINCI+ are both Discovery-class missions. They are budgeted up to $500 million each. EnVision is ESA’s mission launching in the same timeframe. All three missions have target launch dates ranging from 2028 (DAVINCI+, VERITAS) to 2031 (EnVision). As with any large budget mission, these missions have taken a long time to develop. DAVINCI was proposed in 2015, the revised DAVINCI+ proposed again in 2019, and selected in 2021 for a 2028 launch. VERITAS was proposed in 2015, and selected only in 2021. Then there is the seven years of development, testing, and finally launch in 2028. EnVision was selected in 2021, and faces a decade before launch.[5,6,7].
DAVINCI+’s goals include:
1. Understanding the evolution of the atmosphere
2. Investigating the possibility of an early ocean
3. Returning high resolution images of the geology to determine if plate tectonics ever existed.
[PG note: NASA GSFC just posted a helpful overview of this mission.]
Image: The Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission, which will descend through the layered Venus atmosphere to the surface of the planet in mid-2031. DAVINCI is the first mission to study Venus using both spacecraft flybys and a descent probe. Credit: NASA.
VERITAS’s rather similar goals involve answering these questions:
1. How has the geology of Venus evolved over time?
2. What geologic processes are currently operating on it?
3. Has water been present on or near its surface?
EnVision’s goals include:
1. Determining the level and nature of current activity
2. Determining the sequence of geological events that generated its range of surface features
3. Assessing whether Venus once had oceans or was hospitable for life
4. Understanding the organizing geodynamic framework that controls the release of internal heat over the history of the planet
In addition, Russia has the Venera-D mission planned for a 2029 launch that has a lander. One of its goals is to analyze the chemical composition of the cloud aerosols. 
There is considerable overlap in the science goals of the four missions, and notably none have the search for life as a science goal, although the 3rd EnVision science goal could be the preparatory “follow the water” approach before a follow-up mission to search for life if there is evidence that Venus did once have oceans.
As with the Mars missions post Viking up to Perseverance, none of these missions is intended to look directly for life itself. Given the 2021 selection date for all three missions and the end of decade launch dates, it will be somewhat frustrating for scientists interested in searching for life on Venus.
Cutting through the slow progress of the national missions, the privately funded Venus Life Finder mission aims to start the search directly. The mission to look for life is focused on small instruments and a low-cost launcher. Not just one but a series of missions is planned, each increasing in capability. The first is intended to launch in 2023, and if the three anticipated missions are successful, Venus Life Finder would scoop the big science missions in being the first to detect life in Venus should it exist.
Some history of our views about Venus
Before the space age, both Venus and Mars were thought to have life. Mars stood out because of the seasonal dark areas and Schiaparelli’s observation of channels, followed by Lowell’s interpretation of these channels as canals, which carried the implication of intelligence. Von Braun’s “Mars Projekt” (1952) inferred that the atmosphere was thin, but the astronauts would just need O2 masks, and his technical tale had the astronauts discover an advanced Martian civilization. The popular science book “The Exploration of Mars” (1956) written by Willy Ley and Wernher Von Braun and illustrated by Chesley Bonestell, supported the idea of Martian vegetation, speculating that it was likely to be something along the lines of hardy terrestrial lichens.
Unlike Mars, the surface of Venus was not observable, just the dense permanent cloud cover. It was believed that Venus was younger than Earth and that the clouds covered a primeval swamp full of animals like those in our planet’s past. With the many probes starting in 1962 with the successful flyby of Mariner 2, it was determined that the surface of Venus was a hellish 438-482 C (820-900 degrees F), by far the hottest place in the Solar System. Worse, the clouds were not water as on Earth, but H2SO4, in a concentration that would rapidly destroy terrestrial life. Seemingly Venus was lifeless.
Some scientists thought Venus was much more Earth Like in the past, and that a runaway greenhouse state accounted for its current condition. If Venus was more Earth Like, there could have been oceans, and with them, life. On Earth, bacteria are carried up from the surface by air currents and have been found living in clouds and are part of the cloud formation process. Bacteria have been found in Earth’s stratosphere too. Bacteria living in the Venusian oceans would likely have been carried up into the atmosphere and occupy a similar habitat. If so, it has been hypothesized that bacterial life may have evolved to live in the increasingly acidic Venusian clouds just as terrestrial extreme acidophiles have evolved, and that this life is the source of the detected PH3.
The First Science Instrument
Is there any other evidence for life on Venus? Using two instruments, a particle size spectrometer and a nephelometer, the Pioneer Venus probe (1978) suggested that some tiny droplets in the clouds were not spherical, as physics would predict, and therefore might be living [unicellular] organisms.
But these probes could not resolve some anomalies of the Venusian atmosphere that might as a whole, indicate life.
1. Anomalous UV Absorber – spatial and temporal variability reminiscent of algal blooms.
2. Non-spherical large droplets – possible cells
3. Non-volatile elements such as phosphorus that could reduce the H2SO4 concentration and a required element of terrestrial life
4. Gases in disequilibrium, including PH3, NH3
Enter the Venus Life Finder (VLF) team, led by Principal Investigator Sara Seager, whose team includes the noted Venus expert David Grinspoon. The project isfunded by Breakthrough Initiatives. The initial idea was to do some laboratory experiments to determine if the assumptions about possible life in the clouds were valid.
As the VLF document states up front:
The concept of life in the Venus clouds is not new, having been around for over half a century. What is new is the opportunity to search for life or signs of life directly in the Venus atmosphere with scientific instrumentation that is both significantly more technologically advanced and greatly miniaturized since the last direct in situ probes to Venus’ atmosphere in the 1980s.
The big objection to life in the Venusian clouds is their composition: extremely concentrated sulfuric acid. Any terrestrial organism subjected to the acid is dissolved. [There is a reason serial killers use this method to remove evidence of their victims!]
To check on the constraints of cloud conditions on potential life and the ability to detect organic molecules, the VLF team conducted some experiments that showed that:
1. Organic molecules will autofluoresce in up to 70% H2SO4. Therefore organic molecules are detectable in the Venusian cloud droplets.
2. Lipids will form micelles in up to 70% H2SO4 and are detectable. Cell membranes are therefore possible containers for biological processes.
3. Terrestrial macromolecules – proteins, sugars, and nucleic acids – all rapidly become denatured in H2SO4, ruling out false positives from terrestrial contamination
4. The Miller-Urey experiment will form organic molecules in H2SO4. Therefore abiogenesis of precursor molecules is also possible on Venus.
With these results, the team focused on building a single instrument to investigate both the shapes of particles and the presence of organic compounds. Non-spherical droplet shapes containing organic compounds would be a possible indication of life. This instrument, an Autofluorescing Nephelometer, is being developed from an existing instrument, as shown in figure 2.
Figure 2. Evolution of the Autofluorescing Nephelometer (AFN) from the Backscatter Cloud Probe (BCP) (left of arrow) to the Backscatter Cloud Probe with Polarization Detection (BCPD) (right of arrow). The BCPD is further evolved to the AFN by replacement of the BCPD laser with a UV source and addition of fluorescence-detection compatible optics.
All this in a package of just 1 kg to be carried in the atmosphere entry vehicle.
The VLF team has partnered with the New Space company Rocket Lab which is developing its Venus mission. The company has small launchers that are marketed to orbit tiny satellites for organizations that don’t want to use piggy-backed rides with other satellites as part of a large payload. Its Electron rocket launcher has so far racked up successes. The Electron can place up to 300kg in LEO.
For the Venus mission, the payload includes the Photon rocket to make the interplanetary flight and deliver a 20 kg Venus atmosphere entry probe that includes the 1 kg AFN science package. To reach Venus, the Photon rocket using bi-propellant generates the needed 4 km/s delta V. It employs multiple Oberth maneuvers in LEO to most efficiently raise the orbit’s apogee until it is on an escape trajectory to Venus. Travel time is several months.
The Electron rocket, the Photon rocket, and the entry probe are shown in the next three figures.
The photon rocket powers the cruise phase from LEO to Venus intercept. This rocket uses an unspecified hypergolic fuel and will carry the entry probe across the 60 million km trajectory of its 3-month Venus mission.
Figure 3a. Electron small launch vehicle. The Electron ELV has successfully launched 146 satellite missions to date for a low per launch cost. A recent test of a helicopter retrieval of the 1st stage indicates that reusability is possible using this in-flight capture approach, therefore potentially saving costs. The kick stage in the image is replaced by the Photon rocket for interplanetary flight.
Figure 3b. High-energy Photon rocket and Venus entry probe.
Figure 3c. The small Venus probe is a 45-degree half-angle cone approximately 0.2m in diameter. Credit: NASA ARC.
Fast and Cheap
The cost of the mission to Venus is not publicized, but we know the cost of a launch of the Electron rocket to LEO is $7.5m . Add the photon cruise stage, the entry probe, the science instruments, the operations and science teams. All in, a fraction of the Discovery mission costs, but with a faster payback and more focussed science. Rocket Lab has not launched an interplanetary mission before, so there is risk of failure. The company does have other interplanetary plans, including a Mars mission using two Photon cruise stage rockets for a Mars orbiter mission in 2024.
Is the Past the Future?
The small probe and dedicated instrument package, while contrasting with the big science missions of the national programs, harkens back to the early scientific exploration of space at the beginning of the space age. The smaller experimental rockets had limited launch capacity and the scientific payloads had to be small. Some examples include the Pioneer 4 lunar probe  and the Explorer series .
These relatively simple early experiments resulted in some very important discoveries. The lunar flyby Pioneer 4, launched in 1958, massed just 6.67 kg, with a diameter of just 0.23 m, a size comparable to the VLF’s first mission . These early missions could be launched with some frequency, each probe or satellite containing specific instruments for the scientific goal. Today with miniaturization, instruments can be made smaller and controlled with computers, allowing more sophisticated measurements and onboard data analysis. Miniaturization continues, especially in electronics.
Breakthrough StarShot’s interstellar concept aims at have a 1 gm sail with onboard computer, sensors, and communications, increasing capabilities, reducing costs, and multiplying the numbers of such probes. With private funding now equaling that of the early space age experiments, and the lower costs of access to space, there has been a flowering of the technology and range of such private space experiments. The VLF mission is an exemplar of the possibilities of dedicated scientific interplanetary missions bypassing the need to be part of “big science” missions.
Just possibly, this VLF series of missions will return results from Venus’ atmosphere that show the first evidence of extraterrestrial life in our system. Such a success would be a scoop with significant ramifications.
1. Seager S, et al “Venus Life Finder Study” (2021) Web accessed 02/18/2022
2. Clarke A The Exploration of Space (1951), Temple Press Ltd
3. Ley, W, Von Braun W, Bonestell C The Exploration of Mars (1956), Sidgwick & Jackson
4. RocketLab “Electron Rocket: web accessed 02/18/2022 https://www.rocketlabusa.com/launch/electron/
5. Wikipedia “List of missions to Venus” en.wikipedia.org/wiki/List_of_missions_to_Venus
6. Wikipedia “DAVINCI” en.wikipedia.org/wiki/List_of_missions_to_Venus
7. Wikipedia “VERITAS” en.wikipedia.org/wiki/VERITAS_(spacecraft)
8. Wikipedia “EnVision” en.wikipedia.org/wiki/EnVision
9. Wikipedia “Venera-D” en.wikipedia.org/wiki/Venera-D
10. LePage, A, “Vintage Micro: The Second-Generation Explorer Satellites” (2015) www.drewexmachina.com/2015/09/03/vintage-micro-the-second-generation-explorer-satellites/
11. LePage, A, “Vintage Micro: The Pioneer 4 Lunar Probe” (2014)
12. Wikipedia “Rocket Lab Electron”, en.wikipedia.org/wiki/Rocket_Lab_Electron