Venus Life Finder Missions Motivation and Summary
, Christopher E. Carr 4, David H. Grinspoon 5, Bethany L. Ehlmann 6, Sarag J. Saikia 7, Rachana Agrawal 8, Weston P. Buchanan 8, Monika U. Weber 9, Richard French 10, Pete Klupar 11, Simon P. Worden 11, Darrel Baumgardner 12,13 and on behalf of the Venus Life Finder Mission Team †Round 1
Reviewer 1 Report
In "Venus Life Finder Missions Motivation and Summary" the authors present the Venus Life Finder (VLF) missions. This is an interesting concept that takes advantage of the habitable potential of the Venusian clouds.
I find the article is extremely well-written and I have very few comments. They are listed below.
- In general, I'm missing a deeper presentation of the science case. Section 2 serves this purpose, but there are very few references. I believe any mission should refer to works that provide the grounds to justify the effort. Not even the first references on the possibility of life on Venus' clouds (such as Morowitz & Sagan 1967) are mentioned.
- Page 2, Section 2: the authors explicitly refer to "single-celled microbial life". While I understand the motivation for this, I suppose the mission could detect multicellular life, right? Why be so restrictive?
- A more detailed presentation of the ancillary science that can be done with VLF would be interesting.
- Page 4: MEMS is not defined
- Section 5: The mission will bring back 1 L of gas and a few grams of particles. Can these samples be extracted from any place in the atmosphere? Are there theoretically-favoured regions on Venus to perform the search?
In summary, after carefully reading the manuscript, I think it is in good shape, but it does need to be contextualised a bit more, in particular by providing a larger overview of the field and motivation for such a mission.
Finally, I congratulate the authors on the very interesting work whose results I'm looking forward to seeing.
Author Response
We provide responses to the Reviewers’ comments on the Aerospace- 1784333 manuscript. Our response is marked in bold font and the reviewers’ comments are in regular font.
Response to the Reviewer 1:
In "Venus Life Finder Missions Motivation and Summary" the authors present the Venus Life Finder (VLF) missions. This is an interesting concept that takes advantage of the habitable potential of the Venusian clouds.
I find the article is extremely well-written and I have very few comments. They are listed below.
- In general, I'm missing a deeper presentation of the science case. Section 2 serves this purpose, but there are very few references. I believe any mission should refer to works that provide the grounds to justify the effort. Not even the first references on the possibility of life on Venus' clouds (such as Morowitz & Sagan 1967) are mentioned.
The paper is a short summary on the mission objectives of the Venus Life Finder (VLF). It is submitted as a “Communication” and not an “Article”.
We do however understand the reviewer’s concern and have provided more references to past work, both done by other groups as well as ours. This includes citations to past work on the Venusian astrobiology (such as Morowitz & Sagan 1967). We do also cite papers in press in the same Special Issue that expand upon science objectives, instrumentation and technology behind the VLF mission concept study.
We have also added a “VLF at a glance” table that compares the Science objectives of various mission concepts within VLF.
- Page 2, Section 2: the authors explicitly refer to "single-celled microbial life". While I understand the motivation for this, I suppose the mission could detect multicellular life, right? Why be so restrictive?
We appreciate reviewer’s comment on this.
We have deleted the following sentence from the paper: “By life we mean single-celled microbial-type organisms.” to avoid potential misunderstanding that our paper rules out multicellular life.
For the VLF we focus on the microbial single-celled life even if we cannot technically rule out strictly aerial multicellular life. This focus is mainly motivated by the fact that single-celled microbial life is spatially less constrained by the cloud droplet habitat. It is likely that life would reside inside of the cloud droplets to be protected from the outside environment. As habitable space is a limiting factor for life in the Venusian clouds it is reasonable to assume that life would adapt to take less space within a droplet, favoring single-celled life.
- A more detailed presentation of the ancillary science that can be done with VLF would be interesting.
As mentioned above, we have also added a “VLF at a glance” Table 1 that compares the Science objectives of various mission concepts within VLF.
- Page 4: MEMS is not defined
We have defined MEMS (Microelectromechanical systems) and we have also provided citations to the relevant literature on the example instruments.
- Section 5: The mission will bring back 1 L of gas and a few grams of particles. Can these samples be extracted from any place in the atmosphere? Are there theoretically-favoured regions on Venus to perform the search?
We have clarified the motivation for the selection for the altitude region for the sample return mission. We have added the following text in Section 5:
“The target cloud altitude region for sample collection will be informed by the results of both the Rocket Lab entry probe mission (Section 3) as well as the VLF Venus Habitability Mission (Section 4).”
In summary, after carefully reading the manuscript, I think it is in good shape, but it does need to be contextualised a bit more, in particular by providing a larger overview of the field and motivation for such a mission.
We hope that by implementing the above corrections and by providing more references to the previous work we have made the manuscript more clear.
Finally, I congratulate the authors on the very interesting work whose results I'm looking forward to seeing.
Thank you for your thorough review of our manuscript!
Reviewer 2 Report
General comments:
The manuscript Venus Life Finder Missions Motivation and Summary by Seager et al. describes the The Venus Life Finder (VLF) Mission concepts planned in a series of three direct atmospheric probes worked out by an MIT-led consortium. The missions are designed to assess the habitability of the Venusian clouds and search for signs of life or life itself. Dr Seager and her team discusses the conditions and possible scenario for life in the Venusian clouds in the former publications and current manuscript summarizes possible measurements which could approve or disprove earlier provided habitability concepts. The manuscript describes which the most critical measurements could be carry out on small. Mid-large and large mission to Venus to study its atmosphere.
My main concern is that the paper is very minimalistic and sparse on the details. It could (should?) contain much more information about possible life on Venus and the VLF missions. In this respect there is a bit more information on small mission design and very little on the mid and large missions.
The authors put much of impact on astrobiological perspective which is understandable point. Nevertheless, the habitability of the Venus atmosphere is subject of a long controversy (e.g. see recent papers by Rimmer et al.) and the analysis of the V. atmosphere chemistry- if not affected by life- can also be interesting per se allowing understanding new not typical chemical reactions with perhaps implication to understanding the atmospheres of exoplanet. I would also add in the introduction critical comments about life in the V. atmosphere in a few sentences with the references which are surely known to authors.
The manuscript is well-written and I recommend it for the publication in Aerospace after implementation of a few corrections given below.
Specific questions:
P2 l.8 from bottom: What this shows is that sulfuric acid droplets can support a variety of complex chemicals that can in principle be related to life’s building blocks [7].
P3.l.13 from top: please add what large ‘’Mode 3’’ means.
P3. l.16 from top: ‘’…on Earth co-occuring NH3 and O2…’’ It would be necessary to add references.
P3. l.17 from bottom: ‘’The AFN… ‘’ Are there other compounds than organic molecules that can fluoresce, for example simple minerals, grains in droplets (e.g., fluorite, CaF2)? How about presence of micrometeorite, dust… Can the AFN distinguish between these sources?
P3. l.11 from bottom: ‘’it affirms…’’ 1) can the authors explain why only non-spherical particles are associated with life? Couldn't life be present in a spherical liquid droplet? 2) non-spherical droplets could be many things, but most prominently some sort of salt-slurry. Taking this is as an indication for the presence of life is a too strongly phrased.
P4. l. 8 from bottom: ‘’The AFN…’’ One could also mention (estimated) AFN flight instrument weight and dimensions.
P4. l.9. from top:…’’ at about 52 km’’ For readers who are not familiar with this field, the choice for 52 km altitude might seem arbitrary. Can the authors add references and motivation why this level is selected.
P4. l.9. from bottom: …‘’MEMS’’ … Micro-Electro-Mechanical Systems; Do the authors mean the IGOM-A or IGOM-G? Can they provide more details about their functioning.
P5. l.1. from top: …temperature-pressure profiles… The Rocketlab mission will also have these capabilities - the authors can mention this.
P5. l.11. from top: ‘’The total balloon…’’ To be precise, does this mean there is 15 kg science payload?
P5. l.18. from top: A laser desorption spectrometer….’’ Sentence is out of place w.r.t. the sentences before and after about fluid-screen concentrator. Please add reference https://0-www-mdpi-com.brum.beds.ac.uk/2226-4310/9/6/312 and/or https://hal.inria.fr/insu-02937120/.
Author Response
We provide responses to the Reviewers’ comments on the Aerospace- 1784333 manuscript. Our response is marked in bold font and the reviewers’ comments are in regular font.
Response to the Reviewer 2:
The manuscript Venus Life Finder Missions Motivation and Summary by Seager et al. describes the The Venus Life Finder (VLF) Mission concepts planned in a series of three direct atmospheric probes worked out by an MIT-led consortium. The missions are designed to assess the habitability of the Venusian clouds and search for signs of life or life itself. Dr Seager and her team discusses the conditions and possible scenario for life in the Venusian clouds in the former publications and current manuscript summarizes possible measurements which could approve or disprove earlier provided habitability concepts. The manuscript describes which the most critical measurements could be carry out on small. Mid-large and large mission to Venus to study its atmosphere.
My main concern is that the paper is very minimalistic and sparse on the details. It could (should?) contain much more information about possible life on Venus and the VLF missions. In this respect there is a bit more information on small mission design and very little on the mid and large missions.
The paper is a short summary on the mission objectives of the Venus Life Finder (VLF). It is submitted as a “Communication” and not a full “Article”. There are several articles that are going to be published, or are already published, as part of the same Special Issue that aim to cover specific mission concepts or other aspects of the VLF in more detail. We have cited the companion papers in the text to guide the reader to the respective papers for each of the VLF concepts.
However, we understand the reviewer’s concern and we have added a “VLF at a glance” table (new Table 1) that compares the Science objectives of various mission concepts within VLF.
The authors put much of impact on astrobiological perspective which is understandable point. Nevertheless, the habitability of the Venus atmosphere is subject of a long controversy (e.g. see recent papers by Rimmer et al.) and the analysis of the V. atmosphere chemistry- if not affected by life- can also be interesting per se allowing understanding new not typical chemical reactions with perhaps implication to understanding the atmospheres of exoplanet. I would also add in the introduction critical comments about life in the V. atmosphere in a few sentences with the references which are surely known to authors.
We have added a new paragraph about controversy in the introduction,
In Section 2 we have added a short discussion of a non-life explanation to the Venus atmosphere anomaly of SO2 depletion in the cloud layers.
The manuscript is well-written and I recommend it for the publication in Aerospace after implementation of a few corrections given below.
Thank you for accepting our manuscript.
Specific questions:
P2 l.8 from bottom: What this shows is that sulfuric acid droplets can support a variety of complex chemicals that can in principle be related to life’s building blocks [7].
We have corrected this sentence and it now reads:
“What this shows is that sulfuric acid droplets can support a variety of complex chemicals that can in principle lead to the formation of the building blocks of an exotic biochemistry based on concentrated sulfuric acid [7].”
P3.l.13 from top: please add what large ‘’Mode 3’’ means.
Particles in the atmosphere of Venus are divided into three populations – Modes. Particles called Mode 3 are larger than other modes and are likely non-spherical. We have clarified in the text that the population of particles in the clouds that are large and non-spherical is called Mode 3.
P3. l.16 from top: ‘’…on Earth co-occuring NH3 and O2…’’ It would be necessary to add references.
We have included the references and provides a short additional explanation on why significant amounts of co-occurring NH3 and O2 on Earth are exclusively associated with life.
P3. l.17 from bottom: ‘’The AFN… ‘’ Are there other compounds than organic molecules that can fluoresce, for example simple minerals, grains in droplets (e.g., fluorite, CaF2)? How about presence of micrometeorite, dust… Can the AFN distinguish between these sources?
This is the subject of laboratory studies with the AFN that are currently underway. We have added a paragraph on the laboratory tests that are aimed to study the fluorescent behavior of various compounds in concentrated sulfuric acid.
P3. l.11 from bottom: ‘’it affirms…’’ 1) can the authors explain why only non-spherical particles are associated with life? Couldn't life be present in a spherical liquid droplet? 2) non-spherical droplets could be many things, but most prominently some sort of salt-slurry. Taking this is as an indication for the presence of life is a too strongly phrased.
We agree with the reviewer and we have reworded this sentence. It now reads:
“If we can confirm past measurements that indicate some cloud particles are non-spherical, i.e. not liquid, it affirms the possibility that the particles are not made of liquid concentrated sulfuric acid and therefore could be more habitable to life than previously thought. The non-spherical droplets would represent a currently unknown composition, including the possibility of biologically produced ammonium salt slurries [8,11].”
P4. l. 8 from bottom: ‘’The AFN…’’ One could also mention (estimated) AFN flight instrument weight and dimensions.
We have added the volume, mass and power requirements of the AFN in the text.
P4. l.9. from top:…’’ at about 52 km’’ For readers who are not familiar with this field, the choice for 52 km altitude might seem arbitrary. Can the authors add references and motivation why this level is selected.
We have clarified the choice behind the 52 km science operations altitude. We have added the following text:
“The fixed altitude balloon would operate for one to two weeks in the middle to lower cloud region, at about 48 to 52 km altitude where the temperature is habitable (between ~87 °C and ~37 °C respectively [30]). The operational altitude of choice of 52 km is based on temperature, on the presence of the population of Mode 3 particles identified by the Pioneer Venus probe [31–33], and the anomalous gas abundances (Section 2) [12].”
P4. l.9. from bottom: …‘’MEMS’’ … Micro-Electro-Mechanical Systems; Do the authors mean the IGOM-A or IGOM-G? Can they provide more details about their functioning.
We have defined MEMS and we have also provided citations to an example device. We decided not to call out IGOM-A or -G in the paper as we have decided to keep it more general.
P5. l.1. from top: …temperature-pressure profiles… The Rocketlab mission will also have these capabilities - the authors can mention this.
We have mentioned this in Section 3.
P5. l.11. from top: ‘’The total balloon…’’ To be precise, does this mean there is 15 kg science payload?
We have clarified this sentence. It now reads:
“The total balloon mass, i.e. the balloon envelope (15 kg) together with the gondola carrying the science payload and mini probes (30 kg), would be about 45 kg.”
P5. l.18. from top: A laser desorption spectrometer….’’ Sentence is out of place w.r.t. the sentences before and after about fluid-screen concentrator. Please add reference https://0-www-mdpi-com.brum.beds.ac.uk/2226-4310/9/6/312 and/or https://hal.inria.fr/insu-02937120/.
We have rearranged the sentences and cited the required papers. Thank you.
