15:00 〜 15:15
[PPS01-18] CASE FOR RECONSIDERING THE PLANETARY-PROTECTION REQUIREMENT FOR OCEAN WORLD EXPLORATION
★招待講演
キーワード：Astrobiology, Planetary Protection, Ocean Worlds, Icy Moons, Exploration
Introduction: Planetary-protection requirements for exploring solar system ocean worlds rest on a key value: limiting to one in ten thousand the probability that a single viable Earth organism will enter an alien liquid water reservoir [1]. Enforceable under international treaty, the 10-4 forward-contamination requirement governs missions by NASA, JAXA, and ESA. Its relevance increases as these international partners focus on places “with real water” far out in the solar system, where life unrelated to Earth life may have arisen. So it is important to understand the origin of this key requirement, and periodically to revisit the assumptions behind it. Even NASA anticipates that “these requirements will be refined in future years” [2].
The 10-4 requirement traces to the 1940s in the US [1, 3]. Many changes in the intervening half-century justify revisiting the requirement’s rationale: 1) vastly improved technology for assaying biomolecules and organisms; 2) expansion of the definition of self-replicating organisms; 3) expansion of the environmental ranges known to be habitable; 4) deeper understanding of how multi-cellular communities behave differently from single organisms; 5) expansion of the habitable exploration target list to include several icy moons containing vast liquid-water oceans; and 6) a sociological and international context for setting policy quite evolved since the mid-20th century.
The 10-4 requirement may still be appropriate for today’s exploration of places that meet textbook criteria for being habitable. But the requirement might be either technically or socio-culturally outdated, or both. Without validation by an explicit conversation among a broad, international cross-section of stakeholders, mission plans by any nation could be severely disrupted downstream. If the requirement should be modified by international consensus, starting this process now would be advisable.
Pedigree and evolution of the 10-4 requirement: We describe the rationale for the current requirement: its source; quantification drivers in the original debate; how it was determined to be appropriate for humanity’s first contact with Mars in particular and habitable alien environments in general; and its verifiability. We lay out the rationale for reconsidering it now, including how it has been handed down, and its validity given a prospect not envisioned in the 1970s: multiple, vast, interior salt-water oceans, with seafloor hydrothermal activity and organic chemistry.
Viability of life: Many fields affecting our understanding of how life might take hold in ocean-world environments have emerged since the Viking era: 1) biology of extremophiles; 2) detailed scenarios for the origin of life; 3) replication of non-life macromolecules including retroviruses and prions; 4) rapid evolution for survivability as environmental conditions change; and 5) how communities of microorganisms maintain local habitability. This new knowledge affect quantification of survival and replication probabilities.
Planning for low-probability, high-consequence events: We analyze limitations in how humans rationalize events with low probability but high consequence; how systematic human perception biases can be compensated; and how perceptions of risk are normalized and acculturated. We compare the current requirement to other risks in the range from 10-2 to 10-10. We assess how decision responsibility might be distributed across stakeholders, and what voice planetary scientists can have.
Ethical basis for contaminating an alien ecosystem: We frame the low risk of contaminating an off-world ecology as one of many techno-ethical decisions facing humanity today, that must weigh consequences, compare ethical values, and accept uncertainty based on the comparison. The 10-4 requirement may not deserve automatic perpetuation. What status should it have within an international, ethical decision-making process? We contrast a meta-ethical discussion about absolute values with reliance on an arbitrary number governing the absolute necessity of preserving scientific discovery or protecting alien life. We describe how can an enlightened understanding and evolving consensus can flow down into governing policy.
References: [1] Melzer, M., When Biospheres Collide: A History of NASA’s Planetary Protection Programs, 2011, NASA, Washington DC, p.78-84. [2] Conley, C. Planetary Protection for Icy Moons: Update to the 2012 SSB Europa Report, cited 2017, 1/8/2017, https://planetaryprotection.nasa.gov/missiondesign/. [3] Werber, M., Objectives and Models of the Planetary Quarantine Program, 1975, NASA, Washington DC, p. 9-11.
The 10-4 requirement traces to the 1940s in the US [1, 3]. Many changes in the intervening half-century justify revisiting the requirement’s rationale: 1) vastly improved technology for assaying biomolecules and organisms; 2) expansion of the definition of self-replicating organisms; 3) expansion of the environmental ranges known to be habitable; 4) deeper understanding of how multi-cellular communities behave differently from single organisms; 5) expansion of the habitable exploration target list to include several icy moons containing vast liquid-water oceans; and 6) a sociological and international context for setting policy quite evolved since the mid-20th century.
The 10-4 requirement may still be appropriate for today’s exploration of places that meet textbook criteria for being habitable. But the requirement might be either technically or socio-culturally outdated, or both. Without validation by an explicit conversation among a broad, international cross-section of stakeholders, mission plans by any nation could be severely disrupted downstream. If the requirement should be modified by international consensus, starting this process now would be advisable.
Pedigree and evolution of the 10-4 requirement: We describe the rationale for the current requirement: its source; quantification drivers in the original debate; how it was determined to be appropriate for humanity’s first contact with Mars in particular and habitable alien environments in general; and its verifiability. We lay out the rationale for reconsidering it now, including how it has been handed down, and its validity given a prospect not envisioned in the 1970s: multiple, vast, interior salt-water oceans, with seafloor hydrothermal activity and organic chemistry.
Viability of life: Many fields affecting our understanding of how life might take hold in ocean-world environments have emerged since the Viking era: 1) biology of extremophiles; 2) detailed scenarios for the origin of life; 3) replication of non-life macromolecules including retroviruses and prions; 4) rapid evolution for survivability as environmental conditions change; and 5) how communities of microorganisms maintain local habitability. This new knowledge affect quantification of survival and replication probabilities.
Planning for low-probability, high-consequence events: We analyze limitations in how humans rationalize events with low probability but high consequence; how systematic human perception biases can be compensated; and how perceptions of risk are normalized and acculturated. We compare the current requirement to other risks in the range from 10-2 to 10-10. We assess how decision responsibility might be distributed across stakeholders, and what voice planetary scientists can have.
Ethical basis for contaminating an alien ecosystem: We frame the low risk of contaminating an off-world ecology as one of many techno-ethical decisions facing humanity today, that must weigh consequences, compare ethical values, and accept uncertainty based on the comparison. The 10-4 requirement may not deserve automatic perpetuation. What status should it have within an international, ethical decision-making process? We contrast a meta-ethical discussion about absolute values with reliance on an arbitrary number governing the absolute necessity of preserving scientific discovery or protecting alien life. We describe how can an enlightened understanding and evolving consensus can flow down into governing policy.
References: [1] Melzer, M., When Biospheres Collide: A History of NASA’s Planetary Protection Programs, 2011, NASA, Washington DC, p.78-84. [2] Conley, C. Planetary Protection for Icy Moons: Update to the 2012 SSB Europa Report, cited 2017, 1/8/2017, https://planetaryprotection.nasa.gov/missiondesign/. [3] Werber, M., Objectives and Models of the Planetary Quarantine Program, 1975, NASA, Washington DC, p. 9-11.