Question

Solar System Tour. Based on the brief tour in this chapter, which world in our solar system (besides Earth) do you think is most likely to have life? Explain why.

Short answer

Europa is the most likely candidate for life due to its subsurface ocean and geothermal activity.

Step-by-step solution

Understanding the Context

In this exercise, you are asked to determine which celestial body in our solar system, other than Earth, might support life. The key focus is on the potential for a world to have conditions that could support life.

Identify Candidates

First, list the celestial bodies in the solar system known to have conditions potentially suitable for life. Commonly considered candidates include Mars, Europa (a moon of Jupiter), and Enceladus (a moon of Saturn).

Evaluate Mars

Mars is of interest due to evidence of past water flow, polar ice caps, and the possibility of subsurface water. These factors make it a candidate for potential microbial life.

Evaluate Europa

Europa, a moon of Jupiter, is covered with an icy crust, beneath which may lie a subsurface ocean. The presence of liquid water beneath its ice shell makes it a strong candidate for life.

Evaluate Enceladus

Enceladus, a moon of Saturn, shows evidence of geysers ejecting water vapor and organic compounds into space, suggesting a warm ocean beneath its icy surface, which could support life.

Analyze the Possibilities

Compare the features of Mars, Europa, and Enceladus. Consider the presence of liquid water, energy sources, and organic materials that are essential for supporting life.

Conclusion Based on Analysis

Europa is considered the most likely candidate to support life because of its subsurface ocean and potential geothermal energy sources, which provide necessary conditions for life.

Key concepts

Mars

Mars is one of the most intriguing candidates in the search for extraterrestrial life. Known as the Red Planet, it has several features that make it a potential home for microbial life. Evidence suggests that Mars once had flowing water on its surface, as observed by river valleys and lake beds.
Today, significant amounts of water ice exist at its polar caps, which hints at larger water reservoirs beneath the surface. On Mars, scientists are particularly interested in:

• Subsurface water reservoirs — potential for liquid water beneath the surface, similar to aquifers on Earth.
• Past geological activity — suggests Mars has a history of volcanic activity which could have provided energy, necessary for life.
• Methane presence — detected in the atmosphere and might hint at biological processes, as on Earth methane can be produced by microbes.

These factors make Mars a focal point of ongoing astrobiological research and exploration.

Europa

Europa, one of Jupiter’s largest moons, captivates scientists with its smooth, ice-covered surface. Beneath this icy shell, researchers believe exists a vast subsurface ocean. This ocean could hold double the amount of water found on Earth. The interest in Europa stems from its potential to harbor life in this hidden ocean. Important features of Europa include:

• Subsurface ocean — sustained by the heat from gravitational interactions with Jupiter, preventing the water body from freezing.
• Thin oxygen atmosphere — though not breathable, it could be related to chemical processes that might support life.
• Surface features suggestive of liquid movement — like ice fractures and ridges, indicating the dynamic nature of its ocean beneath the ice.

Additionally, potential geothermal activity on Europa could mimic hydrothermal vents on Earth, which are rich in life, making it one of the most promising locations in the solar system for hosting life.

Enceladus

Enceladus, a moon of Saturn, presents a captivating spectacle with its dramatic geysers at its southern pole, which spew water vapor and ice particles into space. These geysers point to an active subsurface ocean beneath its ice-covered exterior. Key features of Enceladus that intrigue scientists:

• Subsurface ocean — believed to be kept warm enough by tidal heating from Saturn, allowing for liquid water under the ice.
• Organic compounds in geysers — suggest complex chemistry similar to that found in life-supporting environments.
• Potential hydrothermal vents — evidenced by mineral-rich water plumes, they could be energy sources that support microbial life.

Enceladus’s complex chemistry and environment make it a compelling target for missions in the quest to discover extraterrestrial life, boosting its status as a key target for astrobiology.

Subsurface Ocean

The discovery of subsurface oceans on celestial bodies like Europa and Enceladus has expanded our understanding of where life might exist beyond Earth. These hidden oceans are significant because they broaden the scope of habitability throughout the solar system. Subsurface oceans are crucial due to:

• Protection from harsh surface conditions — they are shielded from harmful radiation and extreme temperatures.
• Environmental stability — can maintain liquid water over long geological time scales, essential for life’s development.
• Plausible nutrient exchange — might occur at the ocean-ice boundaries or through hydrothermal vents.

These oceans, kept warm by geothermal processes, mirror the conditions of Earth’s deep-sea habitats where life thrives away from sunlight, suggesting similar possibilities on other planets and moons.
This makes them central to the study of astrobiology and the search for life.

Geothermal Energy

Geothermal energy is an important factor in astrobiology because it provides a potential heat source necessary for sustaining life in outer space environments. On icy moons like Europa and Enceladus, geothermal energy could enable subsurface oceans to remain liquid, making them more hospitable. Geothermal factors to consider:

• Tidal heating — generated by gravitational interactions, crucial for maintaining liquid water beneath icy surfaces.
• Volcanic and hydrothermal activity — these processes provide chemical nutrients and energy, analogous to Earth’s oceanic thermal vents.
• Influence on chemical processes — geothermal energy can drive complex chemical reactions that are possible precursors to life.

In environments devoid of sunlight, such as beneath the ice of Europa or Enceladus, geothermal energy may be the critical element supporting ecosystems, just as hydrothermal vents support deep-sea life on Earth.