Question

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. Based on current evidence, the object in our solar system most likely to have a deep, subsurface ocean of liquid water is (a) Mars; (b) Europa; (c) Titan.

Short answer

The best answer is (b) Europa, due to strong evidence of a subsurface ocean.

Step-by-step solution

Understanding the Choices

Let's begin by understanding the options. Mars is known for having water ice at its poles and possibly groundwater. Europa, a moon of Jupiter, is hypothesized to have a subsurface ocean beneath its icy crust. Titan, Saturn's largest moon, has surface lakes and rivers of liquid methane and ethane, with the possibility of subsurface water.

Analyzing Current Evidence

Current scientific evidence, primarily based on data from spacecraft and telescopic observations, indicates that Europa has a thick ice crust with strong hints of a liquid water ocean beneath. This evidence includes surface features that suggest movement and potential water-ice exchange and magnetic field data pointing to a conductive layer beneath the ice.

Considerations for Titan

Although Titan is intriguing with its hydrocarbon lakes and potential for a water-rich interior, current evidence is not as strong or direct for a subsurface ocean as it is for Europa. Investigations from the Cassini mission highlighted its atmospheric and surface characteristics but did not confirm a subsurface ocean.

Evaluating Mars's Potential

Mars has shown signs of past water flows and ice deposits on its surface, yet there's no substantial evidence supporting the existence of a current subsurface ocean, especially a deep one.

Choosing the Best Answer

Given the available evidence indicating a high probability of a subsurface ocean, the object in our solar system most likely to have such an ocean is Europa. This conclusion is based on the observable data and scientific consensus at this time.

Key concepts

Europa

Europa, one of Jupiter's largest moons, has fascinated scientists due to its potential subsurface ocean of liquid water. Covered with a smooth, icy surface, it's believed that beneath lies a vast ocean. This ocean might contain twice as much water as all of Earth's oceans combined. The surface features, such as chaotic terrain, suggest movement which could be caused by the flow of liquid water beneath the ice.

The interest in Europa originates from data collected by spacecraft missions like Galileo, which provided evidence of a subsurface ocean. This evidence includes observations of plumes of water vapor and a magnetic field influenced by a conductive fluid like saltwater under the icy crust.

• Surface cracks and ridges hint at subsurface interactions.
• Europa's ice crust is estimated to be 10-15 miles thick.
• The ocean might be up to 40-100 miles deep.

Jovian Moons

Jovian moons refer to the moons orbiting the gas giant Jupiter. Of the 79 known moons, the four largest, discovered by Galileo in 1610, are known as the Galilean moons. These include Io, Europa, Ganymede, and Callisto.

Each of these moons presents unique characteristics:

• Io: Known for its numerous active volcanoes and is the most geologically active body in the solar system.
• Europa: Famous for its potential subsurface ocean.
• Ganymede: The largest moon in the solar system and may also have a subsurface ocean.
• Callisto: Features an ancient, heavily cratered surface and a possible subsurface ocean.

These moons have been subjects of intense study due to their diverse environments, helping us understand the composition and history of our solar system.

Astrobiology

Astrobiology is the scientific field concerned with the study of life in the universe. It seeks to understand the potential for life on other planets and moons, examining factors such as water, biological molecules, and energy sources. Europa stands out as a focal point in astrobiology due to its potential subsurface ocean.

If Europa's ocean harbors life, it could enhance understanding of life's resilience and adaptability. This would imply that life could exist in conditions previously considered inhospitable, challenging our definitions and expectations of habitability. Scientists focus on

• Chemosynthesis: A process through which organisms might obtain energy in Europa's dark ocean.
• Astrobiological signatures: Chemical markers that could hint at biological activity.

This exploration will involve analyzing Europa's surface and potential plumes to search for these critical signatures.

NASA Missions

NASA has planned several missions aimed at exploring Jupiter's moons, with a particular emphasis on Europa. One such mission is the Europa Clipper, scheduled to launch in the 2020s. Its primary goal is to gather detailed data about Europa's ice shell, subsurface ocean, and surface conditions.

The Europa Clipper will carry a suite of scientific instruments to measure Europa's ice thickness, search for subsurface water, and analyze the moon's surface composition and topography. It will also look for potential water plumes, similar to those observed by previous missions.

• Advanced imaging systems to capture high-resolution images of Europa.
• Mass spectrometry instruments to sample and analyze vapor and particles.
• Magnetometers to detect subsurface ocean characteristics.

These missions aim to uncover Europa's secrets and assess its habitability, laying the groundwork for potential future explorations, including landers that could one day dig beneath the icy surface.