Question

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. Scientists today are interested in searching for life on Mars because (a) we see clear evidence of a past civilization on Mars; (b) Mars contains frozen water ice at its polar caps; (c) evidence suggests that Mars had liquid water on its surface in the distant past.

Short answer

The best answer is (c) because liquid water suggests past conditions could have supported life.

Step-by-step solution

Understanding the Question

The question is asking us to determine why scientists are interested in searching for life on Mars. We need to select the most compelling reason from the given options and explain why it is the best choice.

Evaluating Option A

Option (a) states that the reason is 'we see clear evidence of a past civilization on Mars.' This statement is incorrect because, to date, no evidence of a past civilization has been found on Mars. This option can be ruled out.

Evaluating Option B

Option (b) claims 'Mars contains frozen water ice at its polar caps.' While it is true that Mars has ice caps, the presence of ice does not directly correlate to current life. It suggests a possibility of water, necessary for life, but does not address past life.

Evaluating Option C

Option (c) suggests 'evidence that Mars had liquid water on its surface in the distant past.' This is the most promising option, as liquid water is a key ingredient for life, suggesting that life could have existed when conditions were favorable.

Choosing the Best Answer

Based on the evaluation, option (c) is the best answer. Researchers focus on the history of liquid water on Mars because it increases the likelihood that the planet may have supported life, even if only microbial, at some point.

Key concepts

Mars exploration

Mars exploration has fascinated scientists and the public alike due to its potential to answer the age-old question of whether we are alone in the universe. This exploration involves both robotic missions, such as rovers and orbiters, and the prospect of human missions. Mars' similarities to Earth, such as a day that lasts just over 24 hours and the presence of a solid, rocky surface, make it a prime candidate for exploration compared to other planets.
When scientists plan Mars missions, they aim to understand the planet's geology, climate history, and potential for life. Robotic explorers like the Mars rovers are equipped with sophisticated tools to analyze soil, rock, and atmospheric samples. These missions have revealed a planet that was once much more Earth-like, with flowing rivers and lakes.

• Understanding Mars' atmosphere and surface can help us learn about the planet's history.
• Rovers like Perseverance search for signs of ancient microbial life.
• The hope is to pave the way for future human expeditions.

Liquid water on Mars

The discovery of liquid water on Mars has been a crucial factor in the search for life beyond Earth. While today Mars is a frigid desert, with temperatures that rarely rise above freezing, researchers have identified evidence suggesting that liquid water was once abundant on the Red Planet. This is important because water is essential for life as we know it.
Studies of Mars' surface and geological structures, such as valleys and canyons, indicate they were likely formed by the flow of water billions of years ago. Additionally, certain minerals on Mars can only form in the presence of liquid water, providing further evidence of its historical presence.

• Liquid water increases the likelihood of past life on Mars.
• Subsurface aquifers or intermittent seasonal flows might exist today.
• Understanding water's history on Mars helps us understand climate changes on the planet.

Search for extraterrestrial life

The search for extraterrestrial life is one of humanity's most intriguing pursuits. Mars presents a unique opportunity to investigate this question because of its potential to have once harbored life. Scientists look for biosignatures, which are indicators of past or present life, such as specific chemical patterns or organic molecules.
Mars expeditions aim to uncover whether microbial life ever existed on the planet. Instruments on Mars rovers analyze rocks and soil for chemical traces that could indicate biological activity. Investigations of subsurface environments and recurring slope lineae—a seasonal flow of brine—are particularly promising.

• Mars' conditions in the past were likely to support life.
• Scientific instruments on rovers seek signs of organic compounds.
• Understanding Mars' habitability expands our knowledge of potential life elsewhere.

This search not only informs us about Mars but also supports the broader question of life's prevalence in the universe.