Question

What evidence suggests that water might still flow at or beneath the martian surface today? Why do we think that Mars might still have subsurface liquid water today?

Short answer

Recurring slope lineae, hydrated salts, and radar data suggest possible subsurface liquid water on Mars.

Step-by-step solution

Examine Seasonal Dark Streaks

Start by examining images from Mars orbiters that show recurring slope lineae (RSL). These are dark streaks that appear seasonally on warm Martian slopes. The presence of RSLs suggests the possibility of flowing liquid, possibly briny water, due to their seasonality and temperature correlations.

Analyzing Salts and Brine

Consider the role of salts that have been detected on the Martian surface. Since the presence of salts can lower the freezing point of water, this supports the hypothesis that liquid brine, rather than pure water, might flow transiently. This idea is bolstered by spectrometer data revealing hydrated salts in RSLs.

Ground-Penetrating Radar Observations

Review data from ground-penetrating radar, such as that from the Mars Reconnaissance Orbiter, which indicates significant underground ice reserves. These observations suggest that subsurface liquid water might be kept from freezing by geothermal heat.

Climate and Geological Evidence

Examine Martian climate models and geological formations that suggest underground aquifers might exist. Given Mars' past history of liquid water, hydrothermal activity, and volcanic activity, it is possible that pockets of liquid water remain underground today.

Synthesize Evidence

Combine observations from surface features, radar data, and chemical analysis to support the hypothesis of subsurface liquid water. The recurring nature of certain features and the presence of underground ice strongly indicate that Mars might still harbor liquid water beneath its surface.

Key concepts

Recurring Slope Lineae (RSL)

Recurring Slope Lineae (RSL) are fascinating seasonal features observed on Martian slopes. These dark streaks appear during the warmer months and fade as temperatures cool down. Scientists believe that these changes are strongly linked to the presence of liquid water, albeit not in its purest form. The recurring nature of these slope lineae suggests a repeating process, possibly involving the temporary flow of briny water.

• The streaks are typically observed on steep slopes, which helps the liquid water flow more effectively.
• The brine, rich in salts, might allow the water to remain liquid even on chilly Martian days by lowering its freezing point.
• These features have been extensively documented via high-resolution images sent back by orbiters such as the Mars Reconnaissance Orbiter.

This evidence of seasonal change provides a compelling clue that there might be a liquid water process occurring on Mars today.

Hydrated Salts

The presence of hydrated salts on Mars is crucial in supporting the idea that liquid water might exist there. When scientists speak of "hydrated," they are referring to minerals that contain water molecules as part of their structure. On Mars, the detection of these salts, especially in relation to RSL, has been a game-changer.

• Hydrated salts like perchlorates can drastically lower the freezing point of water, potentially allowing it to stay liquid at temperatures where pure water would freeze.
• The spectrometer data used to detect these salts indicates they are widespread, further supporting the notion of transient salty water flows.
• This briny residue can accumulate and create temporary flows during optimal conditions, explaining the seasonal appearance of RSLs.

Thus, the chemistry of Mars aligns with the visual evidence of liquid flows, strengthening the case for subsurface brines.

Ground-Penetrating Radar

Ground-penetrating radar plays a vital role in uncovering Mars' hidden secrets beneath its surface. This technology has enabled scientists to detect subsurface ice deposits that suggest there might be environments where liquid water could survive.

• These radars can penetrate the Martian surface, sending back valuable data about what lies hidden below.
• The Mars Reconnaissance Orbiter carries such a radar, detecting considerable amounts of frozen water, which indicates potential aquifers below.
• Geothermal heat from the planet's core might prevent these water reserves from freezing completely, crafting a plausible setting for liquid water to exist.

Through these radar observations, a clearer picture emerges of a dynamic and possibly wet Mars beneath its dry and cold exterior.

Martian Climate Models

Martian climate models offer a theoretical framework that helps to understand how Mars' past environments could still hold influence today. These models take into account various factors, such as historical climate changes and geological formations, that indicate where underground water might linger.

• They assess the remnants of past hydrothermal and volcanic activity, which might have left behind liquid water safe havens.
• By simulating past climate conditions, these models help scientists predict where aquifers may still exist below the surface.
• The synergy of these models with observational data shapes a compelling narrative about Martian water, keeping the search for life ever pertinent.

In essence, the combination of climate modeling with the available geological structures paints a cohesive story of a once wetter Mars that might still retain underground water reserves.