We Might Finally Understand What Happened to Mars’ Missing Water

Mars once boasted a sprawling ocean across its surface. Over time, the magnetic field diminished, the atmosphere thinned, and the water vanished. Yet, the total isn’t accounted for. This water must have disappeared somewhere as the red planet transitioned from a watery haven to the dusty landscape we recognize today. So, what happened to it?

A recent study published in National Science Review by researchers from China, Australia, and Italy has uncovered potential vast reservoirs of water located deep beneath the planet’s surface, providing answers about its fate. Unlike the icy reservoirs found elsewhere on Mars, this water is believed to remain in liquid form, making it a promising candidate in the search for extraterrestrial life.

Around 4 billion years ago, liquid water covered much of Mars’s surface. If evenly distributed, this water would have created a global ocean approximately 1,500 meters (4,920 feet) deep, comparable to the volume of the Indian Ocean on Earth today.

While exact figures are still under debate, this estimation highlights a significant discrepancy.

“Estimated losses of liquid water due to atmospheric escape and crust hydration are predicted to be between 10-200 meters (33-656 feet) and 550 meters (1,800 feet) respectively,” stated Waijia Sun, a geophysics professor at the Chinese Academy of Sciences and lead author of the study, as reported by BBC Science Focus.

“Current estimates suggest a total of 20-40 meters (66-131 feet) of water exists in Mars’s atmosphere and as ice in polar or subsurface deposits.”

The “missing water” on Mars, estimated at a range between 710 and 920 meters (2,330 and 3,020 feet), remains unaccounted for, according to Sun and colleagues.

Marsquakes and Meteorites

With NASA’s InSight lander landing on Mars on November 26, 2018, a new perspective of the planet’s interior became available. Equipped with a dome housing a seismometer, it measures seismic activity similar to how earthquakes are monitored on Earth, dubbed “pulsing” by NASA.

The research team utilized measurements from two meteor impacts and seismic waves generated by a “Marsquake.” BBC Science Focus co-author Professor Hrvoje Tkalčić compared this technique to medical ultrasound, allowing glimpses into the Martian interior.

“In essence, earthquake waves generated from distant events travel through the Earth’s crust beneath the seismometer,” explained Tkalčić. “By analyzing their reverberations, we can deduce the thickness of these layers and the depth of boundaries.”

Seismic waves travel faster through rock that contains water. By measuring the velocity of waves resulting from impacts or quakes, scientists can investigate the presence of deep underground water without the need for excavation.

This innovative method, known as the “receiver function,” enabled the team to identify layers approximately 5.4-8 km (3.4-5 miles) below the Martian surface where seismic waves slow down, indicating water’s presence.

At these depths, temperatures are sufficient for liquid water to exist. Researchers estimate that the water present ranges between 520-780 meters (1,700-2,560 feet) beneath the surface.

Could There Be Life on Mars?

If substantial aquifers lie below the Martian surface, it could be an ideal location to search for alien life. Water is a crucial element for life on Earth, sustaining even deep subterranean microorganisms like bacteria and archaea, which constitute around 15% of Earth’s total biomass.

While finding complex life forms is unlikely at such depths on Mars, microbial life remains a distinct possibility.

“The availability of liquid water is viewed as a key factor in our search for life, as it is essential for existence,” noted Tkalčić. “Consequently, pinpointing locations with liquid water on Mars is vital for identifying potential life.”

Additionally, if humanity establishes a presence on Mars, water becomes a critical resource. Excavating kilometers below the surface presents significant engineering challenges, but such obstacles are to be expected in pioneering a human settlement on another planet.

However, before rushing to buy tickets to Mars, Sun and Tkalčić caution that the aquifer’s existence is not yet confirmed. They emphasize the necessity for additional data before reaching any conclusions.

Liquid water is the most plausible explanation supported by current data, but other viable explanations for the observed seismic waves, such as layers of sediment, exist.

On Earth, seismic measurements are taken from numerous seismometers worldwide that cross-validate data points. The situation is different on Mars.

“We must remember that we are limited to data from a single seismometer on a faraway planet. It’s a challenging observational environment, and we are maximizing the quality and quantity of our data,” Tkalčić added.

Researchers aspire that upcoming Mars missions equipped with more seismometers will facilitate more comprehensive studies across the planet. Eventually, we may even analyze the crust for direct chemical evidence of water, and potentially signs of life.

For now, this research offers a hopeful glimpse into what future missions may reveal. Sun remarked: “These findings shed light on the evolution of Mars’s water cycle and its potential habitability, laying a solid groundwork for future inquiries into Martian life and the planet’s climatic history.”

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About Our Experts

Weijia Sun is a professor of geophysics at the Chinese Academy of Sciences, recognized for his work in Earth and Planetary Physics. His research has appeared in prominent journals such as Nature, Geophysical Research Letters, and Journal of Geophysical Research.

Hrvoje Tkalčić heads the Geophysics Department and directs the Warramunga Seismic & Infrasound Facility at the Australian National University. His research focuses on observational seismology, particularly the Earth’s deep structure and dynamics, appearing in journals like Science, Geophysical Research Letters, and Journal of Geophysical Research.