Scientists have long searched Mars for signs of liquid water, including signs like mysterious dark streaks on its surface and signs like hydrated minerals that indicate their existence.
According to this new study, between 30-99% of Earth’s original water has become trapped within special rocks known as hydrous minerals; any remaining amounts either escaped into space or remain underground.
Liquid Water
Recent evidence suggested that Mars was an entirely dry planet with no liquid water reserves, although astronomers had suspected there may have been subsurface lakes on its surface but without concrete evidence for them. Now radar data indicates there may be liquid water under its southern polar ice cap – further suggesting Mars once had more hydrothermally active climate than is apparent today.
Martian water is held captive within its crust within a layer known as the cryosphere, similar to Earth’s permafrost but much deeper, that extends approximately 2.5 kilometers (1.5 miles) near the equator and up to approximately 6.5 km (4 mi) in polar regions. This layer may be sealed off from surface elements by underground fractures similar to what exists under Earth’s glaciers.
As well as cracks, Mars’ cryosphere features numerous ponds and depressions carved by water flow over time. Gale Crater was home to such features, such as geological remains from an ancient lake. These ponds provide evidence that Mars once had wetter climate.
However, more in-depth work must be conducted in order to ascertain whether these water ponds are indeed liquid, and what form they took in the past. Researchers are searching for signs of flowing water and oceans but it could take some time before any definitive evidence is discovered.
Scientists speculate that Mars once had a thicker atmosphere than what it does now, which would have produced warmer conditions and allowed rivers and oceans to form on its surface. Although some water might still exist frozen beneath its surface today, direct observation will likely reveal it sooner or later.
One potential source of Martian water that has been identified is salty brines formed when melting ice and rock erode the ground below it. Scientists are particularly drawn to deposits located in Noachian basin in eastern Mars’ Noachian basin which appear similar to fluvial drainage basins indicating that once upon a time this environment supported substantial liquid water.
Ice
Over the past decade, scientists have unearthed evidence that Mars once held more water than was originally believed. Now it seems liquid water may still exist deep underground as frozen deposits; radar scans of its polar regions have revealed massive blocks of ice while new research indicates another region nearer the planet’s equator may also contain frozen deposits that resemble those captured during earlier discoveries of Martian polar ice; its discovery can be confirmed using radar signals similar to those captured during Martian polar ice research; yet, regardless of its discolorations due to layers of dust particles covering it, it still counts as water ice!
Mars’ water ice is likely stored beneath a thick blanket of carbon dioxide, which serves to regulate its temperature by trapping heat below its surface and keep temperatures down. Only in certain polar areas does sunlight and air pollution allow some sublimation (passing directly from solid to gas without melting), leaving room for greater volumes of ice water on Mars’ equatorial region and with reduced carbon dioxide coverage in some spots, leading to greater volumes of ice water being exposed at certain poles.
Scientists have used topographic data collected by orbiting spacecraft and computer models to pinpoint areas with potential for ice deposits. When studying these areas, signs of water escaping to the atmosphere such as pits on the ground that may have formed when cracks in ice melted are seen – providing scientists a map that pinpoints key locations where ice could form deposits.
Scientists have also observed evidence of hydrous minerals on Mars. These minerals contain liquid water in their crystal structure and may indicate that Mars had wetter environments than had been anticipated.
Scientists have identified sites of hydrated minerals on Mars, hoping that similar techniques used on Earth such as drilling for water or blasting minerals with heat could be employed to extract it from rocky Martian soil and support human life on an impending Martian colony.
Ground Water
An ideal pressure-temperature regime that supports liquid water is one key component for creating stable groundwater on any planet. Porous, permeable layers bounded by aquitards (water-holding barriers) are also essential ingredients, and this new study found that both characteristics were present in Mars polar regions; although much more may lie hidden underground that current radar equipment cannot reach.
Scientists employed active remote sensing (ARS), or active remote sensing, to detect water a kilometer below the surface – far beyond where atmospheric escape could take place, suggesting it’s likely trapped beneath an icy or rock crust.
The team found evidence for a thick, slow-flowing river in Mars’ south polar region that winds its way through several valley networks. These valleys appear to have been cut by streams that fed into troughs in its polar cap trough; suggesting wet periods occurred here in the past. Furthermore, these findings fit with observations made by Curiosity which shows salty slush near its surface of its south polar ice cap.
Researchers also observed sulfate minerals are concentrated near river channels on Mars’ surface, indicative of an active groundwater system on this Red Planet. Sulfates form when water seeps through rocks and reacts with elements like sulfur in its solution to precipitate out as precipitate deposits on its surface. Sulfate deposits on Mars provide further proof of an active groundwater system having existed there in its past.
These findings support previous ice-penetrating radar studies that suggested there may be liquid water beneath Mars’ polar ice caps, yet have drawn criticism from other scientists for not gathering enough data for interpretation. To address this, UT team worked analyzed how radar pulses are absorbed by layers of ice and dust in this region to calculate temperatures which will support even hypersaline water — water with extremely high levels of salt dissolved within — remaining liquid underground.
Subsurface Water
Mars has long fascinated humans, with spacecraft searching its surface for any sign of life or water. Unfortunately, though, finding any liquid water may prove challenging as much of its current moisture may already have frozen into an underground layer known as the cryosphere; similar to Earth’s permafrost but much thicker in some polar regions and mid-latitude regions than here on Earth.
Ice layers protect groundwater from seeping to the surface, so any water that reached it must have been trapped for billions of years before reaching our planet’s surface again. But in some polar and mid-latitude regions, cracks may have opened in this cryosphere that allow groundwater to reach our planet again — these could have been created through meteorite impacts, volcanic activity, faulting or fault lines.
Once water escaped the cracks in an ice layer, it would have flowed down steep slopes before resurfacing at lower elevations, creating valleys, deltas, and other landforms that allude to an earlier time when Earth was warmer and wetter.
Numerous researchers have investigated the possibility that some subsurface water may still exist on Mars today. Their conclusions are based on radar soundings which detect areas with thin enough ice layers for their signal to reflect back onto radar sensors; radar soundings detect areas if their echo signature can be picked up by radar sounders; this water contains salts which help it remain liquid even at temperatures as low as zero degrees Fahrenheit.
Recent results of a new study indicate that subsurface lakes identified by this method may not actually contain liquid water but rather pools of slush or mud, since Mar’s polar regions can reach temperatures as low as -63 degrees Celsius (-81 degrees Fahrenheit), making water in these environments inhospitable; it would immediately transform to ice once exposed to such temperatures.
Scientists behind this latest research are trying to reconcile their observations with their models of how polar glaciers form, but their new models suggest that Mars Express detected bright spots at the southern pole that aren’t lakes of liquid water as had previously been suggested, but rather small pools of slush or mud possibly formed by mixing water and ice together.