For centuries, people have looked to Mars with fascination. The blood red planet named after the Roman god of war has been the subject of numerous books, movies, and artwork, speculating what is on its surface and whether it bears resemblance to our own planet.
Nowadays, astronomers are interested in Mars because of its strikingly similar paleoclimatology to that of Earth, with its polar ice caps, seasonal changes, and predictable weather patterns.
In addition, the discovery of dried lake and riverbeds on the surface of Mars in the 1990s showed that liquid water once flowed on the planet’s surface. The origin of this water, however, remains a mystery. Researchers at MIT suggest water may have been hauled to the surface by hot lava released during volcanic eruptions, but this theory fails to explain the origin of the water.
Astronomers believe that understanding the history of water on Mars is key to discerning whether life ever existed on Mars or whether it may exist in the future. Water has a host of unique chemical properties that allow survival. It has strong adhesive and cohesive properties, high solvency and surface tension, and neutral pH, critical in metabolic pathways, habitats, transportation, and other important life processes.
Water is a cellular solvent, a starting material for photosynthesis, and allows cooling via evaporation – just to name some of its functions. Without the presence of liquid water on Earth, it is believed that life would never have taken hold. As such, studying the presence of water on Mars essentially means studying the possibility of life.
On August 4, 2007, NASA launched the spacecraft Phoenix on an expedition to “follow the water.” Its landing on Mars’ north arctic plain on May 25 the following year marked NASA’s sixth successful landing on Mars and the first successful landing on the polar region of the planet.
Upon landing, Phoenix immediately set to work, excavating and examining Martian soil using its robotic arm and microscopic imager, in hopes of finding evidence for subterranean water. Just five days later, Phoenix found strong evidence of the existence of water-ice in a trench known as Dodo-Goldilocks.
Phoenix also studied the geochemistry of the surrounding dirt to determine what chemicals, minerals, and organic compounds might be combining with water. However, the craft made its final contact with Earth on November 2, 2008, and the mission was declared dead eight days later.
Astronomers focus on finding water beneath the surface of Mars because liquid water cannot exist on its surface, where the climate is too cold and the atmosphere too thin. Mars’ atmospheric pressure averages around 600 Pascals, approximately 0.7 percent of Earth’s atmosphere, and its mean temperature is around -60°C.
The temperature and atmospheric pressure of Mars represent conditions below the triple point of water, which is the state in which gas, liquid, and solid water exist in equilibrium. As a result, solid water sublimes directly into water vapor, bypassing the liquid phase.
The low pressure, low temperature conditions are attributed to Mars’ faint atmosphere. While astronomers tend to agree that Mars lost its liquid water due to the slow degradation of its atmosphere, there is less consensus on the how Mars lost its atmosphere.
One leading theory proposes that solar wind blew Mars’ atmosphere into space. The Sun constantly bombards all planets in the solar system with charged particles, mainly protons and electrons. These particles slowly degrade the compounds that form an atmosphere.
Earth’s magnetic field shields our atmosphere from degradation. However, as Mars lacks a magnetic field, the theory purports that its atmosphere was blown away. Consequently, seventy to ninety percent of Mars’ water evaporated into space or became trapped in subterranean rocks and minerals.
The solar wind theory, however, is challenged by findings from Earth’s sister planet Venus, which has an atmospheric pressure ninety times that of Earth and no magnetic field shielding it from solar wind.
A second theory states that Mars’ weak gravitational field – 38 percent as strong as Earth’s – fails to retain gases in its atmosphere. Finally, some suggest a meteor’s crashing into Mars blew its atmosphere into space.
Phoenix was the first installment of a three-part mission known as the Mars Scout Program (MSP), established by NASA to further our understanding of Martian atmosphere, climate, and past and potential soil habitability. All Mars Scout spacecraft are the winners of a NASA competition: Phoenix, created by Peter Smith from the University of Arizona and costing roughly 420 million dollars, beat out 43 contestants and 3 finalists.
The second installment of the Scout Program, the Mars Atmosphere and Volatile Evolution (MAVEN), will test the three leading theories of atmospheric loss by taking measurements in the ionosphere (the upper atmosphere ionized by solar radiation) and by examining interactions with solar wind.
MAVEN is scheduled to launch November 18, 2013. The third mission spacecraft has not yet been selected, but is expected to launch around 2018. Researchers hope that the MSP will provide insight to some of the questions that Mars has posed for centuries. Until then, we can only speculate and debate.
- NASA Mars website, https://www.nasa.gov/mars
- Official MAVEN mission website, https://lasp.colorado.edu/maven/
- Jakosky, B.M., & Phillips, R.J. (2001) “Mars’ volatile and climate history.” Nature Vol. 412, p. 237-244. https://www2.ess.ucla.edu/~nimmo/ess250/jakosky.pdf