Date: September 16, 2010
Title: Is There Life on Mars?
Podcaster: Stuart Clark
Link: www.stuartclark.com
Description: What are the chances of finding life, no matter how primitive, on Mars?
Bio: Dr Stuart Clark is an award-winning astronomy author and journalist. His books include The Sun Kings, and the highly illustrated Deep Space, and Galaxy. His next book is Big Questions: Universe, from which this podcast is adapted. Stuart is a Fellow of the Royal Astronomical Society, a Visiting Fellow of the University of Hertfordshire, UK, and senior editor for space science at the European Space Agency. He is also a frequent contributor to newspapers, magazines, radio and television programmes. His website is www.stuartclark.com and his Twitter account is @DrStuClark.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by the NASA Lunar Science Institute at lunarscience.nasa.gov/, proud co-Founders of International Observe the Moon Night, around the globe on September 18th. More information at bit.ly/nomn.
Transcript:
IS THERE LIFE ON MARS?
Hello I’m Dr Stuart Clark, astronomy author and journalist. Today I’d like to explore the question: Is there life on Mars?
There are few places on Earth as evocative as Mono Lake, California. The glassy surface stretches off into the distance, and eerie rock formations protrude from the water, like gnarled fingers. In 800,000 years, the lake has seen an ice age come and go and has survived volcanic eruptions. The landscape is how planetary scientists imagine Mars to have been in the past, before the last of the water was lost from its surface, forcing any Martian life that may have existed to struggle for survival.
Mono Lake’s eerie fingers of limestone protrude some three metres from the surface having formed beneath when calcium-rich spring water bubbled up through the alkaline lake to combine and form limestone. These towers, known as tufas, contain an abundance of microfossils, and if astrobiologists could find such structures on Mars, they might reveal whether life ever began on the Red Planet.
The conditions on Mars today are extremely hostile: there are highly reactive chemicals in the ground, there is no air to breathe, and the surface is scoured by ultraviolet radiation and high-speed particles thrown out by the Sun. There is an apparent lack of water and the temperature swings from around 17 degrees Celsius during the day to lower than minus 100 at night.
It may be possible that conditions are right in micro-niches for organisms that would be considered extremophiles if found on Earth, or it’s possible life existed on Mars in the past under different conditions. Planetary scientists are certain Mars began its existence as a world similar to Earth, with many bodies of standing water. If so life may have begun before conditions changed.
In the quest for life on Mars, the mantra is to ‘follow the water’ because life needs a liquid for chemical reactions. Water is a simple molecule, abundant across the Solar System. Until astrobiologists are forced to consider more outlandish alternatives, they look for water first and then, once they find it, look for signs of life there.
NASA’s Viking orbiters revealed geological structures on Mars resembling water-cut features on Earth. The Nanedi Vallis channel meanders for 1.6 miles displaying terraced walls and oxbow curves. Water has run there repeatedly, over long periods of time. Teardrop-shaped ‘islands’ in the mouth of Ares Vallis, suggest floods emptying from the valley onto the surrounding plains. NASA’s 1997 Pathfinder rover encountered many rounded rocks indicating watery erosion.
Mars may once have had a large ocean evidenced by the contrast in its two hemispheres. The southern is mostly high ground, with jagged craters and chasms, whereas the northern is a much smoother low-lying basin implying an earlier ocean. There are two possible shorelines, each stretching for thousands of kilometres around the northern basin, and estimated to be between two and four billion years old.
As the Sun’s deadly radiation eroded the atmosphere, dried up the lakes, seas and even the ocean, some of the water must have been lost to space because, with no magnetic field or ozone layer to protect Mars’s atmosphere, the water molecules would break up. Liberated hydrogen escaped the planet’s gravity into space, whereas the heavier oxygen sank to the surface combining with minerals in the rocks. Any remaining water drained downwards into the rocks and froze. Widespread life would have perished, and the remainder driven into niches.
Most remaining water is thought to be below the surface in icy plains, or deep underground lakes. In 2002, NASA’s Mars Odyssey orbiter showed ice buried a few centimetres down in the northern hemisphere. Phoenix landed in the middle of these plains on 25 May 2008, swiftly verifying large deposits. In the spirit of ‘follow the water’, it boosted the possibility of finding ongoing life on Mars.
It is ironic that as planetary scientists collect more and more data from Mars, they find themselves presented with an increasingly confusing picture as to whether the red planet is habitable or not.
Two radar instruments have been sent to Mars, designed to send radio waves to a kilometre’s depth or more and bounce back from the supposed boundaries between rock layers and water layers but neither has seen anything resembling a lake. Perhaps the water is deeper than anticipated, or simply not there.
On Earth, the fossil record of life’s origin has been lost because of our planet’s restless surface. Driven by the decay of radioactive elements in the Earth’s interior, our continents float on a semi-molten layer, moving by a few centimetres each year in a process called plate tectonics. If the continents rub past one another they produce earthquakes; if they push against each other, they build mountain ranges. If one plate rides roughshod over another, it forces it down into the interior of the Earth, where the rocks are melted and recycled in the form of lava that bursts through volcanoes at the surface, thereby destroying nearly all of the truly ancient rocks and taking with them any traces of the Earth’s first life forms.
This may not be true for Mars; being a smaller planet, there was not enough radioactive heat to begin full-scale plate tectonics. So parts of Mars – like the Moon – must be primordial, dating back to the original formation of the planet. A meteorite called ALH 84001, regurgitated by a glacier near the Allan Hills in Antarctica, was discovered in 1984. Analysis showed it is around 4.5 billion years old, placing it at the very origin of the Solar System.
Small bubbles of gas trapped inside the rock displayed the same composition as the Martian atmosphere. It is thought the rock solidified as part of Mars’s original surface and was blasted during an impact in the late bombardment, around 4 billion years ago. Falling back to Mars, it remained on the surface until another impact, 13 million years ago, sent it careering into space. It crossed paths with Earth some 13,000 years ago.
Then in 1996, NASA showed the world scanning-electron-microscope images of tube-like structures found in a sample of ALH 84001. Clearly distinct from the surrounding rock they looked eerily reminiscent of bacteria fossils found on Earth. Chemical evidence suggested the tubes might indeed once have been alive. However they are only 10–100 billionths of a metre in diameter, one hundred times smaller than a microbe. Other scientists claim they could be made through simple crystallization processes, without the intervention of life.
Now however, we may have our strongest evidence yet of life on Mars.
For several years planetary scientists have been detecting methane on Mars, localized in three regions rather than spread thinly through the atmosphere, and this strongly suggests that it is produced in those regions. Either there is current volcanic activity inside Mars, or there are colonies of living Martian microbes metabolizing under the surface. Either option is quite mind-blowing.
But until we can get to Mars and determine, hands-on, whether it is life or volcanic activity, we will remain uncertain whether there has been, or still is, life on Mars.
End of podcast:
365 Days of Astronomy
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