Looking for Life

By Pam Eastlick

THE STORY OF A SMELLY MOLECULE

A story surfaced last week that could be one of the most important stories of the century. It was overshadowed (and perhaps rightly so) by war and inaugurations and quickly disappeared, but for us science geeks, it caused heads to pop up and point into the wind. We were sniffing for the faint traces of methane. Why? Because methane has been discovered in the atmosphere of Mars. So, why is that news?

Methane (aka CH4) is a very simple gas with a distinctive odor that’s a common component of sewer gas (which gives you some idea that the odor probably does not recall your mind to roses). The C in the chemical formula tells you that it contains the element carbon and it is one of the ‘organic chemicals’.

Carbon loves to bind with other chemicals and methane which has only one carbon is inherently unstable. Methane gas quickly combines with almost any other compound it runs across and become something else.

Because of this rapid combing feature, free methane gas is rare or absent in any atmosphere. And here’s the really important part. As far as we know now (and that is a pretty big caveat), free methane gas can be produced by only two methods. The first is by geologic processes.

Volcanic seeps and eruptions can produce it. There are huge underground reservoirs of ‘natural gas’ on planet Earth. Natural gas consists of methane, ethane, pentane, hexane and many, many other ‘anes’ which are simply chains of carbon molecules with hydrogens stuck on. Atmospheric methane is easily detected around any sort of geologic activity.

Since the planet Mars is the proud possessor of the biggest volcano in the solar system (Olympus Mons: 13 MILES tall) it seems only logical that there would be an incredible amount of methane, sulfur, dust, rocks and all the other indications of volcanic eruptions. Not true, of course; Mars is a ‘dead’ world geologically.

We have orbiting robots around Mars just as we do around Earth. The Mars orbiters do have a unique advantage over their Earth counterparts; they can see the surface of the whole planet whilst the Earth robots can only see 30% of the land on Earth. The Mars robots haven’t seen any trace of volcanic activity. They’ve seen huge landslides and tiny dust devils and melting and thawing ice, but no volcanic activity. And active volcanoes are pretty hard to hide (except on Earth, where most of the planet’s active volcanoes are underwater).

Small gas seeps wouldn’t really be visible to the orbiting eyes and they are a possible source of the atmospheric methane that we’ve recently detected (which was detected, by the way, by telescopes located on top of Earth’s biggest volcano, the island of Hawaii). So the methane could be coming from geologic sources.

But there’s another source of atmosphere methane that’s even more intriguing. You produce methane every day of your life. It’s a common by-product of the bacterial metabolic processes that digest your food for you. Cows produce methane, your dog produces methane, it is produced in abundance by teen-aged boys who find it a great source of humor. Everything that eats produces methane as a result of that eating. Methane production, in short, is a sign of LIFE.

The methane in the atmosphere of Mars could mean, without question, that there’s some kind of life on a ‘dead and lifeless’ planet. There’s not much methane in Mars’ atmosphere, unlike Earth, where cows produce it by the metric ton. There’s not a whole lot of whatever is making it. Small gas seeps fit the bill as could subsurface bacteria that survive the intense Martian cold and thin atmosphere by living underground.

Kids who come to the Planetarium ask me all the time “Miss, is there life anywhere else in the solar system?” I used to tell them that there were only two places where life-as-we-know-it could survive. The atmosphere of Jupiter (still a viable option but there are no plans that I know of on the drawing board to go and check) and Europa, one of the moons of Jupiter. There is one other very viable candidate that I’ll talk about next; and now, I’ll be proud to add Mars.

If there is life on Mars, it’s probably not any more complicated than a bacterium, but those bacteria could tell us volumes of information about the origins of life on our own planet. Do the Martian bacteria have DNA? Are they just like our bacteria or radically different? Did Martian life take a space ride deep inside a rock blasted from the Martian surface by a meteor impact and wind up here on Earth? Are we all Martians? Science is full of surprises and all you have to do is wait for the answers.

WOBBLY MOONS

Besides carbon, the other requirement for life-as-we-know-it is liquid water. Those underground bacteria could easily have access to water on Mars in the form of ice which their internal heat could melt or there could be liquid water below the ice, just as there is in Antarctica.

Liquid water is a comparative rarity in the solar system. There’s literally tons of water, but most of it is ice. Until very recently the only place we knew of with lots of liquid water is Earth. But those roaming robots have shown us that there are at least two other places out there that probably have more liquid water than Earth, much more.

One of them is Europa, the ice moon that circles Jupiter. When we sent robots to orbit Jupiter, we discovered that Europa wobbles as it orbits Jupiter. You can tell if an egg is hard-boiled by spinning it. A hard-boiled egg is a solid body inside and it spins just like a top. A raw egg has liquid inside it and that liquid has two different densities. A raw egg won’t spin; the liquid inside brings it to a quick halt.

The fact that Europa wobbles implies that there’s liquid inside. Since the surface of Europa is frozen water ice, the implication is that the inside of Europa is filled with liquid water with a rock core at the center. Europa probably has a liquid water ocean that’s around 20 miles deep. Europa is about the size of our moon and may contain more liquid water than the seas of Earth.

Today we can only hypothesize about the seas of Europa, but there is another moon that we know a little more about. We have a robot called Cassini in orbit around the planet Saturn and it’s discovered something very interesting about the brightest little moon in the solar system.

The moon’s name is Enceladus, and we’ve known for a long time that the surface had to be made of something very reflective. The surface of Enceladus is solidly frozen water ice and it’s as reflective as new-fallen snow. And Enceladus also wobbles as it goes around Saturn.

Then Cassini found something really interesting. There were what the team called ‘tiger stripes’ at Cassini’s south pole. A closer look during one of Cassini’s scheduled fly-bys of Enceladus revealed these ‘tiger stripes’ were huge cracks in the ice.

Then they discovered something REALLY interesting. Liquid water was erupting from these cracks. We don’t have to infer from the wobble that Enceladus contains liquid water, we KNOW it does.

According to a recent press release from the Cassini team:

New carefully targeted pictures reveal exquisite details in the prominent south polar "tiger stripe" fractures from which the jets emanate. The images show the fractures are about 300 meters (980 feet) deep, with V-shaped inner walls. The outer flanks of some of the fractures show extensive deposits of fine material. Finely fractured terrain littered with blocks of ice tens of meters in size and larger (the size of small houses) surround the fractures.

One highly anticipated result of this flyby was finding the location within the fractures from which the jets blast icy particles, water vapor and trace organics into space. Scientists are now studying the nature and intensity of this process on Enceladus, and its effects on surrounding terr
ain.

Did you notice something very interesting in that second paragraph? If you’re a science geek like me, one phrase stands out like it was in boldface type and red letters. The phrase is “trace organics”.

As a scientist said who studies the moon Europa: “Do you really think you can have a liquid water ocean for five billion years and NOT have life in it?”

Are we alone? More and more evidence is giving us the answer “Probably not!”

The ‘tiger stripes’ on Saturn’s ice moon Enceladus. (Credit: NASA/JPL/Space Science Institute)