Astrobiology & The Search for Life Beyond Earth

Peter McMahon
7 January 2013

Above: A strand of DNA explodes out of an immense spiral galaxy as an artistic ‘suggestion’ that there might be life beyond Earth with its own unique genetic code.

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The quest for life beyond earthThe quest for life beyond Earth is a multi-century rollercoaster that’s captured our imaginations, raised our hopes, dashed those hopes, and then raised them again.

While we haven’t actually found life beyond Earth, it seems like every day brings a scientific discovery that makes (or breaks) the possibility of extraterrestrials.

The study of the origin, evolution, and future of life in the universe (on and off the Earth) is an area of science called astrobiology, and it could someday lead to the discovery of life beyond our home planet.


1800s: ‘Venice’ on Mars?

Mars canal sketchesPercival LowellThe search for life beyond Earth is nearly as old as science, but that search really got underway when we humans gained the technology to zoom-in on other places in the universe.

In 1877, Italian astronomer Giovanni Schiaparelli looked through an early telescope and described what he saw as “canals” on Mars. (The view Schiaparelli might have seen is recreated in the image above, at left, with one of Schiaparelli’s sketches of Mars from around the same time on the right.)

American astronomer Percival Lowell (pictured at right at his observatory in Flagstaff, Arizona) proposed that these canals could have been built by an intelligent civilization. 

Lowell thought such a civilization might have used the canals for irrigation, drawing water from the Martian North and South Poles (which were white in even small telescopes) to regions near and on the way to the equator.


Early 1900s: Venus as a Spring Break Destination??

Venus as compared to earthBetween 1918 and 1930, scientists and authors thought that Venus might be a warmer “twin” of Earth.

But these hopeful dreams of alien societies just next-door to Earth and whole worlds of Caribbean paradises ended once we started peering through larger telescopes and landing robot probes on these planets.


The surface of VenusA Rude Awakening

For example, space probes revealed Venus to be a hellish 600° C oven, with 90 times the surface pressure of Earth, scorched by lightning and sulphuric acid rain.

MarsEven worse for prospects of life in our solar system, higher-power telescope views (at left) and orbiting probes showed that those “canals” Schiaparelli claimed to have seen on Mars were just an optical illusion.

Viking on Mars Since the 1960s, probes, and robotic landers/rovers, have revealed the Red Planet to be a freezing, airless desert.

When we asked those robots to analyse soil they dug up on Mars in the 1970s, 1990s, and last-decade, they didn’t find any alien life – not even microscopic bacteria.


Hope for Life

Rock from MarsHowever, those same probes couldn’t prove there was no life on other planets. In-fact, we’ve since found loads of evidence to suggest that life could exist on some of these worlds.

In 1984, scientists discovered a chunk of rock in Antarctica (seen here at left) that got blasted off Mars by an impact from space. The rock had been floating around the inner solar system for about 16 million years before falling to Earth around 11,000 B.C.E.

Mars rock closeupIn 1996, scientists announced that microscopic bits (seen here in the image to the right) that they found in the rock might be fossilized bacteria from the Red Planet…On the other hand, they said, the tiny bits might just be minerals that formed in shapes that look like microscopic fossils that come from Earth.

While we still don’t know for sure, a 2009 study scoped-out the same rock with technology not available in 1996 and claimed that the formations looked more like fossilized bacteria than minerals.


Water on Mars!

Mars Phoenix touching water on MarsMars Spirit Rover Artist ConceptMeanwhile a fleet of orbiters, landers, rovers and long-distance probes throughout our solar system have proved the existence (beyond Earth) of an essential requirement for life: water.

After their 2004 landings, NASA’s Mars Rovers – Spirit and Opportunity – discovered minerals that can only form in the presence of water. The Mars rovers also discovered evidence of liquid water flowing below the surface of Mars.

Finally (as seen at left) after landing at the Martian South Pole in 2008, NASA’s Phoenix lander photographed and actually touched water on Mars – the first directly-confirmed proof of water on another planet.


Water, Water Everywhere…

Around the same time, space probes across the solar system were chalking-up water discoveries left, right & centre: Jupiter’s cloud layers and its moons Callisto, Ganymede, and Europa all have water in different amounts, we found out.

Planetary scientists even think that Europa (seen closest to Jupiter in the collage of images at left) could have a liquid water ocean under its crust of water-ice, where aquatic aliens could live.

Enceladus artist conceptFurther out, Saturn’s moon Enceladus (whose surface is pictured in the artist’s concept at right) has an atmosphere of water vapour and ice volcanoes that shoot water-ice particles off the surface and into space.

Many other moons and comets have deposits of solid, liquid, and gaseous water. Some scientists even think that life in the universe is routinely distributed by comets and asteroid impacts.


MORE Prospects for Life…

You need more than just water to have life. On the most basic level, life forms have DNA that tells them what they are, what they will be, and how to exist.

In order to have DNA, you need five basic biological compounds, all of which are likely present in the atmosphere of Saturn’s largest moon, Titan. (At left is an image from Titan’s surface with an image from Earth’s Moon included for scale, while right, an image of Titan’s giant lake Ligeia Mare compared to scale with our own Lake Superior.)

This doesn’t mean life exists for sure on Titan, but the fact that such compounds are there at all is amazing. Even at a freezing -170° C, Titan has lakes and seas (it’s the only other body in the solar system to have these besides Earth) made of liquid methane and ethane – hydrocarbons that are also biological compounds that could be useful in sustaining life.


“Alien” Life Found… On Earth?

No, we haven’t really found aliens on Earth, but in the last decade, we’ve found life so strange here that it’s started to validate our beliefs of what alien life off the Earth could be like:

Exhibit A: Super-Bacteria

Mono Lake & the bacteria that live in itDid you know that bacteria (the first life on Earth and an essential part of everything from soil to pneumonia to you digesting food) have been found frozen for years in the Arctic, boiling inside volcanoes, and snuggled-up to hydrothermal vents at the bottom of the ocean.

And they don’t always function as we thought life does: In 2010, scientists discovered a bacterium (shown above, Mono Lake in California, where the bacteria live, and the bacteria themselves, inset) that can even incorporate small amounts of the poisonous element arsenic into its DNA.

Exhibit B: The Mighty (1 mm long) “Water Bear”

Tardigrade“Ew gross! Kill it kill it!” We couldn’t fault you for this being your initial reaction to seeing your first tardigrade – or “water bear” as these eight-legged creatures are affectionately known. With the largest measuring out at around a single millimetre, water bears are hardly the size of Hollywood movie mega-aliens, but they are a form of life that can exist in conditions we used to think impossible.

Also known as “moss piglets”, tardigrades can survive for a few minutes at temperatures as high as 150° C or as low as -272° C (as well as several days as low as -200° C). They can be exposed to the vacuum of space or 1,200 times Earth’s surface pressure. They can have nearly all the water sucked out of them for years and be exposed to 1,000 times the lethal dose of radiation for humans.

And after all that…they’re often still alive! Though tardigrades live on Earth, they have shown us the extremes in which life could exist elsewhere in the cosmos.


Life As We Don’t Know It

Neutron StarIn addition to life as we now know it, there could be life out there that’s truly alien to us, like creatures whose chemical make-up is based on silicon, rather than carbon (every life form on Earth is based on carbon). Imagine it: aliens that would look to be made up of crystals instead of flesh-and-blood.

In his book Extraterrestrials: A Field Guide for Earthlings Canadian space author Terence Dickinson talks about the prospect of two-dimensional life that could exist on a high-gravity neutron star. Neutron stars’ surfaces are so dense that a piece of one the size of a breath mint would weigh more than every human on Earth.


Life Among the Stars

Earth like planetsWe’ve branched out the search for life beyond Earth to the realm past our solar system.

We’re listening for signals from advanced civilizations among the stars… We’re also looking for signs of any life – advanced or not – by searching for Earth-sized planets around other stars and scanning newly-forming solar systems for the signature of water and other elements involved in the process of life.

In the coming decades, we’ll have space probes that can dive below the surface of comets or ice moons and telescopes that can see the atmospheres of planets light years away.

With those, we might even be able to detect the raw building blocks of life or perhaps even emissions from industry and other signs of civilization.

Whether or not we find life beyond Earth anytime soon, though, the search itself will be worth the effort in hopes of finding out how life in other corners of the cosmos is different from us, and (maybe) a little bit the same.

Images courtesy NASA and Peter McMahon/

Peter McMahon

Peter McMahon is a Port Hope, Ontario-based space and astronomy author, journalist, and planetarium presenter who has written/produced for CTV, Discovery Channel, The Toronto Star, Today's Parent, Canadian Geographic, Space Quarterly and the Canadian Space Agency. His latest book - Space Tourism (Kids Can Press, 2011) was chosen as a 2012 selection for the prestigious U.S. Junior Library Guild. You can read his "Wilderness Astronomer" column about stargazing in the great outdoors in each issue of Sky News: The Canadian Magazine of Astronomy & Stargazing, where he is a contributing editor.

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