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Discovering Terra Nova

Jaymie Matthews, Associate Professor, Department of Physics and Astronomy

In the next 10 years, astronomers have a strong chance of discovering a planet that has the right characteristics to allow for life, thanks to new ways of “seeing” planets, and space telescopes like Canada’s MOST space telescope, already searching for terra nova.

Are we alone in the Universe?  If we have neighbours, how far away are they, and will we ever be able to drop by and borrow a cup of sugar?  (Or maybe silicon, depending on their biochemistry.)

Radio astronomers have been trying to answer this question through SETI (the Search for ExtraTerrestrial Intelligence) by listening for artificial signals from space since the 1960's.  But the odds of success are long, and even the most optimistic fan of the movie"Contact" might hesitate to bet on actually making contact in the
next decade.

On the other hand, I'm willing to bet that within ten years, optical astronomers will find a planet aound another star that has the right mass and orbit to allow the possibility of life.  That discovery will be a milestone, in science and philosophy, even if there's no evidence that the planet actually has a biosphere.

A decade ago, Swiss astronomers were surprised to find a giant planet in a tiny orbit around an innocuous Sun-like star called 51 Pegasi.  Since then, planet hunters have turned up about 170 exoplanets around about 130 stars.  This has transformed the study of planetary systems, which used to be based on a sample of exactly one (our Solar System), into a true statistical science. Still, all of those "exoplanets" are more like the inhospitable gas giant Jupiter than the Earth we call home.

Most of these planets have been found using the same basic principle that a traffic cop uses to find that someone is speeding at 100 kph in a 65-kph zone.  The gravity of an unseen planet will cause the star to "wobble" back and forth with the same period as the planet's orbit, moving with the speed of a car on the highway or (for massive planets in small orbits) a passenger jet. Using a technique pioneered at UBC and UVic, astronomers can measure the periodic motions of the star through the Doppler shifts of the star's light, just as the wavelength of a radar wave echo from the bumper of a receding car is shifted by an amount proportional to the speed of the car.

But the wobble induced in a star by a low-mass planet is too small to be measured reliably, so this radial-velocity technique will not turn up any alien Earths.  It would be nice to take a picture of a planet around another star, but that would be equivalent to getting a snapshot of a mote of dust floating a few centimetres from an 800-W streetlamp located over 1000 km from your camera.  That's beyond our capabilities for at least the next decade or two.

One of the easiest ways to "see" an Earth-sized planet would be to watch it pass in front of the star, dimming the star's light during its passage by about 0.01% for a few hours each orbit. Unfortunately, from the ground, the turbulence of the Earth's atmosphere (which causes starlight to twinkle) means that such small dips (called "transits") are lost in the noise.  Making things worse, groundbased measurements can only follow a star for brief intervals of time, with many interruptions. To detect an Earth-like planet at the right distance from its star to be able to support life as we know it, you need to stare at a star for years without interruption.

But that's not all.  To see a transit, the plane of the planet's orbit must be aligned with our direction, so that it crosses in front of the star from our perspective.  This would happen by chance for only 1 out of every 200 stars that actually possess such planets.

Undaunted by such odds and obstacles, like early explorers who wanted to survey unknown terrain, astronomers are moving their search to higher ground.  Actually, above the ground altogether.  Into space.

Canada's MOST space telescope is already searching a small number of stars for planets too small to be detected by other methods, but this is really just the first step.  Next summer, a French satellite called COROT is due to be launched on a mission to stare at two small regions of the sky (nicknamed the "eyes" of COROT) for up to five months each to search for planets among about 50,000 stars.  It may turn up some "hot Earths" in tight orbits -- not too attractive for life, but vital to understanding the formation and evolution of planetary systems.

The bonanza should come after 2008 with an American mission named for the scientist who first recognised the fundamental laws of planetary motion in the 1600's.  KEPLER will stare at hundreds of thousands of stars in a tiny patch of sky for several years, and is expected to turn up dozens of Earth-sized planets whose orbits are in what planet hunters call the "Habitable Zone", at just the right distance for liquid water and the conditions for life to exist.

Think "Goldilocks & The Three Planets". If a planet is too close, it will be too hot.  Too far away, too cold. In the Zone, and it's just right for life.

Astronomers are fairly certain that Earth-like planets are out there in significant numbers, but we won't know until we conduct a sensitive and systematic search. That search is about to begin. Even if we find those planets, experience has taught us that the Universe will have surprises in store for us. Many of the assumptions we currently hold dear may have to be tossed aside when we start to see what other planetary systems are truly like.  There are already hints that our Solar System may not be as typical as we once believed. In fact, the discovery of an Earth-like planet is just one of the "next big things" we can see on the horizon.  The true "next big thing" may blindside us entirely, like the recognition by Hubble of the expansion of the cosmos.

I've already predicted publicly that an Earth-sized exoplanet will be detected in the next five to ten years. (I didn't make a bet, but I said it on CNN, so if I'm wrong, they may send Wolf Blitzer after me.) But the implications of that discovery and those that follow are much harder to predict.

On an astronomical scale, our Earth is a tiny thing. Finding another one like it elsewhere in the Galaxy, however, is likely to be a very big thing, not just to astronomers, but to everyone who looks up into the sky at night and wonders whether we're alone in the Universe.