If other worlds were out there, astronomers knew they were devilishly hard, maybe impossible, to detect. Into this astronomical minefield walked the two Canadians.
They met 40 years ago this month, when Bruce Campbell, a 21-year-old third-year student in engineering and physics at the University of British Columbia, took his first astronomy class. At the front of the lecture hall was Gordon Walker, a 33-year-old, Cambridge-trained Scottish immigrant just starting out as a professor.
Weeks earlier, Neil Armstrong had taken humanity's first step on another world, and the cosmos suddenly seemed more accessible, but Prof. Walker and Mr. Campbell didn't set out to launch the first dedicated search for alien worlds. They were astronomy tech geeks (Mr. Campbell scored top marks in the Walker class, called "astronomical measurements") drawn together by a fascination with building better, faster telescopic equipment.
'WE COULD START LOOKING FOR PLANETS'
In astronomy, the better you see, the more you see. Just as Galileo's radical insights 400 years ago were based on a new telescope with greater acuity, the two knew they were on to something when they made a major leap in the ability to tease apart starlight.
"I heard myself say, 'We could start looking for planets,'" says Prof. Walker, now 73 and still very active in astronomy as an adjunct professor at the University of Victoria.
"I don't know where the idea came from. That's how these things happen in science: Suddenly a light turns on. It's the art of the possible."
What they had developed was an amazingly more accurate way of clocking a star's movement. We think of stars as fixed points of light in the night sky, when in fact they move, a lot. Their thermonuclear nature makes them expand and contract. Also, they rotate just as Earth does on its axis, and they have an orbit, circling a common centre of mass in space along with any planets they have.
Measuring how quickly a star makes this orbit depends on a 150-year-old standard of astronomy called the Doppler method, which involves the same basic physics we experience when we hear changes in the pitch of an ambulance siren as it speeds toward us and then away. With stars, astronomers look for changes in the pitch, or frequency, not of sound waves, but light waves. In this way, they measure a star's speed toward or away from us, called the wobble technique in reference to the star's movement. The bigger the stellar wobble, the bigger or closer the unseen planet.
Astronomers had long known that the accuracy of the Doppler method depends on the ability to dissect light into its various colours, a technique called spectroscopy, and Prof. Walker was "the Jedi knight of spectroscopy," says UBC astronomer Jaymie Matthews, who came to the university in 1988 to conduct research with him.
Mr. Campbell was the Jedi's Luke Skywalker, an "audacious, young astronomer," says Prof. Marcy. He graduated in 1971, but returned to work with Prof. Walker as a post-doctoral researcher in 1976 after earning a doctorate at the University of Toronto. They developed a spectroscopy technique that was a spectacular 100 times more sensitive to the movement of stars.
"They were measuring the velocities of stars, for the first time in history, to plus or minus 10 metres a second," says Prof. Marcy, who began his own exoplanet search after hearing a talk Mr. Campbell gave in the 1980s. "The best that anybody at any observatory in the world had done was plus or minus one kilometre per second."
It was the magic number for planet-hunting. Astronomers knew that massive Jupiter causes our sun to wobble at about 12 metres per second. With the Canadians' technique for using a telescope like a police radar gun, they would be able to spot the wobbles induced by Jupiter-sized exoplanets on stars elsewhere in the Milky Way.
If they were out there.
THEY BEGAN BY HUNTING FOR JUPITER LOOKALIKES
In 1980, after a trial run on the telescope at the Dominion Astrophysical Observatory in Victoria, Mr. Campbell installed their system on the new, much larger Canada-France-Hawaii Telescope atop Mauna Kea, where he was now on staff.
Their plan was straightforward: Assuming that other solar systems existed and were like ours, Jupiter-like exoplanets would take about 12 years to orbit a star, just as Jupiter does. So they began a decade-long search of 26 stars looking for Jupiter-sized exoplanets, ones large enough, they reasoned, to perturb a star's movement to a degree visible with their telescope.
"Out of two dozen stars, and if you observed for a decade or longer, it seemed that it was a sure thing that you'd find something like Jupiter," says UBC's Prof. Matthews.
Three or four times a year, Mr. Campbell, Prof. Walker or University of Victoria astronomer Stephenson Yang, the team's other long-term member, would spend several nights atop Mauna Kea, 14,000 feet above the Pacific, searching for other worlds. They'd start just after dusk and work through the night in winter parkas, enduring altitude-induced headaches, until dawn's light overpowered the stars.