216 Planets Exist Around Other Stars
ler shift and measuring tiny shifts on a spectrograph in the color of the light coming from a
star that would be the result of changes in the star’s motion toward or away from Earth.
Following the death of Duquennoy in 1993, Mayor teamed with graduate student
Didier Queloz and developed a new, more sensitive spectrograph to search for brown
dwarfs. Their new spectrograph was capable of measuring velocity changes as small as 13
meters per second—about the same as the wobble in our sun’s motion caused by Jupiter’s
gravitational tug.
But everyone assumed that such massive planets would take years to orbit a star (as
they do in our system). Thus the wobble from a planet’s tug would take years of data to notice. It never occurred to Mayor to use his new spectrograph and a few months’ worth of
time on a telescope to search for a planet.
Beginning in April 1994, using the Haute-Provence Observatory in southern France,
Mayor and Queloz tested their new spectrograph on 142 nearby stars, hoping to detect a
wobble that would indicate a massive nearby object like a brown dwarf. In January 1995
one star, 51 Peg (the fifty-first brightest star in the constellation Pegasus) caught Queloz’s
eye. It wobbled. It wobbled back and forth every 4.2 days.
They tested the star’s light to make sure it didn’t pulse. They tested to see if sun spots
might create an apparent wobble. The tested to see if 51 Peg puffed up and contracted to create the appearance of wobble. Nothing could account for 51 Peg’s wobble except for a sizable orbiting object.
From the amount of 51 Peg’s wobble they calculated the mass of the object and knew it
was too small to be a brown dwarf. It had to be a planet! They had discovered a planet outside our solar system.
By 2005, several hundred other planets had been located—gas giants speeding around
Mercury-sized orbits; some rocky planets in cozy, not-too-hot-and-not-too-cold orbits;
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