70 DISCOVERMAGAZINE.COM
NASA/JPL- CA
LTECH
/R.
HURT
(SSC)their observations, hoping to find a telltale wobble. As
Latham and Mazeh searched, however, they noticed
something unusual.
Like most astronomers, they were calibrating
their telescope with a standard, constant star, in
this case HD 114762, some 130 light-years away.
But on April 1, 1988, the researchers noticed a pos-
sible variation in the supposedly unchanging object.
Reviewing seven years of archived observations,
and confirming with an independent planet-hunter,
Michel Mayor at the University of Geneva, they found
that tiny shift was consistent. Something was orbiting
HD 114762. They christened the potential exoplanet
following the standard naming conventions for such
an object: HD 114762b.
The object soon proved a strange one. Initial
observations revealed that it took HD 114762b a
mere 84 days to complete one orbit — its “period,”
in astronomer-speak. It also followed an extremely
elliptic path, much more stretched out than the more
circular orbits of our solar system’s planets. The world
was unusually close to its host star, too, just a third of
the average distance between Earth and the sun. And
it was big, far more massive than Jupiter — though
(crucially, it would turn out) the team couldn’t deter-
mine its exact mass.
“It was a giant planet with the same period as
Mercury,” Latham said. “That sounded crazy in those
days.” That, and the stark differences between it and
our solar system’s planets, made such a world seem
downright bizarre.
The trio of researchers started to wonder if they
really had found a planet. But what else could it be?
THREE STRIKES
The obvious other choice was a star; after all, double
star systems litter the cosmos. But HD 114762b
didn’t look like a star — it was too tiny. Stars must be
at least a certain size because without enough mass,
they won’t be able to turn on and begin the process
of nuclear fusion that powers all stars.
Right at that size boundary, however, lie objects
known as brown dwarfs. Often called “failed stars,”
these stellar wannabes have masses 13 to 80 times
Jupiter’s — huge for a planet, but not nearly big
enough to be a full-fledged, fusion-powered star.
(Our sun, for example, weighs around a thousand
times as much as Jupiter.)
The first real brown dwarf candidate was only
found at the end of 1988, just as the team was strug-
gling with classifying their find. If HD 114762b was
too strange to be a planet, maybe it was one of these
weird semi-stars instead?
It’s a reasonable question, so the team’s next
step was straightforward: Find out HD 114762b’s
precise mass, then check to see if it falls within the
range of planets or of brown dwarfs. But that’s easier
said than done. In space, there’s no natural “north,”
so a planet can orbit its star in any orientation. It
could face us, like a clock’s hand going around its
center, or it could appear edge-on. A tiny wobble
could be the result of a wimpy planet, or a huge
world could orbit it at an inconvenient angle for
us to see much of its tugging. Without knowing
which is the case, a star’s wobble can only reveal so
much about an orbiting object’s mass. And, unfortu-
nately, there was no way to determine HD 114762b’s
orbital tilt.
“Finding the orbital inclination of this system is
clearly of great importance,” the team wrote in the
1989 Nature paper announcing the discovery, but the
measurement was “too small to be detected in the
near future.” Stymied by the technology of the time,
the researchers were left with an object that could
very well be a brown dwarf or a planet, and whose
mass, as best as they could figure out, straddled the
line between the two.
“There was a question between the team [mem-
bers] on how to present the discovery,” says Mazeh.
“There was a huge debate.” The idea of: A) a worldOUT THERE
The trio of
researchers
started to
wonder if
they really
had found a
planet. But
what else
could it be?The two worlds
around pulsar
PSR 1257+12, shown
in this rendering,
went down in history
as the first known
exoplanets. They may
soon be dethroned.