Experts spot smallest planet outside solar system
GENEVA
If confirmed, the planetary system around HD 10180, a star more
than 100 light years distant, would be the richest ever discovered.
One astronomer says it's part of a growing body of evidence that
the universe is full of planets -- and that a bunch of them could be
similar to our own.
"The really nice thing about finding systems like this is that
it shows that there are many more out there," said Alan Boss, of
the Washington-based Carnegie Institution for Science, who wasn't
involved with the find. "Mother Nature really had fun making
planets."
Although most of the planets identified are large -- about 13 to
25 times the mass of our home -- those behind the discovery,
announced Tuesday at an international conference in France, say
they're nearly certain they've identified one only 1.4 times the
size of Earth.
That would be the smallest planet ever spotted outside of those
which orbit our own sun.
Scientists have been spotting planets beyond our solar system
for the past 15-odd years, and they've now catalogued some 450. But
most finds have been limited to one or two or three planets,
usually gargantuan balls of gas similar to Jupiter or Saturn.
But at up to seven planets, the new discovery is almost as rich
as our own solar system, which counts eight.
Christophe Lovis of Geneva University, one of the scientists
behind the find, said the first five were most comparable to
Neptune.
"They are made essentially of rocks and ice. They have a solid
core. But on top of that is a layer of gas, of hydrogen and helium
most likely," he said. "They are probably not habitable."
The sixth is possibly a Saturn-like planet, while the seventh,
the smallest, would be so close to its star that its "year" would
take just over a day.
Lovis and his team haven't been able to observe the planets
directly, which is typical. Few planets can be seen against the
blazing light given off by their much more massive parent stars.
The European Southern Observatory compares the challenge to
"spotting a dim candle in front of a raging forest fire."
So the scientists used the observatory's 3.6 meter (11.8 foot)
telescope at La Silla, Chile, to study the star itself. Over six
years, they took 190 measurements, checking it for the telltale
wobbling caused by the gravitational forces of nearby planets.
Boss noted that the method was "biased toward finding the big
guys" because the greater the planet, the greater its gravity and
the more it made its parent star wobble. But he said the discovery
showed that finding smaller planets was still possible.
"This field has gone from zero to close to 500 planets in just
15 years," he said. "Fifteen years we did not know about the big
guys. Earth-like planets are going to be quite commonplace."
The find was made by researchers from Switzerland, France,
Germany, and Portugal and has been submitted to the journal
Astronomy and Astrophysics.