A trio of
planets called super-Earths has been spotted orbiting a sun-like star,
astrophysicists announced today at an international conference in France.
Super-Earths
are more massive than Earth but less massive than Uranus and Neptune. Spotting
true Earth-sized planets is challenging with current technology, but the
presence of super-Earths suggests finding a
world like ours is just a matter of time, researchers say.
The team
located the trio with the HARPS instrument on the European Southern
Observatory's 3.6-meter telescope at La Silla, Chile. They inferred the
existence of the planets by noting the worlds' gravitational affects on the
parent star's orbit. This method is called the radial velocity, or wobble, technique.
In
addition, HARPS astronomers have tallied about 45 new candidate planets with a
mass below 30 Earth masses and an orbital period shorter than 50 days. The
researchers say the deluge implies one out of every three sun-like stars harbors
such planets.
The trio's host
star, HD 40307, is slightly less massive than the sun, and is located 42
light-years away, toward the southern Doradus and Pictor constellations. (A light-year
is the distance light travels in one year, or about 5.88 trillion miles — 9.46
trillion kilometers.)
"We
have made very precise measurements of the velocity of the star HD 40307 over
the last five years, which clearly reveal the presence of three planets," said
team member Michel Mayor of the Geneva Observatory in Switzerland.
The
smallest of the trio weighs in at 4.2 Earth masses and orbits HD 40307 every
4.3 Earth days, while the largest, with a mass 9.4 times that of Earth, has a 20.4-day
orbit. The middleweight is 6.7 Earth masses and has a 9.6-day trek around the
star.
Since Mayor's
1995 discovery of a planet around the star 51 Pegasi, astronomers have noted more
than 270 extrasolar planets, mostly around solar-like stars. Most of these
planets are gas giants
called "hot-Jupiters." The researchers say about one out of every 14
stars outside our solar system harbors a hot-Jupiter.
A basketful
of other new
exoplanets also got the spotlight at the same international conference, where
researchers focused on extra-solar super-Earths.
These
included:
- A duo
orbiting the star HD 181433: a super-Earth (7.5 Earth masses) that orbits its
star every 9.5 days, and a Jupiter-like planet with a nearly three-year
period.
- Two
planets, a 22 Earth-mass planet having a period of four days, and a
Saturn-like planet with a three-year period.
"It is
most probable that there are many other planets present: not only super-Earth
and Neptune-like planets with longer periods, but also Earth-like planets that
we cannot detect yet," said team member Stephane Udry, also of the Geneva
Observatory. "Add to it the Jupiter-like planets already known, and you
may well arrive at the conclusion that planets are ubiquitous."
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