[meteorite-list] FIRST TERRESTIAL (EARTH-LIKE) EXTRA-SOLAR PLANET FOUND

[Sterling K. Webb]

Hi,

    Just announced today, the discovery
of a 5.5 Earth-mass planet, 2.5 AU from
its dim parent star, 28,000 light years
away, using gravitational lensing.
    This is too small to be a Jovian or
gas giant, so it has to be a rocky body.
    Or, since its probable temperature
is -220 degreed C, rock and ice is more
like it.
    Here's the URL and the text of the
article in Nature:

Sterling K. Webb
------------------------------------------

http://www.nature.com/news/2006/060123/full/060123-5.htm

Found: one Earth-like planet
Astronomers use gravity lensing to spot homely planets.
by Mark Peplow

Astronomers say they have found the most Earth-like planet yet outside our 
Solar System. At just 5.5 times the mass of Earth it is one of the smallest 
extrasolar planets ever found, and orbits its star at a distance comparable 
to that of habitable worlds.

Similarly sized extrasolar planets have been found before. But the method 
used to detect them meant we could see smallish planets only when they were 
very close to their suns, and such bodies are battered by scorching 
radiation.

Planet OGLE-2005-BLG-390Lb looks much more like home. It lies about 390 
million kilometres from its star: if it were inside our Solar System, the 
planet would sit between Mars and Jupiter.

It takes ten years for the planet to orbit its parent star, a 
common-or-garden red dwarf that lies about 28,000 light years from Earth, 
close to the centre of our Galaxy.

But sadly this Earth-like body probably isn't crawling with life. Its dwarf 
star is so dim that the surface temperature of this planet is thought to be 
about - 220 °C.

"The search for a second Earth is the driving force behind our research," 
says Daniel Kubas at the European Southern Observatory in Santiago de Chile, 
Chile, part of the team that made the discovery. They are optimistic that 
the clever method they used to spot the planet could soon uncover an alien 
twin to our own world.

Wobbly stars

More than 170 planets have been discovered outside our Solar System. 
Astronomers usually detect them by watching how they make their parent star 
wiggle, a technique known as the Doppler method. This is ideal if you are 
looking for massive planets orbiting very close to their star, which induce 
a lot of wobble.

But there is no way this can be used to find small, blue-green planets 
approximately 150 million kilometres from a yellow sun. It is simply not 
sensitive enough, says Didier Queloz, an astronomer from Geneva Observatory 
in Switzerland who was part of the team that found the first extrasolar 
planet, just 11 years ago1.

The new sighting relies on an effect called gravitational lensing, where a 
massive object such as a star warps space so that it behaves like a lens. 
This means that it bends and slightly magnifies light from a more distant 
star before it reaches our telescopes. Adding a planet to the mix modifies 
the lensing effect by a tiny amount, just enough to work out its mass and 
orbit.

"Microlensing is the fastest way to find small, cool planets, down to the 
mass of the Earth," says Keith Horne, one of the planet's discoverers and an 
astronomer from the University of St Andrews, UK.

Spot the difference

The planet was found by a consortium of 73 astronomers from 12 different 
countries. Its star was first spotted by scientists working on the Optical 
Gravitational Lensing Experiment (OGLE), before the planet itself was 
noticed by astronomer Pascal Fouqué.

OGLE-2005-BLG-390Lb is only the third planet found using the microlensing 
technique so far, but astronomers expect to spot many more. "The other two 
microlensing planets have masses of a few times that of Jupiter, but the 
discovery of a five-Earth-mass planet is a strong hint that these objects 
are very common," says Jean-Philippe Beaulieu of the Astrophysics Institute 
of Paris. Beaulieu is lead author of the paper describing the find in this 
week's Nature.