[Chaos-l] Another solar system like ours

[D Gary Grady]

Astronomers using gravitational microlensing have discovered a solar 
system about 5000 light-years away that looks like a roughly half-size 
model of our own, with two gas giants orbiting a dimmer sun at about 
half the distances of Jupiter and Saturn, and with reasonable chance at 
terrestrial planets closer in. The results give reason to think the 
solar systems like ours aren't uncommon.

Quoting The New York Times article at

http://www.nytimes.com/2008/02/14/science/space/14cnd-planet.html?_r=1&hp&oref=slogin

"Among those who provided crucial data and appeared as lead authors of 
the paper in Science were a pair of amateur astronomers from Auckland, 
New Zealand, Jennie McCormick and Grant Christie, both members of a 
group called the Microlensing Follow-Up Network, or MicroFUN. Ms. 
McCormick, who described herself as “an ordinary New Zealand mother,” 
said she had done her observing with a 10-inch Meade telescope from a 
shed in her back yard."

Following is the full text of the Times article. (The original paper is 
already on the SCIENCE website accessible to subscribers and appears in 
the printed issue bearing today's date.)

(quoting)

Astronomers say they have found a miniature version of our own solar 
system 5,000 light years across the galaxy — the first planetary system 
that really looks like our own, with outer giant planets and room for 
smaller inner planets.

The discovery, they said, means that our solar system might be more 
typical of planetary systems across the universe than had been thought.

“It looks like a scale model of our solar system,” said Scott Gaudi of 
Ohio State University. He led an international team of 69 professional 
and amateur astronomers, who announced the discovery in a news 
conference with reporters on Wednesday. Their results are being 
published Friday in the journal Science.

In the newly discovered system, a planet about two-thirds of the mass of 
Jupiter and another about 90 percent of the mass of Saturn are orbiting 
a reddish star about half the mass of the Sun, at about half the 
distances that Jupiter and Saturn circle our own Sun.

Neither of the two giant planets is a likely abode for life as we know 
it, but, as Dr. Gaudi pointed out, warm, rocky planets — suitable for 
life — could exist undetected in the inner parts of the system. “This 
could be a true solar system analogue,” he said.

Sara Seager, a theorist at the Massachusetts Institute of Technology who 
was not part of the team, said, “Right now in exoplanets we are on an 
inexorable path to finding other Earths.” She praised the new discovery 
as “a big step in finding out if our planetary system is alone.”

Since 1995, around 250 so-called exoplanets have been discovered, but 
few of them are in systems that even faintly resemble our own. In many 
cases, giant Jupiter-like planets are whizzing around inside the orbit 
of Mercury. But are these typical of the universe?

Almost all of those planets were discovered by the so-called wobble 
method, in which astronomers measure the gravitational tug of planets on 
their parent star as they whir around it. This technique is most 
sensitive to massive planets close to their stars.

The new discovery was made by a different technique that favors planets 
more distant from their star. It is based on a trick of Einsteinian 
gravity called microlensing. If, in the ceaseless shifting of the stars, 
two stars should become perfectly aligned with the Earth, the gravity of 
the nearer star can bend and magnify the light from the more distant 
one, causing it to suddenly get much brighter for a few days.

If the alignment is especially perfect, any big planets attending the 
nearer star will get into the act, adding their own little bumps to the 
more distant starlight.

That is exactly what started happening on March 28, 2006, when a star 
5,000 light years away in the constellation Scorpius began to pass in 
front of one 21,000 light years more distant, causing it to flash. It 
was picked up by the Optical Gravitational Lensing Experiment, or Ogle, 
a worldwide collaboration of observers who keep watch for such events.

Ogle in turn immediately issued a worldwide call for continuous 
observations of what is now officially known as OGLE-2006-BLG-109L. The 
next 10 days, as Andrew Gould of Ohio State said, were “extremely frenetic.”

Among those who provided crucial data and appeared as lead authors of 
the paper in Science were a pair of amateur astronomers from Auckland, 
New Zealand, Jennie McCormick and Grant Christie, both members of a 
group called the Microlensing Follow-Up Network, or MicroFUN. Ms. 
McCormick, who described herself as “an ordinary New Zealand mother,” 
said she had done her observing with a 10-inch Meade telescope from a 
shed in her back yard.

Somewhat to the experimenters’ surprise, by clever manipulation they 
were able to dig out of the data not just the masses of the interloper 
star and its two planets but also rough approximations of their orbits, 
confirming the similarity to our own system. David Bennett of Notre 
Dame, said, “This event has taught us that we were able to learn more 
about these planets than we thought possible.”

As a result, microlensing is poised to become a major new tool in the 
planet hunter’s arsenal, “a new flavor of the month,” in the words of 
Dr. Seager. The new system, she said, is just the tip of the iceberg and 
the odds are that a lot of the ones that will be discovered could be 
like ours.

Only six planets, including the new ones, have been discovered by 
microlensing so far and the Scorpius event was the first in which the 
alignment of the stars was perfect enough for astronomers to detect more 
than one planet at once. Their success at doing just that on their first 
try bodes well for the future, astronomers say.

Alan Boss, a theorist at the Carnegie Institution of Washington, said: 
“The fact that these are hard to detect by microlensing means there must 
be a good number of them — solar system analogues are not rare.”


-- 
D Gary Grady
Durham NC USA
dgary at mindspring.com