[extropy-chat] 55 Cancri

[Damien Broderick]

Space.Com - New York, New York, USA

<http://www.space.com/scienceastronomy/060801_science_tuesday.html>http://www.space.com/scienceastronomy/060801_science_tuesday.html

01 August 2006


Habitable Planet Possible Around Nearby Star System

By Robert Roy Britt
Senior Science Writer

[...]

The 55 Cancri system involves three gas giant planets and
another world that could be icy or rocky and is about the size
of Neptune. The setup is 41 light-years from Earth and about 4.7
billion years old, comparable to our Sun.

Astronomers have said since 2002, when a planet was found at
about the same orbital distance from 55 Cancri as Jupiter is
from the Sun, that the star had the potential to harbor an
Earth-sized world.

A new computer simulation shows that amid the giant worlds
orbiting 55 Cancri, a small rocky world could indeed have
formed=97in theory=97and attracted enough water to support life as
we know it.

"Our models show a habitable planet, a planet with mass,
temperature and water content similar to Earth's, could have
formed," said Rory Barnes, a postdoctoral researcher at the
University of Arizona.

Barnes and colleagues ran several simulations of varying
scenarios around four stars, each known to have at least two
giant planets. They put moon-sized planetary embryos into the
systems during their youth and allowed them to evolve for 100
million years.

The idea, based on the leading planet-formation theory, is that
small objects collect more material and, if they don't collide
with another big object, become planets.

Star of the show

Only 55 Cancri consistently yielded a world similar in size and
orbital distance to Earth. Our planet sits in what's called a
habitable zone, just the right distance from the Sun to allow
liquid water.

"Our simulations typically produced one terrestrial planet in
the habitable zone of 55 Cancri, with a typical mass of about
half an Earth mass," said Sean Raymond, a postdoctoral
researcher at the University of Colorado who worked on the
project while a doctoral student at the University of
Washington. "In many of the simulations, these planets accreted
a decent amount of water-rich material from farther out in the
disk."

The research, funded by NASA and the National Science
Foundation, is described in a recent issue of the Astrophysical
Journal.

A computer simulation is of course far from reality. But
research like this can guide astronomers to solar systems worthy
of further investigation as search technology improves.

"Our assumptions are quite optimistic, but not crazy by any
means, and we start our simulations with a decent amount of
material for terrestrial planets to form," Raymond told
SPACE.com. "If we are wrong about this, then only smaller,
perhaps Mars-sized planets could form in the habitable zone."

The best bet

Two other stars yielded little suggestion of habitable worlds.
Another star, named HD 38529, is likely to support an asteroid
belt and objects up to the size of Mars, the simulations
indicate.

"In terms of the systems we looked at, 55 Cancri has the largest
zone between giant planets in which terrestrial planets may form
and remain on stable orbits," Raymond said. "So, I think the
chance of other planets existing in the system is pretty good,
but it's certainly not definitive at the moment."

Other modeling by Raymond has shown that only about 5 percent of
the known giant-planet systems are likely to have Earth-like
planets. But, he and others have said, there may well be many
solar systems similar to our own, in which the giant planets are
all on the outskirts, that simply can't be detected yet.