number of earth-sized candidate
planets found by kepler mission
in first four months of operation
First stars might
still shine today
Slow-burning remnants from
the early universe may exist
By Ron Cowen
Talk about glimmers from the past. Some
of the universe’s first stars may still shine
in the Milky Way 13. 4 billion years after
they formed, new simulations suggest.
The study, reported online February 3
in Science and posted at arXiv.org on January 28, contradicts the prevailing view
that the first stars were all behemoths
that burned brightly and died young.
In their simulations, Paul Clark of
the University of Heidelberg in Germany and his colleagues showed that gas
clouds in the early universe could have
forged several stellar embryos rather
than just one. Clark and another team of
collaborators confirm that finding in an
article posted at arXiv.org on January 31.
Infant stars in each simulated gas
cloud were closely spaced, and the team
suggests that their mutual gravity could
kick the lowest-mass embryo from the
tightly packed group — before that infant
had a chance to grow into a massive,
short-lived star.
A few of these ejected stars could have
survived to the present day—if they
managed to accumulate no more than
As star embryos (white crosses in this simulation) formed from gas clouds in the
early universe, the smallest may have been ejected before having a chance to grow.
A thousand-plus worlds to explore
kepler mission releases details on newly discovered planets
By Ron Cowen
Astronomers have identified 1,235 candidate planets beyond the solar system,
including 54 where life might have a
chance of gaining a foothold.
When extrapolated, the results — which
are based on observations of bright stars
in a tiny patch of sky monitored by NASA’s
Kepler spacecraft —suggest that some
20,000 planets in the Milky Way may lie
at the right distances from their stars for
liquid water to be stable, says Kepler chief
scientist Bill Borucki of NASA’s Ames
Research Center in Mountain View, Calif.
He reported the findings, which come
from Kepler’s first four months of operation, at a February 2 press briefing.
“I’m just exhilarated we’ve found all
these things already, and I’m awed that
there are so many,” Borucki said. The
Kepler contenders are separate from
the more than 500 confirmed extrasolar
planets that astronomers have discovered since 1995. Borucki said he and his
collaborators are confident that at least
90 percent of the candidates will turn
out to be real planets.
Of the 54 potentially habitable candidates, five are roughly Earth-sized and
number of potentially habitable
planets found by kepler mission
during the same time
the equivalent of 80 percent of the sun’s
mass, Clark says.
“This is an interesting and tantalizing result, but it is not based on
computational physics but rather an ad
hoc assumption” about the evolution of
disks surrounding the birth clouds of the
first stars, contends Michael Norman of
the University of California, San Diego.
Clark and his colleagues simulated a
longer period of early star formation than
other teams have — the first 100 to 1,000
years of a process that lasts for several
hundred thousand. Still, the simulations
weren’t long enough to determine the
final masses of the primordial stars, says
Tom Abel of the SLAC National Accelerator Laboratory in Menlo Park, Calif.
The simulation technique is not as mathematically rigorous as other methods, he
says, even though it can probe the star-formation process for longer.
To search for any surviving early stars,
astronomers would need to develop a
way to determine which of the hundreds
of millions at the galaxy’s center are most
likely to be primordial, says Simon White
of the Max Planck Institute for Astrophysics in Garching, Germany, a coauthor
of the January 31 paper.
the other 49 range from twice the size
of Earth to larger than Jupiter. Though
probably gaseous themselves, the larger
planets might be able to support liquid
water — and thus life — on solid moons,
Borucki said. Some of those moons could
be the size of Earth.
“This is definitely our best first look at
the galactic planetary census,” says theorist Greg Laughlin of the University of
California, Santa Cruz, who is not part
of the Kepler team.
Overall, the Kepler census includes
68 planet candidates roughly the size of
Earth, 288 that are a few times the size of
Earth, 662 with diameters about equal to
that of Neptune and 165 the size of Jupiter. About 30 percent of the candidates
belong to multiple-planet systems.
P. Clark/Univ. of Heidelberg
www.sciencenews.org
