From: LARRY KLAES (ljk4@msn.com)
Date: Wed Jan 09 2002 - 07:24:35 PST
GOOD NEWS: HOW THE EARTH WILL SURVIVE WHEN THE SUN BECOMES A SUPERGIANT
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
Press & Communications Office
University of Sussex
Falmer, Brighton, U.K.
08 January 2002
Good news: how the Earth will survive when the Sun becomes a supergiant
The astronomy textbooks will have to be rewritten, say astrophysicists at
the University of Sussex who have re-examined standard calculations about
solar evolution and the distant future of the Earth.
The textbooks tell us that one day the Sun will burn up its nuclear fuel and
expand to an enormous size, finally engulfing its inner planets including
Earth. However, using the latest data based on real stars, the University of
Sussex researchers suggest a (slightly) less
catastrophic future for our planet.
As their hydrogen fuel runs out at the end of their 'lives', stars like the
Sun expand to become a red supergiant of several hundred times their initial
diameter. Most astronomers expect the solar red supergiant to swallow
Mercury, Venus and then Earth in about 7.5 billion years' time, when it has
expanded beyond the orbit of our planet.
But Earth may survive after all, say the Sussex astronomers, if an important
extra detail is considered: the ongoing loss of mass and weakening gravity
while a star is a red supergiant.
Dr Robert Smith, Reader in Astronomy, explains the significance of this
effect: "Taking this into account, the orbit of the Earth would increase
beyond the Sun's outer atmosphere by a small but crucial margin at all
phases of the Sun's evolution -- allowing our planet to continue."
The new calculations are published in the current issue of Astronomy &
Geophysics. They were made by Dr Smith together with Dr Klaus-Peter Schröder
from the University's Astronomy Centre and Kevin Apps, the famous student
stargazer who co-discovered 10 planets while still an undergraduate at
Sussex.
Although the Earth may survive, long before then its surface will have
become too hot to sustain human life. But the good news from the team of
researchers is that it will be 5.7 billion years before our planet becomes a
no-go zone for life -- about 200 million years later than
previously thought.
So, ask the Sussex astronomers, is there anywhere in the solar system that
would be safe, or does our survival depend on finding another star system?
Is it possible to hop outwards from one planet or satellite to the next,
always keeping ahead of the Sun? There are periods, they calculate, when we
could in principle survive on one of the outer planets such as Mars, but
there will be long gaps when none of them is habitable.
Dr Smith concludes: "We had better get used to the idea that we shall need
to build our own survival capsules -- the planets are simply too far apart
for planet-hopping to be a viable solution. Perhaps this is the ultimate
justification for developing an International Space Station."
Notes for editors
For further information, please contact:
Alison Field or Peter Simmons, University of Sussex
Tel. 01273 678888
Fax 01273 877456
email A.Field@sussex.ac.uk or P.J.Simmons@sussex.ac.uk
==============
ANOTHER SCARE OR ANOTHER WORRY? "SUPERNOVA CAUSED MARINE MASS EXTINCTION
2 MILLION YEARS AGO"
>From Andrew Yee <ayee@nova.astro.utoronto.ca>
Office of News and Information
Johns Hopkins University
3003 N. Charles Street, Suite 100
Baltimore, Maryland 21218-3843
Phone: (410) 516-7160 Fax (410) 516-5251
CONTACT:
Michael Purdy, (410) 516-7906, mcp@jhu.edu
EMBARGOED FOR RELEASE ON JAN. 8, 2002 AT 10 A.M. EST
Ancient Supernova May Have Triggered Eco-Catastrophe
An exploding star may have destroyed part of Earth's protective ozone layer
2 million years ago, devastating some forms of ancient marine life,
according to a new theory presented at this week's meeting of the American
Astronomical Society.
The new theory brings together puzzling clues from several different fields
of research, including paleontology, geology and astronomy.
Narciso Benítez, an associate research scientist in astronomy in the Krieger
School of Arts and Sciences at The Johns Hopkins University, says the
"missing smoking gun" that brought the clues together was the revelation
that a stellar cluster with many large, short-lived stars prone to producing
supernovae had passed near Earth's solar system several million years ago.
That discovery, made by co-author and Space Telescope Science Institute
astronomer Jesús Maíz-Apellániz, led Benítez to check the scientific record
for potential effects of nearby supernovae on the Earth.
"Nobody had realized that this cluster of stars that Jesús had tracked,
which is known as the Scorpius-Centaurus OB association, could have been so
close to Earth during the past several million years," Benítez says. "And
when I did a search, one of the first things that popped out was a 1999
finding where a team of German astronomers led by Klaus Knie detected the
presence of a highly unusual isotope of iron in samples of the Earth's crust
drilled from the deep ocean bottom."
Knie had proposed that the iron isotope was debris from a recent supernova
explosion that took place close to Earth. But astronomers had no plausible
candidates for such a nearby explosion until Maíz-Apellániz's work with the
Scorpius-Centaurus association, which is also being presented at this week's
meeting of the American Astronomical Society.
Benítez compared data produced by Maíz-Apellániz and Knie's results, and
found "very good agreement, both in the amount of iron deposited and in its
time distribution."
Benítez consulted with his wife, Matilde Cañelles, an immunologist at the
National Institutes of Health who had done her master's thesis on
microscopic algae, to learn if the paleontological record included an
extinction that had unusual characteristics suggestive of a potential link
to a supernova.
"Such an extinction would have had especially pronounced effects on the
plankton and the marine organisms," Benítez explains.
Cañelles pointed out that evidence existed for a widespread extinction of
plankton and other marine organisms about 2 million years ago, and noted
that scientists are still debating the possible causes of the event.
"Based on the minimal distance we expected for a supernova in the
Scorpius-Centaurus association at that time, I then did some calculations to
explore the potential effects on Earth," says Benítez.
He found that cosmic ray emissions from a supernova could have had a
potentially devastating effect on the Earth's ozone layer, an upper layer of
the atmosphere that absorbs harmful ultraviolet emissions from the sun and
other sources.
"This would have produced a significant reduction in phytoplankton abundance
and biomass, with devastating effects on other marine populations, such as
bivalves," Benítez says.
Benítez emphasizes that the theory, while provocative, is consistent with
the paleontological evidence, and also with the pattern of movement of the
Scorpius-Centaurus group, which would have been at its closest to Earth at
that time.
He concedes, though, that more evidence will be needed to firmly establish
the theory. In particular, more detailed searches for supernova-produced
isotopes in the geological record would show whether there was a tight
temporal correspondence between the supernova explosion and the extinction
event. Isotope searches could also offer crucial information about the
physical processes involved in supernova explosions.
"People study supernovae using telescopes and supercomputer simulations. In
the future, some of the most relevant information in this field may be found
in the deep ocean floor," says Benítez.
While the new theory may further heighten concern about human impacts on the
ozone layer today, Benítez and Maíz-Apellániz say there's no need to worry
about another supernova in the Scorpius-Centaurus group affecting Earth in
the near future. The next star due to explode in the association, Antares,
is now located at a distance of almost 500 light-years, which is too far
away to have a significant effect on our planet.
This research was funded by an Advanced Camera for Surveys grant from NASA,
the Johns Hopkins Center for Astrophysical Sciences, and a grant from the
Space Telescope Science Institute.
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