2005
22 November 2005. Asteroid
Poses Tiny Danger, but It May Be Lured Away.
By HENRY FOUNTAIN, NY Times. Excerpt:
From a human perspective, Earth-crossing asteroids
can have good timing or bad timing. Good timing
is when the asteroid and the Earth don't meet.
Bad timing is when they do. Astronomers say
that a 1,000-foot diameter asteroid discovered
last year may have bad timing. There is a
slight possibility that the rock, 99942 Apophis,
will hit Earth in 2036 after coming within
about 20,000 miles in 2029. A collision could
cause regional devastation on a scale far
worse than last year's tsunami. "The
most likely thing is that it is not going
to be a threat,"
said Rusty Schweikart, the former
Apollo astronaut and chairman of
the B612 Foundation, which is concerned
about protecting Earth from asteroids. "There's
5,499 chances out of 5,500 that it's
going to miss us." The trouble
with Apophis, Mr. Schweikart said,
is that that one chance cannot yet
be ruled out. Better optical and
radar observations are needed to
determine the asteroid's orbit, but
the best measurements cannot be made
until 2013.
That creates a different timing problem. If the threat from Apophis
cannot be ruled out by then, will there be time to deflect it?
Mr. Schweikart's group is not sure and has urged NASA to plan
a robotic mission to put a radio transponder on the asteroid
so that its orbit can be precisely determined. If such a mission
takes 10 years to design and execute, it will still give plenty
of time to plan and carry out a deflection mission. NASA has
said that planning for a transponder mission can wait till after
the more precise measurements are made in 2013. "I have
a very high confidence that we can pinpoint exactly the track
it's going to follow," said Andy Dantzler, director of NASA's
solar system division. In the unlikely event that in 2013 a transponder
mission would still be necessary, there would be enough time
for that and a deflection mission, if needed, as well, he added.
Mr. Schweikart said that NASA's response was "probably fine."
But he added that it made "aggressive
assumptions about how good things
are going to be, and how much we're
going to know." Edward T. Lu,
a current astronaut and a board member
of B612, ... and another astronaut,
Stanley G. Love, have a proposal
for how to go about deflecting the
asteroid: by using a spacecraft to
tow it, but without a tow line. In
a brief paper in Nature, the two
describe how such a gravitational
tractor, hovering near an asteroid
with its engines canted to avoid
the exhaust's hitting the surface,
can slowly pull it into a different
orbit. The pulling force would only
be about one newton, or roughly the
amount of force used to hold a full
cup of coffee.
"But the point is, if you hang
out long enough, it can add up to
a substantial oomph," Mr. Lu
said.
10 May 2005. NASA RELEASE: 05-120. NASA'S
Chandra Observatory Catches X-ray Super-flares. New
results from NASA's Chandra X-ray Observatory
about the Orion Nebula imply super-flares
torched our young solar system. Such X-ray
flares likely affected the planet-forming
disk around the early sun, and may have enhanced
the survival chances of Earth. ..."We
don't have a time machine to see how the young
sun behaved, but the next best thing is to
observe sun-like stars in Orion," said
Scott Wolk of Harvard-Smithsonian Center for
Astrophysics in Cambridge, Mass. "We
are getting a unique look at stars between
one and 10 million years old - a time when
planets form."
A key finding is the more violent
stars produce flares one hundred
times as energetic as the more docile
ones. This difference may specifically
affect the fate of planets that are
relatively small and rocky, like
the Earth. "Big X-ray flares
could lead to planetary systems like
ours, where Earth is a safe distance
from the sun," said Eric Feigelson
of Penn State University in University
Park. He is the principal investigator
for the international Chandra Orion
Ultradeep Project. "Stars with
smaller flares, on the other hand,
might end up with Earth-like planets
plummeting into the star." According
to recent theoretical work, X-ray
flares can create turbulence when
they strike planet-forming disks,
and this affects the position of
rocky planets as they form. Specifically,
this turbulence can help prevent
planets from rapidly migrating towards
the young star. "Although these
flares may be creating havoc in the
disks, they ultimately could do more
good than harm," said Feigelson. "These
flares may be acting like a planetary
protection program." Additional
info at: http://chandra.harvard.edu & http://chandra.nasa.gov
6 April 2005. NASA Release 05-094. Explosions
in Space May Have Initiated Ancient Extinction
on Earth. Scientists
at NASA and the University of Kansas say that
a mass extinction on Earth hundreds of millions
of years ago could have been triggered by
a star explosion called a gamma-ray burst.
The scientists do not have direct evidence
that such a burst activated the ancient extinction.
The strength of their work is their atmospheric
modeling -- essentially a "what if" scenario.
The scientists calculated that gamma-ray radiation
from a relatively nearby star explosion, hitting
the Earth for only ten seconds, could deplete
up to half of the atmosphere's protective
ozone layer. Recovery could take at least
five years. With the ozone layer damaged,
ultraviolet radiation from the Sun could kill
much of the life on land and near the surface
of oceans and lakes, and disrupt the food
chain. Gamma-ray bursts in our Milky Way galaxy
are indeed rare, but the scientists estimate
that at least one nearby likely hit the Earth
in the past billion years. Life on Earth is
thought to have appeared at least 3.5 billion
years ago.
18 February 2005. Cosmic
Explosion Among the Brightest in Recorded
History. NASA Feature. Scientists
have detected a flash of light from across
the Galaxy so powerful that it bounced off
the Moon and lit up the Earth's upper atmosphere.
The flash was brighter than anything ever
detected from beyond our Solar System and
lasted over a tenth of a second.... The scientists
said the light came from a "giant flare" on
the surface of an exotic neutron star, called
a magnetar. .... The light was brightest in
the gamma-ray energy range, far more energetic
than visible light or X-rays and invisible
to our eyes. Such a close and powerful eruption
raises the question of whether an even larger
influx of gamma rays, disturbing the atmosphere,
was responsible for one of the mass extinctions
known to have occurred on Earth hundreds of
millions of years ago. Also, if giant flares
can be this powerful, then some gamma-ray
bursts (thought to be very distant black-hole-forming
star explosions) could actually be from neutron
star eruptions in nearby galaxies.
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