PLEASE NOTE:
*
CCNet - 005/2000 - 13 January 2000
------------------------------------
QUOTES OF THE DAY
"The real comfort is that we are on
track
to finding most of the hazardous
asteroids
before they find us."
-- David Rabinowitz
"This new analysis reduces by half
the estimated
number of these potential hazards to
Earth."
-- Steven Pravdo
"The NEAT team, like most other
groups, assumes a
typical space rock reflects 10 percent
of the sunlight
that hits it. This is based mainly on
the characteristics
of meteorites and a few large asteroids
that are well
studied. A trap with this method is that
space rocks come
in different shades of gray -- some
reflect more sunlight
than others."
-- Michael Paine
(1) ASTEROID POPULATION COUNT SLASHED
JPL/NASA, 12 January 2000
(2) NUMBER OF NEAS ARE FEWER THAN BELIEVED
Yale University, 12 January 2000
(3) NO ESCAPING ASTEROIDS
BBC Online News, 12 January, 2000
(4) ASTEROID HUNTERS DOWNGRADE OVERALL THREAT TO EARTH
EXPLOREZONE, 12 January 2000
(5) ASTRONOMERS REDUCE ESTIMATES OF NEOS
SpaceViews, 12 January 2000
(6) NEOs & THE CHANCE OF COLLISION WITH EARTH
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(7) MASSIVE PLANETS MAY FORM QUICKLY
Andrew Yee <ayee@nova.astro.utoronto.ca>
(8) AND FINALLY: MASS HYSTERIA MAY BE RISING
YAHOO NEWS, 12 January 2000
============
(1) ASTEROID POPULATION COUNT SLASHED
From JPL/NASA, 12 January 2000
http://www..jpl.nasa.gov/releases/2000/neat.html
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Jane Platt (818)
354-0880
FOR IMMEDIATE
RELEASE
January 12, 2000
ASTEROID POPULATION COUNT SLASHED
NASA scientists taking a census of large asteroids in our solar
system
neighborhood have cut their estimate in half.
The revised calculation comes from data gathered by NASA's
Near-Earth
Asteroid Tracking System (NEAT) and published in the January 13
issue
of the journal Nature.
"Until now, scientists thought the population of large,
near-Earth
asteroids was between 1,000 and 2,000, but we've downgraded that
figure
significantly," said Dr. David Rabinowitz, of Yale
University, New
Haven, CT, lead author of the article and NEAT
co-investigator. "We
now believe there are between 500 and 1,000 near-Earth asteroids
larger
than one kilometer (about 0.6 miles) in diameter.
"This newer estimate was made possible by the computerized
technology
of the NEAT camera," Rabinowitz said. The NASA-funded system
began
tracking near Earth asteroids and comets in 1995 with a
charge-coupled
device camera mounted on a 1-meter (39-inch) Air Force telescope
atop
Mount Haleakala on Maui, HI.
The new figures may represent good news in the quest to achieve
NASA's
stated goal of finding 90-percent of all large, near-Earth
asteroids by
2010, according to Pravdo. "Right now we know of 322 large,
near-Earth
asteroids," he said. "That was a fairly small fraction
of the 2,000
asteroids in our previous estimate. With our new calculations of
between 500 and 1,000 such objects, this 322 figure represents a
large
chunk."
While stressing that we must learn more about potential hazards
from
asteroids, Rabinowitz said, "None of the asteroids we've
observed will
hit Earth anytime in the near future."
"This new analysis reduces by half the estimated number of
these
potential hazards to Earth," Pravdo said.
"In the past, we relied on humans poring over photographic
plates of
the nighttime sky," Rabinowitz said. "The problem was,
they didn't know
how many asteroids they were missing, because they couldn't see
faint
objects. People's eyes also became tired and teary and they
overlooked
some objects. Machines don't get tired."
"With this computerized technology, we can find asteroids
more easily
and count them more accurately," said NEAT project manager
Dr. Steven
Pravdo of NASA's Jet Propulsion Laboratory, Pasadena, CA, a
co-author
of the Nature article. "It's important to know your
observational
limits, and with that information, we can develop models for what
we
are not able to see. This makes our estimates even more
accurate."
Additional co-authors on the Nature article are Eleanor Helin of
JPL,
NEAT principal investigator, and Kenneth Lawrence, also of JPL.
Helin
was also principal investigator of the Palomar Planet-Crossing
Asteroid
Survey, a photographic search program, conducted for almost 25
years
until it was discontinued and replaced by NEAT, the electronic
detection program, in 1995. Her efforts were key to the
organization of
the NEAT program.
Data gathered by the asteroid tracking system are processed at
Haleakala, and then undergo post-processing and analysis at JPL.
This
latest asteroid estimate is based on data collected between 1995
and
1998.
The asteroid tracking system has been on hiatus for the past
year, but
plans are in the works to re-activate the system in February
using an
upgraded 1.2 meter (48 inch) Air Force telescope on
Haleakala. In
addition, later this year, NEAT scientists will begin using the
1.2
meter (48 inch) Oschin telescope at Palomar Observatory near San
Diego,
CA.
Additional information on the NEAT project is available at
http://neat.jpl.nasa.gov
. Information on near-Earth objects is
available at http://neo.jpl.nasa.gov
.
The Near Earth Asteroid Tracking System is managed for NASA's
Office of
Space Science, Washington, D.C. by JPL, a division of the
California
Institute of Technology, Pasadena, CA..
============
(2) NUMBER OF NEAS ARE FEWER THAN BELIEVED
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Yale University
CONTACT: Jacqueline Weaver, 203-432-8555 #151
Embargoed for Release: 2 p.m. EST, January 12, 2000
Yale Researcher Finds Number of "Near-Earth Asteroids"
Are Fewer than
Believed
New Haven, Conn. -- The number of "near-Earth
asteroids" that have a
chance, though miniscule, of colliding with Earth this century is
half
what was originally estimated, a Yale researcher says.
"They are the kind of asteroids you hear about in movies
that are about
two-thirds of a mile in diameter and could easily obliterate a
city
because they are coming in at cosmic velocities," said
Research
Associate David Rabinowitz. "The main thing we want to
stress is that
none of the known asteroids are in imminent danger of falling to
earth
and no impacts are predicted in the near future."
It was previously estimated that there are 1,000 to 2,000 such
asteroids in chaotic orbits. Rabinowitz and his fellow
researchers
estimate that these asteroids actually total half that, or 500 to
1,000. Each has a 0.5 percent chance of colliding with Earth in
the
next million years, he said in the article published this week in
the
journal "Nature."
"The reduced number doesn't make us feel that much safer,
but it does
allow us to plan more accurately," Rabinowitz said.
"The goal is to
find the asteroids hundreds to thousands of years before they
even come
close."
The other researchers were Eleanor Helin, Kenneth Lawrence, and
Steven
Pravdo, all of the Jet Propulsion Laboratory at the California
Institute of Technology. They made their observations through a
U.S.
Air Force telescope in Hawaii that was designed to look for
artificial
satellites.
Rabinowitz said smaller asteroids the size of a large house or
hotel
generally burn up or blow up before they hit the ground.
"But an asteroid the size of a city block is more dangerous
because it
could punch through the atmosphere and raise a lot of dust, which
would
change the climate of the Earth," he said. "It would be
like a nuclear
bomb coming in."
Efforts are underway around the world to survey this asteroid
population because most of the threatening bodies remain
undiscovered
and their number is uncertain, the researchers said.
The observations were made using a large-format, charge-coupled
device
and a one meter aperture telescope based on the summit of
Haleakala
Crater on the island of Maui. Earlier photographic methods
required a
trained observer to identify asteroids by visual inspection and
the
accuracy varied according to the skill of the observer. The
automated
method is more consistent and provides a record of every
detectable
asteroid.
The researchers said that, at the current rate of discovery,
about 90
percent of the asteroids probably will be identified in the next
20
years. The goal, however, is to double the current worldwide
detection
rate to complete the program in 10 years.
"If we can find the asteroids in 10 years, that's plenty of
time,"
Rabinowitz said. "If you wait 100 or 1,000 years, that's too
much
time."
Rabinowitz is currently working with Professor Charles Baltay,
chairman
of the Yale Physics Department, to develop one of the world's
largest
electronic cameras. It will be used by Yale astronomers and
physicists
to study the properties of distant galaxies and supernova, and to
study
the expansion of the universe. The new camera also will be used
in
cooperation with astronomers at the Jet Propulsion Lab to
continue the
survey for near-Earth asteroids.
============
(3) NO ESCAPING ASTEROIDS
From the BBC Online News, 12 January, 2000
http://news.bbc.co.uk/hi/english/sci/tech/newsid_600000/600172.stm
It hit the dinosaurs and it could hit us
By BBC News Online Science Editor Dr David Whitehouse
Whether the Earth will be hit by an asteroid is a question of
when, not
if.
Though it is an unlikely event, it will happen given enough time.
We
might be unlucky and it may occur next year or we may have to
wait a
100,000 years before it happens again.
The number of Near Earth Objects (NEO's) is about half of that
previously estimated. But the threat they pose is undiminished,
according to a survey.
The NEO's under scrutiny are between one kilometre and 10 km in
size
(0.6 to six miles). A 1km object would be large enough to cause
considerable local devastation but not global catastrophe
(sic).[1km is ~@ the threshold of global affect]
A 10 km asteroid would devastate life on Earth.
It is thought that the asteroid that hastened the demise of the
dinosaurs 65 million years ago was a 10 km object.
The 1908 impact at Tunguska in Siberia was caused by a comet 700m
wide. [read ~70m]
It flattened trees over an uninhabited area of 1,000 square km.
700 asteroids
The Near Earth Asteroid Tracking (NEAT) project uses an automated
telescope based on Hawaii.
Astronomers there surveyed 35,000 square degrees of the sky
between
March 1996 and August 1998 and detected 45 new NEO's.
From this they deduce that the total number of potentially
hazardous
NEO's out there is about 700.
It is considerably less than previous estimates. Team leader
David
Rabinowitz, of Yale University, says in the journal Nature:
"This
decrease by a factor of two does not substantially affect the
significance of the NEO hazard."
He adds that the new data means that we "can confidently
predict the
level of effort required to survey completely those NEO's capable
of
global devastation".
It is thought that at the current rate it will take about 15
years to
track down 90% of them.
Slow progress
For some astronomers this is fast enough but others think it is
far too
slow and have been pressing the world's governments to take the
NEO
threat more seriously.
There are some signs that their arguments may be bearing fruit.
Last
week the UK Government established a small taskforce to look into
the
threat.
About 100 NEO's are discovered each year and most pose no
conceivable
threat to the Earth at the moment.
But some researchers are worried that the media and the public
will
misinterpret their efforts and consider each new NEO a potential
life-threatening object.
To counter this, last year astronomers devised a hazard-scale for
NEO's
called the Torino scale in which 10 is certain global devastation
and
one no threat at all.
According to Dr David Jewitt of the University of Hawaii:
"No known NEO
has a Torino scale reading of more than one, which is a good
thing as
we have no coherent plan of action should a threat arise."
According to Dr Brian Marsden of the Harvard Centre for
Astrophysics,
who has been called the custodian of asteroid orbits because of
his
co-ordinating role: "The NEO community as a whole still has
a lot to
learn about communicating information on possible NEO threats to
the
public."
Astronomers estimate that there is about a 1% chance that the
Earth
will be hit by a damaging NEO of 10 km size during the next
million
years. For smaller NEOs, say 300 metres in size, the probability
of a
strike in the next 100 years is also 1%.
Such a NEO would be the equivalent of a thousand megaton
detonation and
if it struck a city millions could die.
Copyright 2000, BBC
===========
(4) ASTEROID HUNTERS DOWNGRADE OVERALL THREAT TO EARTH
From EXPLOREZONE, 12 January 2000
http://explorezone.com/archives/00_01/12_asteroid_odds.htm
By Michael Paine Special to space.com
A handful of professional astronomers regularly search the night
skies
for asteroids or comets that may eventually slam into Earth.
Their main
quarries are objects one kilometer (about 1,000 yards) or more
across
-- rocks capable of severe destruction.
Until recently most scientists thought there were about 2,000 of
these
Near Earth Objects (NEOs). Now the astronomers who operate the
Near
Earth Asteroid Tracking (NEAT) project have come up with a lower
estimate: 700. If accurate, the new number would reduce the odds
of a
civilization-destroying impact in any one year from about 1 in
100,000
to about 1 in 300,000, something still more likely than being
dealt a
royal flush in five-card poker.
"I think the new estimates are plausible and that many
colleagues are
accepting them," said the Minor Planet Center's Brian
Marsden, who was
not involved in the research but who collates and analyses
information
about known asteroids and comets.
In the study, David Rabinowitz of Yale University and Eleanor
Helin and
her colleagues, who operate NASA's telescope in Hawaii, analyzed
results for the amount of sky covered by their project. The
results are
described in the Jan. 13 issue of the journal Nature.
Uncertainty remains
Like all NEO estimates, the new one is an educated guess based on
the
amount of sky searched so far and backed up by counts of craters
on the
Earth, as well as on the Moon, Venus and Mars, where the scars of
past
impacts do not erode so quickly. "The real comfort is that
we are on
track to finding most of the hazardous asteroids before they find
us." David Rabinowitz - Yale University
The actual number of one-kilometer NEOs could range from about
500 to
900, Rabinowitz said.
These objects are so small and distant that their size cannot be
measured directly -- the task is equivalent to using a telescope
to
gauge the girth of ant a hundred miles away. Instead, scientists
consider the brightness of the object, assuming that the larger
objects
will appear brighter in the sky.
The NEAT team, like most other groups, assumes a typical space
rock
reflects 10 percent of the sunlight that hits it. This is based
mainly
on the characteristics of meteorites and a few large asteroids
that are
well studied.
A trap with this method is that space rocks come in different
shades of
gray -- some reflect more sunlight than others.
In the dark
Last summer NASA scientists who operate the Deep Space 1
spacecraft
were taught a lesson about dark asteroids. Their pioneering
spacecraft
was supposed to spot and photograph asteroid Braille which,
coincidentally, was discovered by Helin and a colleague in 1992.
Braille is some 1.5-miles end to end, and the spacecraft passed
within
10 miles of it -- a brilliant feat of auto-navigation.
But the elation of the scientists was dampened when no close-up
pictures were beamed back to Earth. It turned out Braille was
much
darker than anticipated, and the imaging system of Deep Space 1
could
not lock onto the asteroid. It's possible that these dark objects
are
more common than previously thought and they have eluded
Earth-based
asteroid search programs.
Other threats
Researchers study Near Earth Objects that are 1 kilometer and
larger
because they pose the most significant risk to the planet for
global
devastation. There are other threats that this study does not
consider,
such as long-period comets that return to the inner solar system
only
rarely and could only be detected a couple of years before
impact.
"Comets are also a significant global hazard, and we are
fortunate that
they impact less frequently (presumably about 10 times less
frequently," Rabinowitz said in an e-mail interview.
"Smaller NEOs
don't have a global effect. Though hazardous on a local level,
they are
not as important in the long run."
A subclass of objects, called Potentially Hazardous Asteroids,
includes
200 rocks in space that are expected to pass within 5 million
miles of
Earth and are estimated to be more than about 600 feet across.
More sensitive equipment will be needed to detect a reasonable
proportion of these objects, experts say.
"The real comfort is that we are on track to finding most of
the
hazardous asteroids before they find us," Rabinowitz said.
Another search effort
In the early 1990s an international group of scientists proposed
the
Spaceguard Survey -- a global search that would find 90 percent
of the
potential civilization destroyers over ten years. Current efforts
fall
far short, but the NEAT scientists point out that their reduced
estimates mean the Spaceguard goal will be easier to reach.
Marsden, of the Minor Planet Center, agrees, but he cautions that
there
is much more to the task than just finding an object. Follow-up
observations are needed to pin down the orbit, he says.
At the current rate of discovery -- about 50-110 per year -- it
will
take about two decades to find all the 1-kilometer NEOs,
Rabinowitz and
his colleagues calculate.
space.com's Robert Roy Britt contributed to this report.
copyright 2000, Explorezone
============
(5) ASTRONOMERS REDUCE ESTIMATES OF NEOS
From SpaceViews, 12 January 2000
http://www.spaceviews.com/2000/01/12a.html
A team of astronomers using data from a NASA telescope has cut in
half
estimates of the number of large near-Earth asteroids believed to
currently exist.
The astronomers, led by David Rabinowitz of Yale University,
believe
that only 500 to 1,000 asteroids one kilometer (0.62 miles) in
diameter
or larger exist in orbits that bring them near the Earth.
Previous
estimates had been in the range of 1,000 to 2,000.
FULL STORY AT http://www.spaceviews.com/2000/01/12a.html
===========
(6) NEOs & THE CHANCE OF COLLISION WITH EARTH
From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
Forwarded from Lisa Lint (lisal@aiaa.org)
Subject: SGV Section AIAA January Dinner Meeting
Near-Earth Objects and the Chance of Collision with Earth
Paul Chodas (JPL)
The average time between globally catastrophic impacts on Earth
is
long, around half a million years, but the consequences of such
events
are so enormous that the hazard must be taken seriously.
Near-Earth
Objects (NEOs) are being discovered at an increasing rate, thanks
largely to search programs funded by NASA, but over half of the
kilometer-and-larger objects remain undiscovered.
Orbits for the known objects have been projected several decades
into
the future to search for collision possibilities, and a few
objects
have been found to have impact chances on the order of one in a
million. Additional tracking data for these objects has removed
the
chance of collision in all but one case.
Paul Chodas is a Research Scientist in the Solar System Dynamics
group
at JPL, where he has worked for 13 years after obtaining a Ph.D.
from
the University of Toronto. He develops techniques for determining
orbits of comets and asteroids and predicting their trajectories.
In
1994, he was responsible for predicting the times and locations
of the
Shoemaker-Levy 9 cometary impacts on Jupiter.
Wednesday, January 19, 2000
6 p.m. Social Hour, 7-9:30 Dinner and Program
new location: Beckham Place Restaurant, 77 West Walnut Street,
Pasadena, CA
parking is free across the street at Parsons
$17 for AIAA Members ($20 without reservations or membership)
Non-Members are encouraged to attend!
For reservations or information, please contact
the AIAA Western Office at (800) 683-AIAA or lisal@aiaa.org
=============
(7) MASSIVE PLANETS MAY FORM QUICKLY
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Don Savage
Headquarters, Washington, D.C. Jan. 12, 2000
(Phone: 202-358-1547)
Bill Steigerwald
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301-286-5017)
RELEASE: 00-03
HUBBLE OBSERVATIONS INDICATE MASSIVE PLANETS MAY FORM QUICKLY OUT
IN THE COLD
A young star may be forming massive planets much earlier and at
greater
distances than current planet formation models predict, according
to
new observations from the Hubble Space Telescope. NASA
astronomers
using the Space Telescope Imaging Spectrograph (STIS) instrument
on
board Hubble discovered that the disk of gas and dust surrounding
a
young star has a gap, possibly caused by gravitational influence
of a
nascent planet.
The gap appears about 30 billion miles from the star, more than
seven
times the distance from the Sun to Pluto, the most remote planet
in our
solar system. The STIS instrument also revealed that the star is
ejecting jets of gas at hundreds of miles per second from its
poles, a
feature usually seen in much younger stars.
"If the clearing in the disk is due to planet formation, it
suggests we
have a lot more to learn about how planets form, but we may be on
the
right track, which is very exciting," said Dr. Carol Grady
of NASA's
Goddard Space Flight Center, Greenbelt, Md. "The potential
planet is
much further away from its star than any known bodies in the
plane of
our solar system, and it is forming much faster than most models
predict."
"This star is also interesting because of its jets,"
adds Dr. David
Devine of Goddard. "Protostellar jets are a byproduct of the
accretion
of material onto a young star, and are thought to have lifetimes
of a
few hundred thousand years or so. It came as a big surprise to
find
them associated with a 4 million year old star. One possible
explanation for these 'old' jets is that the formation of planets
in
the disk results in periodic 'meteor showers' of material falling
onto
the central star, which rejuvenates the jets. In simpler terms,
the
star gets the hiccups while eating dessert."
Grady and Devine will present their results at the winter meeting
of
the American Astronomical Society (AAS) in Atlanta, Georgia, Jan.
12,
and the research will be published in the Astrophysical Journal.
The star, designated HD163296, is approximately 400 light years
away
from Earth in the direction of the constellation Sagittarius (one
light
year is almost six trillion miles). It is about twice as massive
as the
Sun and has an estimated age of 2-10 million years. This is
relatively
young, as stars of its type have lives spanning up to one billion
years.
If the gap in the disk is due to a single planet, the planet has
an
estimated mass 1.3 times that of Saturn. It is likely that the
planet
will gain additional mass as it continues to pull material from
the
disk.
It would have been very difficult to detect the jets and the gap
in the
disk without the use of a coronagraph. Normally, a young star's
bright
light prevents astronomers from seeing material that is close to
it
(imagine a match next to a spotlight). However STIS has a
coronagraph
that blocks the star's light and allows the study of the much
fainter
surrounding material. Unfortunately, the inner part of the disk
can't
be directly seen, because it is obscured by the coronagraph.
However
the astronomers were able to trace the disk to within about 180
AU of
the star (1 AU is the distance from the Earth to the Sun, about
93
million miles (150 million kilometers).
Structures in the jets provide hints of what is happening in the
inner
disk blocked from view by the coronagraph. "We do see dense
clumps in
the jet," said Devine. "They are regularly spaced, and
appear to be
ejected about once every five years."
"One exciting, but speculative, possibility is that there is
another
planet forming in the inner part of the disk," said Grady.
"As the
planet progresses in its orbit, it may periodically disrupt the
disk
and toss material on the star, some of which is ejected as denser
clumps of material in the jets."
"The five-year spacing of the knots in the star's jets may
be related
to a five-year orbital period for any potential companion
object," said
Grady. "This is in the habitable zone for the star, where
liquid water
could exist. However, since the system is young and the object is
still
forming, there is likely a constant rain of meteorites on its
surface.
I wouldn't want to spend a vacation there."
"On the other hand, the knots in the jets may have nothing
to do with
planet formation, and may be due to some unobserved feature of
the star
or disruptions caused by a low-mass companion like a brown dwarf.
A
brown dwarf is an object not quite massive enough to shine by
nuclear
fusion like a star but instead glows dimly with heat left over
from its
formation. If the companion were a low-mass star, it should
produce
X-rays, but other observatories sensitive to X-rays have not seen
any
nearby. However, we can't yet rule out a brown dwarf," said
Grady.
"We have only recently had observatories powerful enough to
tell us
something about planet formation, so the field is very
young," said
Grady. "We don't yet know the full diversity of solar
systems -- if a
star with fast, remote planet formation and jets is common or
rare.
Recent observations of stellar disks, announced at last January's
AAS
meeting, indicate that at least one other star (HD141569) may
have
planets forming rapidly at great distances. If this were a rare
occurrence, we would not expect to find two examples so
quickly."
"We will use Hubble to take longer exposures of HD163296 in
the summer
to see if there is anything else going on in its faint, outer
disk, and
we plan similar observations of 8-10 other stars by September. We
are
very fortunate to be exploring this new frontier, and are
tremendously
excited by future observatories, such as the Space Interferometry
Mission and the Terrestrial Planet Finder, that promise to tell
much
more," said Grady.
In addition to taking pictures, STIS separates light into its
component
colors, much like a prism separates white light into a rainbow.
It
turns out that each element can only emit light of certain
colors, so
by analyzing the light emitted by an object astronomers can
figure out
its composition. Astronomers can also learn about its motion
because
light from an object that is moving toward us is shifted to more
energetic, bluer colors, and light from an object moving away is
shifted to less energetic, more red colors. The effect is similar
to
the way the pitch of the siren on a speeding ambulance appears
to rise as it approaches and fall as it rushes away.
IMAGE CAPTION: [ftp://pao.gsfc.nasa.gov/newsmedia/aas/hst/aas_hst.jpg]
HD 163296 is an isolated young star, seen against a background of
fainter stars in the plane of the Galaxy. Material close to the
star
can only be seen during man-made eclipses with the star blocked
from
our direct view by a coronagraph.
The figure on the left shows a composite image formed from three
coronagraphic observations of HD 163296 obtained with the Hubble
Space
Telescope and the Space Telescope Imaging Spectrograph (STIS),
centered
on the star and covering 1/2 percent of the diameter of the full
moon
on the sky (20"x20"). The image is shown with north up
and east to the
left. The dark, irregularly shaped polygons are regions which
were
obscured by the STIS coronagraph in all three observations. The
disk
surrounding the star is the oval structure resembling Saturn's
rings
running from lower left to upper right (SE to NW) and is shown in
false
color (white is bright, with yellow to red and finally black
corresponding to fainter signals), with the very high dynamic
range
image displayed as the human eye perceives brightness
(logarithmic
stretch). The disk extends to 450 times the Earth-Sun distance.
All of
the material that we can see is at a distance well beyond the
orbit of
Pluto and the known size of our Solar System's Kuiper Belt.
The disk exhibits a surprising amount of structure. There is a
bright
dust ring at 350 times the Earth-Sun distance which can be seen
on
either side of the star's location, together with a darker lane
just
inside it. The dark lane is 0.4" or 50 times the Earth-Sun
distance
across. If this lane is cleared by a single body, the inferred
mass of
the body is 1.3 Saturn masses. Inside the dark lane the disk
becomes as
bright as the outer bright ring, but does not continue to
brighten with
decreasing distance from the star. This suggests that there may
be a
region between 300 and 180 times the Earth-Sun distance which is
partially cleared. The coronagraphic image also reveals three
regions
of nebulosity (the fuzzy, bright features) aligned perpendicular
to the
disk. These features were completely unexpected in a star this
old, and
are more typically detected in association with really young
protostars
which are 10 times younger than HD 163296.
The middle figure shows a spectral image of the vicinity of the
star in
the light of glowing hydrogen gas. In this image, we sample
material
along a 0.2" (24 times the Earth-Sun distance) wide slit
passing
through the nebulosities (vertical axis of the middle image).
Along the
horizontal axis we see the light of the star spread out into its
constituent colors. The nebulosities above the star (NE in the
coronagraphic image) are displaced toward the red, indicating
that the
gas is moving away from us at velocities of 250 miles/second (400
km/s). Below the star, the data reveal a jet of material moving
toward
us at 250 miles/second (400 km/s). This velocity information
enables us
to determine the three-dimensional space orientation of the disk
and
jet system. A cartoon combining the information from the
coronagraphic
image and the spectrum is shown on the right. The nebulosities
seen in
both the image and the spectrum have been identified as ejected
gas
features termed Herbig-Haro objects and collectively are
cataloged as
HH409.
Photo credits: NASA and C.A. Grady and David Devine (NOAO, NASA
Goddard
Space Flight Center), B. Woodgate and R. Kimble (NASA Goddard
Space
Flight Center), F.C. Bruhweiler and A. Boggess (Catholic
University of
America), J.L. Linsky (JILA, University of Colorado and NIST), P.
Plait
(Advanced Computer Concepts), M. Clampin and P. Kalas (Space
Telescope
Science Institute).
For high resolution images of the composite picture, go to:
ftp://pao.gsfc.nasa.gov/newsmedia/aas/hst
SCIENCE BACKGROUND:
HD 163296 is one of the brighter and better studied 2 solar mass
young
stars, and has an estimated age of 2-10 million years, with a
most
probable age estimate of 4 million years. The HD 163296 system
shows
features more commonly associated with older, planetary systems,
and
with younger protostars.
Previous ground-based millimeter observations had shown that the
star
had a large gas and dust disk, while space-based and ground-based
infrared observations had indicated that the disk material
extended in
to very close to the star, much further in than we can image.
Dark
lanes in a dust disk have previously been observed in a somewhat
older
(10 Million years) star, HD 141569 (STScI-PR99-03, which can be
viewed
at oposite.stsci.edu/pubinfo/pr/1999/03/index.html), and not in
younger
systems such as AB Aur (STScI-PR99-21 which can be viewed at
oposite.stsci.edu/pubinfo/pr/1999/21/index.html) at 2-4 million
years.
The STIS data indicate that features interpreted as the effects
of
planet formation occur sooner than predicted by models, and at
larger
distances from the star.
The movement of the nebulosities between the time of the
coronagraphic
images and the spectral observations suggests that the
Herbig-Haro
objects are moving in the plane of the sky with velocities of
approximately 190 miles/second (300 km/s), and that the spacing
between
the brighter knots corresponds to ejections separated by
approximately
5 years. Such a spacing could be due either to stellar activity
cycles,
which have not previously been known to occur in a star of HD
163296's
type, or possibly due to the motion of a companion orbiting the
star
with a 5 year period. Such a period would place the companion
within
the habitable zone, where liquid water can be present on a
planetary
surface, for a star of HD 163296's temperature.
In principle, such a companion could be a low-mass star, a brown
dwarf,
or a planet. If the companion were a low-mass star, it should
produce
X-rays, but other observatories sensitive to X-rays (ROSAT) have
not
seen any X-ray emission from the vicinity of the star. This
suggests
that any companion must be either a brown dwarf, an object not
quite
massive enough to shine by nuclear fusion, but which glows dimly
with
heat left over from its formation, or a planet. The presence of
structure further out in the disk suggesting the presence of at
least
one planetary mass body suggests that the inner companion is more
likely to be a planet. If correct, HD 163296 may be the youngest
known
example of a multiple-planet system and indicates that planets
form
both faster and over a wider zone in their natal circumstellar
disks
than expected.
Where else has Hubble seen hints of planet formation?
http://oposite.stsci.edu/pubinfo/pr/1999/03/index.html
http://oposite.stsci.edu/pubinfo/pr/1999/21/index.html
More about Hubble:
http://www.stsci.edu/hst/
More about the Space Telescope Imaging Spectrograph instrument:
http://www.stsci.edu/hst/#stis
More about Hubble pictures:
http://oposite.stsci.edu/pubinfo/looklike/index.html
=============
(8) AND FINALLY: MASS HYSTERIA MAY BE RISING
From YAHOO NEWS, 12 January 2000
http://dailynews.yahoo.com/h/nm/20000112/sc/health_hysteria_1.html
Mass Hysteria May Be Rising - U.S. Study
BOSTON (Reuters) - Outbreaks of mass hysteria, including fears of
poison gases in the air, may be on the rise and traditional
efforts to
combat them may only make them worse, an article in Thursday's
New
England Journal of Medicine found.
Researchers said it was likely that as fear of bioterrorism or
environmental toxins rose, outbreaks of short-term, widespread,
psychogenic illness were likely to increase.
FULL STORY AT
http://dailynews.yahoo.com/h/nm/20000112/sc/health_hysteria_1.html
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