When dust particles from Comet Wild 2 struck a sponge-like "aerogel"
the Stardust spacecraft, they left carrot-shaped
imprints about a centimeter long.
Mar 20, 2006
Stardust Shatters Comet Theory (2)
Mythic “Oort Cloud” Finds No Support in Comet Dust
It’s now official. Minerals found in Comet Wild 2 dust particles can form
only at high temperatures, and they cannot be distinguished from
minerals found in meteorites and on rocky planets.
Dust particles ejected by Comet Wild
2 have provoked another surprise, contradicting the underlying
assumptions of popular comet theory.
When the Stardust mission returned “pristine comet material”
from Comet Wild 2, project scientists were astonished to discover
minerals that can only form at high temperatures—up to thousands of
degrees Fahrenheit. And the dust
particles reveal no indications of the water that cometologists
Standard theory states that comets
formed billions of years ago in an imagined icy “Oort cloud” at the
very fringe of the Sun’s domain, far beyond the orbit of Pluto. But
the new findings require a quite different history. A NASA news
release on March 13, 2006 summarized the problem with this
“Scientists have long thought of comets as
cold, billowing clouds of ice, dust and gases formed on the edges of
the solar system. But comets may not be so simple or similar. They
may prove to be diverse bodies with complex histories. Comet Wild 2
seems to have had a more complex history than thought”.
The disturbing discovery provoked a burst of
creative attempts to rescue ideas stated as fact for at least thirty
years. Michael Zolensky, Stardust curator and co-investigator at
NASA's Johnson Space Center, Houston, suggested a novel
interpretation that quickly caught on. "It seems that comets are not
composed entirely of volatile rich materials but rather are a
mixture of materials formed at all temperature ranges, at places
very near the early sun and at places very remote from it." One
science writer interpreted Zolensky’s comment this way: “The
findings suggest materials from the center of the solar system could
have traveled to the outer reaches where comets formed”.
So an obsolete theoretical conjecture
persists in human imagination, despite an undeniable fact:
Nothing discovered about comets—over many years of profound
discovery— points to an origin in the remote region assumed.
A rational response will not exclude the question shouted by the new
data. Could something be wrong with earlier suppositions
about the region of comet formation—suppositions that never produced
a successful prediction in the course of the space age?
As for the water (ice), that was supposed to
be the primary constituent of comets. But the anticipated markers of
water on the nucleus of Wild 2 are absent. One mineral present in
the comet particles is olivine, an iron-magnesium silicate. In the
presence of water and even modest heat, olivine will be converted to
another mineral, serpentine. Place olivine in the presence of water
the temperatures indicated for its formation, and it would be
almost instantly converted to serpentine.
According to Stardust principal investigator
Donald Brownlee, “no evidence of water has been detected in the
particles”. One sign of water, for example, would be the presence of
hydrate silicates, Brownlee said, “but so far none of these have
been found in the Stardust samples”.
How, then, are we to reconcile the absence of water signatures in the
comet dust with the fact that cometary comas often
exude an abundance of water (or at least the hydroxyl radical OH).
We answered that question in a three-part series, “Deep
Impact—Where’s the Water?” (first article
here) The OH and
whatever actual water may have been present in the coma were
manufactured in the coma—an acknowledged “chemical factory”.
The vehicle for this process has already been observed—reactions
between the oxygen ions in the coma plasma and the hydrogen ions in
the solar wind. Charge exchange is now known to occur.
The least we can say today is that
most comets contain no appreciable levels of water (i.e.,
most comets are neither “dirty
snowballs” nor “icy dirtballs”), Additionally, it needs to be
emphasized that there is no conflict between Stardust and Deep
Impact data. Brownlee, who is not
prone to overstate theoretical implications, points out that
Stardust collected dust that was released directly from the surface
in jets. "We're confident that the things coming out [of Comet Wild
2] are the same as those that went in”, he told Space.com.
That means the material has not been processed by the chemical factory of the
coma. "We believe that we collected the most pristine samples of a
comet”, he said. Hence, the failure to find a signature of water in
the comet dust is consistent with all of the facts we have presented
in previous discussion.
It is not unreasonable to suggest, therefore, that only one comet model can
make sense of what is otherwise a hopelessly confused picture. This
model is electric. And thanks to the technological successes of the
space age, all of the markers reasonably
expected of an
have been found.
Of course the implications of the electric model do not end with the origin
and dynamics of comets. They extend to virtually all of the
theoretical sciences, and range from questions of electricity in
remote space, to the nature of stars and the violent history of the
Additionally, as we intend to make clear, human memories of cometary
and planetary catastrophe cannot be excluded from this
Coming March 21:
A Partnership of Craters and Rilles
Coming March 23:
Of Comets and Planetary Catastrophe