#Meteorites
10 messages in this thread
To anyone interested,
From time to time there is a couple of us who post messages here concerning
meteorites. Haven't seen any messages here as late so thought I would post one.
Doug, you have made mention of some meteorites being from Venus. Due to the
thick atmosphere, simular gravity to Earth and being closer to the Sun
therefore having to increase energy to go further out in the solar system, I
have alway stated it would be very improbable for such an animal to exist.
Guess what, I have found out that the ureilites are thought to be of a Venus
origion although there is not anywhere near as compelling evidence as the Mars
material which is more than likely a sure thing. Thought this would be of
interest to you.
Anyone that is interest in meteorites please feel free to reply to this message
even though it is not related. I or Joseph Murakami will no doubt be around to
give some feed back. Perhaps there is someone out there that has an extensive
collection who would like to share ideas here with us. We are looking for a
meteorite group where we can all post messages on the subject. If we generate
enough messages maybe they will give us our own area <G>. Later!
–AL
Hi, Al–
Venus rocks would surely be interesting. I am away from my references
(visiting my native CA again), and cannot look up the characteristics of
ureilites until next week. Are they a lot like Earth rocks? What is it about
them that gives them a Venus origin theory?
–Doug
Hi Doug,
The only thing I can say for sure is that it was mentioned in one of the
brochures that is put out by one of the big dealers. So it is more hear say
than fact from my point of view now. They must know or have information that
puts a Venus origion on this material. It is simular in cost to Mars material
(expensive) but its nice to know I have a sample to look at. It has a unique
color to it though mostly grey to tan in color. Looking at it close though it
has a rainbow effect, kind of like when looking at dried shaved beef that has a
colorful look to it. Don't think I'll make a sandwich here though <G>.
Are you going to Tucson this year? In fact when are the shows on?
–AL
Hi, Al and Joseph–
I am back in OK now, and looked up ureilites in "The Meteorite & Tektite
Collector's Handbook" (Bagnall).
Ureilites are coarse-grained olivine-pyroxene achondrites. The large grain
size suggests slow cooling and the grains tend to be oriented, leading Bagnall
to remark "In any event the mixture is difficult to achieve by known
mechanisms." So far, a planetary origin sounds like a viable theory.
They have no chondrites, like Earth rocks. Bagnall seems to say they include
kamacite (nickel-iron), unlike Earth rocks. I would sort of expect Venus rocks
to resemble Earth rocks in these regards (pending the arrival of
samples)(native iron would be more expected under Venus' atmosphere, but I am
somewhat surprised if it is disseminated in olivine; part of the
Venus-impacter, or an orebody mixed in by impact?)
I see ureilites include diamond and lonsdaleite (an "ultra-high-pressure carbon
polymorph"), which are taken as indicators of a terrific impact that knocked the
ureilites loose from their parent body. That is what it would take to bust
them loose from Venus…
Joseph's remarks suggest the diamonds could be interstellar in origin (I assume
lonsdaleite would continue to suggest major impact) – I do not see how they
would be at all common on Venus (no such diamonds are found on Earth, are
there?).
I see no mention of datings – it was the youth of SNC meteorites that best
rules out planetesimals as their source and leave Mars the best bet; without a
too-young date, I would regard planetesimals as equal to Venus as candidates.
Thus far, Venus origin seems possible to me, but with problems. If this is all
there is to go on, I would rate it at best one among many competitive theories.
Hmm.. lonsdaleite .. I had thought buckyballs were the third polymorph of
carbon, but Fleischer's says lonsdaleite and chaoite were there first.
I do not expect to make it to Tucson this year (next year for sure!!), but
things could change…
–Doug
Hi Doug & Joesph,
I have a meteorite book that offers more on the Ureilites origin and may
complicate our theories even greater <G>. From the Meteorites and the Early
Solar System : Ureilites. They are carbonaceous olivine- pyroxene achondrites
whose igneous history is complex (Berkley and Jones 1982; Goodrich et al.
1987).
A two stage model for the formation of the ureilites has been proposed
(Goodrich et al. 1987): chondrite material underwent a large degree of partial
melting (10 – 25%) leaving olivine-pigeonite- plagioclase(?) residues. Later
melting ( <10% ) of mafic cumulates from the earlier magmas produced the
ureilites parent magmas with high Ca/Al ratios and negative Eu anomalies.
Carbon becomes reducing at low pressures and, when the C- bearing ureilite
magmas were intruded into the crust, they equilibrated at varying depths and
were reduced to diffrent extents, losing diffrent amounts of Fe metal ranging
from 20% to 27%. The cumulus urelite minerals then crystallized from the
reduced magmas. That sugests the urelites did not experience a core formation
event. The urelites were finally intruded by less than 1% of an interstitial
liquid, unrelated to the original magmas from which the cumulates formed.
Goodrich et al. (1987) suggests that a large parent body ( > 470 km diameter )
is required to explain the ureilites. ——-> Get this next bit! However new O
isotope data show that ureilites are igneous but not related to each other by
differentiation of a common source, which means they cannot have been formed
by large-scale igneous activity on a single parent body (Clayton et al. 1987).
The model of Takeda involving partial melting of carbonaceous material
therefore deserves serious consideration.
I thought that to be fasinating. Sorry for the long message.
–AL
Hi, Al–
That unrelatedness of ureilites among themselves is indeed intriguing and
suggestive. Such a variety could come from a planet, but would likely have to
be ejected from the planet in many different explosions, not all in one blast.
These processes for producing ureilites seem rather unusual – I doubt Venus can
have an all-ureilite crust, and thus it seems there should be numerous other
types of Venus rocks falling on Earth if the ureilites are such. Granite
meteorites or something else of evident planetary origin would outnumber
ureilites, I suspect…
Counter-reservations: (1) if the method of ejection from Venus is volcanic
rather than by impact, it might favor ureilites over other rocks, and (2)
perhaps the unrelatedness means they came from different parts of the same
vein/batholith/whatever, rather than from different veins as I am assuming,
leaving us with a single Venus-ejection event.
Those high pressures are impressive, but how easy is it to reach such values in
a many-miles-per-second impact of two asteroids? Or were the pressures
maintained too long to be from impact?
I figure one should take this Venus-origin theory with a 470-km grain of salt.
But ureilites could represent something even more exotic and seem quite
interesting regardless.
What long message?
–Doug
Hi Doug,
Here is yet some more information on ureilites. Ureilites are classified in two
groups due to shock. They are low-moderate and very high degree of shock.
Diamond and lonsdaleite found in the ureilites are obviously due to shock
transformation of graphite requiring a minimum peak pressure of 13 GPa. The
upper limit may be as high as 60 Gpa. Thats sound like a planetary strike to me
<G>.
Don't know if the ureilite – Venus association will be answered too soon but
like a lot of other meteorites whos parent bodies need to be solved so does
this association. Also it could be a mistake to assume it came from Venus not
too long ago although possible it could have happened earlier in our systems
history and the meteoroid could have floated near Earth and been flung in a
outward orbit only to return just recently. Don't know if the cosmic radiation
effect on this material supports that idea though.
I do like having the Zagami knowing it is most likely from Mars. Now if the
ureilite is from Venus then all I need is some lunar material (legal) to have
the solar systems three closest bodies to Earth <G>.
–AL
Hey Al,
Do you know of any illegal lunar material???
(Like this forum is very private!)
Joseph
P.S. I liked your long message on Ureilites. I think from my reading that
Ureilites must be igneous and I've come across very similar information to
yours. The interesting thing was the aspect of pressure sensitivity that the
"smelting" of iron out of olivine required and the implication of 100 km as the
minimum depth of igneous formation…
P.P.S. Aren't fullerenes neat??
Hi Joseph,
Do I know of any illegal lunar material??? No!!!! But I do have all of the
pseudo lunar material you can buy!! <<G>>.
Have talked to a couple of my experts on this subject and they say the
ureilite/Venus connection is not based on very good grounds and is
controversial. Seems like someone said this to be able to move meteorites. I
have an interest in any meteorite in which the parent body is known. The Venus
relationship is beginning to develope holes.
–AL
Hi Doug,
I'm back from San Diego. So glad to back here in Honolulu! Found a few
scattered fossil dealers and lots of Moroccan trilobites including whole
multiple plates of 6 inch sized Andalusiana 5-8 individuals in glorious 2×2
feet prepared slabs! Too bad so much of the Moroccan specimens are prepared
with so heavy a hand, bruising and really disfiguring so many of the
specimens…
Regarding Ureilites, I couldn't find the reference to Ureilites and Venus,
though I recall the association somewhere, sometime. Here's some jibberish on
Ureilites: Ureilites are highly a enigmatic differentiated achondritic group
of meteorites with a coarse recrystallized mineral assemblage of olivine,
pigeonite, and graphite in the form of diamond micro-crystals on the order of
10-40 microns size. The abundance of carbon very suggestive of kinship with
carbonaceous chondrites and the abundance of trapped solar nobel gases suggest
ureilites to be very primitive meteorites, probably of solar nebular genesis.
The occurrence of graphite carbon with fayalite olivine in the recrystallized
matrix without the loss of Fe metal from the fayalite via low pressure smelting
processes supports ureilite recrystallizing within parent bodies of nontrivial
sizes, at least 100 km or more in diameter, according to Walker and Grove
(Meteoritics 28, 629-636). Remarkably, the nanodiamonds in Ureilites and
carbonaceous chondrites preceed the formation of the Ureilite "parent body" and
have Xenon isotopes (Xe-HL) supposedly formed in a type II supernova envelope.
But th Venus connection??? Couldn't find anything!
Joseph