Neue Erkenntnisse zur Kollisionstheorie

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Neue Erkenntnisse zur Kollisionstheorie

Wo ist die Theia-Materie?

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1429.html

The proto-Earth as a significant source of lunar material

Junjun Zhang, Nicolas Dauphas, Andrew M. Davis, Ingo Leya, Alexei Fedkin
Nature Geoscience, (2012) doi:10.1038/ngeo1429

A giant impact between the proto-Earth and a Mars-sized impactor named Theia is the favoured scenario for the formation of the Moon. Oxygen isotopic compositions have been found to be identical between terrestrial and lunar samples, which is inconsistent with numerical models estimating that more than 40% of the Moon-forming disk material was derived from Theia. However, it remains uncertain whether more refractory elements, such as titanium, show the same degree of isotope homogeneity as oxygen in the Earth–Moon system. Here we present 50Ti/47Ti ratios in lunar samples measured by mass spectrometry. After correcting for secondary effects associated with cosmic-ray exposure at the lunar surface using samarium and gadolinium isotope systematics, we find that the 50Ti/47Ti ratio of the Moon is identical to that of the Earth within about four parts per million, which is only 1/150 of the isotopic range documented in meteorites. The isotopic homogeneity of this highly refractory element suggests that lunar material was derived from the proto-Earth mantle, an origin that could be explained by efficient impact ejection, by an exchange of material between the Earth’s magma ocean and the protolunar disk, or by fission from a rapidly rotating post-impact Earth.

Hier eine Zusammenfassung auf Deutsch von Florian Freistetter:

http://www.scienceblogs.de/astrodicticum-simplex/2012/03/die-entstehung-des-mondes-war-alles-ganz-anders.php

Kollisionstheorie: http://de.wikipedia.org/wiki/Entstehung_des_Mondes#Kollisionstheorie

Theia: http://de.wikipedia.org/wiki/Theia_%28Planet%29

 

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Neue Simulationen, neue Theorien

A hit-and-run giant impact scenario

http://www.ethlife.ethz.ch/archive_articles/120903_mondenstehung_su/index_EN

http://translate.google.de/translate?hl=de&sl=en&tl=de&u=http%3A%2F%2Fwww.ethlife.ethz.ch%2Farchive_articles%2F120903_mondenstehung_su%2Findex_EN

http://www.sciencedirect.com/science/article/pii/S0019103512002977

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Neues zur Entstehung des Mondes

http://phys.org/news/2012-10-massive-planetary-collision-zapped-key.html
http://www.nature.com/nature/journal/v490/n7420/full/nature11507.html

http://phys.org/news/2012-10-moon-earth-like-composition-giant-impact.html
http://www.sciencemag.org/content/early/2012/10/16/science.1226073.abstract

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Neues zum Alter des Mondes

LINK

Highly siderophile elements in Earth’s mantle as a clock for the Moon-forming impact

Seth A. Jacobson, Alessandro Morbidelli, Sean N. Raymond, David P. O'Brien, Kevin J. Walsh, David C. Rubie

Nature 508, 84–87 (03 April 2014) doi:10.1038/nature13172

LINK

Editor's summary

The age of the Moon has been a focus for geochemists for at least the past three decades. A number of chronometers have been used to address the question but the results differ from method to method, in part because of the varying assumptions required in the calculation of the so-called model ages. Seth Jacobson et al. have used an alternative approach. They run a large number of numerical simulations, some based on early Moon-forming events, others later events. They then arrive at a model-independent correlation between the formation age of the Moon and the amount of mass accreted by the Earth since then, the so-called Late Veneer. The concentration of highly-siderophile (iron-loving) elements observed in the Earth's mantle provides a constraint on the timing and rules out an early Moon-forming event. Instead, the authors calculate that the Moon-forming impact must have occurred at least 40 million years after formation of the Solar System.

According to the generally accepted scenario, the last giant impact on Earth formed the Moon and initiated the final phase of core formation by melting Earth’s mantle. A key goal of geochemistry is to date this event, but different ages have been proposed. Some1, 2, 3 argue for an early Moon-forming event, approximately 30 million years (Myr) after the condensation of the first solids in the Solar System, whereas others4, 5, 6 claim a date later than 50 Myr (and possibly as late as around 100 Myr) after condensation. Here we show that a Moon-forming event at 40 Myr after condensation, or earlier, is ruled out at a 99.9 per cent confidence level. We use a large number of N-body simulations to demonstrate a relationship between the time of the last giant impact on an Earth-like planet and the amount of mass subsequently added during the era known as Late Accretion. As the last giant impact is delayed, the late-accreted mass decreases in a predictable fashion. This relationship exists within both the classical scenario7, 8 and the Grand Tack scenario9, 10 of terrestrial planet formation, and holds across a wide range of disk conditions. The concentration of highly siderophile elements (HSEs) in Earth’s mantle constrains the mass of chondritic material added to Earth during Late Accretion11, 12. Using HSE abundance measurements13, 14, we determine a Moon-formation age of 95 ± 32 Myr after condensation. The possibility exists that some late projectiles were differentiated and left an incomplete HSE record in Earth’s mantle. Even in this case, various isotopic constraints strongly suggest that the late-accreted mass did not exceed 1 per cent of Earth’s mass, and so the HSE clock still robustly limits the timing of the Moon-forming event to significantly later than 40 Myr after condensation.

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Neues und Spannendes zum Thema:

Identification of the giant impactor Theia in lunar rocks

Daniel Herwartz, Andreas Pack, Bjarne Friedrichs, Addi Bischoff

LINK

Science 6 June 2014:
Vol. 344 no. 6188 pp. 1146-1150
DOI: 10.1126/science.1251117

Materials/Methods, Supplementary Text, Tables, Figures, and/or References

PDF-LINK

An analysis of motes of the Moon maker

How did the Moon form? According to the prevailing hypothesis, a Mars-sized body known as Theia smashed into Earth. Herwartz et al. analyzed fresh basalt samples from three Apollo landing sites and compared them with several samples of Earth's mantle. The oxygen isotope values measured in these lunar rocks differ significantly from the terrestrial material, supporting the giant-impact hypothesis.

The Moon was probably formed by a catastrophic collision of the proto-Earth with a planetesimal named Theia. Most numerical models of this collision imply a higher portion of Theia in the Moon than in Earth. Because of the isotope heterogeneity among solar system bodies, the isotopic composition of Earth and the Moon should thus be distinct. So far, however, all attempts to identify the isotopic component of Theia in lunar rocks have failed. Our triple oxygen isotope data reveal a 12 ± 3 parts per million difference in Δ17O between Earth and the Moon, which supports the giant impact hypothesis of Moon formation. We also show that enstatite chondrites and Earth have different Δ17O values, and we speculate on an enstatite chondrite–like composition of Theia. The observed small compositional difference could alternatively be explained by a carbonaceous chondrite–dominated late veneer.

New isotopic evidence supporting moon formation via Earth collision with planet-sized body

LINK

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Everything has a natural explanation. The moon is not a god, but a great rock ...

Anaxagoras / Ἀναξαγόρας


The giant impact hypothesis: past, present (and future?)

William K. Hartmann

Phil. Trans. R. Soc. , published 11 August 2014 doi: 10.1098/rsta.2013.0249

LINK
PDF-LINK

Abstract

At the request of editors, this paper offers a historical review of early work on the giant impact hypothesis, as well as comments on new data. The author hereby claims (whether believable or not) that his interest is to move towards a correct model of lunar origin, not to defend a possibly incorrect idea, just because of being a co-author of a relevant early paper. Nonetheless, the 1974 giant impact hypothesis appears still to be viable.

The origin of the Moon

D. J. Stevenson and A. N. Halliday

Phil. Trans. R. Soc. , published 11 August 2014 doi: 10.1098/rsta.2014.0289

LINK
PDF-LINK

dazu passend:

Origin of the Moon

Alex Halliday talks about an issue he has organised for Philosophical Transactions that summarises the current state of our understanding and the challenges that still remain.

VIDEO

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On the origin and composition of Theia: Constraints from new models of the Giant Impact

Matthias M.M. Meier, Andreas Reufer, Rainer Wieler

Icarus 242:316-328 (2014)
DOI: 10.1016/j.icarus.2014.08.003

PDF-LINK
LINK (abstract)

Knowing the isotopic composition of Theia, the proto-planet which collided with the Earth in the Giant Impact that formed the Moon, could provide interesting insights on the state of homogenization of the inner solar system at the late stages of terrestrial planet formation. We use the known isotopic and modeled chemical compositions of the bulk silicate mantles of Earth and Moon and combine them with different Giant Impact models, to calculate the possible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in each model. We compare these ranges to the isotopic composition of carbonaceous chondrites, Mars, and other solar system materials. In the absence of post-impact isotopic re-equilibration, the recently proposed high angular momentum models of the Giant Impact ("impact-fission", Cuk & Stewart, 2012; and "merger", Canup, 2012) allow - by a narrow margin - for a Theia similar to CI-chondrites, and Mars. The "hit-and-run" model (Reufer et al., 2012) allows for a Theia similar to enstatite-chondrites and other Earth-like materials. If the Earth and Moon inherited their different mantle FeO contents from the bulk mantles of the proto-Earth and Theia, the high angular momentum models cannot explain the observed difference. However, both the hit-and-run as well as the classical or "canonical" Giant Impact model naturally explain this difference as the consequence of a simple mixture of two mantles with different FeO. Therefore, the simplest way to reconcile the isotopic similarity, and FeO dissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic composition and a higher (~20%) mantle FeO content.

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Gratislektüre:

Early formation of the Moon 4.51 billion years ago

PDF

Melanie Barboni, Patrick Boehnke, Brenhin Keller, Issaku E. Kohl, Blair Schoene, Edward D. Young, Kevin D. McKeegan

Science Advances  11 Jan 2017:
Vol. 3, no. 1, e1602365
DOI: 10.1126/sciadv.1602365

"Establishing the age of the Moon is critical to understanding solar system evolution and the formation of rocky planets, including Earth. However, despite its importance, the age of the Moon has never been accurately determined. We present uranium-lead dating of Apollo 14 zircon fragments that yield highly precise, concordant ages, demonstrating that they are robust against postcrystallization isotopic disturbances. Hafnium isotopic analyses of the same fragments show extremely low initial 176Hf/177Hf ratios corrected for cosmic ray exposure that are near the solar system initial value. Our data indicate differentiation of the lunar crust by 4.51 billion years, indicating the formation of the Moon within the first ~60 million years after the birth of the solar system."

[DCOM]

Klasse! 

Das Ergebnis stimmt recht gut mit den Resultaten früherer radiometrischer Datierungen überein, die auf ein Mondalter von 4527 +/- 10 Mio. Jahre kommen:

KLEINE, T. et al. (2005) Hf-W chronometry of lunar metals and the age and early differentiations of the moon. Science 310, 1671–1674. PDF

The  use  of  hafnium-tungsten  chronometry  to  date  the  Moon  is  hampered  by cosmogenic tungsten-182 production mainly by neutron capture of tantalum-181 at  the  lunar  surface.  We  report  tungsten isotope  data  for  lunar  metals,  which contain  no 181Ta-derived  cosmogenic 182W.  The  data  reveal  differences  in  indigenous 182W/184W  of  lunar  mantle  reservoirs,  indicating  crystallization  of  the lunar magma ocean 4.527 +/- 0.010 billion years ago. This age is consistent with the giant impact hypothesis and defines the completion of the major stage of Earth’s accretion.

Grüße, D.U.

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Der Mond ist noch jünger als gedacht: 4,425 ± 0,025 Milliarden Jahre!

Neues zum Thema aus Berlin und Münster. 

A long-lived magma ocean on a young Moon

M. Maurice, N. Tosi, S. Schwinger, D. Breuer and T. Kleine

LINK
PDF

Pressemitteilungen:
DLR-Institut für Planetenforschung
WWU

[Gibeon2010]

Faszinierend, danke für die Infos!