We re-examine the effort to constrain the time-variability of the coupling
constants of the fundamental interactions by studying the anomalous isotopic
abundance of Sm observed at the remnants of the natural reactors which were in
operation at Oklo about 2 billion years ago, in terms of a possible deviation
of the resonance energy from the value observed today. We rely on new samples
that were carefully collected to minimize natural contamination and also on a
careful temperature estimate of the reactors. We obtain the upper bound
$(-0.2\pm 0.8)\times 10^{-17}$ ${\rm y}^{-1}$ on the fractional rate of change
of the electromagnetic as well as the strong interaction coupling constants.
Our result basically agrees with and even suggests some improvement of the
result due recently to Damour and Dyson. Strictly speaking, however, we find
another range of the resonance energy shift indicating a nonzero time variation
of the constants. We find a rather strong but still tentative indication that
this range can be ruled out by including the Gd data, for which it is essential
to take the effect of contamination into account.Comment: 20 pages LaTex including 6 figures. Theoretical interpretation
changed. More detailed discussions on the temperature estimate also adde
Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C,
5.2
−
0.8
+
0.7
(Stat.)
−
2.1
+
1.6
(Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.
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