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Carbon isotope measurements in the Solar System

I make publicly available my literature study into carbon isotope ratios in the Solar System, which formed a part of Woods&Willacy (2009). As far as I know, I have included here all measurements of 12C/13C in Solar System objects (excluding those of Earth) up to and including 1 February 2010. Full references are given. If you use the any of the information here, please reference the paper Woods&Willacy (2009) and this publication.


Introduction
In the course of writing Woods & Willacy (2009), I read a large number of papers on carbon isotopes in the Solar System, and compiled as much data as I could about these isotope ratios, 12 C/ 13 C , into a figure: Fig. 10 of that paper. An updated version of this figure can be found as Fig. 1 in this paper. Here I list all the reference sources I was able to find in the hope that it will help other parties interested in carbon isotope ratios.
Ratios often have to be converted from the delta notation, favoured by meteoriticists. This is simply, expressed in permil ( ). 13C R meas is the measured value of the 13 C/ 12 C ratio, 13C R std is the terrestrial standard, often taken to be the Peedee belemnite (PDB) value of 0.0112372. This quantity can often appear inverted, and particularly in astrophysical literature can be quoted as 12 C/ 13 C std =89. I use this convention here. Uncertainties in reported values are sometimes given in the literature, and I try to include those where possible. Also, ranges in values may be stated when a number of similar measurements have been made. In the tables of data, Tables 1-4, I have interpreted these ranges as errors about the median point. References are given in order that the ratios given in the tables may be verified -I do not claim that these results are free from mistakes. Neither do I claim that this list of data or references is complete. I believe it to be a fairly complete sample of what is available in the astrophysical literature up until February 2010.
There are four tables of data in this paper: Table 1 gives 12 C/ 13 C ratios for the Sun, moon and rocky planets. Table 2 provides data on the outer planets, including the molecule(s) observed to make the 12 C/ 13 C ratio determinations. Table 3 contains 12 C/ 13 C ratios for minor Solar System bodies, such as meteorites and their incorporated pre-solar grains, and interplanetary dust particles (IDPs). The final table, Table 4, gives carbon isotope ratios in comets. Some of the ratios in this table are a result of re-examining the same observational data with new techniques or models. For example, the 12 C/ 13 C ratio in comet Halley was determined to be 65 by Wyckoff et al. (1989); however, the data was re-evaluated with a new model by Kleine et al. (1995), resulting in 12 C/ 13 C=95. For completeness, I keep both results in the table. Sada et al. (1996) contains a useful discussion of revisions to estimates of 12 C/ 13 C in the outer planets. Section 2.1 gives some context into the matter of carbon isotope ratios, and then data tables follow.

Interstellar and Solar System context
The isotope ratio for carbon ( 12 C/ 13 C) in the Solar System is widely accepted to be 89 (Anders & Grevesse 1989;Clayton & Nittler 2004;Meibom et al. 2007), although recent measurements of the solar photosphere have indicated a ratio of 80±1 (Ayres et al. 2006). This is greater than in the local interstellar medium (ISM), where the value is taken to be 77 (Wilson & Rood 1994), greater than the Orion Bar region ( 12 C/ 13 C∼60; Keene et al. 1998;Langer & Penzias 1990), and much greater than the Galactic Centre ( 12 C/ 13 C∼20; Milam et al. 2005;Langer et al. 1984). This galactic gradient (Langer & Penzias 1990) is due to the higher star formation rate in the inner Galaxy (Tosi 1982), where the fraction of 13 C has been enhanced by the 13 C-rich ejecta of evolved, intermediate-mass stars (Iben & Renzini 1983) in the time since the formation of the Solar System.

Planetary bodies and the Sun
See Tables 1 and 2 for data on the minor and major planets, respectively.

Minor bodies of the Solar System
See Tables 3 and 4 for data on minor bodies and comets, respectively. Triangles indicate bulk isotope measurements of the 12 C/ 13 C ratio in meteorites, and have been placed at the radius of the asteroid belt. Comets, indicated by filled stars, have been placed outside of the radius of Neptune, for illustration. Those cometary points in light grey show depreciated measurements, which have been superseded by updated calculations (this is not a conclusive list, and stems mainly from Manfroid et al. (2009)). IDPs (filled squares) have been placed at cometary radii to indicate their likely origin in comets. Note.- † no attempt is made to make this a complete list of measurements for the Earth.    Lambert & Danks (1983) a This value has been subsequently revised.

Statistics
Here I mention some brief and simple statistics: • The mean 12 C/ 13 C ratio for the Sun is 85.0.
• The mean 12 C/ 13 C ratio for the rocky planets and the Moon is 89.8.
• The mean 12 C/ 13 C ratio for the gas-giant planets and Titan is 85.3.
• The mean 12 C/ 13 C ratio for comets is 93.4.
• A weighted mean of all results is 91.0, which is influenced by the high number of cometary measurements with large error bars. Sada et al. (1996) found a similar value of 88.7 for the outer planets.
This research has made use of NASA's Astrophysics Data System Bibliographic Services