Abstract
Introduction: Since their first isolation from meteorites some 35 years ago, tens of thousands of individual pre-
solar grains have been analyzed for their isotopic composition, many of them in an automated way to search for rare
and exotic grains. In 2009, the Presolar Grain Database (PGD), a collection of spreadsheets containing isotope data
on presolar grains, was released [1]. In 2019, after it had become apparent that parts of the PGD had become compro-
mised by accumulating errors over the years, we decided to rebuild the PGD from the ground up by: (1) eliminating
known errors; (2) searching for inconsistencies by comparing with publications, original data files, and/or personal
compilations; and (3) updating and adding data that have been reevaluated and/or published [2]. The initial effort
focused on silicon carbide (SiC), for which an established new version of the PGD now exists, containing data for, as
of this writing, 20,230 individual presolar SiC grains [3,4]. All versions for SiC since the restart of the PGD in 2019
can be found at https://zenodo.org/doi/10.5281/zenodo.8187219. Based on the new PGD, updated rules for SiC grain
type classification were developed to unify previous efforts, taking into account new SiC grain types that have been
proposed over the last three and a half decades [4].
We recently shifted our focus to presolar graphite in order to rebuild the PGD also for this kind of presolar grain
from the ground up.
The new Presolar Grain Database for graphite: While the old PGD showed 2216 entries for graphite grains
attributed to five different publications, rebuilding the database from scratch revealed that 118 grains had double
entries in the old database, typically due to inconsistent labeling. Some grain data, although provided in these publi-
cations, were missing from the old database, while other data could not be attributed to any grains mentioned in these
or in other publications and were therefore removed. Some obviously incorrectly reported data were found, either in
the old PGD or in some of the publications. Some preliminary data had been reported in the old PGD or early publi-
cations but have been reevaluated later, leading to small changes in values of isotope data. Some grain data had been
published prior to the five papers mentioned in the old PGD. The new PGD for graphite now associates each grain
data entry to the first publication we were able to find that contains at least some of its isotope data. With six more
recent publications, the data of which has also been added, the PGD for graphite now contains data for 2122 individual
graphite grains attributed to 18 different publications.
The first version of the PGD for graphite grains as well as all future versions can be found at
https://zenodo.org/doi/10.5281/zenodo.11188115. As with the PGD for SiC, each grain has been given a unique PGD
ID, which is not meant to replace a grain label defined in the original publication, but to prevent confusion from
inconsistent nomenclatures used. Grains have been divided into two types, low-density and high-density grains, using
2.1 g/cm3 as a divider. In addition, lower and upper limits of the density range of the grain separate are provided as
well as information about grain morphology if available.
Discussion and Outlook: As for SiC, we will continue our work on the PGD for graphite in the upcoming years.
So far, we have mainly rebuilt the old database by correcting inconsistencies. Major tasks will be to add more data
from publications not covered by the old database. After adding such data to the PGD for graphite, we will shift our
focus to other kinds of presolar grains, including oxides, silicates, and rarer phases. Furthermore, we are working on
making a first version of Python tools (PGDTools) available later this year, which will allow the user to programmat-
ically interact with current and future databases.
We strongly encourage users of the PGD to give proper credit to the authors of the original papers by also
referencing those publications.
References: [1] Hynes K. M. and Gyngard F. (2009) Lunar and Planetary Science Conference 40, Abstract #1198.
[2] Stephan T. et al. (2020) Lunar and Planetary Science Conference 51, Abstract #2140. [3] Stephan T. and Trap-
pitsch R. (2023) Presolar Grain Database—Silicon Carbide, v1.0, Interdisciplinary Earth Data Alliance (IEDA),
doi:10.60520/IEDA/113069. [4] Stephan T. et al. (2024) Astrophysical Journal Supplement Series 270:27.
