A&A press release: Meteorites record past solar activity (26 September 2006)
Published on 25 September 2006
A&A press release
Released on September 26th, 2006
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Meteorites record past solar activity
Based on the article “Long-term solar activity reconstructions: Direct test by cosmogenic 44Ti in meteorites” by Usoskin et al.
(To be published in Astronomy & Astrophysics Letters, volume 457-3, p. L25)
Original A&A article
Ilya Usoskin (Sodankylä Geophysical Observatory, University of Oulu,
Finland) and his colleagues have investigated the solar activity over
the past centuries. Their study is to be published this week in Astronomy & Astrophysics Letters.
They compare the amount of Titanium 44 in nineteen meteorites that have
fallen to the Earth over the past 240 years. Their work confirms that
the solar activity has increased strongly during the 20th century. They
also find that the Sun has been particularly active in the past few
I. Usoksin and his colleagues have used meteorites to reconstruct past
solar activity. Studying the earlier activity of our Sun is one of the
oldest astrophysical projects, as astronomers began recording the
number of sunspots to trace the Sun's magnetic activity four hundred
Fig. 1 - A sunspot the size of the Earth. Sunspots result from the solar magnetic activity.
Credit: Max Planck Institute for Solar System Research, Dr. Vasily Zakharov. Image taken with the Swedish Solar Telescope on the island of La Palma.
The international team examined a set of nineteen meteorites whose
dates of fall are precisely known, and measured the amount of
Titanium 44 in these meteorites. Titanium 44 is produced by the cosmic
rays in the meteorites while they are outside the Earth’s atmosphere.
After the meteorite has fallen, it stops producing this isotope. By
measuring the Titanium 44 in these meteorites, they are able to
determine the level of solar activity at the time the meteorite fell.
Past solar activity is reconstructed with this technique in an
independent way, that is, one not affected by terrestrial effects. How
high the solar activity was at a given epoch was previously known from
measuring the concentration of
produced at that time. But most of the isotopes found on the Earth – in
Greenland and Antarctic ice sheets or in tree rings, for instance – are
also affected by terrestrial processes, in these examples related to
the Earth’s magnetic field and climate. Until now, reconstructing past
solar activity was thus very uncertain. This is shown by how various
reconstructions that were previously published differ from one other.
In the new study to be published this week in Astronomy & Astrophysics Letters
, the team shows that the Sun is currently particularly active compared to earlier centuries.
 The team includes N. Bhandary (Basic Sciences Research Institute,
Ahmedabad, India), G.A. Kovaltsov (Ioffe Physical-technical Institute,
St. Petersburg, Russia), S.K. Solanki (Max-Planck Institute for Solar
System Research, Katlenburg-Lindau, Germany), C. Taricco (Dipartimento di Fisica Generale, University of Torino, Italy) and I.G. Usoskin
(University of Oulu, Finland).
Long-term solar activity reconstructions: Direct test by cosmogenic 44Ti in meteorites
by I.G. Usoskin, S.K. Solanki, C. Taricco, N. Bhandari, G.A. Kovaltsov.
To be published in Astronomy & Astrophysics
(A&A 2006, 457-3, p. L25)
Full article available in PDF format
Dr. Ilya Usoskin
Sodankyla Geophysical Observatory (Oulu unit)
P.O. Box 3000, FIN-90014 University of Oulu, Finland
Phone: +358-8-553 1377 - Email: ilya.usoskin (at) oulu.fi
Dr. Jennifer Martin
Journal Astronomy & Astrophysics
61, avenue de l'Observatoire
75014 Paris, France
Phone: +33 1 43 29 05 41 - Email: aanda.paris (at) obspm.fr
© Astronomy & Astrophysics 2006