OULU, Finland, Sept. 26 (UPI) -- A Finnish-led international team has used meteorites to investigate the sun's solar activity of past centuries.
Ilya Usoskin at Finland's Sodankyla Geophysical Observatory and colleagues compared the amount of Titanium 44 in 19 meteorites that have fallen to the Earth the past 240 years. They said their findings confirm that solar activity increased strongly during the 20th century. They also find the sun has been particularly active during the past few decades.
The scientists say studying the sun's activity is one of the oldest astrophysical projects, as astronomers began recording the number of sunspots to trace the sun's magnetic activity 400 years ago.
The team examined a set of 19 meteorites whose dates of fall are precisely known, measuring the amount of radioactive isotope Titanium 44 in each meteorite. 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 the isotope.
By measuring the Titanium 44 in the meteorites, the scientists determined the level of solar activity at the time the meteorite fell.
The study appears in the journal Astronomy & Astrophysics Letters.