Lunar soil yields evidence about sun’s dynamic workings
WEST LAFAYETTE, Ind. — Soil collected on the moon by Purdue University
alumnus Eugene Cernan nearly 30 years ago has helped researchers at his
alma mater and the University of California uncover new details about
the workings of the sun.
Physicists at UC Berkeley and Purdue analyzed lunar soil samples for the
presence of an element deposited on the moon’s surface by the solar winds,
a stream of particles constantly being ejected from the sun. The analysis
revealed strong evidence that materials produced in the sun’s atmosphere
do not circulate farther into the interior of the sun before they are
ejected, as some scientists have suggested. Instead, the materials are
created in the atmosphere and then ejected directly outward, spreading
throughout the solar system in the solar wind.
The findings will be reported in the journal Science on Friday (10/12),
in a paper written by Kuni Nishiizumi, a researcher at UC Berkeley’s
Space Sciences Laboratory, and Marc Caffee, an associate professor of
physics at Purdue.
The lunar soil was scooped up by Apollo 17 astronauts Cernan and Harrison
Schmitt, who landed on the moon in 1972. They collected the largest lunar
sample ever brought back to Earth — about 249 pounds of dirt now stored
at the Johnson Space Center in Houston.
“The astronauts did a spectacular job,” Caffee said, noting that robots
are still no substitute for humans in space when it comes to completing
complex assignments.
Cernan, who was the commander of Apollo 17, was the last man to walk
on the moon. He earned a bachelor of science degree in electrical
engineering from Purdue in 1956 and also holds an honorary doctorate
from the university.
Nishiizumi and Caffee analyzed lunar soil for the presence of a
radioactive form of the element beryllium called beryllium-10.
Beryllium-10 is an isotope of beryllium; it contains four protons and
six neutrons in its nucleus, unlike ordinary beryllium, which contains
four protons and five neutrons. This radioactive, unstable form of
beryllium decomposes in 1.6 million years, a period of time called its
half-life. That means any beryllium-10 found in the lunar soil must
have been deposited there long after the moon’s creation, and much of
it has come from the solar winds, Caffee said.
Beryllium-10 is produced in the sun’s atmospheric layers — the
chromosphere and corona — and eventually spewed out, along with
numerous other constituents, in the solar wind.
“The sun is constantly shedding pieces of itself,” Caffee said.
The Earth and other planets are shielded from the solar winds by their
atmospheric envelopes and magnetic fields that surround some planetary
bodies.
“The moon has no atmosphere and no magnetic field, so the solar wind is
not kept in any way, shape or form from hitting the surface of the moon,”
he said.
The researchers extracted beryllium-10 from the lunar soil by treating
the soil with nitric and hydrofluoric acids. Then, the precise quantity
of beryllium-10 contained in the soil was determined by using a piece of
equipment called an accelerator mass spectrometer.
The findings provided strong evidence that the beryllium, and therefore
other constituents produced in the sun’s atmosphere, are ejected
shortly after they are produced in the atmosphere. Some researchers
have suggested that materials produced in the sun’s atmosphere are
pulled into the sun’s interior, where they circulate in convection
currents for millions of years before making their way back to the sun’s
outer atmospheric layers.
The new findings contradict that theory, Caffee said.
Such findings will not only reveal details about the sun’s workings, but
they also will provide new insights into how the sun and the solar system
were formed 4.5 billion years ago.
“Surprisingly, there are a lot of things we still don’t know about the
sun,” Caffee said.
He and Nishiizumi are working on a new NASA mission called Genesis, a
spacecraft launched this summer that will collect particles from the
solar wind.
The spacecraft is expected to complete its mission within two years and
return to Earth.
ABSTRACT
Beryllium-10 from the Sun
K. Nishiizumi and M.W. Caffee
Beryllium-10 (10Be) in excess of that expected from in situ cosmic ray
spallation reactions is present in lunar surface soil 78481; its presence
was revealed with a sequential leaching technique. This excess 10Be,
representing only 0.7 to 1.1 percent of the total 10Be inventory, is
associated with surface layers (
Writer:
Emil Venere, (765) 494-4709, venere@purdue.edu
Sources:
Marc Caffee, (765) 494-5381, mcaffee@physics.purdue.edu
Kuni Nishiizumi, (510) 643-9361, kuni@ssl.berkeley.edu
Purdue News Service:
(765) 494-2096; purduenews@purdue.edu
