Scientists may have to give the Sun a little more credit. Exotic isotopes
present in the early Solar System — which scientists have long-assumed
were sprinkled there by a powerful, nearby star explosion — may have
instead been forged locally by our Sun during the colossal solar-flare
tantrums of its baby years.

The isotopes — special forms of atomic nuclei, such as aluminum-26,
calcium-41, and beryllium-10 — can form in the X-ray solar flares of young
stars in the Orion Nebula, which behave just like our Sun would have at
such an early age. The finding, based on observations by the Chandra X-ray
Observatory, has broad implications for the formation of our own Solar
System.

Eric Feigelson, professor of astronomy and astrophysics at Penn State, led
a team of scientists on this Chandra observation and presents these results
in Washington, D.C., today at a conference entitled “Two Years of Science
with Chandra”.

“The Chandra study of Orion gives us the first chance to study the flaring
properties of stars resembling the Sun when our solar system was forming,”
said Feigelson. “We found a much higher rate of flares than expected,
sufficient to explain the production of many unusual isotopes locked away
in ancient meteorites. If the young stars in Orion can do it, then our Sun
should have been able to do it too.”

Scientists who study how our Solar System formed from a collapsed cloud
of dust and gas have been hard pressed to explain the presence of these
extremely unusual chemical isotopes. The isotopes are short-lived and had
to have been formed no earlier than the creation of the Solar System, some
five billion years ago. Yet these elements cannot be produced by a star as
massive as our Sun under normal circumstances. (Other elements, such as
silver and gold, were created long before the creation of the solar system.)

The perplexing presence of these isotopic anomalies, found in ancient
meteoroids orbiting the Earth, led to the theory that a supernova
explosion occurred very close to the Solar System’s progenitor gas cloud,
simultaneously triggering its collapse and seeding it with short-lived
isotopes.

Solar flares could produce such isotopes, but the flares would have to be
hundreds of thousands of times more powerful and hundreds of times more
frequent than those our Sun generates.

Enter the stars in the Orion Nebula. This star-forming region has several
dozen new stars nearly identical to our Sun, only much younger. Feigelson’s
team used Chandra to study the flaring in these analogs of the early Sun
and found that nearly all exhibit extremely high levels of X-ray flaring —
powerful and frequent enough to forge many of the kinds of isotopes found
in the ancient meteorites from the early solar system.

“This is a very exciting result for space X-ray astronomy,” said Donald
Clayton, Centennial Professor of Physics and Astronomy at Clemson University.
“The Chandra Penn State team has shown that stellar-flare acceleration
produces radioactive nuclei whether we want them or not. Now the science
debate can concentrate on whether such irradiation made some or even all
of the extinct radioactivities that were present when our solar system was
formed, or whether some contamination of our birth molecular cloud by
external material is also needed.”

“This is an excellent example of how apparently distant scientific fields,
like X-ray astronomy and the origins of solar systems, can in fact be
closely linked,” said Feigelson.

The Orion observation was made with Chandra’s Advanced CCD Imaging
Spectrometer, which was conceived and developed for NASA by Penn State
and Massachusetts Institute of Technology under the leadership of Gordon
Garmire, the Evan Pugh Professor of Astronomy and Astrophysics at Penn
State. The Penn State observation team includes Pat Broos, James Gaffney,
Gordon Garmire, Leisa Townsley and Yohko Tsuboi. Collaborators also include
Lynne Hillenbrand of CalTech and Steven Pravdo of the NASA Jet Propulsion
Laboratory.

BACKGROUND:

Isotopes are atoms whose nuclei have different numbers of neutrons. Many
isotopes are unstable, or radioactive, and decay into other elements. A
famous example is carbon-14 whose decay gives scientists the opportunity
to date organic materials over thousands of years.

A rare type of ancient meteorite called carbonaceous chondrites, which are
rocks from the Asteroid Belt whose orbits are perturbed and fall to the
Earth, date back to the formation of our Solar System 4.55 billion years
ago. Studying carbonaceous chondrites gives us a unique window on
conditions in the solar nebula when the Sun and Solar System were forming.
Certain portions of carbonaceous chondrites, small melted pebbles called
Calcium-Aluminum-rich Inclusions or CAIs, have unusually high abundances
of decay products of rare, short-lived isotopes. These include
beryllium-10, calcium-41, 26-aluminum and 53-manganese, among others.

Explaining the presence of these short-lived isotopes, which do not appear
anywhere else in solar system material, has been one of the toughest
challenges of solar system science. The favored explanation has been that
a star exploded in a supernova and triggered a nearby cloud of dust and
gas to collapse to form our Sun and planetary system. But conditions have
to be carefully adjusted for this model, and it cannot be widely applied
to all stars. The principal alternative model is that energetic particles
from violent flares hit particles in the solar nebula and transformed some
of their atoms to radioactive isotopes. A drawback to this model has been
that the level of flaring needed, around 100,000 times the flaring level
of the Sun today, was thought to be impossibly high. However, the X-ray
observations reported here give direct evidence for just this high level
of flaring. In addition, this model readily applied to all young stars and
solar systems, not just a few.