THANKS to a solar flare, astronomers have made the first ever measurements of
the composition of an asteroid. Their findings link the asteroid to the
primordial Universe, and should help researchers decode a wealth of information
from meteorites they have collected on Earth.
Meteorites often originate as asteroids, and by analysing them researchers
can tell what elements the parent asteroid contained. But this doesn鈥檛 reveal
how abundant the elements originally were, because it is impossible to tell
precisely where the fragment came from. Earlier this year, however, the Near
Earth Asteroid Rendezvous (NEAR) spacecraft reached 433 Eros, an asteroid
roughly 34 kilometres long that orbits more than 150 million kilometres farther
out than the Earth.
NEAR is equipped with instruments that measure solar X-rays reflecting off
Eros. These measurements reveal which elements are present and how abundant they
are. Under normal conditions, the reflected X-rays are very weak, so it can take
months to collect enough X-rays to make an accurate reading鈥攋ust as a
camera shutter has to be kept open for a longer period in poor light. However,
during a solar flare the Sun gives off an extra-large dose of X-rays, acting
like a flashbulb. By good fortune, such an event happened on 4 May, allowing
researchers to accurately determine within the space of 30 minutes the
composition of a section of Eros about 6 kilometres across.
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If the asteroid had been altered by heat since its formation鈥攑erhaps
during the Universe鈥檚 infancy鈥攎elting would have caused lighter materials
such as oxygen to accumulate on the surface. Instead, researchers found heavy
materials such as iron evenly mixed with lighter ones. This suggests that Eros
has not undergone this type of change. 鈥淚t鈥檚 reasonable to guess that Eros is a
leftover building block from the very first stage of Solar System formation,鈥�
says Steven Squyres, an astronomer at Cornell University in Ithaca, New York,
who is a member of the NEAR X-ray team.
Squyres says the findings are already helping the team find meteorites with
similar origins. Richard Binzel, an astronomer at the Massachusetts Institute of
Technology who studies asteroids, says making such connections is important. 鈥淎s
we begin to learn where in the Solar System meteorites come from, we鈥檒l be able
to use meteorites as detailed snapshots of what our Solar System was like at the
time it formed,鈥� he says.
Unfortunately, the solar flare only helped reveal a small portion of Eros.
The remainder is now being studied using normal daylight, which is likely to
take months.
