[meteorite-list] 'Rogue' Asteroids May Be The Norm
baalke at zagami.jpl.nasa.gov
Wed Jan 29 13:50:07 EST 2014
>From MIT News: January 29, 2014
contact: Sarah McDonnell, MIT News Office
email: s_mcd at mit.edu phone: 617-253-8923
'Rogue' asteroids may be the norm
A new map of the solar system's asteroids shows more diversity than previously
CAMBRIDGE, Mass. - To get an idea of how the early solar system may have
formed, scientists often look to asteroids. These relics of rock and dust
represent what today's planets may have been before they differentiated
into bodies of core, mantle, and crust.
In the 1980s, scientists' view of the solar system's asteroids was essentially
static: Asteroids that formed near the sun remained near the sun; those
that formed farther out stayed on the outskirts. But in the last decade,
astronomers have detected asteroids with compositions unexpected for their
locations in space: Those that looked like they formed in warmer environments
were found further out in the solar system, and vice versa. Scientists
considered these objects to be anomalous "rogue" asteroids.
But now, a new map developed by researchers from MIT and the Paris Observatory
charts the size, composition, and location of more than 100,000 asteroids
throughout the solar system, and shows that rogue asteroids are actually
more common than previously thought. Particularly in the solar system's
main asteroid belt - between Mars and Jupiter - the researchers found
a compositionally diverse mix of asteroids.
The new asteroid map suggests that the early solar system may have undergone
dramatic changes before the planets assumed their current alignment. For
instance, Jupiter may have drifted closer to the sun, dragging with it
a host of asteroids that originally formed in the colder edges of the
solar system, before moving back out to its current position. Jupiter's
migration may have simultaneously knocked around more close-in asteroids,
scattering them outward.
"It's like Jupiter bowled a strike through the asteroid belt," says Francesca
DeMeo, who did much of the mapping as a postdoc in MIT's Department of
Earth, Atmospheric and Planetary Sciences. "Everything that was there
moves, so you have this melting pot of material coming from all over the
DeMeo says the new map will help theorists flesh out such theories of
how the solar system evolved early in its history. She and Benoit Carry
of the Paris Observatory have published details of the map in Nature.
>From a trickle to a river
To create a comprehensive asteroid map, the researchers first analyzed
data from the Sloan Digital Sky Survey, which uses a large telescope in
New Mexico to take in spectral images of hundreds of thousands of galaxies.
Included in the survey is data from more than 100,000 asteroids in the
solar system. DeMeo grouped these asteroids by size, location, and composition.
She defined this last category by asteroids' origins - whether in a warmer
or colder environment - a characteristic that can be determined by whether
an asteroid's surface is more reflective at redder or bluer wavelengths.
The team then had to account for any observational biases. While the survey
includes more than 100,000 asteroids, these are the brightest such objects
in the sky. Asteroids that are smaller and less reflective are much harder
to pick out, meaning that an asteroid map based on observations may unintentionally
leave out an entire population of asteroids.
To avoid any bias in their mapping, the researchers determined that the
survey most likely includes every asteroid down to a diameter of five
kilometers. At this size limit, they were able to produce an accurate
picture of the asteroid belt. The researchers grouped the asteroids by
size and composition, and mapped them into distinct regions of the solar
system where the asteroids were observed.
>From their map, they observed that for larger asteroids, the traditional
pattern holds true: The further one gets from the sun, the colder the
asteroids appear. But for smaller asteroids, this trend seems to break
down. Those that look to have formed in warmer environments can be found
not just close to the sun, but throughout the solar system - and asteroids
that resemble colder bodies beyond Jupiter can also be found in the inner
asteroid belt, closer to Mars.
As the team writes in its paper, "the trickle of asteroids discovered
in unexpected locations has turned into a river. We now see that all asteroid
types exist in every region of the main belt."
A shifting solar system
The compositional diversity seen in this new asteroid map may add weight
to a theory of planetary migration called the Grand Tack model. This model
lays out a scenario in which Jupiter, within the first few million years
of the solar system's creation, migrated as close to the sun as Mars is
today. During its migration, Jupiter may have moved right through the
asteroid belt, scattering its contents and repopulating it with asteroids
from both the inner and outer solar system before moving back out to its
current position - a picture that is very different from the traditional,
static view of a solar system that formed and stayed essentially in place
for the past 4.5 billion years.
"That [theory] has been completely turned on its head," DeMeo says. "Today
we think the absolute opposite: Everything's been moved around a lot and
the solar system has been very dynamic."
DeMeo adds that the early pinballing of asteroids around the solar system
may have had big impacts - literally - on Earth. For instance, colder
asteroids that formed further out likely contained ice. When they were
brought closer in by planetary migrations, they may have collided with
Earth, leaving remnants of ice that eventually melted into water.
"The story of what the asteroid belt is telling us also relates to how
Earth developed water, and how it stayed in this Goldilocks region of
habitability today," DeMeo says.
Written by: Jennifer Chu, MIT News Office
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