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| (Photo : NASA/ESA) In early days of solar system, Jupiter destroyed everything that came in its way, researchers have found. |
Excerpt from latimes.com
Before Mercury, Venus, Earth and Mars occupied the inner solar
system, there may have been a previous generation of planets that were
bigger and more numerous – but were ultimately doomed by Jupiter,
according to a new study.
If indeed the early solar system was
crowded with so-called super-Earths, it would have looked a lot more
like the planetary systems found elsewhere in the galaxy, scientists wrote Monday in the Proceedings of the National Academy of Sciences.
As
NASA’s Kepler space telescope has found more than 1,000 planets in
orbit around other stars, along with more than 4,000 other objects that
are believed to be planets but haven’t yet been confirmed. Kepler finds these planets
by watching their host stars and registering tiny drops in their
brightness – a sign that they are being ever-so-slightly darkened by a
planet crossing in front of them.
In addition, ground-based
telescopes have detected hundreds of exoplanets by measuring the wiggles
of distant stars. Those stars wiggle thanks to the gravitational pull
of orbiting planets, and the Doppler effect makes it possible to
estimate the size of these planets.
The
more planetary systems astronomers discovered, the more our own solar
system looked like an oddball. Exoplanets – at least the ones big enough
for us to see – tended to be bigger than Earth, with tight orbits that
took them much closer to their host stars. In multi-planet systems,
these orbits tended to be much closer together than they are in our
solar system. For instance, the star known as Kepler-11 has six planets closer to it than Venus is to the sun.
Why
does our solar system look so different? Astrophysicists Konstantin
Batygin of Caltech and Greg Laughlin of UC Santa Cruz summed it up in
one word: Jupiter.
Here’s what could have happened, according to their models:
In
Solar System 1.0, the region closest to the sun was occupied by
numerous planets with masses several times bigger than that of Earth.
There were also planetesimals, “planetary building blocks” that formed
within the first million years after the birth of the sun, Batygin and
Laughlin wrote.
This is how things might have stayed if the young
Jupiter had stayed put at its initial orbit, between 3 and 10
astronomical units away from the sun. (An astronomical unit, or AU, is
the distance between the Earth and the sun. Today, Jupiter’s orbit ranges between 5 and 5.5 AUs from the sun.)
But
Jupiter was restless, according to a scenario known as the “Grand
Tack.” In this version of events, Jupiter was swept up by the currents
of gas that surrounded the young sun and drifted toward the center of
the solar system.
Jupiter,
however, was too big to travel solo. All manner of smaller objects
would have been dragged along too. With so many bodies in motion, there
would have been a lot of crashes.
The result was “a collisional
cascade that grinds down the planetesimal population to smaller sizes,”
the astrophysicists wrote. For the most part, these planetary crumbs
were swept toward the sun and ultimately destroyed, like disintegrating
satellites falling back to Earth.
The planetesimals wouldn’t have
been Jupiter’s only victims. Assuming the early solar system resembled
the planetary systems spied by Kepler and other telescopes, there would
have been “a similar population of first-generation planets,” the pair
wrote. “If such planets formed, however, they were destroyed.”
Jupiter
probably got about as close to the sun as Mars is today before
reversing course, pulled away by the gravity of the newly formed Saturn.
That would have ended the chaos in the inner solar system, allowing
Earth and the other rocky planets to form from the debris that remained.
“This
scenario provides a natural explanation for why the inner Solar System
bears scant resemblance to the ubiquitous multi-planet systems”
discovered by Kepler and other survey efforts, Batygin and Laughlin
wrote.
Although their models show that this is what might have happened, they don’t prove that it actually did. But there may be a way to get closer to the truth.
The
scientists’ equations suggest that if a star is orbited by a cluster of
close-in planets, there won’t be a larger, farther-out planet in the
same system. As astronomers find more exoplanetary systems, they can see
whether this prediction holds up.
Also, if far-away solar systems
are experiencing a similar series of events, telescopes ought to be
able to detect the extra heat thrown off by all of the planetesimal
collisions, they added.
Sadly for those hoping to find life on
other planets, the pair’s calculations also imply that most Earth-sized
planets are lacking in water and other essential compounds that can
exist in liquid or solid form. As a result, they would be
“uninhabitable,” they wrote.
Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/xXjJ7HHKNDo/young-jupiter-wiped-out-solar-systems.html
Young Jupiter wiped out solar system's early inner planets, study says
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