Untuk yang mengikuti perkembangan penelitian dan kajian tentang asal mula
kehiudpn dimuka bumi ini...
--
Web address:
http://www.sciencedaily.com/releases/2012/09/
120924144751.htm
Slow-Moving Rocks Better Odds That Life Crashed to Earth from Space
enlarge
The researchers suggest that ideal conditions for lithopanspermia in the sun's
birth cluster, in the solar system and on Earth overlapped for several hundred
million years (blue shaded area). Rock evidence suggests that the Earth (bottom
line) contained surface water during a period when the relative velocities
between the sun and its closest cluster neighbors (top line) were small enough
to allow weak transfer to other planetary systems, and when the solar system
(middle line) experienced high meteorite activity within the sun's weak
gravitational boundary. If life arose on Earth shortly after surface water was
available, life could have journeyed from Earth to another habitable world
during this time, or vice versa if life had an early start in another planetary
system. (Credit: Image by Amaya Moro-Martín)
ScienceDaily (Sep. 24, 2012) Microorganisms that crashed to Earth embedded in
the fragments of distant planets might have been the sprouts of life on this
one, according to new research from Princeton University, the University of
Arizona and the Centro de Astrobiología (CAB) in Spain.
The researchers report in the journal Astrobiology that under certain
conditions there is a high probability that life came to Earth -- or spread
from Earth to other planets -- during the solar system's infancy when Earth and
its planetary neighbors orbiting other stars would have been close enough to
each other to exchange lots of solid material. The work will be presented at
the 2012 European Planetary Science Congress on Sept. 25.
The findings provide the strongest support yet for "lithopanspermia," the idea
that basic life forms are distributed throughout the universe via
meteorite-like planetary fragments cast forth by disruptions such as volcanic
eruptions and collisions with other matter. Eventually, another planetary
system's gravity traps these roaming rocks, which can result in a mingling that
transfers any living cargo.
Researchers based at Princeton University, the University of Arizona and the
Centro de Astrobiología in Spain used a low-velocity process called weak
transfer to provide the strongest support yet for "lithopanspermia," the idea
that the microorganisms that sprout life came to Earth -- or spread from Earth
to other developing planets -- via collisions with meteorite-like planetary
fragments. Under weak transfer, a slow-moving planetary fragment meanders into
the outer edge of the gravitational pull, or weak stability boundary, of a
planetary system. The system has only a loose grip on the fragment, meaning the
fragment can escape and be propelled into space, drifting until it is pulled in
by another planetary system. (Image by Amaya Moro-Martín)
Previous research on this possible phenomenon suggests that the speed with
which solid matter hurtles through the cosmos makes the chances of being
snagged by another object highly unlikely. But the Princeton, Arizona and CAB
researchers reconsidered lithopanspermia under a low-velocity process called
weak transfer wherein solid materials meander out of the orbit of one large
object and happen into the orbit of another. In this case, the researchers
factored in velocities 50 times slower than previous estimates, or about 100
meters per second.
Using the star cluster in which our sun was born as a model, the team conducted
simulations showing that at these lower speeds the transfer of solid material
from one star's planetary system to another could have been far more likely
than previously thought, explained first author Edward Belbruno, a
mathematician and visiting research collaborator in Princeton's Department of
Astrophysical Sciences who developed the principles of weak transfer.
The researchers suggest that of all the boulders cast off from our solar system
and its closest neighbor, five to 12 out of 10,000 could have been captured by
the other. Earlier simulations had suggested chances as slim as one in a
million.
"Our work says the opposite of most previous work," Belbruno said. "It says
that lithopanspermia might have been very likely, and it may be the first paper
to demonstrate that. If this mechanism is true, it has implications for life in
the universe as a whole. This could have happened anywhere."
Co-authors Amaya Moro-Martín, an astronomer at CAB and a Princeton visiting
research collaborator in astrophysical sciences, and Renu Malhotra, a professor
of planetary sciences at Arizona, noted that low velocities offer very high
probabilities for the exchange of solid material via weak transfer, and also
found that the timing of such an exchange could be compatible with the actual
development of the solar system, as well as with the earliest known emergence
of life on Earth. Dmitry Savransky, a Princeton mechanical and aerospace
engineering doctoral student, conducted the simulations.
The researchers report that the solar system and its nearest planetary-system
neighbor could have swapped rocks at least 100 trillion times well before the
sun struck out from its native star cluster. Furthermore, existing rock
evidence shows that basic life forms could indeed date from the sun's birth
cluster days -- and have been hardy enough to survive an interstellar journey
and eventual impact.
"The conclusion from our work," Moro-Martín said, "is that the weak transfer
mechanism makes lithopanspermia a viable hypothesis because it would have
allowed large quantities of solid material to be exchanged between planetary
systems, and involves timescales that could potentially allow the survival of
microorganisms embedded in large boulders."
All about velocities
The Princeton-Arizona-CAB paper cites two previous studies that present the
odds of solid matter from one planetary system being captured by another as
being more or less dismal.
The first, a 2003 paper published in Astrobiology by Jay Melosh, a Purdue
University earth and atmospheric sciences professor, questioned the probability
that meteorites have ever escaped a terrestrial planet in Earth's solar system
and wound up on a terrestrial planet in another system. The report concluded
that the chances -- about one in 10,000, or 0.01 percent -- are "overwhelmingly
unlikely" considering the speed a meteorite would need to travel (about six
kilometers per second) and the roominess of space.
Belbruno and his co-authors calculated that under this scenario of high
velocities and dispersed planetary systems, the probability of solid material
from any planetary system striking another falls to as little as five in
100,000, or 0.005 percent.
Star birth clusters, which are tightly confined groups of stars and planetary
systems, were introduced as a possible setting for lithopanspermia in a 2005
Astrobiology paper by David Spergel, Princeton's Charles A. Young Professor of
Astronomy on the Class of 1897 Foundation and chair of astrophysical sciences,
and University of Michigan physics professor Fred Adams.
Factoring in velocities of two to five kilometers per second, Spergel and Adams
found that the chances of an exchange of life-bearing rocks between star
systems clustered in groups of 30 to 1,000 could be as unlikely as one in a
million to as good as one in 1,000, or 0.0001 to 0.1 percent, respectively.
Spergel and Adams, however, limited their study to binary stars -- or planetary
systems with two stars -- which might elevate star-to-star solid matter
exchanges, Moro-Martín said.
Nonetheless, in clusters similar to those considered by Spergel and Adams, weak
transfer involves relative velocities of no more than one kilometer per second,
which substantially increases the probability of capture by other stars in the
cluster. In other words, star clusters provide an ideal setting for weak
transfer, Belbruno said.
Chaotic in nature, weak transfer happens when a slow moving object such as a
meteorite wanders into the outer edge of the gravitational pull of a larger
object with a low relative velocity, such as a star or massive Jupiter-like
planet. The smaller object partially orbits the large object, but the larger
object has only a loose grip on it. This means the smaller object can escape
and be propelled into space, drifting until it is pulled in by another large
object.
Belbruno first demonstrated weak transfer with the Japanese lunar probe Hiten
in 1991. A mechanical malfunction left the probe with insufficient fuel to
enter the moon's orbit the traditional way, which is to approach at a high
speed then fire retrorockets to slow down. Instead, Belbruno designed a
weak-transfer trajectory that got the probe into orbit around the moon using a
minimal amount of fuel.
Adams, co-author of the 2005 paper with Spergel, said that the work by Belbruno
and his co-authors succeeds at pulling together the various factors of earlier
lithopanspermia models and adding a substantial new element -- chaos. Adams is
familiar with the study but had no role in it.
"This paper takes the type of calculations that have been done before and makes
an important generalization of previous work," Adams said. "Their work on chaos
in this context also carries the subject forward. They make a careful
assessment of a process that is dynamically quite complicated and chaotic in
nature.
"They are breaking new ground from the viewpoint of dynamical astrophysics,"
Adams said. "Regarding the problem of lithopanspermia, this type of weak
capture and weak escape is interesting because it allows for the ejection
speeds to be small, and these slow speeds allow for higher probabilities of
rock capture. To say it another way, chaos, in part, enhances the prospects for
lithopanspermia."
To the simulator!
Star birth clusters satisfy two requirements for weak transfer, Moro-Martín
said. First, the sending and receiving planetary systems must contain a massive
planet that captures the passing solid matter in the weak-gravity boundary
between itself and its parent star. Earth's solar system qualifies, and several
other stars in the sun's birth cluster would too.
Second, both planetary systems must have low relative velocities. In the sun's
stellar cluster, between 1,000 and 10,000 stars were gravitationally bound to
one another for hundreds of millions of years, each with a velocity of no more
than a sluggish one kilometer per second, Moro-Martín said.
The team simulated 5 million trajectories between single-star planetary systems
-- in a cluster with 4,300 stars -- under three conditions: the solid matter's
"source" and "target" stars were both the same mass as the sun; the target star
was only half the sun's mass; or the source star was half the sun's mass.
The odds of a star capturing solid matter from another planetary system under
these three scenarios are 15 (0.15 percent), five (0.05 percent) and 12 (0.12
percent) in 10,000, respectively, the researchers report -- probabilities that
exceed those under the conditions proposed by Melosh by a factor of 1 billion.
To estimate the actual amount of solid matter that could have been exchanged
between the sun and its nearest star neighbor, the researchers used data and
models pertaining to the movement and formation of asteroids, the Kuiper Belt
-- the solar system's massive outer ring of asteroids -- and the Oort Cloud, a
hypothesized collection of comets, ice and other matter about one light year
from Earth's sun widely believed to be a primary source of comets and
meteorites.
The researchers used this data to conclude that during a period of 10 million
to 90 million years, anywhere between 100 trillion to 30 quadrillion solid
matter objects weighing more than 10 kilograms transferred between the sun and
its nearest cluster neighbor. Of these, some 200 billion rocks from early Earth
could have been whisked away via weak transfer.
For lithopanspermia to happen, however, microorganisms first have to survive
the long, radiation-soaked journey through space.
Moro-Martín and Malhotra consulted a 2009 paper an international team published
in the Astrophysical Journal that determined how long microorganisms could
survive in space based on the size of the solid matter hosting them. That
group's computer simulations showed that survival times ranged from 12 million
years for a boulder up to 3 centimeters (roughly one inch) in diameter, to 500
million years for a solid objects 2.67 meters (nearly nine feet) across.
The researchers estimated that under weak transfer, solid matter that had
escaped one planet would need tens of millions of years to finally collide with
another one. This falls within the lifespan of the sun's birth cluster, but
means that lithopanspermia by weak transfer would have been limited to
planetary fragments at least one meter, or about three feet, in size.
Matching the theory with life
As for the actual transfer of life, the researchers suggest that roughly 300
million lithopanspermia events could have occurred between our solar system and
the closest planetary system.
But even if microorganisms survived the trip to Earth, the planet had to be
ready to receive them. The researchers reference rock-dating evidence
suggesting that Earth contained water when the solar system was only 288
million years old and that very early life might have emerged before the solar
system was 718 million years old.
The sun's birth cluster -- assumed to be roughly the same age as Earth's solar
system -- slowly broke apart when the solar system was approximately 135
million to 535 million years old, Moro-Martín said. In addition, the sun could
have been ripe for weak transfer up to 700 million years after the solar system
formed.
So, if life arose on Earth shortly after surface water was available, there
were possibly about 400 million years when life could have journeyed from Earth
to another habitable world, and vice versa, the researchers report. If life had
an early start in other planetary systems and developed before the sun's birth
cluster dispersed, life on Earth may have originated beyond our solar system.
The paper stops short of calculating the likelihood of extrasolar life taking
root on a terrestrial planet such as Earth, but the higher probability the
researchers determined for solid-matter transfer makes that a more worthwhile
pursuit, Moro-Martín said.
"Our study stops when the solid matter is trapped by the second planetary
system, but for lithopanspermia to be completed it actually needs to land on a
terrestrial planet where life could flourish," Moro-Martín said. "The study of
the probability of landing on a terrestrial planet is work that we now know is
worth doing because large quantities of solid material originating from the
first planetary system may be trapped by the second planetary system, waiting
to land on a terrestrial planet.
"Our study does not prove lithopanspermia actually took place," Moro-Martín
said, "but it indicates that it is an open possibility."
The paper, "Chaotic Exchange of Solid Material between Planetary Systems:
Implications for Lithopanspermia," was published Sept. 12 by Astrobiology, and
was supported by grants from NASA, the National Science Foundation and the
Ministry of Science and Innovation in Spain.
Share this story on Facebook, Twitter, and Google:
Other social bookmarking and sharing tools:
Share on reddit Share on stumbleupon Share on pinterest_share Share on blogger
Share on digg Share on fark Share on linkedin Share on myspace Share on
newsvine | 43
Story Source:
The above story is reprinted from materials provided by Princeton
University. The original article was written by Morgan Kelly.
Note: Materials may be edited for content and length. For further
information, please contact the source cited above.
Journal Reference:
Edward Belbruno, Amaya Moro-Martín, Renu Malhotra, Dmitry Savransky.
Chaotic Exchange of Solid Material Between Planetary Systems: Implications for
Lithopanspermia. Astrobiology, 2012; 12 (8): 754 DOI: 10.1089/ast.2012.0825
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
APA
MLA
Princeton University (2012, September 24). Slow-moving rocks better odds that
life crashed to Earth from space. ScienceDaily. Retrieved September 25, 2012,
from http://www.sciencedaily.com /releases/2012/09/120924144751.htm
Note: If no author is given, the source is cited instead.
Disclaimer: Views expressed in this article do not necessarily reflect those of
ScienceDaily or its staff.
------------------------------------
Post message: [email protected]
Subscribe : [email protected]
Unsubscribe : [email protected]
List owner : [email protected]
Homepage : http://proletar.8m.com/Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/proletar/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/proletar/join
(Yahoo! ID required)
<*> To change settings via email:
[email protected]
[email protected]
<*> To unsubscribe from this group, send an email to:
[email protected]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
