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Monday, January 18, 2010

How Earth Survived Its Birth: New Simulation Reveals Planet Migration Prevents Plunge Into Sun

ScienceDaily (Jan. 8, 2010) — "For the last 20 years, the best models of planet formation -- or how planets grow from dust in a gas disk -- have contradicted the very existence of Earth. These models assumed locally constant temperatures within a disk, and the planets plunge into the Sun. Now, new simulations from researchers at the American Museum of Natural History and the University of Cambridge show that variations in temperature can lead to regions of outward and inward migration that safely trap planets on orbits."

"When the protoplanetary disk begins to dissipate, planets are left behind, safe from impact with their parent star."

"The results of this research are being presented at the 2010 meeting of the American Astronomical Society in Washington, D.C."

"We are trying to understand how planets interact with the gas disks from which they form as the disk evolves over its lifetime," says Mordecai-Mark Mac Low, Curator of Astrophysics and Division Chair of Physical Sciences at the Museum. "We show that the planetoids from which the Earth formed can survive their immersion in the gas disk without falling into the Sun."

"During the birth of a star, a disk of gas and dust forms. The midplane of this dusty disk is opaque and cannot quickly cool by radiating heat to outer space. Until recently, no one has included temperature variation in models of planet formation."

"Co-author Sijme-Jan Paardekooper of the University of Cambridge ran groundbreaking new simulations like that most recently published online ( His work shows that the direction of migration of low-mass planets in disks depends on the detailed temperature structure of the disk. This key insight lays the groundwork for the current work."

"The American Astronomical Society presentation incorporates the results of Paardekooper's local models into the long-term evolution of the temperature and density structure of a protoplanetary disk. The result of the simulation is that, over the lifetime of a disk, planets get trapped in orbits between regions of inward and outward migration. The orbits slowly move inward as the disk dissipates. Once the gas densities drop low enough for the planets to no longer be influenced by disk, the planets are dropped into an orbit similar to the orbits of planets around the Sun. The radius of the orbit at which a planet is released depends on its mass."

"We used a one-dimensional model for this project," says co-author Wladimir Lyra, a postdoctoral researcher in the Department of Astrophysics at the Museum. "Three dimensional models are so computationally expensive that we could only follow the evolution of disks for about 100 orbits -- about 1,000 years. We want to see what happens over the entire multimillion year lifetime of a disk."

"Mac Low is presenting this research at the upcoming American Astronomical Society meetings in Washington, D.C. on January 6 with a press conference on the following day (January 7 at 10:30 am: "Spicing up the solar system.") A research paper is currently submitted to The Astrophysical Journal, authored by Lyra, Paardekooper, and Mac Low. This research was funded by the American Museum of Natural History, the National Science Foundation, and NASA."


"Migration requires some interaction between the planet and fairly large bodies or the gravitational forces are too weak. According to this model, early in the formation of the Solar System, there were lots of Moon-sized to Mars-sized bodies, especially in the outer Solar System. A large planetesimal that crosses near Neptune will lose some energy, fall down near Jupiter and gain energy from it to be ejected into the Oort Cloud. This decreases the size of Jupiter's orbit, and expands the orbits of Saturn, Uranus and Neptune. As Neptune moves outward, it will perturb the orbits of the trans-Neptunian objects (large ice covered bodies of which Pluto is a member). This pushes Pluto/Charon into a highly eccentric, inclined 3:2 resonant orbit that it occupies today."

"In the second model, which does not exclude operation of the first, a planet experiences viscous drag as it plows through the remnants of the dusty nebula from which it formed, losing energy as it goes. Both theory and observation suggest that the migration time to a small orbit for a giant planet formed at a radius of 5 AU is less than 1 Ma. A migrating planet must avoid terminal orbital decay and a disastrous collision with its central star. It may be that the magnetic field of the star sweeps an inner belt or region clear of gas and dust so that the drag on the planet abruptly stops when it reaches this open zone. The planet may remain parked at the outer edge of that hole." source: and source of image:

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Thoughts worth thinking about

"Our subconscious minds have no sense of humor, play no jokes and cannot tell the difference between reality and an imagined thought or image. What we continually think about eventually will manifest in our lives."-Sidney Madwed

Laws alone can not secure freedom of expression; in order that every woman and man present their views without penalty, there must be spirit of tolerance in the entire population.- Albert Einstein Too often we underestimate the power of a touch, a smile, a kind word, a listening ear, an honest compliment, or the smallest act of caring, all of which have the potential to turn a life around. - Leo Buscaglia

A person's true wealth is the good he or she does in the world. - Mohammed

Our task must be to free ourselves... by widening our circle of compassion to embrace all living creatures and the whole of nature and its beauty. -Albert Einstein

The best way to find yourself, is to lose yourself in the service of others. - Ghandi

The unselfish effort to bring cheer to others will be the beginning of a happier life for ourselves. - Helen Keller

Aim for success, not perfection. Never give up your right to be wrong, because then you will lose the ability to learn new things and move forward with your life. Remember that fear always lurks behind perfectionism. Confronting your fears and allowing yourself the right to be human can, paradoxically, make yourself a happier and more productive person. - Dr. David M. Burns

Life is as dear to a mute creature as it is to man. Just as one wants happiness and fears pain, just as one wants to live and not die, so do other creatures. -His Holiness The Dalai Lama

Mankind's true moral test, its fundamental test (which lies deeply buried from view), consists of its attitude towards those who are at its mercy: animals. And in this respect mankind has suffered a fundamental debacle, a debacle so fundamental that all others stem from it. -

Milan Kundera, The Unbearable Lightness of Being

The worst sin towards our fellow creatures is not to hate them, but to be indifferent to them. That's the essence of inhumanity. -George Bernard Shaw

Ego's trick is to make us lose sight of our interdependence. That kind of ego-thought gives us a perfect justification to look out only for ourselves. But that is far from the truth. In reality we all depend on each other and we have to help each other. The husband has to help his wife, the wife has to help the husband, the mother has to help her children, and the children are supposed to help the parents too, whether they want to or not.-Gehlek Rinpoche Source: "The Best Buddhist Writing 2005 pg. 165

The hostile attitude of conquering nature ignores the basic interdependence of all things and events---that the world beyond the skin is actually an extension of our own bodies---and will end in destroying the very environment from which we emerge and upon which our whole life depends.