Building a new planet

Jan 04, 2011
An enhanced optical image showing the inner portion of the disk of dust surrounding the young star AB Aurigae, with knots of material suggestive of the early stages of planet formation. New observations of the dust in a similar system find the grains have grown to sizes of one centimeter, or even larger. Credit: Hubble, and APOD

(PhysOrg.com) -- Astronomers over the past decade have made remarkable progress in the study of extrasolar planets; over 500 distant worlds are now confirmed. Meanwhile, as this active research community continues to discover and characterize more planets and planetary systems, another group of scientists has been asking the question, "Where do these planets come from in the first place?"

There are two ideas commonly advanced to explain the formation of planets. Both start with a disk of gas and dust around a star younger than a few million years old. In one ("bottom-up") scenario, small in the disk (similar to the dust in the interstellar medium) begin to stick together, coagulating over millions of years until kilometer-sized objects are formed. These in turn can coalesce and grow into planets. The second ("top-down") scenario supposes that gas and dust first collects into a planet-sized clump, which then collapses via gravity to form a planet.

New observational studies have tried to discriminate between these two scenarios and refine their various assumptions. CfA astronomer David Wilner and five of his colleagues used the Submillimeter Array, along with several other radio and millimeter telescopes, to probe the dusty disk around the star CQ Tauri, a roughly ten million year old star located only about 300 light-years away.

A dust grain emits most strongly at wavelengths of radiation that are approximately the same as its size; its efficiency radiating at other wavelengths similarly depends on its size. By measuring the spectral behavior of dust emission, therefore, it is possible to determine the ensemble properties of the in a disk. The dust in the (and by implication in the very early disk around a star) has sizes comparable to or smaller than a wavelength of optical light. In contrast, the astronomers found that the dust in the disk of CQ Tauri was huge: consistent with sizes of a centimeter or perhaps even more - almost ten thousand times larger than the typical dust grains in interstellar space. They also report marginal evidence that the dust grains in the inner portion of the disk were larger than those in the outer regions. These new results lend support to models of bottom-up grain growth, and in turn help to explain how, where and when new are made.

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omatumr
1.4 / 5 (9) Jan 04, 2011
"Where do planets come from in the first place?"

The planets that orbit the Sun were ejected from the Sun when it expoded ~5 Gyr (five billion years) ago:

1. "Strange xenon, extinct super-heavy elements, and the solar neutrino puzzle", Science 195, 208-209 (1977).

2. "Comment on isotopic anomalies" in Proceedings of the Robert Welch Foundation Conference on Chemical Research XII. Cosmochemistry, pages 263-272 (1978).

3. "Isotopes of tellurium, xenon and krypton in the Allende meteorite retain record of nucleosynthesis", Nature 277, 615-620 (1979).

With kind regards,
Oliver K. Manuel
Quantum_Conundrum
1.3 / 5 (4) Jan 04, 2011
Oliver:

Your theory doesn't explain where all the hydrogen and helium in the Solar System came from. If the sun was supposedly old enough to explode and produce heavy metals, it should have burned up all the hydrogen and helium in the process.

On the other hand, if the heavy metals came from some other supernova, then there is no explaination as to how the sun could have trapped those materials in stable, circular/elliptical orbits.

Ejecta from a Supernova should have been moving thousands or even ten-thousands of kilometers per second, and would barely even be deflected by the gravity of a neighbouring star, as evidenced by the fact we can actually observe supernova nebula created recently by much, much more massive star systems and neutron stars, and they show no evidence of slowing down or forming planetary acretion..
kevinrtrs
1 / 5 (7) Jan 04, 2011
How on earth are the researchers hoping to overcome the simple physics of momentum - when two rocks collide with each other they tend not to stick together as required by the adherents of accretionary theory. They tend to fly apart into different directions or even explode into smaller fragments.
THen there's the other simple thing - if the dust is radiating then surely it's constituents contain high enough energies to prevent them from clumping together - or is there some magical properties of these dust clouds that I do not get?
omatumr
1 / 5 (5) Jan 04, 2011
Oliver:

Your theory doesn't explain where all the hydrogen and helium in the Solar System came from. If the sun was supposedly old enough to explode and produce heavy metals, it should have burned up all the hydrogen and helium in the process.



All of the hydrogen and helium in the Solar System came from the outer part of the supernova debris. Jupiter, Saturn, and other gaseous planets formed out of those elements.

This short video may help communicate the birth of the Solar System:

youtube.com/watch?v=AQZe_Qk-q7M&feature=related

With kind regards,
Oliver K. Manuel
CSharpner
5 / 5 (6) Jan 04, 2011
There's a "home" video that one of the space shuttle astronauts made while in orbit aboard the shuttle. He had a ziplock bag of "particles"... I don't recall exactly what they were (sand? rice?), but when he shook the bag, they started clumping together. He didn't think anything of it, other than it was neat. He showed it to an astronomer friend of his who's face lit up with excitement and said he just solved one of the mysteries of planet formation. They clumped because of static electricity.

Now, I don't know if that's how all planets form, but that simple video helped provide a strong possibility.
Pyle
5 / 5 (9) Jan 04, 2011
or is there some magical properties of these dust clouds that I do not get?

No magic. You just don't get it.
I suppose Ghod using his noodly appendage is a better explanation?

But to your point, yes, some rocks colliding don't stick together. If two dense equal masses collide with significantly disparate trajectories and sufficiently high relevant velocities then there are bound to be ejecta. However, in an accretion disk the masses aren't dense, nor do they have necessarily large relative velocities. Clouds of matter form that, through gravity, gain density as they grow and absorb more matter. The time scales are sufficiently large. Impact events occur and ejecta is predicted. The accretion theory of planetary formation is the current best fit to the data. Or you can have faith in His noodly appendage.

CS - EM forces are factored into accretion theory. Maybe we will observe "lightning" in one of these accretion clouds to support increasing its role?
DamienS
5 / 5 (4) Jan 04, 2011
How on earth are the researchers hoping to overcome the simple physics of momentum - when two rocks collide with each other they tend not to stick together as required by the adherents of accretionary theory.

No one's talking about rocks colliding, at least not initially. The nebular micron sized dust particles are encrusted with gluey molecular water ice. This ice is different then terrestrial ice. At extremely cold temperatures vapor deposited ice spontaneously becomes electrically polarized, which produces electrostatic forces that stick icy grains together like magnets, eventually forming proto-planets.