Starship Asterisk*

Nitpicker wrote:It seems this asteroid is just not attractive enough.

hownow wrote:

Nitpicker wrote:It seems this asteroid is just not attractive enough.

Funny ... but, maybe literally true? How big is this asteroid? Bigger than a breadbox?

Boomer12k wrote:
So, it is possibly two uneven clumps that have merged...

Nitpicker wrote:It seems this asteroid is just not attractive enough.

BDanielMayfield wrote:
So, gravitationally speaking, how attractive is Itokawa?

neufer wrote:

BDanielMayfield wrote:
So, gravitationally speaking, how attractive is Itokawa?

Any animal that can jump up 4 inches on Earth
can jump off Itokawa into outer space.

orin stepanek wrote:Maybe a recent volcanic ejection that has been in space for only a few thousand years?

TraKtorman wrote:Soil on an asteroid?

geckzilla wrote:
How do asteroids form at all? The can't all have come from volcanic eruptions.
I imagine most start small with the electrostatic forces pulling together clumps of dust.

http://en.wikipedia.org/wiki/Van_der_Waals_force wrote:

[b][color=#0000FF][size=100]Geckos can stick to walls because of Van der Waals forces[/size][/color][/b]

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<<In physical chemistry, the van der Waals' force (or van der Waals' interaction), named after Dutch scientist Johannes Diderik van der Waals (23 November 1837 – 8 March 1923) , is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, the hydrogen bonds, or the electrostatic interaction of ions with one another or with neutral molecules or charged molecules. The term includes:

force between two permanent dipoles (Keesom force)

force between a permanent dipole
and a corresponding induced dipole (Debye force)

force between two instantaneously induced dipoles (London dispersion force).

It is also sometimes used loosely as a synonym for the totality of intermolecular forces. Van der Waals' forces are relatively weak compared to covalent bonds, but play a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics. Van der Waals forces define many properties of organic compounds, including their solubility in polar and non-polar media.>>

http://en.wikipedia.org/wiki/Planetesimal wrote:
<<Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.

A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger bodies. When the bodies reach sizes of approximately one kilometer, then they can attract each other directly through their mutual gravity, enormously aiding further growth into moon-sized protoplanets. This is how planetesimals are often defined. Bodies that are smaller than planetesimals must rely on Brownian motion or turbulent motions in the gas to cause the collisions that can lead to sticking. Alternatively, planetesimals can form in a very dense layer of dust grains that undergoes a collective gravitational instability in the mid-plane of a protoplanetary disk. Many planetesimals eventually break apart during violent collisions, as may have happened to 4 Vesta and 90 Antiope, but a few of the largest planetesimals can survive such encounters and continue to grow into protoplanets and later planets.>>

geckzilla wrote:How do asteroids form at all? The can't all have come from volcanic eruptions. I imagine most start small with the electrostatic forces pulling together clumps of dust.

http://ay201b.wordpress.com/2011/04/11/formation-of-planetesimals/ wrote:
Astronomy 201b: Interstellar Medium and Star Formation
Alyssa A. Goodman, Spring 2012-2013, Harvard College
Formation of planetesimals (Transcribed by Bence Beky)
More: here

<<How do tiny dust particles build up to create compact solids a kilometer in diameter? This is one of the major questions remaining in planet formation research and although much progress has been made, the first half of the book as yet to be written. Here, I will talk about some of the ideas for planetesimal formation.

Low collisions speeds, high binding energies and high energy dissipation during impact facilitate particle growth. The electrostatic and gravitational forces are both possible binding energies but the latter only become important when planetesimals are very massive. The electrostatic interaction involved is typically the van der Waals force; the possibility of charged grains has been discussed but not explored. A collision between two charged particles would have a higher binding energy, making sticking easier. An ice coating also helps!

Chambers (2010) discusses the laboratory observations that have helped us to understand this process, although it is difficult to know exactly what conditions were like in the protoplanetary disk. At very low speeds (much less than 1 m/s), collisions between micrometer-sized dust grains tend to result in the grains loosely sticking together, at intermediate speeds (on the order of 1-10 m/s) more compact aggregates are formed, while at high speeds the grains tend to rebound and growth does not occur. Now, we have conglomerations that have reached millimeter to centimeter sizes and the a different behavior is observed: a collision between a grain and a compact aggregate at speeds less than 10 m/s results in rebound, moderate-speed collisions result in growth of the aggregate, while collisions at high speeds can fragment it.

Growth of planetesimals gets increasingly difficult as sizes approach a meter because binding energies decline while relative velocities increase. According to Chambers (2010), with turbulence disruptive collisions between a meter-sized and a much smaller planetesimal are frequent because relative speeds of 100 m/s are often reached and it is difficult to get larger bodies. Youdin (2008) also discusses other issues (both theoretical and observation) with growing large bodies via collisions. Since we need kilometer-sized planetesimals to proceed with the second half of our story, we have a problem which is usually called the “meter-size barrier” in the literature.>>

neufer wrote:

http://ay201b.wordpress.com/2011/04/11/formation-of-planetesimals/ wrote:
Astronomy 201b: Interstellar Medium and Star Formation
Alyssa A. Goodman, Spring 2012-2013, Harvard College
Formation of planetesimals (Transcribed by Bence Beky)
More: here

<<How do tiny dust particles build up to create compact solids a kilometer in diameter? This is one of the major questions remaining in planet formation research and although much progress has been made, the first half of the book as yet to be written. Here, I will talk about some of the ideas for planetesimal formation.

Low collisions speeds, high binding energies and high energy dissipation during impact facilitate particle growth. The electrostatic and gravitational forces are both possible binding energies but the latter only become important when planetesimals are very massive. The electrostatic interaction involved is typically the van der Waals force; the possibility of charged grains has been discussed but not explored. A collision between two charged particles would have a higher binding energy, making sticking easier. An ice coating also helps!

Chambers (2010) discusses the laboratory observations that have helped us to understand this process, although it is difficult to know exactly what conditions were like in the protoplanetary disk. At very low speeds (much less than 1 m/s), collisions between micrometer-sized dust grains tend to result in the grains loosely sticking together, at intermediate speeds (on the order of 1-10 m/s) more compact aggregates are formed, while at high speeds the grains tend to rebound and growth does not occur. Now, we have conglomerations that have reached millimeter to centimeter sizes and the a different behavior is observed: a collision between a grain and a compact aggregate at speeds less than 10 m/s results in rebound, moderate-speed collisions result in growth of the aggregate, while collisions at high speeds can fragment it.

Growth of planetesimals gets increasingly difficult as sizes approach a meter because binding energies decline while relative velocities increase. According to Chambers (2010), with turbulence disruptive collisions between a meter-sized and a much smaller planetesimal are frequent because relative speeds of 100 m/s are often reached and it is difficult to get larger bodies. Youdin (2008) also discusses other issues (both theoretical and observation) with growing large bodies via collisions. Since we need kilometer-sized planetesimals to proceed with the second half of our story, we have a problem which is usually called the “meter-size barrier” in the literature.>>

Anthony Barreiro wrote:In other words, "this is an active area of research." English translation: "We don't know. Please give us money and we'll put the grad students to work running computer models."

Anthony Barreiro wrote:In other words, "this is an active area of research." English translation: "We don't know. Please give us money and we'll put the grad students to work running computer models." At least we know with reasonable certainty that lots of asteroids exist, so they must have formed somehow!

geckzilla wrote:You take a box of dust on a hyperbolic flight and watch it yourself. I saw a video of a guy doing this but, frustratingly, I can't seem to find it.

APOD Robot wrote:...craters might ... be filled in whenever the asteroid gets ... struck by a massive meteor.