MarkBour wrote: ↑Sat May 25, 2019 6:38 pm
Chunks wrote: ↑Sat May 25, 2019 12:41 am
MarkBour wrote: ↑Fri May 24, 2019 4:33 pm
One of many fascinating questions that this image evokes ... If I saw this rubble on Earth, I would assume that the smaller pieces were formed by the steady erosion breakdown of larger pieces. I'm no geologist, so maybe I would be wrong about that, even on Earth. But for Bennu, where and how would this (size) distribution of rubble arise?
Planetesimal collisional rubble aggregate - bang the rock together,guys!
Are you saying (... planetesimals are generally larger than Bennu). At some point, as larger bodies than Bennu had aggregated, some of their collisions would produce smaller clumps like Bennu that broke off, that were never pulled back in to a larger body? Does this better explain the size distribution of rubble here than a notion that this body formed as its own aggregate, never having been part of a larger body?
https://en.wikipedia.org/wiki/101955_Bennu#Origin_and_evolution wrote:
<<
The carbonaceous material that composes Bennu originally came from the breakup of a much larger parent body—a planetoid or a proto-planet. According to the accretion theory, this material came together 4.5 billion years ago during the formation of the Solar System. Bennu's basic mineralogy and chemical nature would have been established during the first 10 million years of the Solar System's formation, where the carbonaceous material underwent some geologic heating and chemical transformation inside a much larger planetoid or a proto-planet capable of producing the requisite pressure, heat and of course the hydration (if need be)—into more complex minerals. Bennu probably began in the inner asteroid belt as a fragment from a larger body with a diameter of 100 km. Simulations suggest a 70% chance it came from the Polana family and a 30% chance it derived from the Eulalia family.>>
Click to play embedded YouTube video.
The breakup of a larger Austrian Naval parent body
https://en.wikipedia.org/wiki/142_Polana wrote:
<<Polana (minor planet designation: 142 Polana) is a very dark asteroid from the asteroid belt. It was discovered by Johann Palisa on January 28, 1875, and named after the city of Pola (now Pula, Croatia), home of
the Austrian Naval Observatory where he made the discovery. It is a major member of the eponymously named Polana family, which is a subgroup of the
Nysa family. The asteroid has an estimated diameter of about 55.3 km and a low albedo of 0.045. It is orbiting at a distance of 2.419 times the separation of the Earth from the Sun, with an orbital period of 3.76 years and an eccentricity of 0.14. In the Tholen classification scheme, Polana is a primitive carbonaceous asteroid of type F, which is a subdivision of more common C-type. The spectrum of this object suggests the presence of magnetite (Fe
3O
4), which gives it the spectrally blue coloration.>>
[quote=MarkBour post_id=292502 time=1558809501 user_id=141361]
[quote=Chunks post_id=292491 time=1558744915]
[quote=MarkBour post_id=292488 time=1558715583 user_id=141361]
One of many fascinating questions that this image evokes ... If I saw this rubble on Earth, I would assume that the smaller pieces were formed by the steady erosion breakdown of larger pieces. I'm no geologist, so maybe I would be wrong about that, even on Earth. But for Bennu, where and how would this (size) distribution of rubble arise?[/quote]
Planetesimal collisional rubble aggregate - bang the rock together,guys![/quote]
Are you saying (... planetesimals are generally larger than Bennu). At some point, as larger bodies than Bennu had aggregated, some of their collisions would produce smaller clumps like Bennu that broke off, that were never pulled back in to a larger body? Does this better explain the size distribution of rubble here than a notion that this body formed as its own aggregate, never having been part of a larger body?
[/quote][quote="https://en.wikipedia.org/wiki/101955_Bennu#Origin_and_evolution"]
<<[b][u][color=#0000FF]The carbonaceous material that composes Bennu originally came from the breakup of a much larger parent body—a planetoid or a proto-planet.[/color][/u][/b] According to the accretion theory, this material came together 4.5 billion years ago during the formation of the Solar System. Bennu's basic mineralogy and chemical nature would have been established during the first 10 million years of the Solar System's formation, where the carbonaceous material underwent some geologic heating and chemical transformation inside a much larger planetoid or a proto-planet capable of producing the requisite pressure, heat and of course the hydration (if need be)—into more complex minerals. Bennu probably began in the inner asteroid belt as a fragment from a larger body with a diameter of 100 km. Simulations suggest a 70% chance it came from the Polana family and a 30% chance it derived from the Eulalia family.>>[/quote][float=left][youtube]https://www.youtube.com/watch?v=LJTRZI2HThU[/youtube][c][b][color=#0000FF] The breakup of a larger Austrian Naval parent body[/color][/b][/c][/float][quote="https://en.wikipedia.org/wiki/142_Polana"]
<<Polana (minor planet designation: 142 Polana) is a very dark asteroid from the asteroid belt. It was discovered by Johann Palisa on January 28, 1875, and named after the city of Pola (now Pula, Croatia), home of [b][u][color=#0000FF]the Austrian Naval[/color][/u][/b] Observatory where he made the discovery. It is a major member of the eponymously named Polana family, which is a subgroup of the [url=https://en.wikipedia.org/wiki/Nysa_family]Nysa family[/url]. The asteroid has an estimated diameter of about 55.3 km and a low albedo of 0.045. It is orbiting at a distance of 2.419 times the separation of the Earth from the Sun, with an orbital period of 3.76 years and an eccentricity of 0.14. In the Tholen classification scheme, Polana is a primitive carbonaceous asteroid of type F, which is a subdivision of more common C-type. The spectrum of this object suggests the presence of magnetite (Fe[sub]3[/sub]O[sub]4[/sub]), which gives it the spectrally blue coloration.>>[/quote]