by MarkBour » Fri Oct 07, 2016 6:01 pm
Chris Peterson wrote:MarkBour wrote:One of the main things I think he introduced to this discussion is the matter of erosion. Not only erosion by Earth-like processes, but equally relevant, space weathering. We know that comets suffer from this in the extreme.
Actually, comets are among the least space weathered bodies. Space weathering involves chemical and physical changes, largely at the surface, due to interaction with energetic particles and micrometeorites. Most comets (at least, those with shorter periods or those that are in the inner system) have fairly new surfaces, so there is little evidence of space weathering (which is a slow process).
Erosion on comets is due to the evaporation of volatiles and ejection of particulates while near perihelion.
Kind of a bad day for me in Starship Asterisk. But I can learn.
First, I offered an opinion that C67P was probably a single body with a blow-out or melt-out creating its overall shape, whereas I now see that the more careful look seems to indicate otherwise, that C67P is most likely a 2-body "mashup". I don't know if there's much confidence in that analysis, but it seems more likely now. (That analysis was done with images of higher resolution than this day's APOD, by the way.)
Second, I was struggling with what word to use for a comet's overall major degradation process. I was thinking by analogy to what happens on Earth, where erosion is mainly a process caused by external materials (wind, water, etc are not part of the object being eroded), whereas if an ice cream cone on earth melts and drips all over the place, I figured "weather" would be a better word, since warm weather would be the cause.
However, I accept the correction above, from Chris. Better, it seems, to think about what the process is doing to the object in question. So, when a comet [or Frosty the snowman] is melted and begins to dissolve [say, Frosty's arm falls off], due to the warmth of the Sun, this is best referred to as "erosion", because the body is wasting away. We would then reserve "weathering" as a term for the modification of the surface of a body, like the development of a patina on a copper penny.
[quote="Chris Peterson"][quote="MarkBour"]One of the main things I think he introduced to this discussion is the matter of erosion. Not only erosion by Earth-like processes, but equally relevant, space weathering. We know that comets suffer from this in the extreme.[/quote]
Actually, comets are among the least space weathered bodies. Space weathering involves chemical and physical changes, largely at the surface, due to interaction with energetic particles and micrometeorites. Most comets (at least, those with shorter periods or those that are in the inner system) have fairly new surfaces, so there is little evidence of space weathering (which is a slow process).
Erosion on comets is due to the evaporation of volatiles and ejection of particulates while near perihelion.[/quote]
Kind of a bad day for me in Starship Asterisk. But I can learn.
First, I offered an opinion that C67P was probably a single body with a blow-out or melt-out creating its overall shape, whereas I now see that the more careful look seems to indicate otherwise, that C67P is most likely a 2-body "mashup". I don't know if there's much confidence in that analysis, but it seems more likely now. (That analysis was done with images of higher resolution than this day's APOD, by the way.)
Second, I was struggling with what word to use for a comet's overall major degradation process. I was thinking by analogy to what happens on Earth, where erosion is mainly a process caused by external materials (wind, water, etc are not part of the object being eroded), whereas if an ice cream cone on earth melts and drips all over the place, I figured "weather" would be a better word, since warm weather would be the cause.
However, I accept the correction above, from Chris. Better, it seems, to think about what the process is doing to the object in question. So, when a comet [or Frosty the snowman] is melted and begins to dissolve [say, Frosty's arm falls off], due to the warmth of the Sun, this is best referred to as "erosion", because the body is wasting away. We would then reserve "weathering" as a term for the modification of the surface of a body, like the development of a patina on a copper penny.