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Fraser
2008-Sep-03, 09:20 PM
A frequent plot device in the old "Mission: Impossible" television show was the special masks the IMF team used so they could impersonate anyone. Viewers were often surprised to find out who ended up being an imposter. Likewise, astronomers and planetary scientists are considering that a fair amount of Near Earth Objects (NEOs) [...]

More... (http://www.universetoday.com/2008/09/03/asteroid-imposters/)

timb
2008-Sep-04, 12:36 AM
A frequent plot device in the old "Mission: Impossible" television show was the special masks the IMF team used so they could impersonate anyone. Viewers were often surprised to find out who ended up being an imposter. Likewise, astronomers and planetary scientists are considering that a fair amount of Near Earth Objects (NEOs) [...]

More... (http://www.universetoday.com/2008/09/03/asteroid-imposters/)

I'm not sure what the difference is anyway. Is it a matter of composition (eg presence of volatile ices)? or where it came from (eg within the orbit of Neptune or outside)? or that it out-gasses when it gets close enough to the sun?

01101001
2008-Sep-04, 12:52 AM
I'm not sure what the difference is anyway. Is it a matter of composition (eg presence of volatile ices)? or where it came from (eg within the orbit of Neptune or outside)? or that it out-gasses when it gets close enough to the sun?

For instance, Institute for Astronomy Hawaii Research (http://www.ifa.hawaii.edu/research/solar_system.htm):


The NEOs comprise a mixture of escaped main-belt asteroids and dead comets in uncertain proportions. Fernandez hopes to measure the fraction of NEOs which might be dead comets by measuring the albedos. Cometary nuclei are coated in very dark, carbon rich materials that have a distinctively low albedo whereas asteroids are, on the whole, more reflective. In an initial study, 90% of the NEOs having dynamical similarities to comets also had the very low albedos typical of comets, confirming that dead comets persist amongst the NEOs.

Abstract: Connections between asteroids and cometary nuclei (http://journals.cambridge.org/action/displayAbstract;jsessionid=CE3279A7A5A5937591C4081 DEA58CDF9.tomcat1?fromPage=online&aid=414748)


The comets have most primitive, accessible material in the solar system but we do not know what is hidden below the evolved surface layers. Comets must become dormant but we do not know whether the ice is exhausted or sublimation is inhibited (blocked by quenching mechanisms). There must be many dormant comets masquerading as asteroids but we do not know to identify these bodies unless via serendipitous discovery observations. [...] The important questions are: where is the pristine material in the cometary nuclei and in the asteroid-comet transition objects, do comets lose their ice or seal it in? Both the large survey projects and in-situ space missions will help to answer these questions in the near future.

timb
2008-Sep-06, 11:16 AM
For instance, Institute for Astronomy Hawaii Research (http://www.ifa.hawaii.edu/research/solar_system.htm):



Abstract: Connections between asteroids and cometary nuclei (http://journals.cambridge.org/action/displayAbstract;jsessionid=CE3279A7A5A5937591C4081 DEA58CDF9.tomcat1?fromPage=online&aid=414748)

Your quote wasn't particularly helpful. It only suggests that defunct comets are darker than the average asteroid. The first page you linked to says (after describing KBOs):


Comets are icy objects from the outer solar system. They move in orbits that bring them close to the Sun.

and


asteroids are the other leftovers from the formation of the solar system. Most are between Mars and Jupiter, but some have orbits that cross that of Earth.

So an asteroid is any "leftover" that isn't a comet or a KBO. By these definitions if a dead comet has lost its ice, then it is no longer a comet but an asteroid (comets must be icy).

KaiYeves
2008-Sep-06, 07:56 PM
Interesting lead-in.

01101001
2008-Sep-06, 11:16 PM
Has "Ice" been confirmed to be a part a a comets make up?
http://publicaffairs.llnl.gov/news/news_releases/2008/NR-08-01-05.html

Nice citation.


Because of its tail formed by vaporizing ices, Wild 2 is, by definition, a comet.

Abbadon_2008
2008-Sep-07, 04:06 AM
Large chunks of ice == 'Spacebergs'

HenrikOlsen
2008-Sep-07, 08:53 AM
Has "Ice" been confirmed to be a part a a comets make up?
Multiple ways, one way to do so is to compare the spectra of stars when seen directly and with a comet tail in front of them where you'll see absorption of light that clearly shows it started as water1.

I think this method is within the means of a serious amateur who want to confirm things independently.

1) the massive amounts of water vapor in the atmosphere meant that it's absorption by H+ and OH- that are looked for rather that H2O, but the result is the same, there's water.