Are comets asteroids or asteroids comets?

[nicho247]

Hi EUers,

I've been hooked into this forum for a few months and finally have a question worth submitting. I've been educated with the typical science background of asteroids = rocks, comets = ice balls, and am certainly not an expert in space oriented discussions. After watching the majority of the EU conference youtube vid's, and science news youtube vid's, as well as "Episode 3 Symbols of an Alien Sky: The Electric Comet (Full Documentary)" ...

Using wiki to find the official definitions of solar system bodies, I stumbled upon the IAU (International Astronomical Union) website, where they appear to set the definition of said things.

http://www.iau.org/news/pressreleases/detail/iau0603/#3

RESOLUTION 5A

The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:

(1) A "planet" [1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [2], (c) has not cleared the neighbourhood around its orbit, and

(d) is not a satellite.

(3) All other objects [3], except satellites, orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies"."

Comets are small solar-system bodies because they do not meet criteria (b) nor (c) and associated with the notion of "ice" and the "coma".

http://www.iau.org/public/themes/naming/

Comets
A comet is a body made of rock and ice, typically a few kilometres in diameter, which orbits the Sun. Comets may pass by the Sun only once or go through the Solar System periodically. A comet’s tail is formed when the Sun’s heat warms the coma or nucleus, which releases vapours into space.

Interestingly, the IAU website does not appear to define "Small Solar-System Bodies" very well, it is just a catch-all for the things they have defined they are not (aka - not a planet, not a satellite, its a SSSB). Comets are delineated from the others SSSB's with their noticeably observable effects. Also note, non-comet small solar-system bodies are those defined as not made of "ice", and not displaying a "coma", but nothing else. In fact the IAU website goes on to describe how to name them, not how to define them. It is defined by the elimination of their other criteria.

Minor Planets
The assignment of a particular name to a particular minor planet is the end of a long process that can take many decades:

An image for clarity (credit wikipedia/Tahc)



Are asteroids (small solar system bodies) and comets the same thing (from an EU perspective)?

If we are to red-line (remove ICE) from the (IAU) definition of the comet, the distinction between those which "are" and "are not" comets will reside solely on the observation of the "coma". From what I have read on this forum, there is no material difference with comets and other bodies. There is only a difference in orbit, where I see it argued, the orbit as the leading cause of the coma due to "increased charge density" from the electric sun. (credit Rossim)

Said differently, are there any asteroids with comet-like orbits which do not display comet like features (coma)?

"Asteroids*: 643,800 (401,521 numbered**, 242,279 provisional)
Comets***: 5,186 (305 numbered***, 3,515 with provisional designations, 1,366 without designations)"

A ratio of 1 comet to 125 asteroids in our solar system.

Nick

[Sparky]

Said differently, are there any asteroids with comet-like orbits which do not display comet like features (coma)?

None that I have heard about.

But there has been asteroids that display comet like features.

[antosarai]

(...) are there any asteroids with comet-like orbits which do not display comet like features (coma)?

Several, apparently.
Like for instance 3753 Cruithne (http://en.wikipedia.org/wiki/3753_Cruithne).

[neilwilkes]

Don't forget bodies such as Apophis - this has a very similar shape to 67P (the Rosetta mission target) and is almost certainly the way it is because it too once sported a "jet" or "tail" (bad terms those)

[nicho247]

I found a space news from about 1 year ago, regarding P2013/P5, asteroid becomes comet.

Wal stated the material composition between the two are relatively the same, and the main difference is the orbits. Paraphrasing, a comet will change its distance from the sun greatly, while an asteroid will keep it relatively the same.

(...) are there any asteroids with comet-like orbits which do not display comet like features (coma)?

Several, apparently.
Like for instance 3753 Cruithne (http://en.wikipedia.org/wiki/3753_Cruithne).

Hi Antosarai – Thank you for the link. I found it quite interesting, however not comet-like enough. Although this object has a circular orbit, the Sun is offset from the center. This should be creating a delta an electrical potential because the object is moving away from the sun and back toward, however it displays no features (unless I missed in my read).



Is it possible there is a threshold in distance (or delta in electrical potential) for comet-like features to manifest?

Nick

[nicho247]

Don't forget bodies such as Apophis - this has a very similar shape to 67P (the Rosetta mission target) and is almost certainly the way it is because it too once sported a "jet" or "tail" (bad terms those)

Hi Neilwilkes - I found this to be an interesting read as well, and had no idea this was at risk for hitting the earth at one point in time. A quick look at the orbit, appears this is not a candidate to be a comet because of the orbit being circular and does not appear to be move far away enough to manifest comet-like features. Also, the small size might be a prohibitive factor, as wikipedia states comet sizes range from 0.1-0.2km in diameter to 30km. Apophis is listed as 0.3km, close to the minimum observed value.



Do you have any links for the jets or tails?

Nick

[antosarai]

I found it quite interesting, however not comet-like enough. Although this object has a circular orbit, the Sun is offset from the center. This should be creating a delta an electrical potential because the object is moving away from the sun and back toward, however it displays no features (unless I missed in my read).

From what I could find from the Web, 3753 Cruithne has ~5km in diameter (roughly around the same size of Rosetta's 67P Comet) and has a normal elliptic orbit with high orbital eccentricity that takes it from inside Mercury's orbit to outside Mars'.
No mention of cometary activity.

As this YouTube video illustrates:
https://www.youtube.com/watch?v=_-fo7tEFUAc

[Aardwolf]

Said differently, are there any asteroids with comet-like orbits which do not display comet like features (coma)?

Damocloids.

[nicho247]

No mention of cometary activity.

Hi Antosarai - I am thinking there is probably a minimum criteria, i.e. object must originate from outside asteroid belt to be able to display comet like features (backed by historical data). My preliminary findings appear that most comets must originate from at least Jupiter or further out. I assume this loose definition will be proven wrong with more research, but hopefully refined to be more specific.

So my hypothesis could be broken with objects which do originate from Jupiter or further (>= Jupiter) and come closer to the Sun, but do not display a coma or objects which do not originate further than the asteroid belt (< Jupiter) and come closer to the Sun, but do display a coma.

Note : I have found an asteroid & comet database where objects are logged in some CSV format, but am unsure if this will contain the relevant info I am looking for. Need to dig into them further

ftp://ftp.lowell.edu/pub/elgb/astorb.html
as well as
http://www.minorplanetcenter.net/iau/Ep ... es/Comets/

Looking to obtain the following parameters
name
asteroid or comet
closest expected distance to sun
furthest expected distance away from sun
radius of object

Nick

[nicho247]

Said differently, are there any asteroids with comet-like orbits which do not display comet like features (coma)?

Damocloids.

Hi Aardwolf - I have never heard of these types of objects.

For Damocloids in general, "Damocloids are believed to be nuclei of Halley-type comets that have lost all their volatile materials due to outgassing and become dormant. Such comets are believed to originate from the Oort cloud."

This seems to be in conflict with idea of material composition of the comet is irrelevant. Interesting.

5335 Damocles is intriguing. Originates from outside the distance of Jupiter, moves in towards the Sun, but doesn't have comet features. From wikipedia "because its highly inclined orbit does not take it near Jupiter or Saturn."

In attempting to find an image of this object's orbit...I found myself at http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=5 ... &orb=1#orb

Took the following image, and it shows, as wikipedia indicates, it does not orbit our solar system along the plane of the rest of the objects, but at an angle of 60degress. I wonder if this is a factor...



Nick