APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

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Expand view Topic review: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by dougettinger » Tue Nov 16, 2010 5:47 pm

Garry Maxfield wrote:Have a look at the results of The Deep Impact spacecraft & Comet Temple 1
Why do some comets shine in the X Ray spectrum?
The Oort cloud is an assumption that was proposed a long time ago and it still is; an assumption.
Garry, what point are you making by stating that comets shine in the X-ray spectrum ?

Doug Ettinger
Pittsburgh, PA

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Garry Maxfield » Tue Nov 16, 2010 2:14 am

Have a look at the results of The Deep Impact spacecraft & Comet Temple 1
Why do some comets shine in the X Ray spectrum?
The Oort cloud is an assumption that was proposed a long time ago and it still is; an assumption.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by dougettinger » Wed Nov 10, 2010 3:41 pm

BMAONE23 wrote:If you're ever out there in your Titanic Space Ship and hit one, you might think it a 'berg
Actually, this word is spelled 'burgh which is the home of the Pittsburgh Steelers.

Getting more serious, I wish to discuss a piece of one of Neufer's excellent and very appropriate references. The Stardust mission revealed that the tail of Wild 2 had crystalline materials and could only have been "born in fire." The conclusion was that the comets crystalline grains were formed in the hot inner Solar System. Descriptions of most of the comets under study reveal more dirt than volatiles. These dirt or rocky materials had to form and condense in regions of the inner proto-star disk that were hotter and more denser.

How did the forming Solar System sort all those comets enriched with volatiles and store them in a reservoir, that astronomers call the Oort Cloud, which is much more than 100 AU from the Sun ? That reservoir of comets was invented to explain why there is a constant supply of short-lived comets that are still alive and well after more than 4 billion years. Typical comets cannot spew comas of volatiles for more than a tiny fraction of age of the Solar System. So how did this Oort Cloud invention come into being if its materials came from the inner Solar System ? Certainly, no solar wind or radiation pressure could push objects of this size outward beyond the outer planets.

Doug Ettinger
Pittsburgh, PA

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by BMAONE23 » Wed Nov 10, 2010 2:52 pm

If you're ever out there in your Titanic Space Ship and hit one, you might think it a 'berg

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Chris Peterson » Wed Nov 10, 2010 5:29 am

neufer wrote:
Chris Peterson wrote: An iceberg is still a reasonable thing to call an icy body.
I am unfamiliar with the "iceberg" description but perhaps "icy dirtball" is more apropos
The term was used in the APOD caption. We all know that those captions often wax a bit poetic; I really see no problem in that context with using the term "iceberg" to describe a comet.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by neufer » Wed Nov 10, 2010 4:17 am

Chris Peterson wrote:
Garry Maxfield wrote:
Why do astronomers still write that comets are icebergs?
There has never been a probe that has ever found any traces of water on any comet.
For those who write these APOD's, please get your facts correct!
Get the facts right!
There is ample water detected spectroscopically in comet comas.
If it doesn't come from the nucleus, where do you suggest?

Other than that, comets have many ices besides water.
http://www.naoj.org/Pressrelease/2004/04/04/index.html wrote:
Discovery of Water Icy Grains in Comet LINEAR Approaching Earth, April 4, 2004
<<Near infrared spectroscopic observation of Comet LINEAR (C/2002T7) was carried out with the Subaru Telescope in September 2003. After analyzing the spectral data, we discovered water icy grains in the coma of Comet LINEAR. Comet Hale-Bopp was the first example of the detection of water icy grains in a cometary coma, and this time is the second one.

Cometary nuclei are thought to be remnants of planetary sources (called planetecimals) existed in the early solar system. Since it is considered that the cometary nuclei were formed from icy dust (nonvolatile dust covered with ice mantle) in the interstellar medium or the solar nebula, research into such water icy grains in the cometary nuclei is very important to reveal the physical conditions of the early solar system.

It is known from past studies that cometary ices consist of water (H2O) ice (more than 80 %), and the remainder is carbon monoxide (CO) and carbon dioxide (CO2) (about 20 % or less). The CO and CO2 ices are higher volatile materials than water ice, and they are easy to volatilize even in the low-temperature region far from the Sun. It is therefore possible that water icy grains can directly be observed from comets beyond the area of 3 Astronomical Units from the Sun where water icy grains do not volatilize, because the CO and CO2 ices may be the power to release the water icy grains and dust from the cometary nucleus.

We observed Comet LINEAR approaching the Earth at about 3.5 AU from the Sun, and the brightness was only 1/100 of that of Comet Hale-Bopp at the same distance. Comet LINEAR is supposed to become brighter when the comet is getting closer to the Sun; however, it is difficult for the water icy grains to exist in the cometary coma since the water icy grains are heated by the Sun and easily vaporized. The successful detection of the water icy grains in Comet LINEAR was achieved by the high collecting power of the Subaru's 8.2m-primary mirror and the high spatial resolution to resolve the small region where the water icy grains existed.>>
Chris Peterson wrote:
An iceberg is still a reasonable thing to call an icy body.
I am unfamiliar with the "iceberg" description but perhaps "icy dirtball" is more apropos.
http://en.wikipedia.org/wiki/Comet_nucleus wrote: <<Comets are often described as "dirty snowballs", though recent observations have revealed dry dusty or rocky surfaces, suggesting that the ices are hidden beneath the crust. It has been suggested that comets should be referred to as "Icy dirtballs". Cometary nuclei are among the darkest objects known to exist in the solar system. Solar heating drives off volatile compounds leaving behind heavy long-chain organics that tend to be very dark, like tar or crude oil. The very darkness of cometary surfaces allows them to absorb the heat necessary to drive their outgassing. Roughly six percent of the near-earth asteroids are thought to be extinct nuclei of comets which no longer experience outgassing.

On 4 July 2005 at 05:52 UTC, Tempel 1 was deliberately targeted by one component of the NASA Deep Impact probe, one day before perihelion. The impact was photographed by the other component of the probe, recording a bright spray from the impact site. It was also observed by earthbound and space telescopes, which observed a brightening of several magnitudes after the impact. Initial results were surprising as the material excavated by the impact contained more dust and less ice than had been expected. The only models of cometary structure astronomers could positively rule out were the very porous models which had comets as loose aggregates of material. In addition, the material was finer than expected; scientists compared it to talcum powder rather than sand. Other materials found while studying the impact included clays, carbonates, sodium, and crystalline silicates which were found by studying the spectroscopy of the impact. Clays and carbonates usually require liquid water to form and sodium is rare in space. Observations also revealed that the comet was about 75% empty space, and one astronomer compared the outer layers of the comet to the same makeup of a snow bank. Astronomers have expressed interest in more missions to different comets to determine if they share similar compositions or if there are different materials found deeper within comets that were produced at the time of the solar system's formation. The probe's spectrometer instrument also discovered the presence of silicates, carbonates, smectite, metal sulfides (like fool's gold), amorphous carbon and polycyclic aromatic hydrocarbons.>>
http://en.wikipedia.org/wiki/Comet wrote:
<<Isaac Newton described comets as compact and durable solid bodies moving in oblique orbits, and their tails as thin streams of vapor emitted by their nuclei, ignited or heated by the sun. Newton suspected that comets were the origin of the life-supporting component of air. Newton also believed that the vapors given off by comets might replenish the planets' supplies of water (which was gradually being converted into soil by the growth and decay of plants), and the sun's supply of fuel.

As early as the 18th century, some scientists had made correct hypotheses as to comets' physical composition. In 1755, Immanuel Kant hypothesized that comets are composed of some volatile substance, whose vaporization gives rise to their brilliant displays near perihelion. In 1836, the German mathematician Friedrich Wilhelm Bessel, after observing streams of vapor during the appearance of Halley's Comet in 1835, proposed that the jet forces of evaporating material could be great enough to significantly alter a comet's orbit, and he argued that the non-gravitational movements of Encke's Comet resulted from this phenomenon.

However, another comet-related discovery overshadowed these ideas for nearly a century. Over the period 1864–1866 the Italian astronomer Giovanni Schiaparelli computed the orbit of the Perseid meteors, and based on orbital similarities, correctly hypothesized that the Perseids were fragments of Comet Swift-Tuttle. The link between comets and meteor showers was dramatically underscored when in 1872, a major meteor shower occurred from the orbit of Comet Biela, which had been observed to split into two pieces during its 1846 apparition, and was never seen again after 1852. A "gravel bank" model of comet structure arose, according to which comets consist of loose piles of small rocky objects, coated with an icy layer.

By the middle of the twentieth century, this model suffered from a number of shortcomings: in particular, it failed to explain how a body that contained only a little ice could continue to put on a brilliant display of evaporating vapor after several perihelion passages. In 1950, Fred Lawrence Whipple proposed that rather than being rocky objects containing some ice, comets were icy objects containing some dust and rock. This "dirty snowball" model soon became accepted and appeared to be supported by the observations of an armada of spacecraft (including the European Space Agency's Giotto probe and the Soviet Union's Vega 1 and Vega 2) that flew through the coma of Halley's Comet in 1986, photographed the nucleus, and observed jets of evaporating material.

Debate continues about how much ice is in a comet. In 2001, NASA's Deep Space 1 team, working at NASA's Jet Propulsion Lab, obtained high-resolution images of the surface of Comet Borrelly. They announced that comet Borrelly exhibits distinct jets, yet has a hot, dry surface. The assumption that comets contain water and other ices led Dr. Laurence Soderblom of the U.S. Geological Survey to say, "The spectrum suggests that the surface is hot and dry. It is surprising that we saw no traces of water ice." However, he goes on to suggest that the ice is probably hidden below the crust as "either the surface has been dried out by solar heating and maturation or perhaps the very dark soot-like material that covers Borrelly's surface masks any trace of surface ice".

In July 2005, the Deep Impact probe blasted a crater on Comet Tempel 1 to study its interior. The mission yielded results suggesting that the majority of a comet's water ice is below the surface, and that these reservoirs feed the jets of vaporised water that form the coma of Tempel 1. Renamed EPOXI, it made a flyby of Comet Hartley 2 on 4 November 2010.

The Stardust spacecraft, launched in February 1999, collected particles from the coma of Comet Wild 2 in January 2004, and returned the samples to Earth in a capsule in January 2006. Claudia Alexander, a program scientist for Rosetta from NASA's Jet Propulsion Laboratory who has modeled comets for years, reported to space.com about her astonishment at the number of jets, their appearance on the dark side of the comet as well as on the light side, their ability to lift large chunks of rock from the surface of the comet and the fact that comet Wild 2 is not a loosely cemented rubble pile.

More recent data from the Stardust mission show that materials retrieved from the tail of Wild 2 were crystalline and could only have been "born in fire." Although comets formed in the outer Solar System, radial mixing of material during the early formation of the Solar System is thought to have redistributed material throughout the proto-planetary disk, so comets also contain crystalline grains which were formed in the hot inner Solar System. This is seen in comet spectra as well as in sample return missions. More recent still, the materials retrieved demonstrate that the "comet dust resembles asteroid materials." These new results have forced scientists to rethink the nature of comets and their distinction from asteroids.

Forthcoming space missions will add greater detail to our understanding of what comets are made of. The European Rosetta probe is presently en route to Comet Churyumov-Gerasimenko; in 2014 it will go into orbit around the comet and place a small lander on its surface.>>

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Chris Peterson » Tue Nov 09, 2010 11:32 pm

Garry Maxfield wrote:Why do astronomers still write that comets are icebergs?
There has never been a probe that has ever found any traces of water on any comet.
For those who write these APOD's, please get your facts correct!
Get the facts right!
There is ample water detected spectroscopically in comet comas. If it doesn't come from the nucleus, where do you suggest?

Other than that, comets have many ices besides water. An iceberg is still a reasonable thing to call an icy body.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Garry Maxfield » Tue Nov 09, 2010 11:27 pm

Why do astronomers still write that comets are icebergs?
There has never been a probe that has ever found any traces of water on any comet.
For those who write these APOD's, please get your facts correct!
Get the facts right!

Garry Maxfield

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by dougettinger » Tue Nov 09, 2010 8:14 pm

Chris Peterson wrote:
BMAONE23 wrote:It could simply be that at some point in it's early existance, an outgassing event caused the Comet to tumble end over creating the elongated (stretched) central region. Then another similar event on the other lobe slowed/eliminated the tumble
Not likely. Outgassing has only a small effect on the orbit and orientation of comets. The material is ejected at relatively low velocity, and the total mass ejected is small. In other words, the momentum of the lost material is very small compared with the momentum of the nucleus, so there is only a small effect on orbit or orientation.

There are natural mechanisms that cause bodies like this to spin at an ever increasing rate, which may be what has happened here. Depending on the shape of the object, and on various perturbations, spin can easily be on more than one axis (i.e. tumble).
One thing is quite clear about irregular aseroids and comets; they are objects that have been "re-processed". Objects that condense on Earth in water or air even in a gravity field have some symmetry. Materials that condense in a normal vacuum of outer space or in a high density molecular cloud, or in a pristine proto-star disk should show some definite symmetry based on the known physics of condensation. Obviously, these subject, irregular objects been made by either hard or soft collisions of normal condensates that originally had symmetry. And possibly some of the larger collisions beget more smaller collisions before everything reasonably stabilizes. Space probes have observed very close, binary, irregular asteroids connected by gravity that may eventually come together without a hard impact. This may have occurred to Comet Hartley 2. The more interesting thought is how they were created in the first place. Let me whisper this conclusion softly - collisions.

Is our solar system like a bowling alley ? It may take on this quality given gravity, resonance, enough time, a few objects, and some larger collsions to provide enough randomness to make statistical analysis impossible.

Doug Ettinger
Pittsburgh, PA

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by mihondo2010 » Tue Nov 09, 2010 3:02 am

Come on guys... don't you realize this is just the whale probe from Star Trek IV ????
(Just kidding..)
Image

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by nightowl » Tue Nov 09, 2010 2:29 am

Could that shape be due to the the rotation of the comet about its own axis and some sort of surface properties causing preferential heating of the middle during perihelion ?

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by mukhiya » Tue Nov 09, 2010 2:07 am

I believe the smooth surface in the middle of the elongated Hartley2 is due to the process of splitting. The commet is gradually splitting apart either due to internal pressure or due to close encounter with massive gravitating object. It also appears to be a mass of loosely coupled matter ... something like a dough which is wet inside but dry outside.

Mukesh Rao.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Chris Peterson » Tue Nov 09, 2010 12:35 am

BMAONE23 wrote:It could simply be that at some point in it's early existance, an outgassing event caused the Comet to tumble end over creating the elongated (stretched) central region. Then another similar event on the other lobe slowed/eliminated the tumble
Not likely. Outgassing has only a small effect on the orbit and orientation of comets. The material is ejected at relatively low velocity, and the total mass ejected is small. In other words, the momentum of the lost material is very small compared with the momentum of the nucleus, so there is only a small effect on orbit or orientation.

There are natural mechanisms that cause bodies like this to spin at an ever increasing rate, which may be what has happened here. Depending on the shape of the object, and on various perturbations, spin can easily be on more than one axis (i.e. tumble).

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Chris Peterson » Tue Nov 09, 2010 12:31 am

dougettinger wrote:Chris, a respect your last comment. But I believe that the hypothesis that comets come from the Oort Cloud and are perturbed inwardly at random orbits and random times is purely conjecture. No proof of the Oort Cloud is yet available. And I am not so sure that computer modeling has provided good evidence of possible perturbations. If modeling has provided some highly elliptical, inclined orbits from a proposed Oort Cloud, then I am extremely curious of the trigger mechanism ? And what is the range of probability of this trigger occurring (?)
The existence of the Oort cloud is well supported by indirect observations, and is recently supported by finding what appear to be similar zones around other stars. Certainly, there must be something like it out there, given the large number of comets with aphelions very far outside the orbits of the planets. Models readily show perturbations producing long period comets (you can figure out the forces just using simple Keplerian methods, and they are very small). Given the observations of long period comets, simple statistics is all you need to estimate the quantity and orbits of short period comets, and again, observation and theory are in reasonable agreement.

Perturbations may be from gravitational resonance (Jupiter/Saturn), collisions, or even the effects of other stars.
My proposal is also conjecture. But recently observed collisions or results of collisions have been observed in our solar system in our time. And if one hard object hits another hard object instead of a gas planet or the Sun, there will be spray of collisional bodies with expected unusual trajectories which can easily create new comets and/or asteroids.
Collisions happen, of course. But the statistical likelihood, especially in the deep Solar System where planetary resonance effects are much reduced, do not suggest that this mechanism can account for the large number of comets observed.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by BMAONE23 » Mon Nov 08, 2010 10:12 pm

It could simply be that at some point in it's early existance, an outgassing event caused the Comet to tumble end over creating the elongated (stretched) central region. Then another similar event on the other lobe slowed/eliminated the tumble

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by wordesmithe2 » Mon Nov 08, 2010 9:32 pm

The smooth area in the middle of Comet Hartley 2 is obviously evidence of extraterrestial comet/asteroid miners... :rocketship:

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by León » Mon Nov 08, 2010 8:13 pm

Nothing is lost, everything changes, said Lavoussier, just what gives us the image of today. All returns and returns forever, something that no one escapes! ... Nietzsche While "evaporates" the comet will sow the seeds of future comets, which by gravity or static electricity, or whatever future be reborn as a comet, nothing more evident of eternal recurrence.

When consumed as a kite leave their "bones" that we call asteroids, while his soul soda float in the middle until can regroup.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by dougettinger » Mon Nov 08, 2010 7:51 pm

Chris, a respect your last comment. But I believe that the hypothesis that comets come from the Oort Cloud and are perturbed inwardly at random orbits and random times is purely conjecture. No proof of the Oort Cloud is yet available. And I am not so sure that computer modeling has provided good evidence of possible perturbations. If modeling has provided some highly elliptical, inclined orbits from a proposed Oort Cloud, then I am extremely curious of the trigger mechanism ? And what is the range of probability of this trigger occurring (?)

My proposal is also conjecture. But recently observed collisions or results of collisions have been observed in our solar system in our time. And if one hard object hits another hard object instead of a gas planet or the Sun, there will be spray of collisional bodies with expected unusual trajectories which can easily create new comets and/or asteroids.

Doug Ettinger
Pittsburgh, PA

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Chris Peterson » Mon Nov 08, 2010 7:09 pm

dougettinger wrote:Your comment denotes that any comet inside the orbit of Jupiter should have a short life such as 700 years or even granting 70,000 years, especially since it was identified as a "tumbling iceberg". The volatiles such as water are quickly dissapated. However, the APOD article definitely suggests that this comet as do most short period comets come from the early Solar System. The early Solar System harkens to ages beyond 3 or 4 billion years. No comet from these times could have survived. How is such a discrepancy resolved ?
All comets formed very early in the Solar System. Comets were formed and reside at the outskirts of the Solar System, far beyond the orbit of Pluto. Because they are only loosely bound to the Sun, very small perturbations can place them in highly eccentric orbits. We typically see this in long period comets. Occasionally, one of these comets will undergo a second gravitational perturbation, typically with Jupiter. This can reduce the orbital eccentricity, and you are left with a short period comet. These do have short lifetimes, because their volatiles evaporate. "Short" can mean anything from a few hundred years to tens of thousands of years, depending on their original mass and how close they come to the Sun at perihelion (and probably other factors, as well).
Now allow me to propose a resolution to these conundrums. In the near past, shall we say 10,000 to 70,000 years ago, there was a collision with some icy objects or with an object and a larger body with an icy or even watery surface somewhere within the orbits of Earth and Jupiter that created Comet Hartley 2. Does anyone buy my proposal ? Or do you have another resolution ?
I'd argue that your proposal is more complex and harder to support than the current theory regarding the origin of comets, and their orbital dynamics. To be taken seriously, you'd need to show that your explanation is better at describing our observations, and that isn't apparent to me.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Rob Crockett » Mon Nov 08, 2010 6:24 pm

Unbelievable!

After seeing the initial images, I kind of went nuts trying to make some stereo images out of the original images. The originals are separated a little too much in time/rotation for good stereo though:

Image Larger version here: http://www.ledametrix.com/gallery02/har ... x600_a.jpg

I saw some morphed data here and elsewhere, and had to give it a try myself. Here is a tiny video of the morphed data using the closest three medium resolution images:

Image

From there, I made some stereo videos:

Image

and uploaded the full resolution videos in a couple of viewing formats to YouTube:

Crossed pair: http://www.youtube.com/watch?v=bQGJPs61XkM
Parallel Pair: http://www.youtube.com/watch?v=LPpVATOxkL4
Anaglyph (red/cyan): http://www.youtube.com/watch?v=TxtFegWgrWo

The images were rotated, resized based on distance, aligned, and cropped in PS CS4. The 3 images were morphed into 160 images in SqirlzMorph with 30 control points. The uncompressed AVI output was converted into stereo and compressed with StereoPhotoMaker. The morphing works well for the surface of the nucleas, but the jets in space are kind of flattened into a fan-like appearance by the surface morphing.

Are there more images available BETWEEN the originally distributed closest approach images? What an incredible set of data!

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by neufer » Mon Nov 08, 2010 6:02 pm

JWMildren wrote:
Did the EPOXI spacecraft have magnetic field sensors?
I don't think so:
http://en.wikipedia.org/wiki/Deep_Impact_%28space_mission%29 wrote:
<<The Deep Impact/EPOXI spacecraft is about 3.2 meters long, 1.7 meters wide and 2.3 meters high. It includes two solar panels, a debris shield, and several science instruments for imaging, infrared spectroscopy, and optical navigation to its destination near the comet. The spacecraft also carried two cameras, the High Resolution Imager (HRI), and the Medium Resolution Imager (MRI). The HRI is an imaging device that combines a visible-light camera with a filter wheel, and an imaging infrared spectrometer called the "Spectral Imaging Module" or SIM that operates on a spectral band from 1.05 to 4.8 micrometres. It has been optimized for observing the comet's nucleus. The MRI is the backup device, and was used primarily for navigation during the final 10-day approach. It also has a filter wheel, with a slightly different set of filters.>>
JWMildren wrote:
Perhaps we are seeing ferrous material collecting at the poles.
Magnetic fields in a comet immediate vicinity are most likely induced:
http://en.wikipedia.org/wiki/Comet wrote:
<<While the solid nucleus of comets is generally less than 50 km across, the coma may be larger than the Sun, and ion tails have been observed to extend one astronomical unit or more. The observation of antitails contributed significantly to the discovery of solar wind. The ion tail is formed as a result of the photoelectric effect of solar ultra-violet radiation acting on particles in the coma. Once the particles have been ionized, they attain a net positive electrical charge which in turn gives rise to an "induced magnetosphere" around the comet. The comet and its induced magnetic field form an obstacle to outward flowing solar wind particles. As the relative orbital speed of the comet and the solar wind is supersonic, a bow shock is formed upstream of the comet, in the flow direction of the solar wind. In this bow shock, large concentrations of cometary ions (called "pick-up ions") congregate and act to "load" the solar magnetic field with plasma, such that the field lines "drape" around the comet forming the ion tail.>>

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by dougettinger » Mon Nov 08, 2010 5:55 pm

neufer wrote:
orin stepanek wrote:
I'm guessing Hartley is well on it's way to becoming an asteroid.
It doesn't look like it has much water left in its crust.
This is only my opinion and not based on fact. :wink:
http://en.wikipedia.org/wiki/103P/Hartley wrote:
<<The mass of [103P/Hartley] is estimated to be about 300 megatonnes (~50 Great Pyramids of Giza).

Barring a catastrophic breakup or major splitting event, the comet should be able to survive
up to another 100 apparitions (~700 years) at its current rate of mass loss.
Where did Neufer obtain this previous data? I know it is trustworthy as well as his Shakespearean quotes.

Your comment denotes that any comet inside the orbit of Jupiter should have a short life such as 700 years or even granting 70,000 years, especially since it was identified as a "tumbling iceberg". The volatiles such as water are quickly dissapated. However, the APOD article definitely suggests that this comet as do most short period comets come from the early Solar System. The early Solar System harkens to ages beyond 3 or 4 billion years. No comet from these times could have survived. How is such a discrepancy resolved ?

The APOD explanation also claims that Comet Hartley 2 orbits between Jupiter and Earth. Simple knowledge of orbital mechanics would suggest its origin comes from either the neighborhood of Jupiter's orbit or Earth's orbit. And in my educated opinion, irregular shaped, inclined objects as found in most asteroids, comets and planetary satellites are created from collisions and/or the re-combining/breaking apart of two or more collisional items by gravity and/or inertia respectively.

Now allow me to propose a resolution to these conundrums. In the near past, shall we say 10,000 to 70,000 years ago, there was a collision with some icy objects or with an object and a larger body with an icy or even watery surface somewhere within the orbits of Earth and Jupiter that created Comet Hartley 2. Does anyone buy my proposal ? Or do you have another resolution ?

Doug Ettinger
Pittsburgh, PA

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Greyhawk » Mon Nov 08, 2010 5:50 pm

Looks like a rubble pile held together by weak gravity..maybe the rate of spin has caused a differentiation between dust/rock sizes and densities.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by Chris Peterson » Mon Nov 08, 2010 5:44 pm

IdSavant23 wrote:It looks to me like two similar sized comets moving in an almost parallel orbit eventually collided just hard enough to fuse together but not hard enough to allow one to destroy the other or to escape from the other
That would be unlikely almost to the point of impossibility. It is much more likely we are seeing just the opposite: a single body that is slowly pulling itself apart. That is a process that is well understood- bodies in space are acted upon by solar radiation in a way that makes them spin, and increases their spin rate with time. Eventually, the inertial forces associated with the spinning are greater than the gravitational force holding things together, and the body comes apart. This is probably the source of many sporadic meteors (from asteroidal bodies), and the same sort of thing should apply to comets, as well.

Re: APOD: 700 Kilometers Below Comet Hartley 2 (2010 Nov 08)

by IdSavant23 » Mon Nov 08, 2010 5:32 pm

It looks to me like two similar sized comets moving in an almost parallel orbit eventually collided just hard enough to fuse together but not hard enough to allow one to destroy the other or to escape from the other

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