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

[APOD Robot]

700 Kilometers Below Comet Hartley 2

Explanation: What kind of comet is this? Last week, NASA's robotic EPOXI spacecraft whizzed past Comet 103P/Hartley, also known as Comet Hartley 2, and recorded images and data that are both strange and fascinating. EPOXI was near its closest approach -- about 700 kilometers away -- when it snapped the above picture. As expected, the comet has indeed shown itself to be a tumbling iceberg orbiting the Sun between Earth and Jupiter. However, unexpected features on the images have raised many questions. For example, where are all the craters? Why is there a large smooth area around the middle? How much of Comet Hartley 2 is a loose pile of dust and ice shards? Future analyses and comparisons to other comet nuclei may answer some of these questions and, hopefully, lead to a better general understanding of comets, meteors, and the early Solar System.

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[tvalleau]

That smooth middle looks to me like the core spent some time turning on its long axis near or in a narrow source of heat. That would produce the smooth curves and if it was (relatively) recently, would explain the relatively debris-free area as well.

[geckzilla]

But where would a narrow source of heat come from? Seems more likely that the shape and texture of the comet nucleus would indicate its composition and perhaps clues about how it was formed long ago.

[León]

Click to view full size image

It is not the same, but as it seems to Enceladus

[JohnNColes]

Looks a little like what we used to call "necking" when an iron rod was put under tensile strain: the centre would become narrow, elongated & smooth just before the rod snapped. So, I wonder whether the Comet is under some sort of tensile stress along its long axis - maybe due to the mass difference between each end of the "dumbbell" structure?

[Jack S. Clark]

Where did the water come from to make Hartley 2?????

[neufer]

Where did the water come from to make Hartley 2?????

Click to view full size image

Hydrogen left over from the big bang plus: Oxygen, Carbon, Silicon, Sulfur, Calcium, Iron, etc. from the nucleosynthesis inside of extinct short lived supergiant giant stars combined in space to form H₂O, CH₄, SiO₂ and many other simple molecules which could then condense into planets, comets, etc.

"The surface of the Earth is the shore of the cosmic ocean. On this shore, we've learned most of what we know. Recently, we've waded a little way out, maybe ankle-deep, and the water seems inviting. Some part of our being knows this is where we came from. We long to return, and we can, because the cosmos is also within us. We're made of star stuff. We are a way for the cosmos to know itself."

[emc]

Are there many watery (ice) containing comets (and asteroids?)?… And they are a potential source for the Moon’s recently discovered water?

So Hartley 2 a byproduct of the Sun’s and subsequent solar system evolution?

So the building blocks for life support and everything else in our solar system stems from the evolution of the Sun? Therefore, the Sun’s birth and evolution is the engine behind the composition of Hartley 2?

The smooth area does appear to be an indication of Hartley 2 having been “stretched” at some point in its history. A puzzle, puzzles, everywhere puzzles.

[orin stepanek]

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.

[zbvhs]

Why it should hold together at all is a mystery. Strange stuff, gravity.

[TEMOHLER]

,,,©¿©,,, Well, the science is all cool.. but the name Hartley 2.. could we change it to "The Chicken Leg"™.. Anyway, the smooth middle could be from rubble from the past being pulled in by graity, and rolling around like a grinder before it was ejected over time from the comet.

[neufer]

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.

<<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.

_______ Julius Caesar Act 2, Scene 2

CALPURNIA: When beggars die, there are no comets seen;

• The heavens themselves blaze forth the death of princes.

.
_______ Act 4, Scene 3

BRUTUS: __ [Enter the Ghost of CAESAR]
.

• How ill this taper burns! Ha! who comes here?
  I think it is the weakness of mine eyes
  That shapes this monstrous apparition.
  It comes upon me. Art thou any thing?
  Art thou some god, some angel, or some devil,
  That makest my blood cold and my hair to stare?
  Speak to me what thou Art.

[Chris Peterson]

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.

It is an extremely active comet, which implies lots of volatiles are still present. Comets don't seem to appear icy right on their surface, so you can't really use an image to test this. Hartley has a huge gas coma around it right now, extending hundreds of thousands of kilometers. The probe was inside that during the flyby. At this scale, the coma is invisible (just like a bright nebula would be invisible from inside).

Whether a "comet" ever becomes an "asteroid" is a matter of definition. Usually, an asteroid is thought of as a rocky body that formed in the inner Solar System, while a comet is a rocky/icy body that formed much further out. They are distinguished by different formation processes, different material content, and different types of orbits. Certainly, though, comets eventually lose their volatiles and become similar in some respects to asteroids- whatever term you want to use for them at that point.

[neufer]

Certainly, though, comets eventually lose their volatiles and become similar in some respects to asteroids.

• <<When Harry S. Truman ran for the Senate in Missouri in 1922 he arrived at Jackson County's biggest summer picnic at Oak Grove, by biplane. Truman, with a former World War I pilot, had circled the site dropping brochures to the estimated 4,000 residents below, many of whom watched as the candidate - once the plane had landed Truman climbed from his seat and threw up. "Our candidate got out... and gave forth with a lot of things I know he didn't eat," said Truman friend Eddie McKim. "He was as green as grass. I think it was his first flight, but he mounted the rostrum and made a speech.">>
  - _Harry S. Truman: his life and times_ By Brian Burnes

[Chris Peterson]

Are there many watery (ice) containing comets (and asteroids?)?

All comets are icy bodies, with high water content. Asteroids appear to contain trace amount of water.

And they are a potential source for the Moon’s recently discovered water?

They are the most likely source. And not just for the Moon- comets might also be the source of most of the water on Earth.

So Hartley 2 a byproduct of the Sun’s and subsequent solar system evolution?

Yes. (I might ask, where else would you think it might come from?)

So the building blocks for life support and everything else in our solar system stems from the evolution of the Sun? Therefore, the Sun’s birth and evolution is the engine behind the composition of Hartley 2?

It's more complex, since depending on the "building blocks" involved, there is material that predates the Sun. Certainly, water was present in the presolar nebula, as were some organics. So the present contents of the Solar System are partly the product of processes in the last 4.7 billion years, and partly the product of earlier processes.

The smooth area does appear to be an indication of Hartley 2 having been “stretched” at some point in its history. A puzzle, puzzles, everywhere puzzles.

It has been suspected for a while that comets (and many asteroids as well) are not solid bodies, but piles of debris. This means that they can shift shape from external or internal forces. It makes it much easier to understand why this comet looks the way it does, if you assume that it consists of two roughly spherical bodies made up of boulder-sized rock and ice, with a region of gravel and dust-sized material between them, all separated nicely by gravitational and centrifugal forces.

[emc]

[

So Hartley 2 a byproduct of the Sun’s and subsequent solar system evolution?

Yes. (I might ask, where else would you think it might come from?)

I was thinking a neighboring star.

I appreciate your answers... you are a good teacher.

[JWMildren]

Did the EPOXI spacecraft have magnetic field sensors? Perhaps we are seeing ferous meterial collecting at the poles.

[mkelly]

It obviously comes from the cosmic chicken. That is a large drumstick.

[Ann]

BRUTUS: __ [Enter the Ghost of CAESAR]
.

• How ill this taper burns! Ha! who comes here?
  I think it is the weakness of mine eyes
  That shapes this monstrous apparition.
  It comes upon me. Art thou any thing?
  Art thou some god, some angel, or some devil,
  That makest my blood cold and my hair to stare?
  Speak to me what thou Art.

Speak to me what thou Art!!!!



What, me Art?

Ann

[IdSavant23]

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

[Chris Peterson]

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.

[Greyhawk]

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.

[dougettinger]

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.

<<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

[neufer]

Did the EPOXI spacecraft have magnetic field sensors?

I don't think so:

<<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.>>

Perhaps we are seeing ferrous material collecting at the poles.

Magnetic fields in a comet immediate vicinity are most likely induced:

<<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.>>

[Rob Crockett]

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:

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:



From there, I made some stereo videos:



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!