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Post Info TOPIC: Comet 9/P Tempel 1
Blobrana


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Ephemeris
Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   Mag    mag2
2010 12 17    16 10 13.1 -18 56 12   2.4136  1.5333    20.7    13.1  12.1  18.1
2010 12 18    16 13 25.4 -19 08 46   2.4095  1.5316    21.0    13.3  12.0  18.1
2010 12 19    16 16 38.3 -19 21 09   2.4055  1.5300    21.2    13.4  12.0  18.1
2010 12 20    16 19 51.9 -19 33 19   2.4015  1.5284    21.4    13.6  12.0  18.1
2010 12 21    16 23 06.1 -19 45 17   2.3976  1.5269    21.6    13.7  12.0  18.1
2010 12 22    16 26 20.9 -19 57 03   2.3937  1.5255    21.9    13.9  12.0  18.1
2010 12 23    16 29 36.4 -20 08 36   2.3899  1.5241    22.1    14.0  12.0  18.1
2010 12 24    16 32 52.4 -20 19 56   2.3862  1.5228    22.3    14.2  12.0  18.1
2010 12 25    16 36 09.1 -20 31 03   2.3824  1.5215    22.5    14.4  11.9  18.1
2010 12 26    16 39 26.3 -20 41 56   2.3788  1.5204    22.8    14.5  11.9  18.1
2010 12 27    16 42 44.1 -20 52 36   2.3751  1.5192    23.0    14.7  11.9  18.1
2010 12 28    16 46 02.5 -21 03 02   2.3715  1.5182    23.2    14.8  11.9  18.1
2010 12 29    16 49 21.3 -21 13 15   2.3680  1.5172    23.5    15.0  11.9  18.1
2010 12 30    16 52 40.7 -21 23 13   2.3645  1.5163    23.7    15.1  11.9  18.1
2010 12 31    16 56 00.6 -21 32 57   2.3611  1.5154    23.9    15.2  11.9  18.1


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Blobrana


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It's been more than three years since NASA's Deep Impact mission hurled an 815-pound copper-clad bullet into the path of Comet 9P/Tempel 1, and scientists are still struggling to understand the gigantic plume of dust and water vapour that spewed into space from the target point.
A big part of the problem is that the gigantic cloud obscured the comet's nucleus until long after the main spacecraft had passed by. To this day, the mission team can only guess at the size of the crater created by Deep Impact's frontal assault. By one well-regarded estimate, it could be anywhere from about 25 m to more than 100 m across depending on whether the cometary surface was hard or fluffy.

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Blobrana


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Title: Comet 9P/Tempel 1: Interpretation with the Deep Impact Results
Authors: Satoru Yamamoto, Hiroshi Kimura, Evgenij Zubko, Hiroshi Kobayashi, Koji Wada, Masateru Ishiguro, Takafumi Matsui
(Version v2)

According to our common understandings, the original surface of a short-period comet nucleus has been lost by sublimation processes during its close approaches to the Sun. Sublimation results in the formation of a dust mantle on the retreated surface and in chemical differentiation of ices over tens or hundreds of meters below the mantle. In the course of NASA's Deep Impact mission, optical and infrared imaging observations of the ejecta plume were conducted by several researchers, but their interpretations of the data came as a big surprise: (1) The nucleus of comet 9P/Tempel 1 is free of a dust mantle, but maintains its pristine crust of submicron-sized carbonaceous grains; (2) Primordial materials are accessible already at a depth of several tens of cm with abundant silicate grains of submicrometer sizes. In this study, we demonstrate that a standard model of cometary nuclei explains well available observational data: (1) A dust mantle with a thickness of ~1-2 m builds up on the surface, where compact aggregates larger than tens of micrometers dominate; (2) Large fluffy aggregates are embedded in chemically differentiated layers as well as in the deepest part of the nucleus with primordial materials. We conclude that the Deep Impact results do not need any peculiar view of a comet nucleus.

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Blobrana


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Title: Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact
Authors: G.P. Tozzi, H. Boehnhardt, L. Kolokolova, T. Bonev, E. Pompei, S. Bagnulo, N. Ageorges, L. Barrera, O. Hainaut, H.U. Kaeufl, F. Kerber, G. LoCurto, O. Marco, E. Pantin, H. Rauer, I. Saviane, C. Sterken, M. Weiler

On 4 July 2005 at 05:52 UT, the impactor of NASA's Deep Impact (DI) mission crashed into comet 9P/Tempel 1 with a velocity of about 10 km/s. The material ejected by the impact expanded into the normal coma, produced by ordinary cometary activity.
The characteristics of the non-impact coma and cloud produced by the impact were studied by observations in the visible wavelengths and in the near-IR. The scattering characteristics of the "normal" coma of solid particles were studied by comparing images in various spectral regions, from the UV to the near-IR.
For the non-impact coma, a proxy of the dust production has been measured in various spectral regions. The presence of sublimating grains has been detected. Their lifetime was found to be about 11 hours. Regarding the cloud produced by the impact, the total geometric cross section multiplied by the albedo was measured as a function of the colour and time. The projected velocity appeared to obey a Gaussian distribution with the average velocity of the order of 115 m/s. By comparing the observations taken about 3 hours after the impact, we have found a strong decrease in the cross section in J filter, while that in Ks remained almost constant. This is interpreted as the result of sublimation of grains dominated by particles of sizes of the order of some microns.

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Blobrana


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Two years ago, NASA's Deep Impact spacecraft dropped an 820 lb copper projectile onto Comet Tempel 1, unleashing an explosion that made headlines around the world.
Deep Impact's prime mission was to punch a hole in Tempel 1 and look inside, giving researchers their first glimpse of a comet's internal structure.
Unfortunately, Deep Impact sailed away before the impact cloud had time to dissipate, so "we were never able to see the crater because the cloud of debris was so thick".
Now, NASA is going back for a second look.

"We're sending another spacecraft back to Tempel 1, the Stardust probe" - Michael New of NASA Headquarters.

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Blobrana


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The Thickness and Formation Age of Surface Layer on Comet 9P/Tempel 1
Cometary nuclei are believed to contain important information on the condition of the solar nebula, but there is little observational data available on their interior structure. Our ground-based observations of NASAs Deep Impact event show that comet 9P/Tempel 1 has a surface layer consisting of small (sub-micron sized) carbonaceous grains whose thickness is several tens of cm. This suggests that comet 9P/Tempel 1 contains at several tens of cm of depth material that has not metamorphosed since this comet left the trans-Neptunian region. This further implies that many short-period comets may maintain the components they had upon leaving the trans-Neptunian region at ~ 1 m of depth from the surface even after numerous perihelion passages.

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Blobrana


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Comet 9/P Tempel 1
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Deep Impact Extended Mission Could Probe Deeper Into Solar System Origin
In July, 2005, the Deep Impact spacecraft released a probe that blasted a crater in comet Tempel 1, spilling its elements into space so scientists could discover its composition. The assault was justified because comets are thought to be leftovers from the formation of our solar system, so learning more about them helps to understand how our solar system came to be.

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Blobrana


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Carey Lisse of Johns Hopkins University and his colleagues studied the collision through 12 infrared spectrographs taken by Spitzer from July 2 through July 5. Prior to impact, Tempel 1 displayed the same streaming dust as any other comet, pushed back from the cometary body by the sun's radiation. But after the early-morning impact, Tempel 1 revealed itself to be made of water ice and gas, carbonates, polyaromatic hydrocarbons, silicates, sulphides and other elements.

This mix of components does not match current models of comet dust. Some of the minerals detected require temperatures between 1,100 and 1,400 degrees Kelvin--only found as close to the sun as Mercury--as well as volatile gases such as methane that only remain stable at temperatures below 100 K. This means that there must have been some form of mixing over large distances going on in the nebula that gave birth to the sun billions of years ago.

The spectra also hint that water must have been abundant in the area where the comet formed and that Tempel 1 is not as carbon-rich as some of its peers; carbon-based materials appear to make up only 20 percent of this comet compared to as much as 50 percent of others. Nevertheless, the material in Tempel 1 matches that ejected by Comet Hale-Bopp in 1995 and that means that these comets formed in broadly similar ways, the researchers argue. Science published the paper analysing the spectra online yesterday.

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A temperature map of the nucleus with different spatial resolutions. The context image (in black and white) is a HRIVIS image taken just before impact. The colour bar in the middle gives temperature in Kelvins. The sun is to the right in all images.

These data were acquired with the IR spectrometer using signal between 1.8 and 2.2 µm and modelled to contain both a reflected and an emitted component. After this model is applied, the resulting number is a temperature which is represented by different colours with red being the highest and purple the coldest.


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The derived temperature varies from 260 ± 6 K to 329 ± 8K. Shadows are the coolest temperatures, and the point directly below the sun is hottest. These temperatures indicate that the thermal inertia of the surface (the quality of the surface describing the ability to conduct and store heat) is low. In other words, on Tempel 1, it is hot in the sun and cold in the shadows. A value for thermal inertia is estimated at <100 W/K/m²/s½.

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Blobrana


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Tempel 1
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Comet Tempel-1 could have been formed in the region of the solar system occupied by Uranus and Neptune today, according to analysis of the comet's debris blasted into space by NASA's Deep Impact mission. The observation supports a scenario for the solar system's youth, where the planets Uranus and Neptune may have traded places and scattered comets to deep space.

"Our observation is a definitive investigation revealing the composition of comet Tempel-1" - Dr. Michael Mumma, Goddard Space Flight Centre.

Mumma and his team used the powerful Keck telescope on top of Mauna Kea, Hawaii, to analyse in great detail light emitted by Tempel-1 gas ejected by the impact.
Using a spectrometer, the team was able to determine the comet's chemical composition by separating its light into its component colours.
Mumma is lead author of a paper on this research that appeared in Science on September 15th.


The development of Tempel-1 on impact night, as observed with NIRSPEC instrument on the Keck-2 telescope. (A – C): Three images taken with the slit-viewing camera, in light reflected from the polished slit plate. The white area in the centre is the coma, a cloud of dust and gas surrounding the comet. The black band extending left-right in each panel locates the spectrometer entrance slit. (A): The appearance of Tempel-1 just before impact. (B): The comet 27 minutes after impact. (C): The comet 69 minutes after impact.
Image credit: NASA/W. M. Keck Observatory/Michael Mumma

By observing Tempel-1 before, during, and after impact, the team was able to distinguish surface gas from the impact debris, and they discovered that the interior has a different chemistry.

"The amount of ethane (C2H6) in the cloud around the comet was significantly higher after impact than before" - Michael Mumma.

There are two possible explanations for this. In the first, the surface crust is different from the interior due to solar heating. The interior, however, is all the same. In the second, the interior is a mix of regions with different compositions because the nucleus is actually composed of smaller "mini-comets" (cometesimals), each with a different chemistry. Deep Impact could have just so happened to hit one of these cometesimals, while the gas seen before impact might have came from a different region on the comet with different chemistry. Multiple impacts in different regions of the comet would have been needed to determine which scenario is correct.
If the first scenario is correct, the comet could have formed in the region now bounded by the orbits of Uranus and Neptune, based on its interior chemistry. Different chemicals get frozen into a comet depending on its location. A comet that forms farther from the sun will have greater amounts of ices with low freezing temperatures, like ethane, than a comet that forms closer to the sun. By measuring the relative amounts of each chemical, astronomers can estimate where a comet formed.

Formation in this location supports a theory that the gas giant planets Uranus and Neptune formed closer to the sun than their current locations. The theory, proposed by Dr. Alessandro Morbidelli of the Observatoire de la Cote d'Azur, Nice, France, and his team, says that gravitational interaction between the gas giant planets and numerous small planets left over from the solar system's formation (planetesimals) brought the giant planets into an unstable orbital configuration.
Neptune and Uranus were tossed outward and could have exchanged orbits. As they migrated outward, their gravity disrupted a large disk of comets that had formed in the region where Uranus and Neptune currently reside. Some were scattered into deep space, to a roughly spherical region called the "Oort cloud" that surrounds our solar system at about 10,000 times the earth-sun distance. Others were directed to the Kuiper belt, a region beyond Neptune that extends to several hundred times the Earth-sun distance.

If some Kuiper belt comets have similar chemistry to some Oort cloud comets, it would support this model of the solar system's rowdy early days by showing that certain comets had a common origin despite very different final destinations. Tempel-1 shares certain orbital characteristics with the "ecliptic" comets, a group that likely comes from the "scattered" Kuiper belt.

"The amount of ethane in Tempel-1, however, is similar to the amount in the dominant group of comets that come from the Oort cloud region" - Michael Mumma.

Its chemical similarity to Oort cloud comets supports the idea that some Kuiper belt and Oort cloud comets formed in the same place. This research was funded by NASA, the National Science Foundation and the National Research Council.

source

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