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Post Info TOPIC: Comet 9/P Tempel 1
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RE: Comet Tempel 1
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ESA's XMM-Newton observations of Comet 9P/Tempel 1 revealed that the object is a weak X-ray source.



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These data were acquired on 4 July 2005 by one of the EPIC X-ray cameras on board the spacecraft during the post-impact observation phase.

XMM-Newton observed that Tempel 1 emits X-rays, as suspected from previous observations of comets, but this emission is very weak. It is not certain whether it is possible to obtain spectral data which indicate the mechanisms by which the comet's X-rays are produced.
Further analysis of the XMM-Newton data is needed to confirm this.

There are two theories to explain why comets emit X-rays. In the first theory, X-rays are produced by a charged exchange between neutral particles present in the comet's coma and ionised particles carried by the solar wind. This has been demonstrated already for several comets in the past.
The second explanation is that the X-rays are just solar X-rays scattered by the dust present in the coma. This could happen during comet outbursts, as observations of Comet Hale-Bopp indicated in 1996. A combination of both mechanisms is also possible.

Even without the task of analysing these weak X-rays, observing the X-ray emission from moving objects like Tempel 1 is already a complex enough task for an X-ray telescope. In fact, XMM-Newton is best suited to studying 'fixed' X-ray sources in the sky. Special planning and processing techniques were required to overcome this observational challenge.

During the observations, XMM-Newton was pointed in the direction of the comet as if it was fixed in the sky, and its instruments were exposed to the radiation (photons) coming from it.
The photons coming from the moving comet were received by the relatively stationary XMM-Newton instruments. Scientists used the arrival time and direction associated with each detected photon to deduce its distance from the comet's nucleus.
Every photon was then 'transformed' mathematically, as if it came from a 'virtual' comet fixed in the sky like the more distant stars.
In this way, scientists could treat the comet as a non-moving object.
Scientists then 'cleaned' the data files, by removing those times where the cosmic background radiation was disturbing the observations.

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This diverse landscape is the surface of comet Temple 1's nucleus as seen by the Deep Impact probe's Impactor Targeting Sensor.



Within minutes of recording the rugged view, the landscape had changed dramatically though, as the impactor smashed into the surface near the two large, half kilometre-sized craters at the centre.
Indications are that the probe penetrated well below the surface before vaporising, sending a relatively narrow plume of debris blasting back into space. Researchers are still speculating on the final size of the crater produced by the impactor, but material continues to spew from the impact site and has caused the faint comet to brighten significantly.
Determining the crater dimensions and analyzing the debris ejected from the comet's interior will provide premier insights into the formation of comet Tempel 1, a primordial chunk of our own solar system.


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The impact occurred at 07:52 CEST but because the comet has already set in Chile at that time, observers at the La Silla Paranal Observatory could only start observing several hours later.
The first observations were done in the infrared by TMMI2 at the 3.6m telescope at La Silla, at 21:20 CEST (still daylight in Chile).


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TIMMI2 images of Comet Tempel 1, before (left) and after (right) impact.

At sunset in Chile, all 7 telescopes of the La Silla Paranal Observatory went into operations.
The FORS2 multi-mode instrument on Antu, one of the 8.2m Unit Telescope of the VLT array, took stunning images, showing that the morphology of the comet had dramatically changed: a new bright fan-like structure was now visible.


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FORS2 images of Comet Tempel 1, before (top) and after (bottom) impact.

Other telescopes have provided observations of the comet as well.
NACO took some images of the central part of the coma, while UVES performed high-dispersion spectroscopy of the comet, in order to compare with the previous nights. First estimates indicate the emission lines to be more pronounced by 10 to 20 %.


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SOFI image in the J-band of Comet Tempel 1 after the impact.

At La Silla, the SOFI instrument at the NTT telescope, imaged the comet in the near-infrared. An image in the J-band also shows the dust shell from the impact in the south-western quadrant of the coma.
The very inner coma (indicated by the white box) shows on-going enhanced activity compared to the pre-impact level.

Scientists using the Swift satellite also witnessed the impact.

Swift provided the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting optical light, ultraviolet, X-rays and gamma rays.
Different wavelengths reveal different secrets about the comet.
So far, after a set of eight observations each lasting about 50 minutes, Swift scientists have seen a quick and dramatic rise in ultraviolet light, evidence that the Deep Impact probe struck a hard surface, as opposed to a softer, snowy surface.
More observations and analysis are expected in the coming days from teams at NASA and Penn State and in Italy and the United Kingdom.


29 June (before impact): Movie showing the comet Tempel 1 tracking across the sky on 29 June 2005 using the Swift Ultraviolet/Optical Telescope (UVOT) through an ultraviolet filter centred on 2600 Angstroms. This sequence covers 40 minutes of elapsed time.




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For roughly an hour around impact time, the Spitzer space telescope took in data every two seconds.
That gave astronomers a `continuous view` of the event.
After that phase, Spitzer slowed down its data collection rate and broaden its wavelength coverage, allowing astronomers to identify cosmic particles with longer wavelength emission.

Spitzer will continue to collect data on the comet until August 17, 2005.

"Spitzer has a crucial role in this mission. Data from Spitzer will be able to tell us exactly what comes out of the comet, in a wavelength region that no one else can explore" - Dr. Carl Grillmair, staff scientist at the Spitzer Science Centre.

More later....


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The Hubble Space Telescope has snapped an image of Comet 9P/Tempel 1 just a few days before the Deep Impact spacecraft rendezvoused with the comet.


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This image, taken on the morning of June 30, 2005, shows an undisturbed and quiet comet.
This Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) image of Tempel 1 shows a slightly larger view of the comet than was seen in Hubble images released last week.
This image of the comet shows the dusty inner coma around the nucleus, but the solid nucleus itself is below Hubble's resolution. The nucleus was at a distance of 134 million kilometres when the image was taken.

The ACS/WFC image is a composite of data taken with blue and red filters onboard Hubble.
A quiescent comet is seen in this pre-impact image along with elongated star trails. As the telescope was locked on the movement of the comet, the background stars left small trailed arcs during the time the exposures were taken.


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At 05:52 GMT, the Deep Impact spacecraft's probe smashed into the surface of Comet Tempel 1's nucleus at ten kilometres per second.



The well-targeted impactor probe was vaporised as it blasted out an expanding cloud of material, seen here 13 seconds after the collision.
The image is part of a stunning series of frames documenting the event from the high resolution camera onboard the flyby spacecraft.
Tempel 1's potato-shaped nucleus is approximately 5 kilometres across as seen from this perspective.
Camera's onboard the impactor probe were also able to image the nucleus and impact site up-close ... until about 3 seconds before the impact.
Of course, telescopes nearer to planet Earth followed the event, detecting a significant brightening of comet Tempel 1.

More pictures

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Dust and gas are seen in these images of Comet 9P/Tempel 1, as observed with the 1-metre ESA Optical Ground Station (OGS) telescope, located at the Observatorio del Teide on Tenerife, Canary Islands.

Two different filters have been used in different visible light observations to study different aspects of the comet's nature. Red 'broadband' filters allowed the detection of dust, while blue 'narrowband' filters, filtering only carbon gaseous compounds, allow the observations to concentrate mainly on the gas emissions of the comet.



The first set of images here were taken with a broadband red filter, four days before and about 15 hours after the impact respectively. The images were exposed for 10 minutes and show the dust coma of the comet. The dust brightness has increased by 50 percent.

A strong jet has recently appeared as a direct result of the impact, pointing north-north-east. The overall coma is very asymmetric in appearance. All structures must have been created by the outburst triggered by the impact.



The second set of images of Tempel 1 from the OGS telescope use a narrowband filter (C2 emission band). They show the coma gas mixed with smaller-sized dust particles than observed in the broadband red filtered image.
The observations were taken two days before and about 16 hours after the impact respectively. Also here the coma brightness has increased by 50 percent. Again the same strong jet is visible.



In the third set of images, Tempel 1 is seen about 16 hours after the impact. The two images show the refection of blue (BC filter) and red (RC filter) light from the dust cloud surrounding the comet nucleus.
These reflections show different dust particle sizes, with blue particles being smaller than red particles.
It is clear that the jet structure of the smaller dust particles points towards the north (BC image), whereas the jet composed of larger dust particles (RC image) is rotated by about 45 degrees towards the north-east.
This means that the direction in which the dust particles were ejected from the comet nucleus after impact seems to depend on the particle size.

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Image credit: NASA/JPL-Caltech/UMD


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-- Edited by Blobrana at 00:00, 2005-07-05

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Nasa quicktime movie of impact

-- Edited by Blobrana at 22:54, 2005-07-04

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These pictures of comet Tempel 1 were taken by NASA's Hubble Space Telescope. They show the comet before and after it ran over NASA's Deep Impact probe.

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