The Nucleus of Comet Tempel 1 - few meters AND few seconds?

[TomiKazi]

There appears to be a slight incongruity in the caption at the photojournal site from which this image originates. At 10km/sec, 4 seconds prior to impact the probe would have been 40km from the surface, not 'a few meters', right? Or am I missing something here.

I suspect the description meant to say it was 4msec - but then again, that would imply a VERY fast CCD capture and transmission; or it meant to say within a few kilometers of the surface - but then again, 40km is not a few. So I'm a bit at a loss of where this inconsistency comes from. Thanks in advance for any clarification on this.

[craterchains]

That one had me scratchin my head too,

[S. Bilderback]

The photo is a computer compiled image using image data from various photos, some taken up to 500km away and others within a few meter. That's why the greatest detail of the photo is just above the impact site.

[TomiKazi]

I understand the part about the image being a compilation of images taken at various distances from the target. What has me confused is the following:

The impact site has the highest resolution because images were acquired until about 4 sec from impact or a few meters from the surface.

Taken together with the speed of the probe, which was 10km/sec, the until about 4 sec part contradicts the few meters from the surface part, since 4 seconds from impact the probe was 40km away from the surface, no?

[ta152h0]

What I find fascinating is what looks like a deep fresh crater farther north. Wonder is there is any photographic evidence of a recent kabooom ??

[makc]

...is there is any photographic evidence of a recent kabooom ??

how about this one:

[S. Bilderback]

"Taken together with the speed of the probe, which was 10km/sec, the until about 4 sec part contradicts the few meters from the surface part, since 4 seconds from impact the probe was 40km away from the surface, no?"

I see your point, the next questions to ask are - what was the exposure time of the last image, how did the image stay focused at that speed? If the last exposure was near 4 sec., it could count for the discrepancy.

[neufer]

Explanation: Approaching the nucleus of comet Tempel 1 at ten kilometers per second, the Deep Impact probe's targeting camera recorded a truly dramatic series of images. Successive pictures improve in resolution and have been composited here at a scale of 5 meters per pixel -- including images taken within a few meters of the surface moments before the July 4th impact. Analyzing the resulting cloud of debris, researchers are directly exploring the makeup of a comet, a primordial chunk of solar system material. Described as a recipe for primordial soup, the list of Tempel 1's ingredients - tiny grains of silicates, iron compounds, complex hydrocarbons, and clay and carbonates thought to require liquid water to form - might be more appropriate for a cosmic souffle, as the nucleus is apparently porous and fluffy. Tempel 1's nucleus is about five kilometers long, with the impact site between the two large craters near the bottom.

The Nucleus of Comet Tempel 1 (in color)

This highly processed image is composed of numerous frames captured by both components of the Deep Impact spacecraft shortly before the impactor spacecraft crashed into the nucleus of comet Tempel 1 on July 4, 2005. The color comes from three frames captured through red, green, and blue filters on the flyby craft's High-Resolution Imager, which suffered from blurred vision. The detail comes from numerous images of the nucleus captured by the Impact Targeting Sensor. Since the two cameras had slightly different points of view, the color image has been warped to line up with the more detailed impactor image. Credit: NASA / JPL / UMD / Daniel Macháček and Emily Lakdawalla

• * Dimensions: 7.6 × 4.9 km
  * Density: 0.62 g/cm³
  * Escape velocity ~ 6.5 km/h (even Barney can run that fast)
  * Mass: 7.5 × 10¹³ kg
  * Rotation: 40.7 hours

<<Tempel 1 was discovered on April 3, 1867 by Wilhelm Tempel, an astronomer working in Marseille. It was subsequently observed in 1873 and in 1879. However, Tempel 1's orbit occasionally brings it sufficiently close to Jupiter to be altered. This event occurred in 1881 (closest approach to Jupiter of 0.55 AU), lengthening the orbital period to 6.5 years. Perihelion also changed, increasing by 50 million kilometres, rendering the comet far less visible from Earth. Photographic attempts during 1898 and 1905 failed to recover the comet, and astronomers surmised that it had disintegrated.

Tempel 1 was re-discovered 13 orbits later, in the 1960s after British astronomer Brian G. Marsden performed precise calculations of the comet's orbit, taking into account Jupiter's perturbations. Marsden found that further close approaches to Jupiter in 1941 (0.41 AU) and 1953 (0.77 AU) had decreased both the perihelion distance and the orbital period to values smaller than when the comet was initially discovered (5.84 and 5.55 years, respectively). These approaches moved Tempel 1 into its present libration around the 1:2 resonance with Jupiter. Despite an unfavorable 1967 return, Elizabeth Roemer of the Catalina Observatory took several photographs. [Her] June 8, 1967 exposure (Tempel 1 had passed perihelion in January) that held the image of an 18th magnitude diffuse object very close to where Marsden had predicted the comet to be.>>