(image above: Wikimedia commons).

Comet Tempel 1 is a short-period comet with an orbital period of approximately 5.5 years and a perihelion of about 1.5 AUs (an AU or "astronomical unit" is a unit that is roughly the mean earth-sun distance, and the perihelion of 1.5 AUs means that Comet Tempel 1's orbit takes it further from the sun than the orbit of Mars but not as far as Jupiter).  

The comet was discovered in April of 1867 by Ernst Wilhelm Leberecht Tempel, of France, who was looking for comets at the time (see this discussion of the comet's history from the NASA webpage). As that page explains, the comet was observed that year using telescopes until it was lost from sight in August of 1867, but it was reacquired at its next visit in 1873, then again in 1879 (when Tempel himself recovered visual observation of his discovery), after which it was lost to observers on earth until 1967.

In 1967, Professor Elizabeth Roemer, an American astronomer, took several photographic images of the area in space where the comet was predicted to reappear.  Her initial inspection of the plates turned up nothing, but upon re-checking them the following year she noticed a very faint (18th magnitude) object near the location that the comet's return had been calculated to be, in the plate from June 8th of 1967.  Later analysis of the comet confirmed that this image was indeed Comet Tempel 1, reacquired after all those years.

On its next visit in 1972, Professor Roemer and another astronomer successfully recovered observation of Comet Tempel 1, and it has since been observed on every subsequent visit, according to the NASA site linked above.  

The most remarkable history of the comet, however, was yet to take place.  In 1999, planning began for a mission to study the composition of comets by firing a "smart impactor" into a comet, releasing material from the comet into space from the impact.  This material could then be observed up close by the spacecraft that had fired the impactor, and the spectrometry and other data studied to reveal information about the makeup of the comet itself.

The mission was dubbed "Deep Impact," and the Deep Impact spacecraft was launched from Cape Canaveral Air Force Station (Cape Kennedy) in January of 2005, on its way to a rendezvous with Comet Tempel 1 in July of the same year (see this NASA page for details of the launch).  The Deep Impact spacecraft was a two-part system consisting of the flyby spacecraft (described as being about 11 feet by 8 feet by 7 feet) and the smart, instrumented, self-guiding impactor (which weighed about 816 pounds counting fuel at the time it was launched).  The impactor was made largely of copper (it was 49% copper) to minimize interference with the comet's material.

At this time eight years ago, Deep Impact was speeding towards Tempel 1, taking images as it approached.  From the images, scientists have calculated that the comet's nucleus is roughly 7.6 kilometers (4.7 miles) by 4.9 kilometers (3.0 miles), and venting or outgassing sporadically as it orbits the sun.  At twenty-four hours before intended impact, the impactor separated from the flyby vehicle and shot towards the comet's nucleus.

What happened next is astonishing.  The impactor successfully struck the comet and created an enormous cloud of debris (often referred to as the "ejecta" by scientists writing about the event).  The spectral analysis revealed a host of amazing material from the comet, including organic material!  How did that get there!?

In addition to this perplexing discovery, scientists found numerous materials in the debris cloud that also create some explanatory difficulties.  This discussion of the analysis of the ejecta pubished in 2006 indicates that the spectral analysis of the debris thrown up by the tremendous impact included: "both crystalline and amorphous (glassy) silicates, amorphous carbon, carbonates, clay minerals (phyllosilicates), water in both the gaseous and solid states and sulfides."  This page on the NASA website also discusses the material ejected when the impactor struck the comet.

Dr. Walt Brown, the originator of the hydroplate theory, provides extensive discussion of comets in his book (which can be read in its entirety online or purchased for reading in hardcopy), because comets have so many features which confound conventional theories, but which can be satisfactorily explained by the hydroplate theory (previous blog posts on this topic can be found here and here, for example, or found by using the blog-specific search window at the upper left of this page). 

Dr. Brown points out that the ejecta from the impact of the 2005 mission pose numerous problems for conventional comet theorists.  For example, the fact that the comet contains crystalline dust is difficult to explain if comets form in deep space.  Dust formed in outer space should be noncrystalline, posing a serious problem to the theory that comets form in a hypothetical "Oort cloud" beyond the solar system, as well as to other theories that posit a deep-space origin for comet dust, as Dr. Brown explains in the section of his book comparing various comet-origin theories in detail (that section begins here).  

Dr. Brown also notes that the organic material found in the comets poses serious problems for most conventional comet theories.  Vegetation or bacteria capable of producing the organic readings found in the spectra of Comet Tempel 1 would not be expected to originate in the cold, dark reaches of space where most conventional theorists believe comets come from.

Additionally, note that the 2006 list of debris ingredients includes silicates (which Dr. Brown points out contain considerable oxygen, "a rare commodity in space"), carbonates (they found calcium carbonates, or limestone, a mineral that forms in liquid water -- something difficult to explain in the frigid vacuum of space where the Oort cloud is supposed to reside), and clay (another mineral substance that requires liquid water).

All of these findings, however, including the presence of organic methane in the comet's ejecta, are completely predictable if the origin of comets was the planet earth!  According to the hydroplate theory, comets originated when subterranean supercritical water was ejected at tremendous velocities during the events surrounding a catastrophic flood in earth's past.  

Dr. Brown's explanation of this comet-origin theory can be found in the paragraph that begins below the long table (Table 13) on this webpage (a little over halfway down the webpage).  He explains that: "Carried up with the water were eroded dirt particles, minerals that form only in scalding-hot, high-pressure, liquid water, pulverized organic matter (especially cellulose from preflood forests), and even bacteria."  This explanation accounts for all of the surprising features of the composition of Comet Tempel 1.

For example, silicates are one of the most common components of earth's crust, and the fact that they contain oxygen is no problem if they originated on earth.   According to Dr. Brown's theory, the material that escaped earth's atmosphere and formed comets originated in the hot, mineral-rich water that had been trapped beneath the earth's surface under great pressure.  This theory would explain the presence of minerals and clays that form only in the presence of hot, liquid water (see this portion of Dr. Brown's book, point 7 near the bottom of the webpage).  Dr. Brown's theory also explains the organic materials: "Organic compounds—including methane, ethane, and the amino acid glycine—are found in comets,1 because that water contained pulverized vegetation from preflood forests (as well as bacteria and other traces of life) from within hundreds of miles of the globe-encircling rupture."

Further, comets contain significant amounts of heavy hydrogen -- about twice the amount that is found in the oceans on earth today.  This actually accords quite well with the hydroplate theory:
Comets are rich in heavy hydrogen, because the water in the subterranean chambers was isolated from other water in the solar system. Our oceans have half the concentration of heavy hydrogen that comets have. So, if half the water in today’s oceans came from the subterranean chambers (as assumed on page 118), then almost all heavy hydrogen came from the subterranean chambers. (This will become even more clear after reading the radioactivity chapter on pages 350395.)  
Other theories have difficulty explaining the presence of this heavy hydrogen because, as Dr. Brown explains, "The concentration of heavy hydrogen in comets is 20-100 times that of interstellar space and the solar system as a whole.  Evidently, comets came from an isolated reservoir."

This information is probably not common knowledge to many members of the general public.  This NASA page discussing the ejection plume mentions the "substantial amount" of organic material measured and speculates that other similar comets "could have brought this material to Earth early in our planet's history."  Such speculation, however, does not provide much detail as to how that organic material could have gotten into the comets in the first place.  A far more likely conclusion at this point, given all the evidence discussed above, seems to be that earth sent the organic material out into space, rather than the other way around.

The evidence in support of the hydroplate theory is extremely wide-ranging and not limited to our planet (although there is plenty of evidence here on earth as well, from the tops of the tallest mountains to the bottom of the deepest trenches of the Pacific).  The mysterious properties of comets rank high among the list of evidence that is very difficult for conventional theories to handle, but which strongly support the hydroplate theory's explanation of the events of the ancient past.