The bombardment of comets
Possibly, comets brought water to Earth
To see exactly what is in the comet, it is necessary to analyse its substance with the help of different high sensitive devices, bringing samples to Earth. But aboard a small spacecraft such devices are difficult to place, because the size of the station Stardust 1,7×0,7×0,7 meters – about the same size as the Desk. How to take a sample of matter, flying from the comet’s nucleus at high speed? Space standards Stardust was moving slowly relative to the comet, about one and a half times slower than fly around the Earth artificial satellites. However, even this speed was several times greater than that of the bullet, the station flew over one second 6 km from the Contact of dust particles with the container of solid material at this speed (more than 20 thousand km/h) would have led to their strongest heating and evaporating. The only way to mildly catch and stop these dust particles, turned out to be a trap made of unique material – aerogel, which was established in 1931, but the big distribution has not received.
Now he takes on a second life thanks to its heat-insulating properties. 99.8% of the aerogel consists of air and 0.2% silicon dioxide, in other words, the quartz, and is a solid substance with a porous structure, resembling a sponge, the pores of which do not see their diametrical 20 nanometers (i.e. at the length of 1 mm is placed 50 thousand of such time). Aerogel . used at the station, Stardust, hit the “Guinness Book of records” as the solid with the lowest density of 3 mg/cm 3. It is 1,000 times easier than quartz glass, although their chemical composition is the same.
While approaching the comet the spacecraft resembled ready for battle knight, clad in armor, – shields of multiple layers of ceramic “fabric” Nextel were not only installed on the instrument compartment, and on each of the solar panels, spread out in two wings. It was assumed that these screens will protect the station from impacts of dust and even a small, pea-sized, stones. 31 December 2003 station Stardust entered the cloud of rarefied matter of the comet, stretching for hundreds of kilometers around its core. And on January 2, 2004 came close to the comet nucleus at a distance of 240 km. it Turned out that flying among the dust was not safe – on-Board sensors showed that the external (absorbing) layer of a protective screen has been broken big dust particles not less than 12 times. However, subsequent layers remained intact. Met three times especially dense jets of gas-dust emissions, during a passage through which the protective screen for a second hit about 1 million tiny particles. When the station approached the comet, the dust trap was pushed out of the protective container and positioned perpendicular to the flow of the material flying from the comet nucleus. The smallest particles of the comet, rushing with huge speed, they are stuck in Israeli, the thickness of which gradually slowed their rapid flight. In braking process, the dust particles left a footprint in the form of a narrow tunnel about 200 times its diameter. This trail and they will find with a microscope before removing for investigation. 6 hours after meeting with comet aerolia panel stuck in it a few tens of mg of dust was Packed in a protective capsule. Scientists expect that delivery on the Ground they will be able to detect not less than 1 000 dust particles of relatively large size is with diameter more than 15 μm (4 times thinner than a hair). In addition to collecting comet dust for the first time the station took pictures of the cometary nucleus from a very close distance. The detailed pictures showed a rather unusual form of relief and instead of the expected two or three gas jets averaged more than two dozen streams of gas and dust rising from under the surface of the comet. Judging by the pictures, the Sun-warmed ice in some parts of the core immediately becomes a gas, bypassing the stage of liquid state. A jet of this gas jut fly away into space at a speed of several hundred kilometers per hour. On Photos is clearly visible solid surface of the comet nucleus covered with craters by depth up to 150 m, sharp peaks with a height of 100 m and sharp cliffs. The largest crater diameter of 1 km is 1/5 of the diameter of the comet’s nucleus. The impression is that the core material is very strong, holding steep slopes of the crater slopes in pristine condition, do not allow them to crumble or spread. None of the three dozen celestial bodies in detail, photographed from space stations (the planets, moons and asteroids) similar relief is still not met. It is possible that such features of the structure of the surface characteristic of the nuclei of comets and solar-induced erosion.
Bombing in space
To penetrate deep into the comet’s nucleus and learn the properties of material not only on the surface of cometary nuclei, but also in the subsoil thereof – such a task would La put before the American automatic station Deep lmpact (“whack”), launched at the beginning of 2005 to the side of comet Tempel-1 . This comet has an elongated core size 11x5x5 km (slightly smaller than that of comet Halley) rotating once around its axis in 42 hours. Approaching the target, the station went on parallel with her course. After some time separated from it, the device lmpactor (“Drummer”), consisting primarily of large blocks of copper. While the machine flew to the nucleus of a comet, bumped into him a few small particles, slightly changed trajectory, “the Striker”. Using sensors that are configured to search for the brightest object, the device is restored to the desired direction of movement and continued on to the target.
A day later, on 4 July 2005, lmpactor at high speed of 10.3 km/s (37 000 km/h) collided with a comet. However, due to huge temperatures, encountered during impact, thermal explosion occurred, turning the device the size of a household washing machine, a mass of 370 kg in a cloud of dust and gas. As to the comet’s substance to its surface layer left by the explosion at a great height. It was a flash of light, very surprised researchers because it was brighter than expected. The ejected material is fully dispersed only after 12 hours. Processing the data obtained during the observation of this collision, showed that the substance of the upper layer of the comet is very different from that expected there to detect. It was thought that its core is a huge block of ice with inclusions of stone rocks, possibly in the form of small fragments like gravel. Actually it turned out that the comet nucleus consists of a very friable material, resembling not even a pile of stones, and a huge lump of dust in the pores which account for 80%.
When there was a collision of the probe with the comet’s nucleus, the ejected substance was off by a tall narrow column. This is possible only for very loose and light soil. whether its a denser substance, the dispersion of the emissions would have been lower and wider, and if the comet was made of stone, the material scattered in the form of a low and wide craters. The results of this spectacular experiment in space led to the emergence of a new model of the structure of cometary nuclei. In the past, the core was considered contaminated snow ball or snow-covered lump of soil, and now it is regarded as a very loose body, a slightly elongated shape (like potatoes), consisting of powder or dust. It remains unclear how such a “fluffy” substance can be preserved craters, hills and sharp escarpments of the surface which are clearly visible in images of the nucleus of comet Tempel-1, as obtained from the station itself Deep lmpact and separated from her drum machine, which gave the last image just before the collision. These detailed images show that the surface is not smooth and not covered with dust – it has a very distinct, sharp forms of relief and looks about the same as the surface of the moon, with many craters and small hills. Trying to combine the data obtained in a single picture, the researchers recalled the notorious Tunguska meteorite.