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Moment of truth
The Voyager I spacecraft is the most distant man-made object in the universe. It was launched in 1977 and as in 2002, it was more than 8 billions miles from the Earth.

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ptyalin Biol.
Also called salivary amylase, it is an enzyme that digests carbohydrates. It is present in mammalian saliva and is responsible for the initial stages of starch digestion, into maltose and dextrin. The enzyme works at a slightly alkaline condition (pH 5.6-6.9). When it is swallowed, the enzyme is inactivated by the gastric acid in the stomach.

pulsar Astron.
Object that emits radiation in the form of rapid pulses with a characteristic pulse period and duration. Generally used to describe the pulsed radiation from a rotating neutron star.

Punnett Square Biol.
A chart that shows the possible combination of genes that are passed from one generation to another. It can show probability of occurrence of phenotype or genotype. It indicates how traits are passed from one generation to the next, as was discovered by G. Mendel in 1860s.

pumice rock Geol.
An acidic igneous rock which formed from volcanic lava that cooled quickly above ground. It is porous with full of cavities due to gasses that were escaped while liquid lava is cooled and solidified. It is also very light and can even floats in water. Pumice rock is in fact a siliceous glass and not a mixture of minerals. It is used as decorative landscape stone and, when ground to powder, as an abrasive and for polishing.

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