The matter surrounding a comet’s core is vaporized and forms a very bright halo of gases and an enormous cloud of hydrogen envelopes the head of the comet.
A comet is a tiny, icy body in space that may be identified by its stunning tail when viewed from Earth. Only when a comet is getting close to sun, the ice and particles that make up the comet's core heat up and start to dissolve. 
Therefore,the material encircling the centre vaporises and creates a very bright halo of gases and a sizable cloud of hydrogen. Most comets follow a solar orbit. The atmosphere of gas created by the ice melting is what causes the coma.
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the breakdown of food molecules
        
                    
             
        
        
        
Each time one organism eats another organism, a transfer of energy occurs.in the form of sugars which an organism breaks down for energy.