The composition of a planet can be checked from the radiations of the spectrum. Large number of dark lines can be found in a spectrum. From these dark lines we can find the various elements existing on that surface. If we want to check that which component is present in large amount and which is present in small amount. Then it can be done by checking the intensities of the spectrum lines.
From the observations it is found that the percentage amount of nitrogen gas present in earth’s atmosphere is nearly 78%, oxygen is 21% and carbon dioxide is .03%. The remaining percentage is of the water vapors, hydrogen gas, etc. The atmosphere of Jupiter planet consists mainly of methane, helium and hydrogen. Mars and Venus consist mainly of carbon dioxide
