  Since 990 is divisible by ten, the answer is 990. If you were rounding off 994 the answer would also be 990. If you were rounding off 995, the answer would be 1,000.
Jupiter is the largest and most massive planet in the solar system. It was named after the chief Roman god. It is a gas giant composed of liquid and gaseous matter, and has many moons. Some of the storms in its atmosphere have lasted hundreds of years.
Jupiter is made up predominantly of hydrogen. The simple, basic gas, a prime ingredient on the sun, accounts for 90 percent of the atmosphere. Nearly 10 percent is composed of helium. A very small fraction of the atmosphere is made up of compounds such as ammonia, sulfur, methane, and water vapor. Traveling from the outermost edges of Jupiter toward its center, pressure and temperature goes up. These increases cause the gases to separate into layers.