Q. Are the planets perfectly round?
A. No. All planets spin, and this makes them flattened at their poles. Look especially at pictures of Jupiter and Saturn, the fastest-spinning planets, and see how squashed they are at the poles.

Q. Which planets has the shortest day?
A. Jupiter. Its day lasts less than 10 hours.

Q. Which planet has the longest year?
A. Pluto. Its year lasts more than 247 Earth years.

Q. Which was the last planet in the Solar System to be discovered?
A. Again Pluto, in 1930.

Q. Is Pluto the farthest planet from the Sun?
A. Usually, but not always. Its path sometimes brings it closer to the Sun than Neptune.

Q. Are there planets going around other stars?
A. Yes, astronomers have discovered more than 200 planets in orbit around stars other than the Sun.

Q. How long would it take radio signals to reach Earth from Pluto?
A. About 5½ hours. Radio signals travel at the speed of light – 186,282 miles (300,000 kilometers) per second.

Q. Which planets have the most moons?
A. Jupiter and Saturn, with at least 60 each.

Q. Which moon is closest to its parent planet?
A. Phobos. It circles Mars at a distance of just 5,761 miles (9,270 kilometers).

Q. What are Saturn's rings made of?
A. Millions upon millions of icy rocks, ranging in size from less than an inch to several feet in diameter.
Q. Which is the biggest volcano in the Solar System?
A. Olympus Mons on Mars. It is 15½ miles (25 kilometers) high and 370 miles (600 kilometers) across at the base.

Q. Which is the biggest canyon in the Solar System?
A. Valles Marineris, again on Mars. It is nearly 2,500 miles (4,000 kilometers) long, as much as 125 miles (200 kilometers) wide, and 3¾ miles (6 kilometers) deep – many times larger than our own Grand Canyon.