Man has been to the moon. It has been the first step towards future exploration in space. When compared with the distances between Earth and the other planets, the distance between the Moon and Earth is very short indeed. Mars, the nearest planet to Earth is millions of miles away! Traveling to the planets will be man's next step. Such travels will be more challenging than the trip to the moon and certainly more exciting and dangerous. Recently, two American spaceships, Viking 1 and 2, landed on Mars trying to discover whether that planet has any life on it. So far the signs of life on Mars has neither been confirmed nor ruled out  . Russians have discovered that the surface of Venus is so hot that it is almost certain that there is no life there. Also the atmosphere of Venus is extremely dense and the pressure is nearly a hundred times greater than that of the Earth's atmosphere. Scientists believe man may find planets which have the same conditions as those we have on Earth, but man should realize Earth will be his only home for a long time and begin to love and care for it. Based on the passage, traveling to the planets will be   _  .
man's first step much easier and even more interesting for more exciting and dangerous man's final aim