Is there intelligent life on other planets? For years, scientists said “no” or “we don’t know”. But today this is changing. Seth and Alex are astronomers (天文学家). They believe there must be intelligent life on other planets. They also think we might soon communicate with these beings.

Why do Seth and Alex think intelligent life exists on other planets? The first reason is time. Scientists believe the universe (宇宙) is about 12 billion years old. “This is long enough for other planets to have intelligent life,” say Seth and Alex. The second reason is size—the universe is so vast. “Tools like the Hubble Telescope (哈勃望远镜) have shown that there are at least 100 billion galaxies (星系) in the universe,” says Seth. “And our galaxy, the Milky Way, has at least 100 billion stars. Some planets going around these stars might be similar to Earth.”

In the past, it was hard to look for signs of intelligent life. But now, powerful telescopes allow scientists to discover smaller planets—the size of Mars or Earth—in other solar systems. These planets might have intelligent life.

Have intelligent beings from space already visited Earth? “Probably not,” says Alex. “It’s a long way away. However, intelligent beings may contact us in other way, such as using radio signals. In fact, they might try to communicate with us in the past, but we didn’t have the right tools to receive their messages. However, this is changing. By 2025, we could make contact with other life forms in our universe and we even might help each other.”

Venus (金星) is close to the Earth. It is the second planet from the Sun. The Earth is the third planet from the Sun. Venus is similar (相似的) to the Earth in size and mass (质量). So people often describe it as “the Earth’s sister planet”.

Scientists have been learning about Venus for a long time. First, they looked at Venus through telescopes (望远镜). But Venus is covered with thick clouds. Scientists could not see Venus well through the clouds. So they made guesses at it.

For a long time, scientists thought that Venus had water and plants. They thought Venus might have animals too. But they didn’t know for sure.

Then scientists found a way to learn more about Venus. In the 1960s, they began sending probes (航天探测器) to Venus. The probes flew through the thick clouds. They took pictures of Venus up close. They found out many things too. The probes sent the pictures and things they found out back to the scientists.

Scientists have worked out when our Sun will die. It won’t be any time soon. It will be in 10 billion years. The scientists are from the University of Manchester in the UK. They predict that in about 5 billion years from now, the Sun will turn into a “red giant”. This is the scientific name given to a star at the end of its life. When our Sun becomes a red giant, its centre will shrink (收缩) . Its outer layers will expand (膨胀) as far as Mars. This means Earth will be burnt and disappear. After our Sun turns into a red giant, it will become a bubble of gas and space dust. The scientists say no humans will be on Earth when the Sun dies out.

The Sun is still quite young in space years. It is just 4.6 billion years old. This means it is only around one third into its lifespan (寿命) . Professor Albert Zijlstra, a scientist from the University of Manchester, explained what happens at the end of a star’s life. He said, “By this point in the star’s life, it is running out of fuel. Then it turns off and dies.” Professor Zijlstra was happy that modern science can count the age of stars and what will happen to them. “We even have found out what the Sun will do when it dies.” He said.