Human: Why is it that we haven’t found any planets that are similar to Earth? Assistant: 
Well, we haven’t found any Earth-like planets yet. But we haven’t searched very hard. If you look at the number of planets that have been discovered, you’ll see that we have found more than 20000 planets in the last decade. And the number keeps growing! There are more than 20 billion stars in our galaxy alone. So there are billions of planets that we haven’t discovered yet.