A: Mr. Liu, can I ask you some questions about Mars?

B: Sure, go ahead.

A: Is Mars hot?

B: Mars might look red-hot. But don't let its color fool you. Mars is much farther away from the sun than Earth. So it gets less light and heat.

A: Why "Mars"?

B: Mars takes its name from the Roman god of war (罗马战神). In China, the red color makes people think of fire. So they call the planet "fire star".

A: Are there Martians on Mars?

B: Unluckily, we haven't found any "people" on Mars yet. They are kind of like Santa Clause. Nobody can see them, but many people believe they are real.

A: Will we lose weight on Mars?

B: Living on Mars could be good in many ways. For example, you might not need to go on a diet to lose weight. If you weigh 50kg on Earth, you will only weigh 19kg on Mars. This is because the surface gravity (表面重力) on Mars is only about 38 percent of that on Earth. Do you want to know your weight on Mars? Just multiply your weight by 0.38. That's it.

A: Thank you. We know a lot about Mars now.

B: You're welcome.

Imagine that you have woken up on the first day of your vacation. You enjoy a delicious breakfast, take a walk on the beach, and read the morning newspaper as you drink coffee. You are feeling happy and relaxed. But you may start to feel bored by the time the late afternoon comes around!

If you have ever felt like this, you're not alone. It turns out that having unlimited (无限的) free time is not always as great as we expected. What is the best amount (数量) of free time for our happiness?

Researchers tried to answer this question by surveying tens of thousands of people, collecting data (数据) on how they spent their time and how happy they were. After looking at the data, the research team found that having less than two hours of free time a day, was not enough to be happy. People with under two hours of free time a day usually had more stress. It means that they were simply too busy with work to get their happiness.

The fact that being too busy cuts happiness is true. It might lead to the answer that more free time is simply better. Surprisingly, having a lot of free time is not a panacea (灵丹妙药) for happiness. People surely get a certain sense of joy from finishing tasks. Having more than five hours of free time a day makes us lose the sense of joy. It is in fact cutting our happiness. But I think it is how we spend our free time that matters. When free time is used in more active ways, like playing a team sport, then five or more hours a day can keep of even produce happiness. However, spending five or more hours of free time alone can stop happiness.