Are we humans alone in space? Scientists have been working on this question for a long time. And recently, new discoveries offer more hope that some form of life existed on Mars in the past, and perhaps is still there at present.

According to a new report in the book Science, the Mars Explorer Curiosity has found more methane (甲烷) in the Martian air. It might suggest the possibility of life.

During the last 20 months, Curiosity has found methane many times, and four of them, it tested at a level 10 times higher than usual. “It’s a great increase,” said Christopher Webster, the lead scientist.

This new finding has made a big change. In September 2013, Curiosity found almost no sign of methane on Mars. Just weeks later, however, the explorer picked up the gas.

Methane is also found in Earth’s air, and comes from animal and plant life, as well as from the environment itself. If there’s methane in Mars’ air, where is it coming from? Scientists aren’t sure.

“There are many possible sources, such as actions between water and rock,” guessed Sushil, a scientist of the Curiosity team.

But the scientists have left the possibility open that microbes (微生物) could be the methane’s source. Also, for the first time, Curiosity found other organisms (有机物) in the rocks of Mars. Organisms are thought to be the basis to form life. Scientists aren’t sure where these organisms come from. They could either have formed on Mars or landed on Mars by meteorites (陨石).

For the next three years, Curiosity will keep looking for more organisms in rocks and exploring Mars.

“Is there life out there?” is a question which scientists are trying to answer. They look for life in space. In recent years, they have turned their attention to Europa, the sixth closest moon of Jupiter (木星).

Europa is a little smaller than the moon and is covered by ice. Its surface is too cold for anything to live there. Scientists want to know what lies under the ice, for that is where any life on Europa would most likely be.

For years, scientists believed all life on the earth depended on the sun. The discovery of chemosynthetic (化学合成的) life has changed scientists’ idea—planets with oceans (海洋) and hydrothermal vents (热液喷口) might also support life.

Europa does have oceans. In fact, Europa appears to have more oceans than the earth does. The ice on this moon’s surface covers what appears to be moving water. Do these oceans have hydrothermal vents? Scientists do not know yet. If they do, the oceans of Europa might support life. Only a space travel to Europa would tell for certain.

Scientists are studying the closest possible environment they can find on the earth: Lake Vostok. Like Europa’s oceans, Lake Vostok is miles under a frozen surface. It does not receive direct sunlight, either.

So like Europa, the lake cannot support photosynthetic (光合作用的) life. If scientists find life in the lake, it would support the idea that there might also be life on Europa.