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.

Mars（火星）is a planet and is the 4th closest planet to the Sun. The distances from the Sun to Mars is more than 141 million miles. Mars is the largest planet in the solar system（太阳系）, which makes Mars the 2nd smallest planet in the solar system. Mars is one of the four planets in the solar system that is a rocky planet. These rocky planets are called “Terrestrial（类地的） Planets”.

It’s not known when Mars was found and by whom as Mars has been known for a very long time, and one of the planets that can be seen from the Earth without a telescope（望远镜）. Mars’s orbit（轨道）around the Sun is the 4th fastest orbit of all the solar system planets. Mars is red in colour and is very cold. Not the coldest of planets in the solar system but very cold all the same. The temperature on Mars is on average 80 degrees, and can get a lot colder at times.

At times in the summer near the Mars the temperature can reach 70 degrees. You may think it’s warm enough to live; however, the atmosphere（大气层）is over 95%. Mars orbits the Sun in 687 days, which means 1 Earth year on Mars is 687 days.

The idea of life in outer space has been talked about for a long time. Some scientists say that life development on Earth was far too unlikely for it to have happened anywhere else. Things had to be perfect for us to make it on this planet.

Other scientists say that space is too big. Stars and other planets are far too numerous for there to be no other life in the universe.

For many years, there have been reports of visitors from other planets. People all around the world have claimed to see alien spaceships or even aliens themselves.

There have been glimpses of these so-called UFOs (unidentified flying objects) flying through the air and they have even ben captured on video. Some Americans believe that the U.S. Army found an alien spaceship crashed in the desert and then lied to the press about it. Although these sightings may be true, scientists have not found significant evidence that aliens exist.

If you go out into the countryside on a clear night and look up, you can see thousands of stars. Those stars make up a tiny part of our universe. There are more stars, planets, and galaxies than we can count. Even the smartest scientists can’t even come close to defining how big space is. The number of possible stars and planets out there is bigger than our ability to count. If we are really on the only planet that can sustain life, then we are very special in a universe full of amazing things.