Top science stories of 2013: Mars, a new mammal, a meteor

WASHINGTON -- It has been a thrilling year of discovery in many areas of science, but also a sobering time -- federal funding cuts threaten the future of innovation, and rising carbon dioxide levels foreshadow environmental and health challenges linked to climate change.

This was the year we learned that Mars was habitable billions of years ago, and also that Lady Gaga reportedly intends to be the first artist to sing in outer space in 2015 (will the papa-paparazzi follow?).

Let's take a spin around some of the major science stories from 2013:

In 2012, we celebrated the spectacular acrobatic arrival of NASA's Curiosity rover on Mars. But this year, Curiosity proved its worth as an extraterrestrial scientist, bringing humanity the tantalizing knowledge that life could have once thrived on Mars.

Throughout 2013, scientists announced results from the rover's analyses that revealed new secrets of the Red Planet's history. Clay formations in Mars' Yellowknife Bay indicate an environment that was once favorable to microbial life. The soil contains about 2% water by weight. We also know more about the composition of the planet's atmosphere, which is only 1% as thick as our own.

Meanwhile, a company called Mars One announced its intentions to land four lucky astronauts on Mars in 2025 to begin the first human colonies there. The technology doesn't exist yet to bring anyone back, the company said, so whoever goes will have to stay. More than 200,000 prospective astronauts found this idea attractive enough to apply.

A different group, the Inspiration Mars Foundation, said it wants to send a man and a woman to pass by Mars in 2018, in a round-trip flight without stopping. This made us wonder: Could you survive 501 days in space with your spouse?

Buzz Aldrin, best known for his Apollo 11 moonwalk, has Mars on the mind, too. He wrote on CNN that "we should direct the focus of NASA efforts on establishing a permanent human presence on Mars by the 2030 to 2040 decade."

For more on this CNN story, click here.