- NASA says there really could have been life on Mars
- Voyager 1 is the first human-made object to leave the solar system
- Scientists discover a new adorable mammal called the olinguito
- Asteroids pass by, and a meteor explodes over Russia
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:
Mars is the word
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."
Elsewhere in space
Further afield, one of the biggest space milestones of the year was the crossing of Voyager 1 out of the solar system. There's no border crossing agent out there, so scientists had to figure out on their own whether the probe had truly entered uncharted territory.
The probe, which launched with its twin, Voyager 2, in 1977, made history as the first human-made object to leave the heliosphere, the magnetic boundary separating the solar system's sun, planets and solar wind from the rest of the galaxy. We didn't get confirmation from scientists until well after the actual event took place, though. A study in the journal Science suggests the probe entered the interstellar medium around August 25, 2012.
Also, scientists put together a picture of the universe as a baby, in greater detail than ever before. Thanks to the new data from the European Space Agency's Planck space telescope, which studies light left over from the Big Bang, scientists now believe that the universe is about 100 million years older than they thought.
A space telescope with a different mission, called Kepler, gave us hope for finding distant planets with life, but also suffered serious setbacks.
Three Kepler planets announced this year, located about 1,200 light-years away, are considered some of the best candidates so far for hosting life. And astronomers still have two years' worth of Kepler data to plow through, said Bill Borucki, the project's principal scientist. (Using different instruments, astronomers separately found other potentially habitable planets in the Gliese 667 system).
The Kepler space telescope has led scientists to believe that most stars in our galaxy have planets circling them. But the spacecraft ran into some trouble this year: The failure of a control mechanism used to keep the device focused on distant stars with pinpoint accuracy. But NASA says it still hopes to find another role for the craft, which has confirmed the existence of more than 135 planets since its launch in 2009.
In the sky, closer to home
As we tracked the progress of machines that humanity sent out of this world, we also watched out for approaching space rocks -- and not all of them flew by gently.
A whopper of an asteroid gave Earth its closest shave in recorded history. At 150 feet wide, "2012 DA14" slipped in below the moon's orbit on February 15 and squeaked by our planet just 17,200 miles from its surface.
In a twist worthy of Tolstoy, as astronomers watched that well-tracked rock approach, a different asteroid plunged into Earth's atmosphere and exploded high over the Russian city of Chelyabinsk.
Scientists determined the meteor was about 60 feet (17 meters) across and packed the punch of about 30 Hiroshima-type atomic bombs when it blew up. Researchers have been collecting and studying the fragments ever since, and in October, a suspected chunk weighing 570 kilograms (1,257 pounds) was hauled out of a nearby lake for study.
NASA's Near Earth Object Program keeps a close eye on the asteroids that pass the planet almost daily, but they don't catch everything. Ukrainian astronomers discovered asteroid 2013 TV135 on October 8, while NASA was closed during the government shutdown. The asteroid had already passed by Earth on September 16.
Old species and new
Back on Earth, the animal kingdom got several important additions this year. Some had been extinct for millions of years; some are alive now, and were just hard to find.
Archicebus achilles was the name of the species represented by the oldest primate skeleton found, as described in the journal Nature in June. It is considered to be a missing link between two groups: the anthropoids and the tarsiers. The 2.8-inch-long cutie lived about 55 million years ago.
Then along came a different creature that looks even more cuddly, and it's alive today. Called the olinguito, the Smithsonian described the mammal's appearance as a "a cross between a house cat and a teddy bear," even though we know the latter isn't a real animal. Such discoveries don't happen often; the olinguito is the first mammalian carnivore species to be newly identified in the Americas in 35 years, says Kristofer Helgen, curator of mammals at the Smithsonian's National Museum of Natural History.
The Cape Melville Leaf-Tailed Gecko is also among the species discovered in 2013. This primitive-looking lizard, along with two other vertebrates and a "host of other interesting species" that may also be new to science, have been isolated in a remote mountain range in Australia for millions of years.
Probing the world of ancient humans
We're also learning more about the world of our ancient relatives, although there's not enough information to use the word "ancestor."
A remarkable find in Dmanisi, Georgia, gave us the most complete skull ever of an individual from the early Homo genus. It is the fifth example of an ancient hominid, a bipedal primate mammal that walked upright, at this site.
Scientists involved in the discovery proposed that these individuals are members of a single evolving Homo erectus species, examples of which have been found in Africa and Asia. They also said that what have traditionally been called distinct species from this period -- Homo ergaster, Homo rudolfensis and Homo habilis -- could actually be variations on a single species, Homo erectus.
That's a radical departure from how ancient human relatives are currently classified. Other experts said the skull is an important find, but disagreed with the controversial theories regarding Homo erectus membership.
Another potential game-changer was the reconstruction of the nearly complete mitochondrial genome of an ancient human relative. It is the oldest DNA to be recovered from an early humanlike species, and is about 400,000 years old.
The sequencing technique used in this study, said senior author Svante Paabo, "opens a possibility to now do this at many other sites, and really begin to understand earlier human evolution."
It's heating up on Earth
Scientists are also hoping to help our own species understand the perils associated with climate change. The phenomenon raises the likelihood of severe weather events and is predicted to damage agriculture, forestry, ecosystems and human health.
A key symbolic moment was when the average concentration of atmospheric carbon dioxide hit 400 parts per million in Mauna Loa, Hawaii, in May. Such levels haven't been seen in about 3 million years, said J. Marshall Shepherd at the University of Georgia.
Rising atmospheric CO2 leads to overall warming. By 2100, the Earth will be warmer than ever, authors of a Science study said in March.
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change, released in September, found increasing evidence that ice sheets are losing mass, glaciers are shrinking, Arctic sea ice and global snow cover is decreasing, and permafrost is thawing in the Northern Hemisphere. And the researchers said they were more certain than ever that humans are responsible for at least half the increases in global average temperatures seen since the 1950s.
While the concept of man-made climate change remains controversial politically, the debate among scientists and governments has shifted toward what can be done to limit the carbon emissions blamed for trapping heat in the atmosphere, how to deal with the expected effects, and who should pick up the cost for the poor countries analysts say are likely to be hit the hardest.
A U.N. conference on the topic struggled to reach consensus despite a dramatic plea from a representative of the typhoon-ravaged Philippines. Global emissions were on track to top a record 39 billion tons, though the United States and Europe managed to cut their carbon dioxide releases.
With legislative action likely to fail in the U.S. Congress, the Obama administration took steps on its own to try to rein in emissions and beef up the defenses of vulnerable communities.
Sequester, shutdown suck money out of science
It takes funding to do scientific research, and it's a big problem when the stream stops. The one-two punch of $85 billion in forced spending cuts and a federal government shutdown bit deeply into American science in 2013.
The National Science Foundation, which supports research and education in non-medical science and engineering, said it would be awarding 1,000 fewer grants in 2013.
Nearly half the recipients who get federal science funding say they've recently laid off or will lay off scientists and researchers, according to a survey by 16 scientific societies. The National Institutes of Health, the largest supporter of U.S. biomedical research, said 20,000 researchers and technicians would lose jobs as $1.6 billion was eliminated from its $31 billion budget.
Then, a Republican drive to defund President Barack Obama's signature health care law led to the partial shutdown of federal offices. Hundreds of thousands of government workers were furloughed during the 16-day impasse, including 97% of NASA's employees.
Fun with physics
But science is still moving forward, sometimes even toward what looks like science fiction.
Physicists said they had taken a step in the direction of making an invisibility cloak, albeit a small step. Their method can make objects "invisible" within a limited range of light waves -- specifically, microwaves.
And remember the light sabers in "Star Wars"? Scientists said in September that they had made "light-matter," molecules made of particles of light called photons that don't behave like traditional light.
Speaking of particles, we're learning more than ever about what scientists had hoped to find with a $10 billion machine called the Large Hadron Collider. The Higgs boson explains why matter has mass. Physicists announced the discovery last year, but are even more confident now, and the Nobel Prize in Physics was awarded to the theorists who predicted the particle.
The collider is turned off for upgrades, but physicists at the European Organization for Nuclear Research, or CERN, told CNN they have a lot more data to look through. More on the "God particle" (yes, we know that's a misnomer) may be in the details.
There's plenty more to find out about our universe in 2014. Let's see if there's enough money to support it.
What were your favorite science stories from 2013? Tell us in the comments.