Science mattered more than ever in 2013. Climate science questions raged after Super Typhoon Haiyan pummeled the Philippines. And scientific expertise figured in disarmament debates in Syria and in Iran's proposed halt to its nuclear activities.
Meanwhile, on the pure research front, investigators made plenty of intriguing discoveries in 2013. With plenty to choose from, and argue over, here's a top five list of some favorites from the year.
1. Space gets more crowded. "Buy land, they're not making it anymore," Mark Twain famously advised investors. Twain never heard of exoplanets, of course. Caltech researchers suggested this year that at least 100 billion such worlds orbit stars in our Milky Way galaxy. That's a lot of new real estate. (See "Smallest Exoplanets Found—Each Tinier Than Earth.")
Of course, not all of them are places you would want to live. A November analysis from NASA's Keck Observatory team suggested that one in five stars may have Earth-size planets orbiting in their "habitable zones"—zones that could be friendly to surface oceans. A more recent climate analysis of habitable zones said that number may be too high, but that is still plenty of planets.
2. Human embryonic stem cells cloned.
After more than a decade of false starts, Oregon Health and Science University researchers announced they had cloned human embryos and collected stem cells from them. They also grew the cells into specialized skin and heart cells, a first step toward using them in transplant medicine.
The key to the team's success turned out to be the addition of caffeine to the cloning process. Now researchers will seek to discover whether these cells or similar "induced" stem cells, made without embryos, will have the most medical use.
3. Voyager reaches edge of the solar wind.
One of the year's biggest announcements came from news that actually happened in 2012. The aftershocks of a pair of solar storms in September confirmed that NASA's venerable Voyager 1 spacecraft had actually entered interstellar space. (See "Voyager 1 Leaves Solar System, NASA Confirms.")
"It is an incredible event, to send the first human object into interstellar space," study lead author Donald Gurnett, of the University of Iowa in Iowa City, told National Geographic.
NASA had long been hoping to announce that the far-flung spacecraft, launched in 1977, had passed the edges of the solar wind. Voyager 1's twin, Voyager 2, is also expected to soon reach interstellar space.
4. Mars lake looks hospitable to ancient life.
NASA's Curiosity rover continued to make historic tracks in 2013, finding that a vanished lake on the red planet could have supported life there more than three billion years ago.
The discovery is seen as vindication of NASA's efforts to look for past habitable conditions on Mars. The $2.5 billion rover next heads for Mount Sharp, in the center of Gale Crater, its original destination after landing. (See also: "Did Life on Earth Come From Mars?")
5. Lord of the Rings looking more like a documentary.
The human family tree suddenly sprouted some funky-looking shoots after a year of ancient DNA and fossil discoveries.
At the Dmanisi site in the Republic of Georgia, for example, researchers reported that what seemed like a lot of different-looking early human species likely were just one, Homo erectus. They based the claim on the discovery of a 1.8-million-year-old skull blessed with a mixture of more ancient and more recent characteristics. (See "Beautiful Skull Spurs Debate on Human History.")
On the genetic front, what looked like a Neanderthal bone in a Spanish cave turned out to actually possess the genes—the oldest DNA yet sequenced—of a different vanished early human species, the Denisovans.
Meanwhile, Siberia's Denisova cave, where Denisovan fossils were first discovered in 2008, yielded a toe bone that belonged to a Neanderthal woman from perhaps 140,000 years ago. (See "Ancient Incest Uncovered in Neanderthal Genome.")
This finding suggests that archaic humans mated with Homo erectus, as well as with some early modern humans in prehistory. A lot of modern people have a little archaic human in their genes, it turns out.
We hear a lot about dark matter, and how physicists are ever on the hunt for it. But how do you look for something you can't even see?
While dark matter is thought to make up five-sixths of all matter in the universe, scientists don't know what this strange stuff is made of. True to its name, dark matter is invisible — it does not emit, reflect or even block light. As a result, dark matter can currently be studied only through its gravitational effects on normal matter. The nature of dark matter is currently one of the greatest mysteries in science.
If dark matter is made of such superheavy particles, astronomers could detect evidence of them in the afterglow of the Big Bang, the authors of a new research study said.
Previous dark matter research has mostly ruled out all known ordinary materials as candidates for what makes up this mysterious stuff. Gravitational effects attributed to dark matter include the orbital motions of galaxies: The combined mass of the visible matter in a galaxy, such as stars and gas clouds, cannot account for a galaxy's motion, so an additional, invisible mass must be present. The consensus so far among scientists is that this missing mass is made up of a new species of particles that interact only very weakly with ordinary matter. These new particles would exist outside the Standard Model of particle physics, which is the best current description of the subatomic world.
Some dark matter models suggest that this cosmic substance is made of weakly interacting massive particles, or WIMPs, that are thought to be about 100 times the mass of a proton, said study co-author McCullen Sandora, a cosmologist at the University of Southern Denmark. However, despite many searches, researchers have not conclusively detected any WIMPs so far, leaving open the possibility that dark matter particles could be made of something significantly different.
Now Sandora and his colleagues are exploring the upper mass limit of dark matter — that is, they're trying to discover just how massive these individual particles could possibly be, based on what scientists know about them. In this new model, known as Planckian interacting dark matter, each of the weakly interacting particles weighs about 1019 or 10 billion billion times more than a proton, or "about as heavy as a particle can be before it becomes a miniature black hole," Sandora told Space.com.
A particle that is 1019 the mass of a proton weighs about 1 microgram. In comparison, research suggests that a typical human cell weighs about 3.5 micrograms.
The genesis of the idea for these supermassive particles "began with a feeling of despondency that the ongoing efforts to produce or detect WIMPs don't seem to be yielding any promising clues," Sandora said. "We can't rule out the WIMP scenario yet, but with each passing year, it's getting more and more suspect that we haven't been able to achieve this yet. In fact, so far there have been no definitive hints that there is any new physics beyond the Standard Model at any accessible energy scales, so we were driven to think of the ultimate limit to this scenario."