Top 10 Science Stories of 2015

It’s been a busy year for scientists: medical breakthroughs; newly discovered human ancestors; genes and neurons; Earth’s troubled species; and enticing findings from Mars, Pluto, and beyond. Here are 10 science advances that made a big impact in 2015.

1. WE GOT UP CLOSE AND PERSONAL WITH PLUTO.

NASA

After a 9.5-year, 3-billion-mile journey, NASA’s intrepid New Horizons spacecraft finally reached Pluto in July, sending back high-resolution images of the dwarf planet and its moon, Charon. At its closest approach, the craft passed within 7800 miles of Pluto’s surface—close enough to reveal bizarre ice mountains and vast, crater-free plains, seemingly divided into “cells” dozens of miles wide. There’s evidence of geological activity within the last 100 million years—a mere eye-blink compared to the age of the solar system—which came as a surprise to scientists, who imagined Pluto to be a geologically “dead” world. Charon, meanwhile, has cliffs that run for hundreds of miles, and canyons more than six miles deep. The findings will keep planetary scientists busy for years.

2. WE OPENED THE DOOR TO CUSTOM DNA.

An organism’s development is governed by its DNA—but what if you could manipulate that DNA at will? The era of custom “gene editing” now looms on the horizon, thanks to a tool known as CRISPR-Cas9, which allows researchers to “swap out” sections of a genome faster and more cheaply than ever before. Earlier this year, scientists developed gene-edited mosquitos that are resistant to malaria and gene-edited African pigs that are immune to swine fever; the FDA, meanwhile, recently approved a fast-growing, gene-edited salmon for human consumption.

Are genetically engineered humans next? Scientists in China have already done the first experiments on human embryos, in a bid to correct faulty genes that cause disease. The embryos in those studies were non-viable, but even so there’s been a storm of controversy. Some argue in favor of human gene modification, in the hope of engineering human beings with less susceptibility to devastating illnesses such as cancer and dementia—while others see any such research as the start of a slippery slope leading to a world divided between genetic haves and have-nots.

3. WE MAY HAVE FOUND A NEW MEMBER OF THE HUMAN FAMILY TREE.

Berger et al. ineLife.

Pieced together from 1500 bones found deep in a cave near Johannesburg, South Africa, Homo naledi—claimed to represent a new species of human ancestor—caused a sensation when the finding was announced in September. (“Naledi” means “star” in Sesotho, one of South Africa’s official languages.) Its bones tell a complicated story. The small skull and ape-like shoulders suggest it may be among the earliest members of the human family tree, while the shape of the feet and ankles indicate it walked upright. And yet the highly curved fingers hint at the tree-climbing prowess of its ancestors.

But is it really a new species? Some skeptics believe the bones could belong to early members of Homo erectus, a well-documented human ancestor that lived from about 1.9 million years ago to about 70,000 years ago—or even an isolated offshoot of Homo sapiens. It would help if we knew exactly when Homo naledi flourished; unfortunately, scientists haven’t been able to date the bones yet.

4. WE DISCOVERED THAT WE MAY BE CAUSING A SIXTH MASS EXTINCTION.

Over the past 450 million years, the Earth has witnessed five “mass extinction events”—catastrophes in which an asteroid impact or volcanic activity triggered rapid climatic change and a dramatic loss of biodiversity. The most severe of these was the event that killed off the dinosaurs—and three-quarters of all species—some 66 million years ago. Scientists believe we’re now on the brink of a sixth such mass extinction event—only this time, the culprit is human activity. In a study published in the journal Science Advances in June, biologists found that our planet is losing animal species at 20 to 100 times the average “background” rate, and that the rate is increasing. “The smoking gun in these extinctions is very obvious, and it’s in our hands,” Todd Palmer, a biologist at the University of Florida and a co-author of the study, told the Washington Post. 

5. WE PENETRATED THE BLOOD-BRAIN BARRIER FOR THE FIRST TIME.

Injecting drugs into the body is routine—unless you’re targeting the brain, which is protected by the “blood-brain barrier,” a film-like coating that surrounds the blood vessels in the brain. The barrier prevents harmful substances from entering the brain—but also stands in the way of certain treatments (for example, chemotherapy drugs targeting brain tumors). In November, doctors in Toronto used tightly focused ultrasound waves to penetrate the barrier for the first time. The technique could pave the way for the treatment of an array of illnesses, from brain cancer to Alzheimer’s disease. 

6. WE FOUND LIQUID WATER ON MARS.

Getty Images

Mars, with its many similarities to Earth, has long been the most enigmatic planet in our solar system—and it became even more beguiling in September, when NASA scientists announced that they’d found evidence for flowing water on the planet’s surface. Images from the Mars Reconnaissance Orbiter reveal dark streaks that appear during the Martian summer, likely the result of seasonal “flows.” A caveat: the water is briny and extremely salty, and scientists are far from certain that it’s capable of supporting life. And while it would be great to go there (or send a robotic ambassador) for a close-up view, there’s a very real danger of contaminating the area with microbes from Earth.

7. WE CONFIRMED THAT “SPOOKY ACTION AT A DISTANCE" IS REAL.

It’s one of the most bizarre features of the quantum world: The notion that two particles, even if they’re far apart, can be “entangled” quantum mechanically. When two particles are entangled, measuring the properties of one particle instantly gives you information about the other, regardless of the distance between them. The notion of entanglement dates back to a paper written by Einstein and two colleagues in the 1930s, although he later dismissed the idea as “spooky action at a distance.” But beginning in the late '70s, ever-more sophisticated experiments suggested entanglement is real. In October, physicists in the Netherlands managed to entangle two electrons almost a mile apart—and they say they’ve ruled out all of the loopholes which made earlier experiments inconclusive. And while it all may sound pie-in-the-sky, scientists say that the research could eventually lead to the development of ultra-fast “quantum computers,” with potentially game-changing applications in medicine, cryptography, and artificial intelligence.

8. WE IMPLANTED FALSE MEMORIES IN MICE.

iStock

We think of memories like pages in a scrapbook, or pictures in a photo album, but in practice, our memories are often wrong. “False memory syndrome” is now recognized as a real phenomenon in the scientific literature, and psychologists are eager to learn more about how erroneous memories form. Animal studies may shed some light. In March, neuroscientists in France described how they were able to implant false memories into mice while the animals slept. They used electrodes to directly stimulate specific nerve cells within the brain, causing the mice to associate certain locations with rewards. After waking, the mice “remembered” those associations, spending more time in the locations where they (incorrectly) recalled receiving a reward. The researchers hope their work will help explain how false beliefs form in humans.

9. WE THEORIZED THAT DARK MATTER WIPED OUT THE DINOSAURS.

We don’t usually think of events in deep space influencing life on Earth—after all, astrology was debunked centuries ago. But if physicist Lisa Randall is right, there may be a subtle but important connection between an exotic form of matter that permeates the universe, and the evolution of life on our blue-green world. In her book Dark Matter and the Dinosaurs, Randall suggests that a thin disk of dark matter—a kind of matter that responds to gravity, but not to light—might periodically perturb the orbit of comets at the far edges of our solar system. That might be what happened 66 million years ago, when a wayward comet is believed to have slammed into the Earth, triggering catastrophic climate change and dooming not only the dinosaurs but three-quarters of all species. It’s a controversial theory, but it could gain support, Randall says, if we can detect the gravitational influence of the alleged dark-matter disk. Read an excerpt from Dark Matter and the Dinosaurs on Science Friday.

10. WE FOUND A WEIRD STAR—OR MAYBE E.T.? (MAYBE NOT.)

Artist's representation of a crumbling Dyson sphere orbiting KIC 8462852. Image credit: Danielle Futselaar // SETI International

You wouldn’t think it’s anything special from its name—KIC 8462852—but the peculiar star, located about 1500 light-years from Earth, set the Internet abuzz in September when it was suggested that it might be home to an advanced alien civilization (“might” being the key word, of course). Data from the Kepler space telescope showed that the star undergoes strange variations in brightness over time. Kepler is specifically designed to detect planets that may periodically pass in front of a star, causing it to dim—but KIC 8462 displayed a more unusual pattern, with more substantial dimming at irregular intervals. A swarm of comets was said to be the most likely explanation. But one of the astronomers also suggested the possibility of an “alien megastructure”—perhaps some variation of the “Dyson sphere,” a vast artificial structure that an advanced civilization might build surrounding a star, popularized by physicist Freeman Dyson in the 1960s.

Later, radio astronomers aimed the Allen Telescope Array in California at the star, just in case it was emitting alien chatter. It was not. The latest thinking is that it’s probably comets after all. The lesson? When it’s a choice between aliens and something else, it’s always been something else (so far), and that’s most likely the case this time. But for getting people’s attention, little green men beat icy snowballs every time.