2015 boldly went where we have not gone before

2015 was a great year for medical and scientific discovery, from New Horizons generating excitement after sending back images of Pluto's unexpected landscapes — towering mountains and smooth plains — to the discovery of Homo naledi, which changed the face of the human story by adding a baffling new branch to the family tree. Other big stories included the quest to understand climate change; new understanding about driverless cars (they are too polite); and the brave new world of gene editing and microbiomes. Story, SH2

1. Pluto

Dwarf planet or no, Pluto stole the space show this year. Every set of photos the New Horizon spacecraft sent back blew the previously captured images out of the water. The Pluto flyby on July 14 — a mission launched nearly a decade ago — was a gorgeous moment of global excitement over science. And Pluto's complexity — which rivals that of such "real" planets as Mars — goes to show us that our galaxy is bursting with things we don't understand.

2. Kepler, Mars and space

Tons of exoplanets were found by Kepler, a space telescope that should have been put out of commission by a hardware failure ages ago and yet has survived. The dwarf planet Ceres teased us for months with a smattering of mysterious bright spots. Scientists found evidence of water on Mars right now, and evidence that the water that used to be there was plentiful and long-lasting — perhaps so much so that life could have evolved there — and why all that water vanished.

In April, NASA's top scientist declared that he believed we'd find signs of life beyond Earth within the next decade. Physicist Stephen Hawking stamped his name on a $100 million hunt for intelligent aliens. Meanwhile, NASA sent an astronaut — Scott Kelly — on a yearlong mission to monitor the effects of long-term spaceflight while his identical twin, retired astronaut Mark Kelly, stayed home and will provide medical comparisons.

3. The microbial explosion

4. Gene editing

This year, Chinese scientists edited the human genome for the first time using CRISPR, a cut-and-paste gene-editing tool. While actually editing the genome of a viable human is probably pretty far off, but scientists are already working on editing animals so their organs are better suited for human transplant. The technology has raised a host of ethical quandaries.

5. Ebola meets the eye

Months after Dr. Ian Crozier thought he was cured of Ebola, his doctors found that his left eye was teeming with the virus. With careful treatment, Crozier's sight — and his eye color, which turned blue from green — eventually returned. But his case was an early warning that Ebola can lurk undetected in a recovered patient's body.

6. Climate change preview

7. Healthier hearts, high cost

Two new drugs that make levels of LDL cholesterol, the so-called bad cholesterol, plunge to new lows were approved. There is no question that PCSK9 inhibitors are potent, but their approval also introduced an expensive new era in heart disease prevention. Praluent costs $14,600 a year and Repatha costs $14,100 a year. As a health insurance executive put it, "If this is the new normal to treat common and chronic conditions, how can any health system sustain that cost?"

8. Driverless cars

Cars drive better than people, and that is a problem when they have to share the road. Those are the early indications from Google's driverless car experiment. Driverless cars seem to behave particularly safely, more so than their human counterparts. An early version could not get through a four-way stop because it kept waiting for (not as polite) human drivers to give the Google car its turn.

9. Other good things

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