From water on Mars to the Homo naledi

In 2015, scientists made high profile discoveries in caverns deep below the Earth’s surface and on chilly worlds far from the sun. Some advances raised ethical dilemmas or provoked scientific controversy. Others, however, were pure triumphs of the human craving to question and explore.

Pluto’s first close up

Downgraded to a dwarf planet in 2006, Pluto was judged unworthy of serious interest. In July, the New Horizons spacecraft proved the doubters wrong after becoming the first Earthly caller to drop by the tiny, icy body at the fringe of the solar system.

In a fleeting but productive visit, the craft captured photos showing that Pluto is a far more lively and complex world than scientists ever dreamed, boasting cracked plains, tall mountains, and what look like ice volcanoes. No one imagined „this good of a toy store,” said New Horizons leader Alan Stern.

A new type of human

A scientist’s physiqueis generally irrelevant to the process of discovery. But it took six small boned researchers to excavate the fossils of a new human like species dubbed Homo cheap jerseys naledi, whose remains were found in a cramped cave in South Africa and revealed in September.

The trove of fossilized bone recovered from the cave suggests naledi was a strange hybrid, adept at climbing trees like an ape but also at walking, like today’s humans. The bodies may have been carefully interred in the cave, which would be surprising behavior for a species far more primitive than our own.

Water on Mars

Mars was once awash with water in the form of rivers, lakes, even huge deltas. Now those aquatic features survive only as geologic landmarks carved by the once abundant moisture.

But scientists reported in September that long lines that appear and vanish on the Martian surface with the seasons show hints of the wet stuff. The lines are more like tracks of moist soil than flowing streams and are too salty to host life, but they’re the first liquid water known on the Red Planet.

Gene editing of embryos

After scientists announced a few years ago that they haddevised a cheap, fast method for editing genes, the new technique, known as CRISPR, took science by storm. So, too, did worries about the safety and ethics of the method.

Making clear that such worries were well founded, in April scientists reported that they’d used CRISPR to tinker with the genome of human embryos, a historical first that prompted a global uproar. This month an international scientific panel urged researchers not to allow gene edited human cells to be used to establish a pregnancy.

Earliest stone tools

Today’s humans and our immediate relatives belong to a family group called Homo whose earliest members date to 2.8 million years ago. But in May, scientists announced that they’d found stone tools dating back an extra 500,000 years well before our nearest ancestors walked the Earth.

The simple stone cutting implements were found close to a Kenyan site where a separate team has found fossils of an apelike human relative. Perhaps that relative crafted the tools, which, at 3.3 million years old, are some 700,000 years older than the previous record holders.