The U.N.'s climate chief urged country negotiators Monday to "build bridges" at talks in Bonn towards a new, global pact that received fresh endorsement from world leaders last month.

The six-day forum must lay the foundations for the annual round of ministerial-level U.N. talks to be held in Lima in December, Christiana Figueres told delegates as the meeting opened.

It may not have been love as we know it, but around 385 million years ago, our very distant ancestors -- armored fish called placoderms -- developed the art of intercourse.

So suggest a team of evolutionary scientists, who point to the fossil of a placoderm species blessed with the name of Microbrachius dicki.

A comet the size of a small mountain whizzed past Mars on Sunday, dazzling space enthusiasts with the once-in-a-million-years encounter.

The comet, known as Siding Spring (C/2013 A1), made its closest encounter with Mars on Sunday at 2:27 pm (1827 GMT), racing past the Red Planet at a breakneck 126,000 miles (203,000 kilometers) per hour.

A top secret U.S. robot space plane landed back on Earth on Friday after a 22-month orbit, officials said, although the craft's mission remains shrouded in mystery.

The unmanned X-37B, which looks like a miniature space shuttle, glided into the Vandenberg Air Force Base in California after having launched on December 11, 2012, on a mission that military officers say is still strictly secret.

A month after world leaders pledged to curb the threat of climate change, their words will be put to the test when talks for a new global pact resume in Bonn next week.

Negotiators will gather from Monday, tasked with ironing out differences over how to save Earth from potentially catastrophic climate damage.

Argentina launched its first domestically built communications satellite Thursday.

The ARSAT-1 satellite is the first to be constructed with local technology in Latin America. It was built by a crew of about 500 scientists over seven years at a cost of $250 million. The satellite was launched from a base in French Guiana and is to orbit 22,000 miles (36,000 kilometers) above Earth.

A pair of American astronauts stepped outside the International Space Station Wednesday for a spacewalk to do repairs and upkeep at the orbiting outpost, NASA said.

Reid Wiseman and Barry "Butch" Wilmore finished their spacewalk after six hours and 34 minutes, right on schedule, the U.S. space agency said.

A fast-moving comet is about to fly by Mars for a one-in-a-million-year encounter with the Red Planet, photographed and documented by a flurry of spacecraft, NASA said.

The comet, known as Siding Spring (C/2013 A1), has a core about a mile (1.6 kilometers) wide in diameter, but is only as solid as a pile of talcum powder.

Australia's Environment Minister Greg Hunt has pledged to end the extinction of native mammal species by 2020, with a focus on culprits such as feral cats.

Hunt said Australia had the worst rate of mammal loss in the world and the nation's "greatest failure" in environmental policy was protecting threatened species.

A forerunner of today's crocodiles that lurked in coastal waters and estuaries some 150 million years ago measured 9.26 meters (some 30 feet) from snout to tail, scientists reported Wednesday.

Paleontologists from half a dozen European countries took a fresh look at the classification of so-called crocodylomorphs that go by the name of Machimosaurus.