An "unprecedented" thousands of dead fish washed up in Rio's heavily polluted Guanabara Bay this week, deepening fears for the health of competitors at the 2016 Olympics and alarming fishermen.

Detritus including dead animals, television sets, sofas and shoes have all been found in the waters, which will host sailing competitions at next year's Rio games.

The discovery of another bright light on the dwarf planet Ceres has NASA scientists perplexed as the U.S. Dawn probe prepares to enter the orbit of the largest object in the asteroid belt and possibly resolve the mystery.

The images taken nearly 29,000 miles (46,000 kilometers) from Ceres show that a bright spot on the planet scientists previously discovered appears next to another slightly darker spot, NASA said in a news release.

Brazilian astronomers said Friday they had found two star clusters forming in a remote part of our Milky Way galaxy where such a thing was previously thought impossible.

Seen from above, the Milky Way has arms of stars, gas and dust flailing out in a spiral shape from the centre.

French President Francois Hollande called Thursday for a climate change "alliance" with the Philippines that could spur similar co-operation between rich and poor nations at a crucial U.N. summit.

Hollande made the appeal shortly after landing in the Philippines with two of France's leading actresses for a trip aimed primarily at mobilising global action in the fight against global warming.

Astronomers said Wednesday they had detected an "impossibly large" and ancient black hole that challenges theories about how these phenomena grew in the early Universe.

With a mass 12 billion times that of our Sun, the black hole formed about 900 million years after the Big Bang that created the Universe 13.7 billion years ago -- a very short period in galactic history, the surprised team reported in the journal Nature.

A spacewalking astronaut ended up with unwanted water in his helmet Wednesday after breezing through a cable and lube job outside the International Space Station.

The leak was scarily reminiscent of a near-drowning outside the orbiting complex nearly two years ago.

Australian researchers said Thursday they have created two jet engines using 3D printing in what is described as a world-first that has attracted the interest of major manufacturers and engineering firms.

The machines -- produced using the template of a gas turbine engine from French aircraft engine maker Safran, which supplies Airbus and Boeing -- demonstrated the potential 3D printing had to produce high-quality products, researchers from Melbourne's Monash University said.

Two American astronauts Wednesday stepped out on the second of three spacewalks to prepare the International Space Station for the arrival of commercial capsules ferrying astronauts in the coming years.

Commander Barry "Butch" Wilmore and flight engineer Terry Virts emerged from the station airlock after placing their suits on internal battery power at 6:51 am (12:51 GMT), NASA said.

European surgeons and engineers have devised a mind-controlled bionic hand that restores function almost as well as a flesh-and-blood transplant, but without the risk of rejection, a research paper said Wednesday.

The three Austrian beneficiaries of the unprecedented technique had suffered injuries in car and climbing accidents to the "brachial plexus" -- a network of nerves running from the spine to the upper limbs.

Why do humans and other mammals have eyelashes?

Experts have been batting rival theories around for years.