Air pollution levels in China's cities improved in the first six months of this year, environmental campaign group Greenpeace said Wednesday, but remained far worse than global and domestic standards.

Average levels of PM2.5 -- airborne particulates small enough to deeply penetrate the lungs -- declined 16 percent in 189 cities that were ranked both this year and last, Greenpeace said in a press release.

Japanese space scientists are on the hunt for a new name for an asteroid that may contain the secret of life, with a public competition beginning Wednesday.

The asteroid, which currently goes by the rather prosaic "1999 JU3" is the intended destination for a Japanese spacecraft, which mission controllers hope will be able to gather samples and bring them back to Earth.

The Alaska Volcano Observatory says underground activity is increasing at Cleveland Volcano in the Aleutians Islands.

The observatory recorded an explosion at the volcano at 8:17 a.m. Tuesday, but no ash has been detected. Ash above 20,000 feet would threaten trans-Pacific flights.

Native American ancestors reached the New World in a single, initial migration from Siberia at most 23,000 years ago, only later differentiating into today's distinct groups, DNA research revealed Tuesday.

Most scientists agree the Americas were peopled by forefathers who crossed the Bering land and ice bridge which connected modern-day Russia and Alaska in Earth's last glacial period.

The explosion last month of SpaceX's Falcon 9 rocket was caused by a failed support piece, or strut, that allowed a helium bottle to burst free inside the rocket's liquid oxygen tank, CEO Elon Musk said Monday.

"One of those struts broke free during flight," Musk told reporters on a conference call to discuss the June 28 blast on what was supposed to be a routine cargo mission to the International Space Station.

Circus bear Mura wound up in the world's biggest brown bear sanctuary in the heart of Romania's Carpathian mountains after refusing to perform any longer, following five years of unbearable abuse.

Caged, beaten and starved by their owners, 80 bears rescued from captivity have been taken in to be healed of trauma at the "Libearty" sanctuary, but the process can be slow.

British cosmologist Stephen Hawking on Monday launched the biggest-ever search for intelligent life in the universe in a 10-year, $100-million (143-million-euro) project to scan the heavens.

The Breakthrough Listen project, backed by Russian Silicon Valley entrepreneur Yuri Milner, will be the most powerful, comprehensive and intensive scientific search ever undertaken for signs of extra-terrestrial intelligent life.

Artur Bilsky's Institute of Thermophysics recently sought to buy equipment from a Japanese company that was a routine purchase a few years ago. The request was turned down "categorically," said Bilsky, a researcher at the institute.

Hundreds of other Russian scientists are reporting similar experiences of being refused sale of scientific equipment from abroad, or seeing research papers curtly turned down by Western publications. The reason, they believe, is a combination of sanctions against Russia over its actions in Ukraine and rising hostility to Russia in the West seeping into the scientific community.

The National Air and Space Museum is launching a crowdfunding campaign to conserve the spacesuit Neil Armstrong wore on the moon.

The campaign begins Monday, marking 46 years since Armstrong's moonwalk in 1969. Conservators say spacesuits were built for short-term use with materials that break down over time.

Europe's robot lab Philae has fallen "silent" on the surface of a comet zipping towards the Sun, said ground controllers Monday who fear it may have shifted out of radio contact.

"The lander could have moved," the German Aerospace Center (DLR) said in a statement, adding: "even a slight change in its position could mean that its antennas are now obstructed".