A British tree thought to be up to 5,000 years old has started to change sex, a "rare and unusual" phenomenon not fully understood by scientists, a botanist said Monday.

The Fortingall Yew, in Perthshire, central Scotland has for hundreds of years been recorded as male, but has recently begun sprouting berries, suggesting that at least part of the tree is changing gender.

A massive space rock that will shave by Earth on Halloween looks like a dead comet with a skull face, NASA said after gaining a closer look at the spooky space junk.

Astronomers initially thought the object was an asteroid when they spotted it in early October, and named it Asteroid 2015 TB145.

Two NASA astronauts stepped out on a spacewalk Wednesday for upgrades and maintenance at the orbiting International Space Station, the U.S. space agency said.

Spaceflight veteran Scott Kelly, who is in the midst of a year-long stint at the ISS, began the first spacewalk of his career at 8:03 am (1203 GMT), according to a live broadcast on NASA television.

Bracing for a tsunami like the one that devastated Japanese communities during a 2011 mega-earthquake, coastal communities from British Columbia to California have been grappling with how to protect people from a similar catastrophe.

One of those towns is constructing the nation's first structure built as a vertical tsunami refuge.

An international scientific expedition has spotted up to 25 individual specimens of a near-extinct small porpoise in Mexico's Gulf of California, amid efforts to save the critically endangered vaquita marina.

The environment ministry said Monday that the rare sightings of the world's smallest porpoise were made during the first 20 days of the Vaquita Expedition 2015, which started on September 26.

Endangered orangutans are falling victim to a devastating haze crisis that has left them sick, malnourished and severely traumatized as fires rage through Indonesia's forests, reducing their habitat to a charred wasteland.

Rescuers at a center for the great apes on Borneo island are considering an unprecedented mass evacuation of the hundreds in their care, and have deployed teams on hazardous missions to search for stricken animals in the wild.

An unmanned NASA spacecraft is about to make its deepest dive ever into the icy spray emanating from the underwater ocean on Saturn's moon, Enceladus.

The tiny moon orbiting the sixth planet from the sun stunned scientists when they discovered it had an icy plume in 2005.

Haze from Indonesian forest fires has spread to the southern Philippines, disrupting air traffic and prompting warnings for residents to wear face masks, authorities said Friday.

The large southern Philippine island of Mindanao is more than 1,200 kilometres (745 miles) from the nearest fires but the haze has become a worsening problem over the past week, aviation authorities said.

A big asteroid is hurtling toward Earth and will shave past our planet on Halloween, but astronomers say there's no need to be spooked -- it's definitely not on a collision course.

Early estimates put its size of the asteroid -- called 2015 TB145 -- at about 1,542 feet (470 meters) in diameter, according to the astronomy website Earth and Sky.

Albert Einstein's general theory of relativity is about to celebrate its 100th anniversary, and his revolutionary hypothesis has withstood the test of time, despite numerous expert attempts to find flaws.

"Einstein changed the way we think about the most basic things, which are space and time. And that opened our eyes to the universe, and how the most interesting things in it work, like black holes," said David Kaiser, professor of the history of science, technology and society at  the Massachusetts Institute of Technology (MIT).