A pair of spacewalking astronauts wrapped up battery improvements outside the International Space Station on Monday, completing a job begun last fall.

NASA's Jessica Meir and Christina Koch installed the last new battery in a set of six launched to the orbiting lab in September. They also removed two old batteries in their second spacewalk in under a week to upgrade the station's solar power grid.

This marked the women's third spacewalk together. They conducted the world's first all-female spacewalk last October, replacing a failed charging device that bumped the battery replacements into this year.

The women had just completed the battery work when Koch inadvertently deployed the hand controller on her emergency jet pack, called a Safer. Meir hurried over to get the controller back in its proper place. Koch called her "my hero."

Mission Control cautioned that, given the current set-up, "we would not count on Christina's Safer" in an emergency. NASA's spacewalking astronauts always wear small Safer jet packs in case they become untethered from the station and float away. It's never been needed.

During last Wednesday's spacewalk, Koch's helmet lights and camera came loose. She later found a faulty latch in the helmet assembly and replaced it before floating out Monday.

Koch has been aboard the space station for more than 10 months, the longest single spaceflight by a woman. She returns to Earth in just over two weeks.

NASA gradually has been replacing the space station's 48 aging, original-style nickel-hydrogen batteries with new and more powerful lithium-ion batteries. Only half as many of the new batteries are needed. So far, 18 new batteries have been installed over the past three years and  36  old ones removed.

Another batch of six new batteries will be launched to the orbiting lab this spring to complete the power upgrade. The old batteries, meanwhile, will be discarded in a supply ship.

These oversized, boxy batteries keep all the space station's systems running when the outpost is on the night side of Earth, drawing power from the sprawling solar wings. They're not easy to handle: Each is about a yard, or a meter, tall and wide, with a mass of about 400 pounds (180 kilograms.)

"To our astro-sisters, we wish you the best of luck on this," astronaut Andrew Morgan radioed from inside Monday.

 In all, five spacewalks were needed to complete the battery work this time around.

Morgan and Italian astronaut Luca Parmitano will venture outside Saturday to complete repairs to a cosmic ray detector on the space station. The science instrument's cooling system had to be replaced, an intricate job requiring four spacewalks.

The possibility that a new virus in central China could spread between humans cannot be ruled out, though the risk of transmission at the moment appears to be low, Chinese officials said Wednesday.

Forty-one people in the city of Wuhan have received a preliminary diagnosis of a novel coronavirus, a family of viruses that can cause both the common cold and more serious diseases. A 61-year-old man with severe underlying conditions died from the coronavirus on Saturday.

While preliminary investigations indicate that most of the patients had worked at or visited a particular seafood wholesale market, one woman may have contracted the virus from her husband, the Wuhan Municipal Health Commission said in a public notice.

The commission said the husband, who fell ill first, worked at the Huanan Seafood Wholesale Market. Meanwhile, the wife said she hasn't had any exposure to the market.

It's possible that the husband brought home food from the market that then infected his wife, Hong Kong health official Chuang Shuk-kwan said at a news briefing. But because the wife did not exhibit symptoms until days after her husband, it's also possible that he infected her.

Chuang and other Hong Kong health officials spoke to reporters Wednesday following a trip to Wuhan, where mainland Chinese authorities briefed them on the outbreak.

The threat of human-to-human transmission remains low, Chuang said, as hundreds of people, including medical professionals, have been in close contact with infected individuals and have not been infected themselves.

She echoed Wuhan authorities' assertion that there remains no definitive evidence of human-to-human transmission.

The outbreak in Wuhan has raised the specter of SARS, or severe acute respiratory syndrome. SARS is a type of coronavirus that first struck southern China in late 2002. It then spread to more than two dozen countries, killing nearly 800 people.

China sent a new optical remote-sensing satellite for commercial use into planned orbit from the Taiyuan Satellite Launch Center in north China's Shanxi Province on Wednesday morning.

The satellite, belonging to the Jilin-1 satellite family, also named Red Flag-1 H9, was launched by a Long March-2D carrier rocket at 10:53 a.m. Beijing time.

The new satellite, developed by the Chang Guang Satellite Technology Co., Ltd., has a super-wide coverage and a resolution at the sub-meter level. It is also capable of high-speed data storage and transmission.

It will work with the 15 satellites of the Jilin-1 family already sent into orbit to form a constellation that will provide remote-sensing data and services for governmental and industrial users.

Via the same carrier rocket, three small satellites including NewSat7 and NewSat8 developed by an Argentinian company were also sent into space.

The Long March-2D carrier rocket was developed by the Shanghai Academy of Spaceflight Technology under the China Aerospace Science and Technology Corporation.

Wednesday's launch was the 325th mission of the Long March series carrier rockets.

Scientists analysing a meteorite have discovered the oldest material known to exist on Earth, reports BBC.

They found dust grains within the space rock - which fell to Earth in the 1960s - that are as much as 7.5 billion years old.

The oldest of the dust grains were formed in stars that roared to life long before our Solar System was born.

A team of researchers has described the result in the journal Proceedings of the National Academy of Sciences.

When stars die, particles formed within them are flung out into space. These "pre-solar grains" then get incorporated into new stars, planets, moons and meteorites.

"They're solid samples of stars, real stardust," said lead author Philipp Heck, a curator at Chicago's Field Museum and associate professor at the University of Chicago.

A team of researchers from the US and Switzerland analysed 40 pre-solar grains contained in a portion of the Murchison meteorite, that fell in Australia in 1969.

"It starts with crushing fragments of the meteorite down into a powder," said co-author Jennika Greer, from the Field Museum and the University of Chicago.

"Once all the pieces are segregated, it's a kind of paste, and it has a pungent characteristic - it smells like rotten peanut butter."

This whiffy paste was then dissolved in acid, leaving only the stardust.

"It's like burning down the haystack to find the needle," said Philipp Heck.

To work out how old the grains were, the researchers measured how long they had been exposed to cosmic rays in space. These rays are high-energy particles that travel through our galaxy and penetrate solid matter.

Some of these rays interact with the matter they encounter and form new elements. The longer they are exposed, the more of these elements form. The researchers used a particular form (isotope) of the element neon - Ne-21 - to date the grains.

"I compare this with putting out a bucket in a rainstorm. Assuming the rainfall is constant, the amount of water that accumulates in the bucket tells you how long it was exposed," said Dr Heck.

Measuring how many of the new elements are present tells scientists how long the grain was exposed to cosmic rays. This in turn informs them how old it is.

Some of the pre-solar grains turned out to be the oldest ever discovered.

Based on how many cosmic rays had interacted with the grains, most had to be 4.6-4.9 billion years old. For comparison, the Sun is 4.6 billion years old and the Earth is 4.5 billion.

However, the oldest yielded a date of around 7.5 billion years old.

The Murchison meteorite fell to Earth in 1969

More to be found

Dr Heck told BBC News: "Only 10% of the grains are older than 5.5 billion years, 60% of the grains are "young" (at) 4.6 to 4.9 billion years old, and the rest are in between the oldest and youngest ones.

"I am sure there are older pre-solar minerals in Murchison and other meteorites, we just haven't found them yet."

Previously, the oldest pre-solar grain dated with neon isotopes was around 5.5 billion years old.

The findings shed light on a debate over whether or not new stars form at a steady rate, or whether there are highs and lows in the number of new stars over time.

"Thanks to these grains, we now have direct evidence for a period of enhanced star formation in our galaxy seven billion years ago with samples from meteorites. This is one of the key findings of our study," said Dr Heck.

The researchers also learned that pre-solar grains often float through space stuck together in large clusters, like granola. "No one thought this was possible at that scale," Philipp Heck explained.

Astronomers have discovered a titanic wave of star-forming gases practically right under our noses in the Milky Way.

Harvard University scientists reported Tuesday that this massive structure has been hiding out in the Milky Way galaxy's spiral arm closest to Earth.

The researchers were building a 3-D map of our galaxy's interstellar matter, using a star census gathered by Europe's Gaia spacecraft when they spotted the wave-shaped structure.

It's an astounding 50 quadrillion miles (85 quadrillion kilometers) long and it's home to tens of thousands of baby stars, with the potential for countless more stellar births, according to the paper published in the journal Nature.

All these stellar nurseries, or star-forming blobs of gas, are interconnected, according to Harvard's Catherine Zucker. Together, they form this wavy, gassy filament, why this shape is still a puzzle.

The sun is just 500 light years away from the wave at its closest point, according to lead author Joao Alves.

The team was shocked by the discovery. No one expected "we live next to a giant, wave-like collection of gas — or that it forms the local arm of the Milky Way," Harvard's Alyssa Goodman said in a statement.

What's more, the structure dubbed Radcliffe Wave — after a Harvard institute — contains stellar nurseries once thought to belong in a ring-shaped band around the sun. The wave contains gases equivalent to 3 million times the mass of the sun.

"It has completely transformed our understanding of our galactic `neighborhood,' " Zucker said in an email. It "has been right in front of our noses ... for millions of years, but we could not see it clearly until now."

Launched in 2013, the Gaia spacecraft has measured the distances to close to 1 billion stars in our galaxy, providing a precious, colossal data base for uncovering huge structures like the Radcliffe Wave, according to scientists.

Zucker said by charting the 3-D positions of nearby stellar nurseries, "we have finally been able to see our corner of the Milky Way in a new light, revealing this gigantic wave before us."

The wave was invisible in 2-D, requiring new 3-D mapping techniques to be detected, the researchers said at the American Astronomical Society's meeting in Hawaii.

The next step, she said, is to figure out its origin and determine whether there are more massive waves lurking out there.