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An unopened letter that was mailed back in 1697 but never delivered has been read by researchers who have developed a way to virtually "unfold" sealed letter packets without having to actually break the seal.

The new technique, described in the journal Nature Communications, should allow historians to learn more about "letterlocking," the practice of using elaborate slits, folds, creases and tucks to turn a flat sheet of paper with a written message into a tamper-resistant package.

Updated at 5:40 p.m.

A panel of experts that advises the Centers for Disease Control and Prevention has given its blessing to a new one-shot vaccine for COVID-19.

When Linsey Marr looks back at the beginning of 2020, what strikes her is how few people in the world really understood how viruses can travel through the air.

"In the past year, we've come farther in understanding airborne transmission, or at least kind of beyond just the few experts who study it, than we have in decades," says Marr. "Frankly, I thought it would take us another 30 years to get to where we are now."

Look up at the night sky and, if you're away from city lights, you'll see stars. The space between those bright points of light is, of course, filled with inky blackness.

Some astronomers have wondered about that all that dark space — about how dark it really is.

Last week, craving sweets, Colin Purrington remembered the Twinkies.

He'd purchased them back in 2012 for sentimental reasons when he heard that Hostess Brands was going bankrupt and Twinkies might disappear forever.

"When there's no desserts in the house, you get desperate," says Purrington, who went down to the basement and retrieved the old box of snack cakes, fully intending to enjoy several.

Scientists say they've detected a gas in the clouds of Venus that, on Earth, is produced by microbial life.

The researchers have racked their brains trying to understand why this toxic gas, phosphine, is there in such quantities, but they can't think of any geologic or chemical explanation.

The mystery raises the astonishing possibility that Venus, the planet that comes closest to Earth as it whizzes around the sun, might have some kind of life flourishing more than 30 miles up in its yellow, hazy clouds.

Mike Brown has been using the Hubble Space Telescope pretty consistently for most of the past three decades since it launched in 1990. But recently he had an experience with Hubble that he never had before.

With the annual flu season about to start, it's still unclear exactly how influenza virus will interact with the coronavirus if a person has both viruses.

This year's flu season in the Southern Hemisphere was weirdly mild.

A surprisingly small number of people in the Southern Hemisphere have gotten the flu this year, probably because the public health measures put in place to fight COVID-19 have also limited the spread of influenza.

That makes public health experts hopeful that the U. S. and other northern countries might be spared the double whammy of COVID-19 and a bad flu season this winter.

Still, they warn against complacency and say people still need to get vaccinated against the flu.

Updated at 6:40 p.m. ET

Two NASA astronauts are back on Earth after their space capsule splashed down in the Gulf of Mexico, off the coast of Pensacola, Fla.

The last time any NASA astronauts came home by splashing down was in 1975 — and back then, they were in an Apollo space vehicle. This time, the astronauts were in a white, bell-shaped capsule owned by SpaceX.

The White House has touted the fact that its coronavirus task force provided each state with a list of labs that could potentially test for the virus, but officials in a number of states told NPR that the lists did not actually help them increase testing.

As the coronavirus sweeps across the globe, one pattern remains consistent: Men seem harder hit by the virus than women and are more likely to have severe illness or die.

At least in the United States, however, it seems that men are less likely to seek out testing for the virus when they feel sick.

When researcher Josh Santarpia stands at the foot of a bed, taking measurements with a device that can detect tiny, invisible particles of mucus or saliva that come out of someone's mouth and move through the air, he can tell whether the bedridden person is speaking or not just by looking at the read-out on his instrument.

The World Health Organization says the virus that causes COVID-19 doesn't seem to linger in the air or be capable of spreading through the air over distances of more than about 3 feet.

But at least one expert in virus transmission said it's way too soon to know that.

The latest figures on coronavirus tests run so far in the U.S. were put at about 552,000, according to government officials during the Thursday's briefing of the White House Coronavirus Task Force.

"The testing is going very, very well," President Trump said.

At a time when the nation is desperate for authoritative information about the coronavirus pandemic, the country's foremost agency for fighting infectious disease outbreaks has gone conspicuously silent.

"I want to assure Americans that we have a team of public health experts," President Trump said at Tuesday evening's coronavirus task force briefing — a bit of reassurance that probably would not have been necessary if that briefing had included anyone from the Centers for Disease Control and Prevention.

Scientists can get very excited about what they study, and that means they can be pretty jazzed when what they study gets turned into one of the official emojis of the world and enters our shared visual language.

But sometimes that enthusiasm is tempered by more complex feelings, which is the case with some of the latest emojis that are about to hit our smartphones.

Consider the "rock" emoji.

NASA is at a critical juncture in its push to get people back to the moon by 2024, with key decisions expected within weeks.

This effort to meet an ambitious deadline set by the Trump administration last year faces widespread skepticism in the aerospace community, even as the new head of human spaceflight at NASA insists that it can succeed.

India's space agency says that four astronaut candidates have been selected for its first human mission, targeted to launch by 2022, but they've not been publicly named or identified.

India hopes to join the United States, Russia and China as the world's fourth nation capable of sending people to space. It has been developing its own crewed spacecraft, called Gaganyaan (or "sky vehicle" in Sanskrit), that would let two to three people orbit Earth on a weeklong spaceflight.

Artificial stone used to make kitchen and bathroom countertops has been linked to cases of death and irreversible lung injury in workers who cut, grind and polish this increasingly popular material.

The fear is that thousands of workers in the United States who create countertops out of what's known as "engineered stone" may be inhaling dangerous amounts of lung-damaging silica dust, because engineered stone is mostly made of the mineral silica.

Science has some bad news for the bearded: young children think you're really, really unattractive.

A new study suggests that, until they reach puberty, kids are strongly anti-beard — although children with bearded fathers did feel more warmly toward facial hair.

A drone called Dragonfly will be buzzing around Saturn's largest moon in 2034, if all goes according to plan.

That's because NASA has picked a mission to the icy moon Titan for its next major foray out into the solar system.

Updated at 8:40 a.m. ET, Friday

The vote to redefine the kilogram was, as expected, unanimous, with representatives from more than 50 countries saying "yes" or "oui" at the historic meeting in Versailles, France.

Bill Phillips, a Nobel laureate from the National Institute of Standards and Technology in Maryland, told the assembled delegates that basing the kilogram's official definition on a hunk of metal held in a vault was "a situation that is clearly intolerable."

Wednesday was the day astronomers said goodbye to the old Milky Way they had known and loved and hello to a new view of our home galaxy.

A European Space Agency mission called Gaia just released a long-awaited treasure trove of data: precise measurements of 1.7 billion stars.

It's unprecedented for scientists to know the exact brightness, distances, motions and colors of more than a billion stars. The information will yield the best three-dimensional map of our galaxy ever.

If signs of life are found on a planet beyond our solar system sometime in the next decade, they'll most likely be on a planet discovered by a NASA satellite that's scheduled to launch on Monday.

The mission is called TESS, short for Transiting Exoplanet Survey Satellite, and it will spend two years scanning almost the entire sky to search for alien worlds.