Like a phoenix (凤凰), some stars may burst to life covered in “ash,” rising from the remains of stars that had previously passed on.

Two fireballs covered in carbon and oxygen, ashy byproducts of helium fusion (氦聚变), belong to a new class of stars, researchers report in the March Monthly Notices. Though these burning objects are not the first stars found covered in carbon and oxygen, they are the first discovered to have helium-burning cores.

“That merger (并合) tells you the star must have evolved differently,” says study author Nicole Reindl.

The stars may have formed from the merger of two white dwarfs (白矮星), the remaining hearts of stars that exhausted their fuel, Reindl further explains. One of the two was rich in helium, while the other contained lots of carbon and oxygen. These two white dwarfs had already been orbiting one another, but gradually drew together. Eventually the helium-rich white dwarf “ate” its partner, leaving carbon and oxygen all over its surface, just as a messy child might get food all over their face.

Such a merger would have produced a star covered in carbon and oxygen to burn nuclear fusion in its core again, says Tiara Battich, a German astrophysicist.

To test this idea, Battich copied the evolution, death and eventual merger of two stars on his computer and simulated (模拟) the process. He found that putting together a carbon-and-oxygen-rich white dwarf and a more massive helium one could explain the compositions of the two stars observed by Reindl and her colleagues.

“But this should happen very rarely,” Battich says. In most cases the opposite should occur, because carbon-oxygen white dwarfs are usually the more massive ones. For the rarer case to occur, two stars slightly more massive than the sun must have formed at just the right distance and the right time.

"The origins story Battich proposes demands a very specific and unusual set of circumstances, " says Simon Blouin, a Canadian astrophysicist. “But in the end, it makes sense.”

A new study focuses on K2-18b, an exoplanet (系外行星) like the earth discovered in 2015, orbiting a red dwarf star (矮星) close enough to receive about the same amount of radiation from its star as the earth does from the sun.

Recently, scientists have discovered gas giants that have water in their atmospheres, but this is the least massive planet ever to have water detected in its atmosphere. ''The water detection was quite clear to us relatively early on, lead author Bjorn Benneke, a professor at the Institute for Research on Exoplanets at the Universite de Montreal, '' told Space.com in an interview.

Studies have suggested that planets with hydrogen-rich atmospheres could host certain forms of life, Benneke said. However, a news release reads: ''K2-18b's large atmosphere is extremely thick and creates high-pressure conditions, which likely prevents life as we know it from existing on the planet’s surface. '' While these researchers found evidence for liquid water clouds on K2-18b because of its lack of surface, rain wouldn't pour on the planet. Without a real surface, so to speak, landing on the planet would also be nearly impossible, especially because the gas is so thick and has such an incredibly high pressure that any earthr-created space-craft sent there would be devastated.

Benneke suggests that, possibly, this planet is formed by rock absorbing large amounts of gas, like a vacuum (真空) cleaner. This absorbed gas would have more than doubled the planet and increased its volume eightfold.

To come to these conclusions, the research team analyzed the data from Hubble Space Telescope observations that they made between 2016 and 2017 of the K2-18b planet passing in front of its star eight times. It allows scientists to detect distinct characters of water in a planet's atmosphere. This team plans to expand this research even further by studying K2-18b with NASA's James Webb Space Telescope, which is set to launch in 2021. This type of research, Benneke said, is leading toward a final goal of ''being able to study the earth-like planets. '' ''We are not quite there yet. '' he said, ''but this is really exciting. ''

UFO is short for Unidentified Flying Object. It’s also called Flying Saucer. It is one of the most popular topics in the 20^thcentury. With films likeClose Encounters of the Third Kind andETin the 1970s came a rapid increase in reports of flying saucers and men from Mars. More than 20 countries said their people once saw the UFO and there were over 1,200 reports about the UFO. Some even said they saw aliens.

In July, 1916, Gaynor was a nine-year-old girl and lived in North Wales. One day, on her way home from school, she saw a silver object in a field not far from her home. The object looked like a saucer. Gaynor was very scared. She stayed in the tall grass and watched the door of the strange object open. She saw two aliens wearing silver suits get ou. Then they use something to examine the ground. They were short and had pink eyes. After about half an hour, the two aliens went back into the object. Then it took off. When Gaynor got home, she told her mother about her unusual experience, but her family decided to keep quiet about it. They didn’t want others to laugh at their daughter. However, 18 months later, Gaynor told her story to UFO scientists. They found out that Gaynor told the truth.