4 . Studies of Mercury — the planet closest to the sun-show that it has shrunk by about 11 kilometers across since the solar system’s birth 4.5 billion years ago. As the planet cooled and contracted (收缩), its surface had many long curved ridges (山脊) similar to the wrinkles on a bad apple.

A new research on these ridges, called lobate scarps (瓣状陡坡), has found more of them, with steeper faces, than ever before. The discovery suggests that Mercury shrank by far more than the previous estimate, says Paul Byrne, a planetary scientist. The finding helps explain how Mercury’s huge metallic core (中心) cooled off over time. It may also finally settle the differences between theoretical scientists, who had predicted a lot of shrinkage, with observers who had not found evidence of that — until now. “We are resolving a four-decade-old argument here,” Byrne added.

Planetary scientists have been arguing over Mercury’s lobate scarps ever since the Mariner 10 spacecraft flew past the planet three times in 1974-1975. Researchers can use measurements of the length and height of the scarps to calculate how much planetary shrinkage they represent. That shrinkage is a product of Mercury’s strange structure — “like a core floating through space with a thin outer blanket,” says Byrne. Most of the planet is made of that large core, and so it would have cooled rapidly as heat rushed toward its surface.

The latest data, coming from NASA’s MESSENGER probe and covering the entire planet, showed many lobate scarps with sharp steeper faces, Byrne said. It also uncovered details on another kind of surface feature that may be related to shrinkage. These “wrinkle ridges” are less pronounced than the lobate scarps but may also have formed during contraction. Combined, the data on the lobate scarps and the wrinkle ridges suggest that Mercury’s diameter (直径) has shrunk by 11.4 kilometers, Byrne said.

5 . An international team of scientists says it has discovered two new “super-Earth” type planets about 100 light-years away, one of which may be suitable for life. Unlike any of the planets in our solar system, the two newly-discovered super-Earths are larger than Earth, but lighter than icy planets like Uranus and Neptune.

Researchers at Belgium’s University of Liège announced that they found another one while using Earth-based telescopes to confirm the existence of a different planet initially discovered by a NASA satellite in the same solar system.

NASA’s satellite found planet LP 890-9b, which is about 30% larger than Earth and orbits its sun, LP 890-9, in just 2.7 days. ULiège researchers used their telescopes in Chile and Spain to take a closer look at the planet with high-precision cameras. That’s when the scientists discovered another planet, LP 890-9c, which is 40% larger than Earth and takes 8.5 days to orbit its sun.

Francisco Pozuelos, a researcher at the Institute of Astrophysics of Andalusia, said that the planet could be suitable to life despite being a mere 3.7 million miles from its sun. Earth, by comparison, is located over 93 million miles away from our sun. “Although this planet orbits very close to its star, the amount of stellar irradiation (恒星辐射量) it receives is still low, and could allow the presence of liquid water on the planet’s surface, so long as it has a sufficient atmosphere,” Pozuelos said. That’s because although LP 890-9 is by far larger than its planets, it is about 6.5 times smaller than our sun and is roughly half as cool temperature-wise as our sun, he added. “This explains why LP 890-9c, despite being much closer to its star than the Earth is to the Sun, could still have conditions that are suitable for life,” said Pozuelos.

7 . Having a conversation on Mars would be difficult. That’s partly because Mars can be really cold, and your teeth may be shaking. But it’s also because the Red Planet’s thin atmosphere of mostly CO3 doesn’t carry sound well. In fact, someone speaking next to you on Mars would sound as quiet as if they were talking 60 meters away on Earth.

A team studied some of the first sound recordings ever made on the Red Planet. The recordings had been picked up by a microphone on American Perseverance rover (探测器). This space robot has been exploring Mars since February 2021.

The recordings Perseverance got weren’t the sounds of events on Mars. They were noises made when the rover fired a laser (激光) at small rocks nearby. These data allowed the researchers to measure the speed of sound on Mars — and discovered a surprise. Within the range of human hearing, high sounds travel at about 250 meters per second. Low sounds travel slower — about 240 meters per second. Those low waves will travel just a few meters before becoming unhearable. Unexpectedly, the higher sounds die away over even shorter ranges.

When a sound wave moves through air or a fluid, it adds energy to the molecules (分子) around it. Air will gradually move that energy around. This is called the relaxation effect. For sound waves traveling through air, relaxation depends on the frequency of the sound and the type of molecules in the air. On Mars, the relaxation after a high sound happens faster than after a low sound. That’s because the atmosphere has low pressure and is mostly composed of (由……组成) CO₂.

Measuring the speed of sound can give scientists an exact way to study the Martian atmosphere. Air pressure, temperature and humidity (湿度) all affect the speed of sound. So, by measuring changes in the speed of sound over time, researchers can learn more about Martian weather. With Perseverance broadcasting more sounds back to Earth, scientists will be able to study bow its soundscape changes over the course of Martian seasons.

8 . When it comes to black holes, we are caught between a rock and a hard place. In the 1970s, Stephen Hawking showed that all black holes give off thermal radiation(热辐射)and eventually evaporate(蒸发). In doing so, they seemed to be destroying information contained in the matter that fell into them, therefore going against a rule of quantum mechanics(量子力学): information cannot be created or destroyed.

Some argued that the outgoing “Hawking radiation” preserved the information. However, if this were the case, then given certain assumptions, the event horizon(视界)—— the black hole’s boundary of no return—— would become intensely energetic, forming a firewall. But such firewalls go against the theory of general relativity, which says that space-time near the event horizon should be smooth. The black hole firewall paradox was thus born.

Now, Sean Carroll at the California Institute of Technology and his colleagues have shown that the paradox disappears when the evolution of black holes is understood in the context of the many-worlds interpretation of quantum mechanics.

The quantum state of the universe is described by something called the global wave function(全局波函数). According to traditional quantum mechanics, whenever there are many possible outcomes for physical process, this wave function ”collapses“ to represent one outcome. But in the many-worlds Interpretation, the wave function doesn’t collapse-rather, it branches, with one branch for each outcome. The branches evolve independently of each other, as separate worlds.

In this way of thinking, the formation of a black hole and its evaporation due to Hawking radiation lead to multiple branches of the wave function. An observer monitoring a black hole also splits into multiple observers, one in each branch.

The new work shows that from the perspective of an observer in a given branch, space-time behaves as described by general relativity and the black hole has no firewall.

But does that imply loss of information? No, says team member Aidan Chatwin-Davies, also of Caltech. That is because the principle of preservation of information applies to the global wave function and not to its individual branches, he says. Information is preserved across all branches of the global wave function, but not necessarily in any one branch. Given this case, a black hole that doesn’t lose information and yet has a smooth, uneventful event horizon without a fire wall isn’t a contradiction.

Yasunori Nomura at the University of California at Berkeleyy has independently arrived at some similar conclusions in his work. He agrees that the many-worlds approach resolves the paradox around information loss from black holes. “Many worlds should be taken seriously,” he says.

9 . It’s more than 384,000km from Earth. We can see it most nights. And it’s not made of cheese! I am, of course, talking about the Moon. Astronauts have taken giant steps to explore this natural satellite floating in space, but despite it being out of reach for most of us,     1    .

The Moon, obviously, provides moonlight. A full moon, seen roughly once a month, can light up our way on an otherwise dark night. But while this lunar light can be impressive to look at,     2    . One study showed that during or around the full moon, those studied spent less time in deep sleep, slept for less time and reported having poorer sleep, despite sleeping in a dark room not exposed to moonlight.

    3    . One study suggested animals are more likely to bite us during a full moon. And many moons ago, it was thought the Moon induced lunacy — the word derives from the Latin word ‘lunaticus’, meaning ‘moonstruck’, and evolved from the idea that celestial changes could cause periods of insanity.     4    . They will avoid a full moon at all costs because, although the added moisture in the soil at this time may give a fuller and juicier grape, the additional water is thought to dilute the taste of the fruit, which results in a less successful vintage.

The Moon might affect our behaviour too. Writing about this for BBC Future, Claudia Hammond explains one interesting theory. Just as the Moon’s gravitational pull affects the tides, it exerts its influence on the water in our bodies. But she points out “the Moon is smaller than the Earth, so its gravitational pull is correspondingly less powerful. What’s more, it exerts the same force on us regardless of whether it’s new or full.”     5    . So, like the Moon being made of cheese, we must be careful what we believe!

10 . It is hard to imagine that plants or animals could ever exist on Mars. But scientists continue to look for evidence. NASA, America’s space agency, has found evidence that, a long time ago, there was surface water on the Mars. Scientists believe water is necessary for life as we know it. So since that discovery, they have been looking for chemicals that would be present if there once was or still is life on the planet.

At a December 13 meeting in California, NASA scientists reported an important discovery on Mars. They said for the first time that they had found very small amounts of boron(硼). Boron is important because it could help build RNA molecules(分子). And RNA molecules are important because they are one of the basic building parts for life.

One of the next steps in the scientists’ search for life on Mars comes soon. The next spacecraft is planned to launch. It will bring rocks from Mars back to Earth. Scientists in Britain are getting ready for those Mars rocks now. Before this, using a powerful microscope(显微镜), they have already examined 200-million-year-old volcanic rocks found deep in the Pacific Ocean. The microscope showed holes on the rocks caused by tiny living things called microbes(微生物). Microbes are the oldest form of life on Earth.

Next, the scientists in Britain will examine rocks which contain ancient material from Mars. The material comes from a time when Mars would have been more likely to support life. The scientists hope to get the same findings in the rocks from Mars as the ones they saw in the ocean rocks. If they do, they predict that the rocks coming directly from Mars will also show signs of life. That, in turn, could finally prove that we are not alone in the universe.