Podcast: Not long ago, scientists confirmed that the sun is not unique— Other stars have their own planets. This was a discovery that was centuries in the making, but what would it mean for Earth and our place in the universe today?
What does home mean? What makes it special? What secrets can looking up at the stars tell us about the land beneath our feet?
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Not out of the solar system yet
Our world – Earth – means everything to us. Its size, distance from the sun, and the sun itself are just right for the formation of liquid water and life like us. Yet in recent decades, and even centuries, scientists and philosophers have been looking up to the stars and asking themselves the same questions:How special is the earth?? Are these characteristics rare, or even unique? In other words, in the vast universe, such planets are actually not rare?
Over the past few decades, we have been exploring our place in the universe. At every turn, researchers discover new surprises.
Jack Liesall:” for planetary explorationthere is a general theme, that isDiversity. When we look, everything is more diverse than expected”.
This is Jack Liesall, a space scientist at NASA's Ames Research Center. He saw firsthand how researchers uncovered these details and diversity. You see, if we go back 50 years, the number of known planets at that time actually didn't change much compared to the past few centuries.
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There are three categories of planets in the solar system: the gas giants (Jupiter and Saturn), the ice giants (Uranus and Neptune), and the rocky planets (Mercury, Venus, Mars, and of course Earth).
“One of the most fascinating questions is whether Earth is unique or if it is just one of a series of terrestrial planets that somehow fill the gap between Venus and Mars.”
This is a passage from a review titled “The Atmospheres of Mars and Venus” published in the “Annual Review of Astronomy and Astrophysics” in 1971. Just how different Earth was from its two neighbors, and why, was a very open question at the time.
Jack Lissall: “I think in the middle of the 20th century, there were still people who thought that Mars might be very much like Earth. This idea was very popular in the early 20th century.”
Over time, we have studied the planets in our solar system in more detail. In the 1970s, a large number of Soviet and American landers competed to land on our neighbors Venus and Mars. The Voyager probes, launched in 1977, visited four outer planets in the solar system. Each mission provides more pieces to the solar system puzzle, revealing what the planets are made of, how similar and unlike them they are, and how and when they — and the entire solar system — formed.
Astrophysicist Ewine van Dishoeck of Leiden University in the Netherlands is co-editor of the Annual Review of Astronomy and Astrophysics. She witnesses how our understanding of Mars, Venus, and Earth has evolved over time:
Evan Van Dishock: “Maybe theirThe way of birth is very similarbut we learned that over the next 4.5 billion years, theirEvolution in very different ways. This is why Earth is now a unique planet in the universe. Venus and Mars may have started out with similar water contents, but they evolved very differently. “
In this way, the Earth may not be so special: other planets may have had water from the beginning, and our planet, the Earth, is just a little lucky because of its special distance from the sun and a few other key factors. But in fact, there are some very important factors that make Earth special.
Paul Butler: “Of course, the most special thing about the Earth is that it gave birth to us – life.”
Paul Butler is a member of the Carnegie Institution for Science. In the 1970s, Earth was both ordinary and extraordinary. Ordinary in that it was just another Earth-like planet; special in that it was the only home to life in the universe as we know it. But there is an important limitation to this view. A few decades ago, we only knew of one star orbited by planets – the Sun. This means, as a 1971 review explained:
“Of all the planets that may exist in the universe, only nine have been studied by humans.”
But discussing whether Earth is special in the context of the universe cannot be limited to its location in the solar system.People are on a mission to explore other starsDo you really have your own planet?,as well asAnalyze the characteristics of these planets.
Evan Van Deschock: “I think there was certainly a lot of speculation about other planetary systems at the time. Whether there are any unique planets like Earth now is a valuable question, and both views have been raised.”
In fact, as early as hundreds of years ago, some people proposed the idea of planets outside the solar system. In 1584, Italian philosopher Giordano Bruno believed:
There are countless suns in the universe, and there are infinite earths orbiting these suns, just like the seven planets we can see orbiting the sun near us.
exoplanet
Copernicus' heretical views may have led to his execution 16 years later. Three hundred years later, in the 18th and 19th centuries, exoplanets seemed to be “discovered” one after another.For example, as early as 1855, someone observed a pair ofAnomalies in the motion of stars orbiting each otherto speculate on the existence of exoplanets.
Reports of new planets increased during the 20th century, but then a problem arose.
Jack Lissauer: “In the 1960s and early 1980s, news about the first discovery of exoplanets made headlines. These news stories claimed that the planets they reported were the first exoplanets discovered by humans, but they Everyone claiming that they discovered it for the first time must be wrong.”
In fact, nearly all of these reported “first discoveries” have been disproven as more evidence has emerged.
Some researchers, like Jack Lissall, whom we just met, don't want to wait until a confirmed discovery finally comes.Instead, they work to come up withtheoryto show what is possible. In his 1993 review titled “Planet Formation,” Jack noted:
“We only know exactly one planetary system – our own solar system. So, for now, theoretical models provide us with the best way to estimate the abundance of planetary systems in our galaxy. and diversity…”
Of course, with only one solar system and some evidence of disks of material around young stars, such studies are fraught with speculation. Looking back now, Jack sees the limitations of his research work.
Jack Lissall: “If people make detailed predictions, the results are often not satisfactory, but generally speaking, we basically stillWorking hard in the right direction. “
Paul, meanwhile, was unkind in his assessment of early theoretical work on the formation of planets beyond our solar system.
Paul Butler: “One thing that every theory of planet formation has in common is that they allRidiculously bad, simply irrelevant. We were trapped by our limitations. “
But in 1993, these models were unverifiable. It is hoped that more constraints will “eventually” be obtained by actually observing other planetary systems.
The word “eventually” seemed far away at that time. After all, observing exoplanets will require many technological breakthroughs.astronomers needSensitive spectroscopy techniquesto detect the tiny movements of stars so that they can be shownThere is the gravitational pull of a planetin the movement that affects it.At the same time, they also needPowerful computing power and storage spaceto process this data.
Discovery of the first exoplanet
Two years later, in 1995, there was an announcement of the discovery of the first exoplanet around a sun-like star.The characteristics of this strange planet candidate are very strange – it seemsMass close to Jupiterbut unlike Jupiter, which is far away from the sun, this star isorbiting a star at close rangeit takes about four days to complete a circuit.
Paul Butler: “Most people thought that was wrong because, first of all, all claims of finding exoplanets up to that point were false. Second, everyone knew that inThere cannot be a planet like Jupiter in an orbit every four days, this idea is very absurd. We happened to be able to observe with the telescope four nights the following week. We went in skeptical, thinking it would be impossible to see the results.At the end of those four days, we were shocked by the results. ThoseThe data is completely correct. Such a thing actually exists, it has a four-day orbit, and they really accomplished a feat. The news quickly spread around the world. For the next three or four days, our phones rang off the hook. The New York Times, the Washington Post, and various scientific magazines are constantly contacting us. “
The overwhelming coverage from the media was overwhelming. But this is understandable, because this is the first time humans have reported another extraterrestrial galaxy. The New York Times reported this on October 20, 1995:
If these findings are confirmed by further research, they could have far-reaching philosophical and scientific implications. The belief that our solar system is unique will be undermined, and the possibility of other extraterrestrial galaxies means that there is a greater chance that other alien life – perhaps intelligent life – exists in the universe.
But not everyone is so excited. In fact, Evan remembers the academic response to the experiment being completely different.
Evan Van Disok: Of course, that makes perfect sense. Of course, its strange orbit makes the planet's composition and structure surprising. But I think everyone is waiting for this result. In a way, there's been so many negative results from exoplanet exploration that it's like, “What's going on? What went wrong? Where did we go wrong? Why can't we see these exoplanets?” ?” The results of this experiment now make us relieved that we have finally found these exoplanets.
Whether it was relief or revelation, this was the first time that humans had a glimpse of an exoplanet, and they were able to understand that there are such huge differences between other planets in the universe and other planets in the solar system around us. While some planetary scientists have considered the possibility of such a massive planet orbiting so close to its star, that's certainly not the focus of the search for exoplanets.
Jack Lissall: This is why it took scientists so long to discover this extraterrestrial galaxy, because scientistsLooking for something more similar to our solar system. Maybe a closer “Jupiter”, or a bit more massive, or something like that.
Over the next few months, more of these so-called “hot Jupiters” were discovered by scientists, showing how common these seemingly extraordinary planets actually are. Paul – who we just heard describing his verification of the first exoplanet – discovers the next exoplanet. In 1998, he co-authored a review in the Annual Review of Astronomy and Astrophysics detailing the first eight planets to be discovered. This review titled “Detection of Giant Planets in the Extrasolar System” also recalls the process of this research in detail.
For 2000 years, scientists have simultaneously presented cutting-edge scientific arguments for and against the existence of exoplanets.
This review reads:
The large eccentricities and small orbits of Jupiter-mass companions discovered so far validate Copernicus' theory.
In other words, these giant planets and the tiny orbits they move in further complete the Copernican model of the universe: that is, the earth is neither the center nor the typical image of the universe.
More exoplanets
But the research doesn't end there. After all, all the planets discovered so far are reminiscent of the largest planet in the solar system: Jupiter, a giant gas planet.So the question now is: can astronomers track another one?Earth-like exoplanets? In another article in the same issue in which Paul details the first eight exoplanet discoveries, this review titled “The Astronomical Search for Earth-Like Planets and Signs of Life” details how much work scientists currently have to do:
For the detection of exoplanets, there is still a lot of room for technological progress that humans need, even to detect terrestrial planets in the exoplanets closest to the solar system… Humans need to be able to detect and process extreme contrast and dynamic range Ability.
The research required years of work, new telescopes, new tools and techniques. But even in 1998, these goals were still in the horizon.
We live in a lucky era. Our deep space exploration technology is powerful enough to support the dream goals of scientists in the past few eras: finding exoterrestrial planets and extraterrestrial life.
With the development of technology and the advancement of the times, astronomers are more capable of discovering exosolar-like galaxies.The first exoplanets were discovered by astronomers by observing the wobble of the planet's host star, a phenomenon that also revealed the planet'stiny gravitational drag.But at the same time, more and more astronomers are reportingThe phenomenon in which a star's light dims slightly when a planet passes in front of it. The combination of these methods allowed scientists to report the discovery of the first possible rocky planet in 2009. In the same year, a satellite specifically designed to search for exoplanets was launched. The operation of the Kepler space telescope allows astronomers to observe the brightness of stars with unprecedented frequency.
Jack Liesall: We developed a new subject area, and it went from nothing in 1995 to one of the major pillars of astronomy. No one could have predicted how quickly this field would grow to the size it has today.
Along with the many newly discovered exoplanets, scientists are also discovering more and more unexpected galaxies.For example, haveExtremely eccentric orbitA planet whose orbit is completely different from the nearly circular orbit of our Earth. Or,Orbiting two stars instead of oneorbiting planets.Also, planets that are reminiscent of Earth in size, but whoseOrbital distance is closeror aroundaround smaller starsrun.
Evan Van Disok: If you look back at the history of our discovery of exoplanets, I think we lacked a little bit of imagination. I think we now know that there are many other kinds of galaxies in the universe that we can't even imagine. and various other planets.
Paul – an astronomer involved in the discovery of thousands of planets – enjoys discovering all these surprises.
Paul Butler: The interesting thing about this process is,The theorists are wrong every step of the way. In every discovery of a new planet, the observations have driven theorists crazy. But as an observer, this is basically the best result.
Astronomers are constantly seeking to learn as much as possible about these planets. It is not uncommon for scientists to predict the size and mass of exoplanets. But given that the distance between the closest exoplanets to the solar system and Earth is about 700,000 times the distance between Earth and Mars, other details of exoplanets are difficult to observe. However, astronomers have discovered interesting features of these planets. These features range from the planet's volcanic activity to orbiting satellites. Piecing together what little information humans can gather could help astronomers answer one of the most intriguing questions: whether there is life on these exoplanets.
Paul Butler: Unless aliens are extraordinarily kind to us and send us their TV shows or their Encyclopedia Britannica or whatever their broadcasts are, we're not going to have easy contact with extraterrestrial life. .
It is unknown that we have yet captured such an electromagnetic wave signal, although we are still diligently hunting for them. To move closer to proactively searching for extraterrestrial life, exoplanet astronomers are looking for the best evidence they can hope for: the atmospheres of exoplanets.
An exoplanet's atmosphere is the only clue to whether a planet is capable of supporting life or potentially habitable. At the same time, the planet's atmospheric environment is a window for us to observe the planet's temperature, habitability, and biometric gases.
This quote is from a 2010 review article titled simply “Exoplanet Atmospheres.” The article was published in the Annual Review of Astronomy and Astrophysics.
The study of “hot Jupiters” occupies the vast majority of atmospheric science research…
Although these “hot Jupiters” do not have the possibility of harboring life, these articles also explore what kind of atmospheric environments are more likely to support extraterrestrial life. The article provides a detailed analysis of the factors in the Earth's atmospheric environment that are conducive to the nurturing of life. Astronomers are hoping to find these atmospheres conducive to the nurturing of life in exoplanets.
At present, astronomers can still only make preliminary analyzes to confirm what they have observed.The atmosphere of a rocky planet. Many are banking on a new generation of telescopes to open windows into these distant worlds.
Evan Van Disok: I think for the planetatmosphereResearch must be the next hot spot in the search for exoplanets. Now we can statistically determine the number and types of planets. However, further observations of these planets are now greatly needed, and these atmospheres provide information about planet formation as well as whether the planets are habitable.
The field has grown rapidly in the twenty-five years since the first exoplanets were discovered. As more and more new planets are discovered and more detailed information is obtained, scientists now seem to have a very clear answer to the first question: How special is the Earth? Or, how special do you think the earth is?
Evan Van Disok: Just how special or unique Earth is remains a mystery. Of course we know that there must be other terrestrial planets in the universe, and we also know that the orbital positions of these terrestrial planets in the universe are just right for the existence of liquid water. But I don't think we'll get a definite answer when we're dealing with other stars like our sun.
Jack Liesall: The reason it's hard for humans to get these results is because these planets are extremely difficult to find. If we need to estimate what the sizes and orbital periods of Earth-like planets have in common, we have to extrapolate from the data we have.
Inferring the similarities in sizes and orbits of exoplanets orbiting stars relies on scientific assumptions. And, given that the behavior of exoplanets is often not accurately predicted by researchers, these assumptions may also be wrong or misplaced. The development of new technologies is critical to discovering new planets and hidden features of planets, and is critical to revealing just how unique our planet is.
Evan Van Disok: I think what we've achieved in studying other planets is just the tip of the iceberg. So all of these questions are now at the stage where we actually have the technology to start answering them. It will take quite some time, possibly decades, before we can answer some of the questions. But at least we're the first generation of scientists who have the technology needed to be able to study these questions, so we can start to answer some of these very basic questions.
At the same time, as we have come a long way over the past half-century or so—to study exoplanets, our planetary neighbors, and the solar system—the dimensions of these questions have become very broad.
Jack Liesall: We don't know any better about exoplanets now than we did 50 years ago about the planets in our own solar system.
Although there are still many unfinished tasks in the study of planets, for Paul, the next research goal is now very obvious.
Paul Butler: The goal of this research is to find a second Earth. Of course, there's also the $60 billion question: Could these planets support life? Is life common or rare?
So what is the status of the earth in the universe? How special is the Earth? Over the past half century, we have sent probes to our neighbors and glimpsed thousands of planets around distant stars. These results show that there are all kinds of planets in the universe and suggest that there may be not just one, but countless Earth-like planets in the universe. Or maybe our planet is one of the lucky ones in the universe in ways we don't yet understand, and that are more unusual than we thought. No matter how our future observations influence our answers, we will always have a unique relationship with the Earth beneath our feet.
Evan Van Disok: Every time I look at the Earth, I think, “Wow, we have such a beautiful planet, we should take better care of it.” Is the Earth unique? We still can't answer this question. But we still deserve to understand that the planet we live on is incredibly beautiful.
Paul Butler: From personal emotional experience, it is difficult for us to discover a beautiful planet. For humans, we will never find another neighbor like Earth. We did evolve onto this planet in every way possible. I know a lot of people dream of going into space, but I really have no interest in going into space. If I have three or four days and nothing better to do, I don’t mind lying on the beach.
Author: Adam Levy
Translation: wnkwef; *0
Proofreading: There is a lot to gain
Original link:The search for exoplanets