Some ‘water worlds’ like Jupiter’s moon Europa could potentially be habitable for life. NASA/JPL-Caltech/SETI InstituteDaniel Apai, University of Arizona The search for life beyond Earth is a key driver of modern astronomy and planetary science. The U.S. is building multiple major telescopes and planetary probes to advance this search. However, the signs of life – called biosignatures – that scientists may find will likely be difficult to interpret. Figuring out where exactly to look also remains challenging. I am an astrophysicist and astrobiologist with over 20 years of experience studying extrasolar planets – which are planets beyond our solar system. My colleagues and I have developed a new approach that will identify the most interesting planets or moons to search for life and help interpret potential biosignatures. We do this by modeling how different organisms may fare in different environments, informed by studies of limits of life on Earth.
New telescopes to search for life
Astronomers are developing plans and technology for increasingly powerful space telescopes. For instance, NASA is working on its proposed Habitable Worlds Observatory, which would take ultrasharp images that directly show the planets orbiting nearby stars. My colleagues and I are developing another concept, the Nautilus space telescope constellation, which is designed to study hundreds of potentially Earthlike planets as they pass in front of their host stars.Future telescopes, like the proposed Nautilus, could help search the skies for habitable planets.Katie Yung, Daniel Apai /University of Arizona and AllThingsSpace /SketchFab, CC BY-ND These and other future telescopes aim to provide more sensitive studies of more alien worlds. Their development prompts two important questions: “Where to look?” and “Are the environments where we think we see signs of life actually habitable?” The strongly disputed claims of potential signs of life in the exoplanet K2-18b, announced in April 2025, and previous similar claims in Venus, show how difficult it is to conclusively identify the presence of life from remote-sensing data.
When is an alien world habitable?
Oxford Languages defines “habitable” as “suitable or good enough to live in.” But how do scientists know what is “good enough to live in” for extraterrestrial organisms? Could alien microbes frolic in lakes of boiling acid or frigid liquid methane, or float in water droplets in Venus’ upper atmosphere? To keep it simple, NASA’s mantra has been “follow the water.” This makes sense – water is essential for all Earth life we know of. A planet with liquid water would also have a temperate environment. It wouldn’t be so cold that it slows down chemical reactions, nor would it be so hot that it destroys the complex molecules necessary for life. However, with astronomers’ rapidly growing capabilities for characterizing alien worlds, astrobiologists need an approach that is more quantitative and nuanced than the water or no-water classification.
A community effort
As part of the NASA-funded Alien Earths project that I lead, astrobiologist Rory Barnes and I worked on this problem with a group of experts – astrobiologists, planetary scientists, exoplanet experts, ecologists, biologists and chemists – drawn from the largest network of exoplanet and astrobiology researchers, NASA’s Nexus for Exoplanet System Science, or NExSS. Over a hundred colleagues provided us with ideas, and two questions came up often: First, how do we know what life needs, if we do not understand the full range of extraterrestrial life? Scientists know a lot about life on Earth, but most astrobiologists agree that more exotic types of life – perhaps based on different combinations of chemical elements and solvents – are possible. How do we determine what conditions those other types of life may require? Second, the approach has to work with incomplete data. Potential sites for life beyond Earth – “extrasolar habitats” – are very difficult to study directly, and often impossible to visit and sample. For example, the Martian subsurface remains mostly out of our reach. Places like Jupiter’s moon Europa’s and Saturn’s Moon Enceladus’ subsurface oceans and all extrasolar planets remain practically unreachable. Scientists study them indirectly, often only using remote observations. These measurements can’t tell you as much as actual samples would.Mars’ hot, dusty surface is hostile for life. But scientists haven’t been able to study whether some organisms could lurk beneath.NASA/JPL-Caltech/Malin Space Science Systems To make matters worse, measurements often have uncertainties. For example, we may be only 88% confident that water vapor is present in an exoplanet’s atmosphere. Our framework has to be able to work with small amounts of data and handle uncertainties. And, we need to accept that the answers will often not be black or white.
A new approach to habitability
The new approach, called the quantitative habitability framework, has two distinguishing features: First, we moved away from trying to answer the vague “habitable to life” question and narrowed it to a more specific and practically answerable question: Would the conditions in the habitat – as we know them – allow a specific (known or yet unknown) species or ecosystem to survive? Even on Earth, organisms require different conditions to survive – there are no camels in Antarctica. By talking about specific organisms, we made the question easier to answer. Second, the quantitative habitability framework does not insist on black-or-white answers. It compares computer models to calculate a probabilistic answer. Instead of assuming that liquid water is a key limiting factor, we compare our understanding of the conditions an organism requires (the “organism model”) with our understanding of the conditions present in the environment (the “habitat model”). Both have uncertainties. Our understanding of each can be incomplete. Yet, we can handle the uncertainties mathematically. By comparing the two models, we can determine the probability that an organism and a habitat are compatible. As a simplistic example, our habitat model for Antarctica may state that temperatures are often below freezing. And our organism model for a camel may state that it does not survive long in cold temperatures. Unsurprisingly, we would correctly predict a near-zero probability that Antarctica is a good habitat for camels.A hydrothermal vent deep in the Atlantic Ocean. These vents discharge incredibly hot plumes of water, but some host hearty microorganisms.P. Rona / OAR/National Undersea Research Program (NURP); NOAA We had a blast working on this project. To study the limits of life, we collected literature data on extreme organisms, from insects that live in the Himalayas at high altitudes and low temperatures to microorganisms that flourish in hydrothermal vents on the ocean floor and feed on chemical energy. We explored, via our models, whether they may survive in the Martian subsurface or in Europa’s oceans. We also investigated if marine bacteria that produce oxygen in Earth’s oceans could potentially survive on known extrasolar planets. Although comprehensive and detailed, this approach makes important simplifications. For example, it does not yet model how life may shape the planet, nor does it account for the full array of nutrients organisms may need. These simplifications are by design. In most of the environments we currently study, we know too little about the conditions to meaningfully attempt such models – except for some solar system bodies, such as Saturn’s Enceladus. The quantitative habitability framework allows my team to answer questions like whether astrobiologists might be interested in a subsurface location on Mars, given the available data, or whether astronomers should turn their telescopes to planet A or planet B while searching for life. Our framework is available as an open-source computer model, which astrobiologists can now readily use and further develop to help with current and future projects. If scientists do detect a potential signature of life, this approach can help assess if the environment where it is detected can actually support the type of life that leads to the signature detected. Our next steps will be to build a database of terrestrial organisms that live in extreme environments and represent the limits of life. To this data, we can also add models for hypothetical alien life. By integrating those into the quantitative habitability framework, we will be able to work out scenarios, interpret new data coming from other worlds and guide the search for signatures of life beyond Earth – in our solar system and beyond. Daniel Apai, Associate Dean for Research and Professor of Astronomy and Planetary Sciences, University of Arizona This article is republished from The Conversation under a Creative Commons license. Read the original article.
Why Downtown Los Angeles Feels Small Compared to Other Cities
Downtown Los Angeles often feels “small” compared to other U.S. cities, but that’s only part of the story. With some of the tallest buildings west of the Mississippi and skyline clusters spread across the region, LA’s downtown reflects the city’s unique polycentric identity—one that, if combined, could form a true mega downtown.
Panorama of Los Angeles from Mount Hollywood – California, United States
When people think of major American cities, they often imagine a bustling, concentrated downtown core filled with skyscrapers. New York has Manhattan, Chicago has the Loop, San Francisco has its Financial District. Los Angeles, by contrast, often leaves visitors surprised: “Is this really downtown?”
The answer is yes—and no.
Downtown LA in Context
Compared to other major cities, Downtown Los Angeles (DTLA) is relatively small as a central business district. For much of the 20th century, strict height restrictions capped most buildings under 150 feet, while cities like Chicago and New York were erecting early skyscrapers. LA’s skyline didn’t really begin to climb until the late 1960s.
But history alone doesn’t explain why DTLA feels different. The real story lies in how Los Angeles grew: not as one unified city center, but as a collection of many hubs.
Downtown Los Angeles
A Polycentric City
Los Angeles is famously decentralized. Hollywood developed around the film industry. Century City rose on former studio land as a business hub. Burbank became a studio and aerospace center. Long Beach grew around the port. The Wilshire Corridor filled with office towers and condos.
Unlike other cities where downtown is the place for work, culture, and finance, Los Angeles spread its energy outward. Freeways and car culture made it easy for businesses and residents to operate outside of downtown. The result is a polycentric metropolis, with multiple “downtowns” rather than one dominant core.
A Resident’s Perspective
As someone who lived in Los Angeles for 28 years, I see DTLA differently. While some outsiders describe it as “small,” the reality is that Downtown Los Angeles is still significant. It has some of the tallest buildings west of the Mississippi River, including the Wilshire Grand Center and the U.S. Bank Tower. Over the last two decades, adaptive reuse projects have transformed old office buildings into lofts, while developments like LA Live, Crypto.com Arena, and the Broad Museum have revitalized the area.
In other words, DTLA is large enough—it just plays a different role than downtowns in other American cities.
View of Westwood, Century City, Beverly Hills, and the Wilshire Corridor.
The “Mega Downtown” That Isn’t
A friend once put it to me with a bit of imagination: “If you could magically pick up all of LA’s skyline clusters—Downtown, Century City, Hollywood, the Wilshire Corridor—and drop them together in one spot, you’d have a mega downtown.”
He’s right. Los Angeles doesn’t lack tall buildings or urban energy—it just spreads them out over a vast area, reflecting the city’s unique history, geography, and culture.
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A Downtown That Fits Its City
So, is Downtown LA “small”? Compared to Manhattan or Chicago’s Loop, yes. But judged on its own terms, DTLA is a vibrant hub within a much larger, decentralized metropolis. It’s a downtown that reflects Los Angeles itself: sprawling, diverse, and impossible to fit neatly into the mold of other American cities.
Dive into “The Knowledge,” where curiosity meets clarity. This playlist, in collaboration with STMDailyNews.com, is designed for viewers who value historical accuracy and insightful learning. Our short videos, ranging from 30 seconds to a minute and a half, make complex subjects easy to grasp in no time. Covering everything from historical events to contemporary processes and entertainment, “The Knowledge” bridges the past with the present. In a world where information is abundant yet often misused, our series aims to guide you through the noise, preserving vital knowledge and truths that shape our lives today. Perfect for curious minds eager to discover the ‘why’ and ‘how’ of everything around us. Subscribe and join in as we explore the facts that matter. https://stmdailynews.com/the-knowledge/
Century City: From Hollywood Backlot to Business Hub
Century City, originally part of 20th Century Fox’s backlot, transformed into a prominent business district in Los Angeles during the 1950s amid the decline of cinema. Developer William Zeckendorf envisioned a mixed-use urban center, leading to iconic skyscrapers and establishing the area as a hub for law, finance, and media, blending Hollywood history with modern business.
Before Century City became one of Los Angeles’ premier business districts, it was part of 20th Century Fox’s sprawling backlot, used for filming movies and housing studio operations. By the 1950s, as television rose and movie attendance declined, 20th Century Fox faced financial challenges and decided to sell a portion of its land.
Traffic On 405 Freeway In LA With Century City In The Background
Developer William Zeckendorf envisioned a “city within a city”—a modern, mixed-use urban center with office towers, hotels, and entertainment facilities. Branded Century City, the name paid homage to its studio roots while symbolizing LA’s vision for the future.
The first skyscrapers, including the Gateway West Building, set the tone for the district’s sleek, futuristic skyline. Architects like Welton Becket and Minoru Yamasaki helped shape Century City’s iconic look. Over time, it evolved from Hollywood’s backlot to a corporate and legal hub, attracting law firms, financial institutions, and media companies.
Today, Century City stands as a testament to Los Angeles’ postwar optimism, westward expansion, and multi-centered urban growth—a unique blend of Hollywood history and modern business.
Dive into “The Knowledge,” where curiosity meets clarity. This playlist, in collaboration with STMDailyNews.com, is designed for viewers who value historical accuracy and insightful learning. Our short videos, ranging from 30 seconds to a minute and a half, make complex subjects easy to grasp in no time. Covering everything from historical events to contemporary processes and entertainment, “The Knowledge” bridges the past with the present. In a world where information is abundant yet often misused, our series aims to guide you through the noise, preserving vital knowledge and truths that shape our lives today. Perfect for curious minds eager to discover the ‘why’ and ‘how’ of everything around us. Subscribe and join in as we explore the facts that matter. https://stmdailynews.com/the-knowledge/
Local governments provide proof that polarization is not inevitable
Local politics help mitigate national polarization by focusing on concrete issues like infrastructure and community needs rather than divisive symbolic debates. A survey indicates that local officials experience less partisanship, as interpersonal connections foster recognition of shared interests. This suggests that reducing polarization is possible through collaboration and changes in election laws.
Local officials get to participate in events such as ribbon cuttings, celebrating projects they may have helped make happen. NHLI/Eliot J. Schechter via Getty Images
But things are much less heated at the local level. A survey of more than 1,400 local officials by the Carnegie Corporation and CivicPulse found that local governments are “largely insulated from the harshest effects of polarization.” Communities with fewer than 50,000 residents proved especially resilient to partisan dysfunction.
Why this difference? As a political scientist, I believe that lessons from the local level not only open a window onto how polarization works but also the dynamics and tools that can help reduce it.
Problems are more concrete
Local governments deal with concrete issues – sometimes literally, when it comes to paving roads and fixing potholes. In general, cities and counties handle day-to-day functions, such as garbage pickup, running schools and enforcing zoning rules. Addressing tangible needs keeps local leaders’ attention fixed on specific problems that call out for specific solutions, not lengthy ideological debates.
By contrast, a lot of national political conflict in the U.S. involves symbolic issues, such as debates about identity and values on topics such as race, abortion and transgender rights. These battles are often divisive, even more so than purely ideological disagreements, because they can activate tribal differences and prove more resistant to compromise.When mayors come together, they often find they face common problems in their cities. Gathered here, from left, are Jerry Dyer of Fresno, Calif., John Ewing Jr. of Omaha, Neb., and David Holt of Oklahoma City. AP Photo/Kevin Wolf
Such arguments at the national level, or on social media, can lead to wildly inaccurate stereotypes about people with opposing views. Today’s partisans often perceive their opponents as far more extreme than they actually are, or they may stereotype them – imagining that all Republicans are wealthy, evangelical culture warriors, for instance, or conversely being convinced that all Democrats are radical urban activists. In terms of ideology, the median members of both parties, in fact, look similar.
These kinds of misperceptions can fuel hostility.
Local officials, however, live among the human beings they represent, whose complexity defies caricature. Living and interacting in the same communities leads to greater recognition of shared interests and values, according to the Carnegie/CivicPulse survey.
Meaningful interaction with others, including partisans of the opposing party, reduces prejudice about them. Local government provides a natural space where identities overlap.
People are complicated
In national U.S. politics today, large groups of individuals are divided not only by party but a variety of other factors, including race, religion, geography and social networks. When these differences align with ideology, political disagreement can feel like an existential threat.
Such differences are not always as pronounced at the local level. A neighbor who disagrees about property taxes could be the coach of your child’s soccer team. Your fellow school board member might share your concerns about curriculum but vote differently in presidential elections.
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Mayors can find themselves caught up in national debates, as did Minneapolis Mayor Jacob Frey over the Trump administration’s immigration enforcement policies in his city. AP Photo/Kevin Wolf
These cross-cutting connections remind us that political opponents are not a monolithic enemy but complex individuals. When people discover they have commonalities outside of politics with others holding opposing views, polarization can decrease significantly.
Finally, most local elections are technically nonpartisan. Keeping party labels off ballots allows voters to judge candidates as individuals and not merely as Republicans or Democrats.
Nevertheless, the relative partisan calm of local governance suggests that polarization is not inevitable. It emerges from specific conditions that can be altered.
Polarization might be reduced by creating more opportunities for cross-partisan collaboration around concrete problems. Philanthropists and even states might invest in local journalism that covers pragmatic governance rather than partisan conflict. More cities and counties could adopt changes in election law that would de-emphasize party labels where they add little information for voters.
Aside from structural changes, individual Americans can strive to recognize that their neighbors are not the cardboard cutouts they might imagine when thinking about “the other side.” Instead, Americans can recognize that even political opponents are navigating similar landscapes of community, personal challenges and time constraints, with often similar desires to see their roads paved and their children well educated.
The conditions shaping our interactions matter enormously. If conditions change, perhaps less partisan rancor will be the result.
The Bridge is a section of the STM Daily News Blog meant for diversity, offering real news stories about bona fide community efforts to perpetuate a greater good. The purpose of The Bridge is to connect the divides that separate us, fostering understanding and empathy among different groups. By highlighting positive initiatives and inspirational actions, The Bridge aims to create a sense of unity and shared purpose. This section brings to light stories of individuals and organizations working tirelessly to promote inclusivity, equality, and mutual respect. Through these narratives, readers are encouraged to appreciate the richness of diverse perspectives and to participate actively in building stronger, more cohesive communities.
