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.
Greenland’s Inuit have spent decades fighting for self-determination
The article highlights the Inuit communities in Greenland amid global discussions about the island’s ownership, particularly regarding U.S. President Trump’s interest. It chronicles the Inuit’s historical presence, their traditional lifestyles, and the ongoing struggle for self-determination. Despite colonial influences, modern Kalaallit strive for recognition and independence.
Amid the discussion between U.S. President Donald Trump and Danish and European leaders about who should own Greenland, the Inuit who live there and call it home aren’t getting much attention.
The Kalaallit (Inuit of West Greenland), the Tunumi (Inuit of East Greenland) and the Inughuit (Inuit of North Greenland) together represent nearly 90% of the population of Greenland, which totals about 57,000 people across 830,000 square miles (2.1 million square kilometers).
We are Arcticanthropologists who work in a museum focused on the Arctic and its people. One of the areas we study is a land whose inhabitants call it Kalaallit Nunaat, or land of the Kalaallit. Known in English as Greenland, it is an Indigenous nation whose relatively few people have been working for decades to reclaim their right to self-determination.
For nearly 5,000 years, northwestern Greenland – including the area that is now the U.S. Space Force’s Pituffik Space Base, formerly known as Thule Air Force Base – was the island’s main entry point. A succession of Indigenous groups moved eastward from the Bering Strait region and settled in Siberia, Alaska, Canada and Greenland.
Approximately 1,000 years ago, the ancestors of the Inuit living in Greenland today arrived in that area with sophisticated technologies that allowed them to thrive in a dynamic Arctic environment where minor mishaps can have serious consequences. They hunted animals using specialized technologies and tools, including kayaks, dog-drawn sleds, complex harpoons, and snow goggles made from wood or bone with slits cut into them. They dressed in highly engineered garments made from animal fur that kept them warm and dry in all conditions.
Their tools and clothing were imbued with symbolic meanings that reflected their worldview, in which humans and animals are interdependent. Inughuit families who live in the region today continue to hunt and fish, while navigating a warming climate.Local people fish from a small boat by an iceberg with an ice cave, near Ilulissat, in 2008. Bryan Alexander, courtesy of the Peary-MacMillan Arctic Museum, Bowdoin College, CC BY-NC-ND
Arrivals from the east
At Qassiarsuk in south Greenland, around the time Inuit arrived in the north, Erik the Red established the first Norse farm, Brattahlíð, in 986, and sent word back to Iceland to encourage others to join him, as described in an online exhibit at the Greenland National Museum. Numerous Norse families followed and established pastoral farms in the region.
As Inuit expanded southward, they encountered the Norse farmers. Inuit and Norse traded, but relations were sometimes tense: Inuit oral histories and Norse sagas describe some violent interactions. The two groups maintained distinctly different approaches to living on the land that rims Greenland’s massive ice sheet. The Norse were very place-based, while the Inuit moved seasonally, hunting around islands, bays and fjords.
As the Little Ice Age set in early in the 14th century, and temperatures dropped in the Northern Hemisphere, the Norse were not equipped to adjust to the changing conditions. Their colonies faltered and by 1500 had disappeared. By contrast, the mobile Inuit took a more flexible approach and hunted both land and marine mammals according to their availability. They continued living in the region without much change to their lifestyle.
A center of activity
In Nuuk, the modern capital of Greenland, an imposing and controversial statue of missionary Hans Egede commemorates his arrival in 1721 to establish a Lutheran mission in a place he called Godthåb.
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In 1776, as trade became more important, the Danish government established the Royal Greenland Trading Department, a trading monopoly that administered the communities on the west coast of Greenland as a closed colony for the next 150 years.
By the 19th century some Kalaallit families who lived in Nuuk/Godthåb had formed an educated, urban class of ministers, educators, artists and writers, although Danish colonists continued to rule.
Meanwhile, Kalaallit families in small coastal communities continued to engage in traditional economic and social activities, based on respect of animals and sharing of resources.
On the more remote east coast and in the far north, colonization took root more slowly, leaving explorers such as American Robert Peary and traders such as Danish-Greenlandic Knud Rasmussen a free hand to employ and trade with local people.
A 1944 ad urging U.S. customers to buy shortwave radios touts contact with the people of Greenland as one benefit. Courtesy of the Peary-MacMillan Arctic Museum, Bowdoin College, CC BY-NC-ND
World War II brought the outside world to Greenland’s door. With Denmark under Nazi control, the U.S. took responsibility for protecting the strategically important island of Greenland and built military bases on both the east and west coasts. The U.S. made efforts to keep military personnel and Kalaallit apart but were not entirely successful, and some visiting and trading went on. Radios and broadcast news also spread, and Kalaallit began to gain a sense of the world beyond their borders.
The Cold War brought more changes, including the forced relocation of 27 Inughuit families living near the newly constructed U.S. Air Force base at Thule to Qaanaaq, where they lived in tents until small wooden homes were built.
In 1953, Denmark revised parts of its constitution, including changing the status of Greenland from a colony to one of the nation’s counties, thereby making all Kalaallit residents of Greenland also full-fledged citizens of Denmark. For the first time, Kalaallit had elected representatives in the Danish parliament.
Denmark also increased assimilation efforts, promoting the Danish language and culture at the expense of Kalaallisut, the Greenlandic language. Among other projects, the Danish authorities sent Greenlandic children to residential schools in Denmark.
In Nuuk in the 1970s, a new generation of young Kalaallit politicians emerged, eager to protect and promote the use of Kalaallisut and gain greater control over Greenland’s affairs. The rock band Sumé, singing protest songs in Kalaallisut, contributed to the political awakening. https://www.youtube.com/embed/qe-f6jleXFs?wmode=transparent&start=0 Sumé, a rock band singing in Kalaallisut, the Greenlandic language, helped galvanize a political movement for self-determination in the 1970s.
In a 1979 Greenland-wide referendum, a substantial majority of Kalaallit voters opted for what was called “home rule” within the Danish Kingdom. That meant a parliament of elected Kalaallit representatives handled internal affairs, such as education and social welfare, while Denmark retained control of foreign affairs and mineral rights.
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However, the push for full independence from Denmark continued: In 2009, home rule was replaced by a policy of self-government, which outlines a clear path to independence from Denmark, based on negotiations following a potential future referendum vote by Greenlanders. Self-government also allows Greenland to assert and benefit from control over its mineral resources, but not to manage foreign affairs.
Today, Nuuk is a busy, vibrant, modern city. Life is quieter in smaller settlements, where hunting and fishing are still a way of life. While contemporary Greenland encompasses this range of lifestyles, Kalaallit are unified in their desire for self-determination. Greenland’s leaders have delivered this message clearly to the public and to the White House directly.
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Why Arizona Republicans Are Pushing Back on Light Rail to the State Capitol — and What It Means for the West Valley
Arizona’s debate over a proposed light rail extension to the State Capitol has intensified. Supporters argue it promotes connectivity and equity, while Republicans oppose it due to cost concerns and a preference for car-centric infrastructure. The outcome will impact future west-side transit expansions and shape regional transportation priorities.
Arizona’s long-running debate over public transit has flared up again, this time over a proposed Valley Metro light rail extension that would bring rail service closer to the Arizona State Capitol complex. While Phoenix and Valley Metro leaders argue the project is a logical next step in regional mobility, Republican leaders at the state Capitol have mounted strong opposition — creating uncertainty not just for this segment, but for future west-side expansions.
The Case for the Capitol Light Rail Extension
Supporters of the project, including Valley Metro officials, Phoenix city leaders, transit advocates, and many west Phoenix residents, argue that extending light rail toward the Capitol area is both practical and symbolic.
From a planning standpoint, the Capitol is a major employment center that draws thousands of workers, visitors, and students. Transit planners say rail access would reduce congestion, improve air quality, and provide reliable transportation for residents who already depend heavily on public transit.
Proponents also emphasize equity. West Phoenix has historically received fewer infrastructure investments than other parts of the metro area, despite strong transit ridership. For supporters, extending rail service westward is about connecting communities to jobs, education, and government services — not politics.
Why is Arizona fighting over a light rail line to the State Capitol?
There is also a broader regional argument: light rail lines function best as part of a connected network. Leaving a gap near a central civic destination, supporters say, undermines long-term system efficiency.
Why Republican Lawmakers Are Opposed
Republican leaders in the Arizona Legislature see the project very differently.
One major issue is cost. GOP lawmakers frequently point to the rising price of light rail construction, which has increased significantly over the past decade. They argue that rail projects deliver limited benefit compared to their expense and that bus service or roadway improvements could move more people at lower cost.
Usage is another concern. Critics note that light rail serves a relatively small percentage of total commuters in the Phoenix metro area and requires ongoing public subsidies to operate. From this perspective, expanding rail further — especially into politically sensitive areas like the Capitol — is viewed as fiscally irresponsible.
There is also a political and legal dimension. In recent years, Republican lawmakers passed legislation restricting light rail construction near the Capitol complex. While framed as a land-use and security issue, critics argue it reflects deeper ideological opposition to rail transit and urban-oriented infrastructure.
Finally, some GOP leaders simply prefer different transportation priorities. Arizona remains a car-centric state, and many Republican officials believe future investments should focus on highways, autonomous vehicle technology, or flexible transit options rather than fixed rail.
A Political Standoff with Real Transit Consequences
The dispute has become a high-stakes standoff between the Republican-controlled Legislature and Democratic leaders at the city and regional level. While lawmakers may not be able to directly cancel the project, they have significant leverage through funding approvals, oversight committees, and future legislation.
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This uncertainty creates challenges for Valley Metro, which relies on long-term planning, federal funding commitments, and voter-approved local taxes. Transit systems work best with predictability — and political volatility can drive up costs or delay construction.
What This Means for West Valley Light Rail Expansion
The biggest question is what happens next for west Phoenix and the broader West Valley.
If the Capitol-area extension is altered or blocked, Valley Metro may be forced to redesign routes that avoid the restricted area, potentially making service less direct or less useful. That could weaken the case for future westward expansions toward areas like Maryvale or even farther west.
On the other hand, the controversy has also drawn renewed attention to west-side transit needs. Some advocates believe the political fight could energize local support, leading to stronger community backing and clearer messaging about why rail matters in west Phoenix.
Long term, the outcome may set a precedent. If state lawmakers successfully limit rail construction through legislative action, it could signal tighter constraints on future expansions. If cities push forward despite opposition, it may reaffirm local control over transportation planning.
The Bigger Picture
At its core, the debate over light rail to the Arizona State Capitol reflects a broader clash of visions for the region’s future: one focused on dense, transit-oriented growth, and another centered on fiscal restraint and automobile mobility.
For residents of the West Valley, the stakes are tangible. The decision will shape access to jobs, education, and public services for decades. Whether the project moves forward as planned, is rerouted, or delayed entirely, it will leave a lasting imprint on how — and for whom — the Valley’s transit system grows.
As Phoenix continues to expand westward, the question remains unresolved: will light rail be allowed to follow?
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A severe winter storm that brought crippling freezing rain, sleet and snow to a large part of the U.S. in late January 2026 left a mess in states from New Mexico to New England. Hundreds of thousands of people lost power across the South as ice pulled down tree branches and power lines, more than a foot of snow fell in parts of the Midwest and Northeast, and many states faced bitter cold that was expected to linger for days.
The sudden blast may have come as a shock to many Americans after a mostly mild start to winter, but that warmth may have partly contributed to the ferocity of the storm.
As atmospheric and climate scientists, we conduct research that aims to improve understanding of extreme weather, including what makes it more or less likely to occur and how climate change might or might not play a role.
To understand what Americans are experiencing with this winter blast, we need to look more than 20 miles above the surface of Earth, to the stratospheric polar vortex.On the morning of Jan. 26, 2026, the freezing line, shown in white, reached far into Texas. The light band with arrows indicates the jet stream, and the dark band indicates the stratospheric polar vortex. The jet stream is shown at about 3.5 miles above the surface, a typical height for tracking storm systems. The polar vortex is approximately 20 miles above the surface. Mathew Barlow, CC BY
What creates a severe winter storm like this?
Multiple weather factors have to come together to produce such a large and severe storm.
Winter storms typically develop where there are sharp temperature contrasts near the surface and a southward dip in the jet stream, the narrow band of fast-moving air that steers weather systems. If there is a substantial source of moisture, the storms can produce heavy rain or snow.
In late January, a strong Arctic air mass from the north was creating the temperature contrast with warmer air from the south. Multiple disturbances within the jet stream were acting together to create favorable conditions for precipitation, and the storm system was able to pull moisture from the very warm Gulf of Mexico.The National Weather Service issued severe storm warnings (pink) on Jan. 24, 2026, for a large swath of the U.S. that could see sleet and heavy snow over the following days, along with ice storm warnings (dark purple) in several states and extreme cold warnings (dark blue). National Weather Service
Where does the polar vortex come in?
The fastest winds of the jet stream occur just below the top of the troposphere, which is the lowest level of the atmosphere and ends about seven miles above Earth’s surface. Weather systems are capped at the top of the troposphere, because the atmosphere above it becomes very stable.
The stratosphere is the next layer up, from about seven miles to about 30 miles. While the stratosphere extends high above weather systems, it can still interact with them through atmospheric waves that move up and down in the atmosphere. These waves are similar to the waves in the jet stream that cause it to dip southward, but they move vertically instead of horizontally.A chart shows how temperatures in the lower layers of the atmosphere change between the troposphere and stratosphere. Miles are on the right, kilometers on the left. NOAA
You’ve probably heard the term “polar vortex” used when an area of cold Arctic air moves far enough southward to influence the United States. That term describes air circulating around the pole, but it can refer to two different circulations, one in the troposphere and one in the stratosphere.
The Northern Hemisphere stratospheric polar vortex is a belt of fast-moving air circulating around the North Pole. It is like a second jet stream, high above the one you may be familiar with from weather graphics, and usually less wavy and closer to the pole.
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Sometimes the stratospheric polar vortex can stretch southward over the United States. When that happens, it creates ideal conditions for the up-and-down movement of waves that connect the stratosphere with severe winter weather at the surface.A stretched stratospheric polar vortex reflects upward waves back down, left, which affects the jet stream and surface weather, right. Mathew Barlow and Judah Cohen, CC BY
The forecast for the January storm showed a close overlap between the southward stretch of the stratospheric polar vortex and the jet stream over the U.S., indicating perfect conditions for cold and snow.
This is what was happening in late January 2026 in the central and eastern U.S.
If the climate is warming, why are we still getting severe winter storms?
Earth is unequivocally warming as human activities release greenhouse gas emissions that trap heat in the atmosphere, and snow amounts are decreasing overall. But that does not mean severe winter weather will never happen again.
One factor may be increasing disruptions to the stratospheric polar vortex, which appear to be linked to the rapid warming of the Arctic with climate change.The polar vortex is a strong band of winds in the stratosphere, normally ringing the North Pole. When it weakens, it can split. The polar jet stream can mirror this upheaval, becoming weaker or wavy. At the surface, cold air is pushed southward in some locations. NOAA
Additionally, a warmer ocean leads to more evaporation, and because a warmer atmosphere can hold more moisture, that means more moisture is available for storms. The process of moisture condensing into rain or snow produces energy for storms as well. However, warming can also reduce the strength of storms by reducing temperature contrasts.
A warmer environment also increases the likelihood that precipitation that would have fallen as snow in previous winters may now be more likely to fall as sleet and freezing rain.
There are still many questions
Scientists are constantly improving the ability to predict and respond to these severe weather events, but there are many questions still to answer.
Much of the data and research in the field relies on a foundation of work by federal employees, including government labs like the National Center for Atmospheric Research, known as NCAR, which has been targeted by the Trump administration for funding cuts. These scientists help develop the crucial models, measuring instruments and data that scientists and forecasters everywhere depend on.
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This article, originally published Jan. 24, 2026, has been updated with details from the weekend storm.
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