At first glance, such an extreme environment seems completely inhospitable. Daytime temperatures can reach roughly 1,000 to 2,000 Kelvin, while the night side is so cold that particle motion effectively stops. Yet new research suggests these worlds may not be as hostile to life as they appear.

“Just looking at the extreme temperatures on the day and night sides — like 1,000-2,000 Kelvin on the day side and absolute zero on the night side — might lead one to conclude these exoplanets are too harsh for life. But,” says Daisuke Noto, a postdoctoral researcher in Hugo Ulloa’s Penn GEFLOW Lab at the University of Pennsylvania, “life might find a way.”

In a study published in Nature Communications, Noto and collaborators from the Japan Agency for Marine-Earth Science and Technology and Hokkaido University found that “such exoplanets may be more tolerant of sustaining life as ‘tidal locking’ can contribute to maintaining moderate thermal environments locally by distributing heat flux laterally.”

Why Tidally Locked Exoplanets Are So Common

The findings challenge a common assumption about planets that always show the same face to their stars. According to Noto, worlds with permanent day and night are actually much more common than planets like Earth, which experience a regular day and night cycle.

“Many celestial bodies like moons and planets that are very close to their parent stars are what we call tidally locked,” he explains. “Meaning, as they spin around on their axes and orbit around their parents, those rates/frequencies match, leading to the phenomena like us only seeing one side of our moon.”

This constant orientation creates a dramatic temperature contrast across the planet. Instead of focusing on surface conditions alone, the researchers wanted to understand what happens deep inside the planet, specifically within the mantle, the thick rocky layer between the crust and the core.

Recreating an Alien Planet in the Lab

Rather than relying only on computer simulations, the team built a physical laboratory model to mimic the interior of a tidally locked planet.

“Building an actual exoplanet in the lab wasn’t in the budget,” Noto jokes.

Instead, the researchers used a tabletop rectangular tank filled with viscous glycerol and tiny thermochromic liquid crystals that change color as temperatures shift. Similar experimental systems have long been used to study how heat moves through slow moving materials, making them useful stand ins for the rocky interiors of planets.

Unlike weather or ocean currents, which are strongly influenced by Earth’s rotation and gravity, convection inside a rocky mantle is driven mainly by differences in temperature and density. To reproduce those conditions, the team installed four thermostats around the tank to heat and cool different regions, creating temperature gradients similar to those expected between the permanently illuminated side, the permanently dark side, the surface, and the deep interior of a tidally locked exoplanet.

A Planetary Heat Engine

The experiments revealed a remarkably stable pattern. Hot material consistently rose beneath the day side, flowed across the upper region, cooled as it reached the night side, then sank before returning through the lower mantle. The result was one continuous circulation loop that behaved like a steady planetary heartbeat.

“It’s not chaotic like Earth’s mantle,” Noto says. “It’s slow and steady. Predictable. Kind of boring — but in a good way.”

The researchers also observed occasional mushroom shaped plumes rising from the heated base of the tank. Unlike volcanic hotspots on Earth, such as those beneath Hawaii or Iceland, these plumes remained fixed in one location rather than drifting over time.

Measurements of heat transport, known as Nusselt numbers, were comparable to those seen for Earth’s mantle. That finding suggests some tidally locked exoplanets could maintain localized geothermal environments that provide conditions favorable for life, particularly in more temperate mid latitudes.

What This Could Mean for Alien Life

The steady circulation pattern may influence more than just surface temperatures. Noto believes it could also affect the movement of a planet’s liquid core, potentially generating magnetic fields that differ from Earth’s familiar dipole field.

“That’s something we couldn’t test in this experiment,” he says, “but it’s an exciting direction for future work.”

Looking Beyond Other Worlds

Noto and Ulloa are continuing to develop similar laboratory models to investigate a wide range of geophysical processes. Earlier research from the Penn GEFLOW Lab explored how heat and mass move through confined spaces, providing new insight into the role of fluids in hydrothermal systems.

“We are planning on further extending the experimental methods to delve deeper into different systems on our planet in different contexts, the possibilities are, quite literally, out of this world,” says Noto.

Daisuke Noto is a postdoctoral researcher in the School of Arts & Sciences at the University of Pennsylvania.

Hugo Ulloa is an assistant professor in the Department of Earth and Environmental Science in Penn Arts & Sciences.

Other authors include Takehiro Miyagoshi and Takatoshi Yanagisawa of the Japan Agency for Marine-Earth Science and Technology; and Tomomi Terada and Yuji Tasaka of Hokkaido University.

The discovery challenges a long standing assumption that higher rates of photosynthesis naturally lead to greater tree growth. If trees continue taking in carbon without turning much of it into new wood, less carbon may remain locked away over the long term.

Trees Keep Capturing Carbon After Growth Stops

Forests play a major role in slowing climate change because trees remove carbon dioxide (CO₂) from the atmosphere and store much of it in their trunks, branches, and roots. Scientists have generally expected that rising atmospheric CO₂ levels would boost photosynthesis, leading to faster growth and increased long term carbon storage.

The new findings suggest the relationship is more complicated. While trees may continue absorbing additional carbon, much of it does not necessarily become new wood. Instead, that carbon may be used to produce leaves, fuel short lived metabolic processes, or serve other functions, reducing the amount of carbon stored in forests compared with previous expectations.

The results could have important implications for climate forecasting.

“Right now, most models assume that if you have photosynthesis, you have growth. We find that’s not the case,” says lead author Mukund Palat Rao, an ecoclimatologist at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School. “Just because there is more photosynthesis might not necessarily mean more tree growth in the future.”

Why Photosynthesis and Growth Are Different

During photosynthesis, plants use sunlight to convert CO₂ and water into sugars while releasing oxygen back into the atmosphere. The captured carbon remains inside the plant, but it is not all used to build wood.

Some of that carbon becomes woody tissue in the trunk, branches, and roots, where it can remain stored for decades, centuries, or even millennia. The rest supports the production of leaves and fruit, is temporarily stored as starch, or is converted into compounds released into the soil to nourish microbial communities, improve nutrient uptake, and help defend the tree against disease.

Because wood stores carbon for such long periods, understanding how much of the carbon captured through photosynthesis ultimately becomes woody biomass is critical for estimating how forests help slow climate change.

“Understanding how photosynthesis and growth are linked is very important from the perspective of understanding how forests will store carbon over long time scales,” says Rao.

Tracking Trees Across the United States

Scientists had previously suspected that carbon uptake and tree growth were not always synchronized, but there had been too few detailed observations to fully understand why.

To investigate, Rao and his colleagues combined several sources of data. They analyzed satellite imagery capable of detecting photosynthesis at 137 oak forest sites across the eastern United States and California. They also used instruments that measured CO₂ levels in tree canopies every hour and sensors attached to tree trunks that tracked tiny changes in trunk size throughout the day. (Trees tend to expand at night as roots take up water, then shrink slightly in daytime as they transpire water, with the long-term trajectory adding up to growth.) The team also incorporated tree ring records and temperature data spanning 1950 through the present.

Together, these datasets provided daily measurements of photosynthesis, carbon uptake, and tree growth.

Trees Stop Growing Months Before Photosynthesis Ends

The researchers found a clear separation between growth and photosynthesis.

At eastern U.S. sites, oak trees typically grew from May through July but continued photosynthesizing into October. About 36 percent of their annual carbon assimilation occurred after growth had already stopped in late summer.

California oaks showed a different seasonal schedule but the same overall pattern. Growth generally occurred between December and April, then slowed during mid summer and ended by August even though photosynthesis continued. Roughly 26 percent of the trees’ yearly carbon uptake happened after growth had ceased.

According to Rao, the explanation is straightforward. Tree growth depends on internal water pressure, and that pressure drops quickly during hot, dry conditions.

“The moment you have dry and hot conditions, growth activity stops pretty instantly while photosynthesis seems to continue at a slightly decreased rate,” says Rao.

What Happens to the Extra Carbon?

Some of the carbon captured after growth ends is saved to help fuel growth when the next growing season begins. The remainder is used to produce new roots and leaves or is oxidized to keep living cells functioning through the winter.

Researchers still do not know exactly how much of that carbon eventually becomes long term woody biomass versus how much returns to the atmosphere over shorter time periods. However, the findings suggest that projections of forests growing larger and storing substantially more carbon in a warmer, CO₂ rich world may need to be reconsidered.

The team also found that the disconnect between photosynthesis and growth became even stronger during years when local weather swung between unusually wet and unusually dry conditions. Because climate change is expected to increase this kind of variability in many regions, the pattern could become more common in the future.

Rao and his colleagues are now investigating whether similar patterns occur in other tree species, forest ecosystems, and climates. He expects the degree of separation between photosynthesis and growth will vary across different forests, but says many questions remain unanswered.

“I don’t really have answers yet,” he says. “There are many questions still left to address.”

The research, which relied on lab grown retinal tissue, was published in the Proceedings of the National Academy of Sciences.

Lab Grown Retinas Reveal How Sharp Vision Forms

“This is a key step toward understanding the inner workings of the center of the retina, a critical part of the eye and the first to fail in people with macular degeneration,” said Robert J. Johnston Jr., an associate professor of biology at Johns Hopkins who led the research. “By better understanding this region and developing organoids that mimic its function, we hope to one day grow and transplant these tissues to restore vision.”

To investigate how the human eye develops, the researchers used organoids, small clusters of tissue grown from fetal cells that closely mimic parts of the retina. After observing these lab grown retinas over several months, the team identified the cellular events that shape the foveola, the tiny region at the center of the retina responsible for the sharpest vision.

The study focused on cone photoreceptors, the light sensing cells that provide daytime and color vision. These cells eventually become blue, green, or red cones, each responding to different wavelengths of light. Although the foveola makes up only a small portion of the retina, it is responsible for about half of all human visual perception. Unlike the rest of the retina, where all three cone types are present, the foveola contains only red and green cones.

A Surprising Transformation of Cone Cells

Humans are unusual in having three different cone types that together allow a broad range of color vision. Exactly how this specialized pattern develops has remained a mystery for decades. According to Johnston, scientists have struggled to study this process because common research animals such as mice and fish do not develop the same arrangement of photoreceptor cells.

The new findings suggest that the cone pattern in the foveola is established through a coordinated sequence of events early in fetal development. During weeks 10 through 12, a small number of blue cones appear in the developing foveola. By week 14, however, those cells have changed into red and green cones.

The researchers found that this happens through two separate mechanisms. First, retinoic acid, a molecule derived from vitamin A, is broken down, reducing the formation of new blue cones. Then thyroid hormones drive the remaining blue cones to convert into red and green cones.

“First, retinoic acid helps set the pattern. Then, thyroid hormone plays a role in converting the leftover cells,” Johnston said. “That’s very important because if you have those blue cones in there, you don’t see as well.”

Challenging a Longstanding Theory

The results offer a new explanation for a question that has puzzled vision researchers for decades. The prevailing theory suggested that blue cones formed in the center of the retina and later migrated outward. Instead, the new evidence indicates those cells remain in place but change their identity into red and green cones, producing the specialized arrangement needed for sharp vision.

“The main model in the field from about 30 years ago was that somehow the few blue cones you get in that region just move out of the way, that these cells decide what they’re going to be, and they remain this type of cell forever,” Johnston said. “We can’t really rule that out yet, but our data supports a different model. These cells actually convert over time, which is really surprising.”

Potential for Future Vision Restoration

The researchers believe these discoveries could eventually support new approaches to treating vision loss. Johnston’s team is continuing to improve its retinal organoids so they more closely resemble the function of the human retina. Better models could help scientists produce healthier photoreceptor cells for future cell replacement therapies targeting diseases such as macular degeneration, which currently has no cure.

“The goal with using this organoid tech is to eventually make an almost made-to-order population of photoreceptors. A big avenue of potential is cell replacement therapy to introduce healthy cells that can reintegrate into the eye and potentially restore that lost vision,” said Hussey, who is now a molecular and cell biologist at cell therapy company CiRC Biosciences in Chicago. “These are very long-term experiments, and of course we’d need to do optimizations for safety and efficacy studies prior to moving into the clinic. But it’s a viable journey.”

Until now, every confirmed video or observation of a live goblin shark came only after the animal had been accidentally caught on a fishing line and brought to the surface. Divers could briefly examine the sharks, but the animals typically died soon afterward. The new research, published in the Journal of Fish Biology, reports two healthy goblin sharks observed in the wild. One was seen near a seamount close to Jarvis Island, while the other was recorded along the slope of the Tonga Trench.

Often described as “living fossils,” goblin sharks are the sole surviving members of a shark family that dates back nearly 125 million years. The newly documented encounters significantly expand both the species’ known geographic distribution and the depths at which it is known to live.

Goblin Shark Breaks Depth Record

“Seeing the most iconic of all the deep-sea sharks alive and looking healthy in its natural habitat is a unique honor,” said Aaron Judah, lead author of the paper and doctoral candidate working in the Deep-Sea Fish Ecology Lab and Deep-Sea Animal Research Center (DARC) in the Department of Oceanography at the UH Mānoa School of Ocean and Earth Science and Technology. “I was also very surprised about how deep this species was found. The observation from the slope of the Tonga Trench is nearly 700 meters deeper than this species was known to live.”

Judah explained that the Tonga Trench sighting also establishes a new depth record for the entire order of Lamniformes, also known as the mackerel sharks. This group includes familiar species such as the great white shark, basking shark, and mako shark.

Before these discoveries, goblin sharks were known only from relatively limited regions off the western United States, Australia, and Japan in the Pacific Ocean, along with small areas of the Atlantic and Indian Oceans. The two new sightings, both from the Central Pacific, greatly expand the species’ known range.

Archived Footage Reveals a Hidden Discovery

The first observation came to light after Judah spoke with colleagues at DARC in 2025. They mentioned a possible goblin shark recorded during a 2019 Ocean Exploration Trust expedition aboard the E/V Nautilus, which explored deep sea ecosystems around Kingman Reef, Palmyra Atoll, and Jarvis Island within the Pacific Remote Islands Marine National Monument.

“I was shocked to hear this because this species was not to be known to be in the Central Pacific,” said Judah.

The expedition used the remotely operated vehicle Hercules, which recorded extensive video footage that was later archived for public access and annotated by researchers at UH Mānoa. After reviewing the recordings, Judah confirmed that a goblin shark had indeed been captured on video during a livestreamed dive at an unnamed seamount northwest of Jarvis Island. (See video link after the article below.)

Second Sighting Confirms Expanded Range

The second encounter occurred during a 2024 expedition to the Tonga Trench aboard the R/V Dagon as part of the Inkfish Open Ocean Expedition, led by scientists from the Minderoo-UWA Deep-Sea Research Center. A baited camera mounted on a bottom lander captured rare footage of another goblin shark swimming freely in its natural environment.

“The Goblin Shark is one of these deep-sea charismatic animals that I never thought we’d see alive, and then to do so was amazing, but to then learn that colleagues in Hawai’i also saw one was just incredible,” said Alan Jamieson, professor and founding director at Minderoo-UWA Deep-Sea Research Center and study co-author who documented the 2024 sighting.

Why These Discoveries Matter

Judah said the findings demonstrate why traditional natural history research remains essential, especially in the deep ocean, where many species are still poorly understood.

“It is really important that we still perform natural history work,” Judah emphasized. “New discoveries like this demonstrate that there is still so much to explore in our deep ocean home. Given the newly-expanded geographic range of the goblin shark, this species can be included in regional management and a nationʻs biodiversity list, whereas, beforehand we didnʻt know it was even there!”