NASA’s Webb Studies How Planet Survived Death of its Star - UNIVERSE

NASA’s James Webb Space Telescope is giving us new insight into the far-future of solar systems like our own, as the agency continues to reveal the secrets of the universe and our place in it. Billions of years ago, a Sun-like star nearing the end of its life swelled tremendously in size to become a red giant before ejecting its outer layers, leaving a hot, remnant core known as a white dwarf. As a red giant, the star should have engulfed and destroyed any nearby planets. Yet astronomers have found a Jupiter-sized exoplanet orbiting the white dwarf every 34 hours at a separation of less than 2 million miles (3 million kilometers).

To solve the mystery of how this exoplanet survived, an international team of astronomers used NASA’s James Webb Space Telescope to watch the Jupiter-sized exoplanet WD 1856 b transit its host star, measuring the planet’s temperature and detecting molecules in its atmosphere. They found the planet is significantly warmer than expected and determined how it most likely reached its very tight orbit around the white dwarf star. The results are a window into the future of planets like Jupiter after the death of the Sun, billions of years into the future.

The results published Wednesday in the journal Nature.

WD 1856 b was discovered in 2020 by scientists using NASA’s TESS (Transiting Exoplanet Survey Satellite) and the retired Spitzer Space Telescope. It orbits the white dwarf WD 1856+534, which is located about 80 light-years from Earth. “The planet is about the size of Jupiter, but the white dwarf it orbits is the size of Earth, so the planet is seven times larger than its star," said lead author Ryan MacDonald of the University of St. Andrews in the United Kingdom.

WD 1856 b orbits extremely close to its host star, a distance 50 times closer than Earth orbits the Sun. If WD 1856 b had originally been orbiting at that distance, it would have been obliterated while the star was a red giant. How did it survive the death of its host star and end up in its current position?

Image: Exoplanet WD 1856 b (Artist's Concept)

Exoplanet WD 1856 b, shown in this artist’s concept, is a gas giant that orbits its star at a distance 50 times closer than Earth orbits the Sun. Observations by NASA’s James Webb Space Telescope determined the planet’s temperature and detected molecules in its atmosphere.

Artwork: NASA, ESA, CSA, Ralf Crawford (STScI)

How big, how hot

The new study used Webb to watch the planet passing in front of its star. This transit yielded unique information about the planet’s mass, which is between four and eleven times the mass of Jupiter.

The team also was able to determine the planet’s temperature. During the transit, light from the star was partly blocked, but infrared light was reduced less than other wavelengths. The difference was infrared light emitted by the planet from its own heat. The data indicated that the planet has a temperature of about 260 degrees Fahrenheit (126 degrees Celsius) — significantly hotter than it would be if its only source of heat was the light from the white dwarf. This puzzling discovery turned out to be the key fact that proved how the planet must have reached its current orbit.

Christopher O’Connor of Northwestern University in Illinois, a co-author on the paper, was responsible for tracing the temperature of the planet back in time. O’Connor said, “The big question is how WD 1856 b ended up where it is today, and there are two theories. One is that the planet was swallowed by the host star as it was dying, and managed to survive on the inside. The other is that migration took place due to the gravitational effect of other objects in the system. The white dwarf is part of a triple star system, and the companion stars could have influenced WD 1856 b’s orbit.”

The researchers realized that there was no source of energy present to generate that heat today, so it must be residual energy from an earlier time when the planet was heated. Using models of how sub-stellar objects like WD 1856 b cool down over time, coupled with the new data from Webb, the team was able to project its temperature back in time and deduce how long ago the heating must have happened. The timing is key to determining whether the heating was from being engulfed by the red giant or occurred during an inward migration

They concluded that the heating most likely happened between 3 and 5.5 billion years after the star became a white dwarf. In this scenario, the planet was on a wide orbit that kept it safe from the star during its destructive red giant phase, and only migrated to its present location later on. “As the planet moved inward, its interactions with the strong gravity of the white dwarf will have caused it to warm up considerably, and it has been cooling ever since,” said O’Connor.

Light from the star passing through the planet’s atmosphere also picked up information about its chemical composition. “We saw the telltale signatures of small cloud particles and hydrocarbons, most likely methane, which is the first time we have seen an atmosphere on a planet transiting a dead star,” said co-author Victoria Boehm of Cornell University. “We recently observed four more transits of WD 1856 b with Webb to take a deeper look into its atmospheric chemistry and can’t wait to see the results.”

Image: Exoplanet WD 1856 b (Transmission Spectrum)

NASA’s James Webb Space Telescope measured the constituents of exoplanet WD 1856 b as it passed in front of its star, finding signs of methane. WD 1856 b orbits a white dwarf star the size of Earth. As a result, the planet blocks more than half of the star’s light.

Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)

Solar system’s possible future

In approximately five billion years, the Sun will run out of hydrogen fuel in its core and swell up more than 100 times larger than it is now into a red giant star. It will then shed its outer layers and end its life as a white dwarf star. Mercury, Venus, and possibly the Earth will be destroyed by the red giant. However, the fate of the more distant planets, particularly the gas giants, is unclear. Finding and studying planets in orbit around the remnants of Sun-like stars after their death is a means of learning what might happen in our own solar system in the far future.

“We’re used to looking back in time when we use telescopes, but this is the first time we have been able to look forward to what might happen to the outer planets around the remnant of a Sun-like star,” said MacDonald. “It’s like using a time machine to peer into the distant future of our solar system.”

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

To learn more about Webb, visit: https://science.nasa.gov/webb 

Source: NASA’s Webb Studies How Planet Survived Death of its Star - NASA Science  

Antarctic ozone loss drove unexpected Southern Ocean cooling, climate model shows - Earth - Earth Sciences - Environment

A melting iceberg floats in the sea surrounding Antarctica. Credit: Pixabay.

The Southern Ocean has long stood out as an oddity in the global climate system. While most of the planet's surface oceans have warmed in response to rising greenhouse gases, waters circling Antarctica showed an unexpected tendency to cool during the late 20th and early 21st centuries. This cooling coincided with a period when Antarctic sea ice briefly expanded before its more recent decline, adding to the mystery.

A new modeling study, published in Geophysical Research Letters, helps clarify part of this puzzle.

Using climate model experiments focused specifically on changes in the stratospheric ozone layer, the researchers show that human-driven depletion of ozone over Antarctica likely played a significant role in cooling the Southern Ocean between 1982 and 2005. The findings suggest that changes high in the atmosphere can cascade downward to shape ocean temperatures and even influence sea ice around the continent.

Winds of change

The ozone hole formed largely because of human-made chemicals released in the 20th century. It cools the lower stratosphere, the layer of the atmosphere above where weather happens, and changes the temperature difference between the polar regions and the tropics. Those shifts in temperature help change the strength and position of the strong westerly winds that circle Antarctica.

Shouwei Li of Princeton University and colleagues found that ozone loss strengthens these winds and pushes them closer to the continent. This shift is not limited to the atmosphere but extends down to the ocean surface, where it changes how the wind moves seawater and helps set up conditions that cool the Southern Ocean.

When these winds strengthen and shift poleward, they also change how the ocean moves. One key process is called Ekman transport, in which surface waters are pushed by the wind and gently curved by Earth's rotation. In the Southern Hemisphere, this usually drives surface water northward when the westerly winds become stronger.

The study shows that ozone-driven wind changes enhance this northward movement of surface water south of about 46°S latitude. This carries cold water away from Antarctica and spreads it farther north, helping to cool much of the Southern Ocean surface. At the same time, the changing winds also reshape surface temperature patterns, reinforcing the movement of cold water and strengthening the cooling effect.

Other processes can partly counter this cooling. For example, changes in surface heat exchange with the atmosphere can add heat to the ocean in some regions. But in this case, that warming is not strong enough to overcome the wind-driven cooling, which remains the dominant effect over the study period.

Annual mean sea surface temperature trends over the Southern Ocean from satellite observations, and simulations of stratospheric ozone-only and historical data over 1982–2005. Credit: Li et al, 2026.

Hidden feedbacks

Beyond surface transport, the study also highlights slower processes occurring beneath the ocean's mixed layer, the upper layer of ocean water that is directly influenced by wind and waves. When winds intensify, they can increase upwelling, drawing deeper waters toward the surface.

In the Southern Ocean, those deeper waters can be relatively warmer than the surface, meaning this process can eventually contribute to warming rather than cooling.

However, this warming effect appears weaker and slower than the immediate wind-driven cooling. The researchers describe a two-step response: an initial, rapid cooling driven by horizontal transport of cold water, followed by a more gradual and partial warming linked to vertical mixing and upwelling.

Climate model simulations show that these opposing effects do not cancel each other out on decadal time scales. Instead, the sustained strengthening of wind-driven transport keeps the Southern Ocean cooler than it would otherwise be under greenhouse gas forcing alone.

Reframing a climate paradox

One consequence of this cooling signal is its influence on Antarctic sea ice. The models suggest that ozone-driven cooling contributed to regional sea ice expansion, particularly in areas such as the Ross Sea. This aligns with observations of sea ice growth in certain parts of the Southern Ocean during the satellite era, even as global ice trends moved in the opposite direction.

However, the effect is not uniform. Some regions show sea ice increases, while others still experience declines. This patchwork pattern reflects the complex balance among wind changes, ocean heat transport, and regional feedbacks involving temperature and salinity.

Importantly, the study finds that while ozone depletion contributes to these patterns, it is not strong enough on its own to explain the full observed changes in Antarctic sea ice.

The results also help explain why climate models often show warming in the Southern Ocean over recent decades, even though observations show periods of cooling.

When all major influences are included—greenhouse gases, aerosols, natural variability and ozone changes—the strong warming from greenhouse gases still dominates. Ozone depletion acts like a regional cooling influence, but it is not strong enough to overturn the overall global warming signal.

By isolating the role of ozone depletion, the study highlights a broader point: The Southern Ocean is not responding to a single cause, but to several competing influences acting at the same time. It also shows that the unusual cooling trend is not solely a mystery of ocean circulation, but a fingerprint of human-driven changes. 

by Hannah Bird, Phys.org

edited by Sadie Harley, reviewed by Andrew Zinin 

Source: Antarctic ozone loss drove unexpected Southern Ocean cooling, climate model shows