Arctic Sea Ice Reaches 2026 Annual Minimum Extent - NASA Science

 

Daily images of ice cover in the Arctic Ocean show sea ice melting around the pole from March 15, 2026 to Sept. 12, 2026.

Trent Schindler/NASA’s Scientific Visualization Studio

Arctic sea ice reached its annual minimum extent on Sept. 12, according to NASA and the National Snow and Ice Data Center (NSIDC) at the University of Colorado Boulder. The ice covered an estimated 1.78 million square miles (4.6 million square kilometers), tying 2008, 2010, and 2025 for the 10th-lowest minimum in the satellite record.

The 2026 minimum is consistent with patterns observed in the satellite record. The past 20 years, from 2007 through 2026, have produced the 20 lowest annual Arctic sea ice minimum extents observed since continuous satellite measurements began in late 1978.

Arctic sea ice grows during the dark, cold autumn and winter and retreats as temperatures rise during spring and summer, typically reaching its lowest extent in September. Weather conditions can cause substantial differences in the amount of ice that melts from one summer to another.

Over the last decade, for example, increased cloud cover has prevented solar radiation from further accelerating the melt of sea ice, according to Linette Boisvert, a sea ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

That has contributed to relatively stable September sea ice extent in recent years. “We’ve plateaued, but we’re still low relative to the earlier part of the record,” said Walt Meier, a senior research scientist at NSIDC.

Antarctic sea ice extent approaches annual maximum

At the opposite end of the planet, Antarctic sea ice is approaching its annual maximum following a fluctuation during August.

Sea ice around Antarctica declined by roughly 116,000 square miles (300,000 square kilometers) over a six-day period before resuming its seasonal growth. Meier said the decline appeared to be associated with weather conditions that pushed and compacted the thin, mobile ice near its outer edge.

“Those types of things happen all the time,” Meier said. “But the magnitude of it certainly is unusual.”

Antarctic sea ice varies more from year to year than Arctic sea ice because, in contrast to the Arctic, it is not surrounded by land and can respond more freely to changing wind and weather conditions. But Antarctic sea ice extent at its annual maximum has generally been lower in recent years. Because of this large year-to-year variability, Boisvert and Meier remain cautious about characterizing the change as a long-term trend.

Scientists have tracked polar sea ice from space for nearly five decades. During that time, NASA and the National Oceanic and Atmospheric Administration (NOAA) used a series of satellite instruments to maintain a continuous sea ice record, beginning with NASA’s Nimbus-7 satellite, which began observations in October 1978. The record continued with instruments aboard Defense Meteorological Satellite Program satellites beginning in 1987 and NASA’s Aqua satellite from 2002 to 2011. Today, scientists continue the record using data from the Advanced Microwave Scanning Radiometer 2 (AMSR2), launched in 2012 aboard JAXA’s (Japan Aerospace Exploration Agency) GCOM-W satellite.

Antarctic sea ice typically reaches its annual maximum in late September or early October. NASA and NSIDC will announce the 2026 maximum after scientists confirm that seasonal ice growth has ended.

Media contact: Elizabeth Vlock

NASA Headquarters

James Riordon

Senior Science Writer 

Source: Arctic Sea Ice Reaches 2026 Annual Minimum Extent - NASA Science

Light beam 'swims' upstream through a quantum fluid by violating Newton's third law - Physics Optics & Photonics - Quantum Physics

Experimental results of upstream and downstream motion. Credit: Physical Review A (2026). DOI: 10.1103/lwyj-7m5f

Just as a leaf drifts along with a stream, objects in other moving fluids normally drift along with the flow. That is, unless they exert energy to move against it. Although it may be less intuitive, light waves or photons work similarly. To move against a stream of light, an object or particle, like a photon, must either have an external force acting on it or actively use energy to move upstream.

In a new study, published in Physical Review A, a team of physicists demonstrates how a beam of light can "swim" upstream in a quantum fluid of light by breaking action-reaction symmetry and reshaping how the surrounding forces affect the flow.

Non-reciprocal interactions and upstream motion

Matter is not in equilibrium when it is actively creating a force to oppose motion, like a motorized boat moving up a river. Newton's third law of motion states that for every action, there is an equal and opposite reaction. This is also known as action-reaction symmetry.

Action-reaction symmetry is not broken just because something is out of equilibrium, but this symmetry can be broken when particles exhibit non-reciprocal interactions. In these interactions, one object influences another differently than the other influences it. In non-reciprocal interactions, internal interactions can be converted into net momentum.

Scientists have proposed that these unusual interactions could create active behavior in quantum-like systems. Upstream motion has been demonstrated in previous experiments, but the mechanism involved vortex shedding, which imparts a net upstream recoil momentum and still obeys Newton's third law. The new study is the first to use non-reciprocal interactions, violating action-reaction symmetry.

A swimming light beam driven by nonreciprocal interactions

The team involved in the new study combined theoretical scattering analysis, computer simulations and laboratory experiments. They sent two timed laser beams through a nonlinear crystal, with one representing the fluid and the other representing the swimmer. By tilting the fluid beam, they were able to control its transverse flow direction and speed. In their experiments, the narrow laser beam, acting as the swimmer, moved opposite to the flow of a broader optical fluid. In the usual reciprocal setup, the beam instead moved downstream, providing a direct comparison.

The study authors write, "The swimmer tends to reshape the fluid, passing through it asymmetrically, which in turn exerts on the swimmer a force opposite to the fluid flow direction. Such a counterintuitive process stems from the nonreciprocity of their mutual interactions, which results in an inverted recoil compared to that in equilibrium systems."

The upstream motion is due to the asymmetric distribution of the fluid caused by the swimmer. The intensity of the fluid on one side of the swimmer is higher than that on the other side. By adjusting fluid speeds and densities, they also found that the upstream motion was strongest at intermediate fluid speeds and densities, rather than at the highest or lowest values.

The experiments involved an optical analog of a quantum fluid, not a demonstration using material quantum fluids such as ultracold atoms or liquid helium. However, the study offers a test bed for studying active-like behavior under non-reciprocal interactions. Future research could test whether related effects occur in other quantum platforms, such as atomic gases or engineered quantum materials.

The study authors write, "This study advances the fundamental understanding of nonreciprocal interactions in the quantum regime, providing key insights for designing novel quantum devices with active functionalities."

by Krystal Kasal, Phys.org

edited by Gaby Clark, reviewed by Robert Egan 

Source: Light beam 'swims' upstream through a quantum fluid by violating Newton's third law