Cracking Antarctic Sea Ice

January 19

January 20

A satellite image shows sea ice along Antarctica’s Ross Island near McMurdo Station. Buildings and fuel tanks are visible on land. The start of a straight channel, cut by an icebreaker through the sea ice, is visible toward the right, originating from small area of dark open water.

NASA Earth Observatory

A satellite image of the same area shows a completed channel cut by an icebreaker through the sea ice. The ship channel stretches about 10 kilometers from open water on the right to McMurdo Station on the left.

NASA Earth Observatory

January 19

January 20

‘Tis the season for long and ruler-straight cracks in McMurdo Sound’s sea ice. Though natural breaks in sea ice are called leads, the better term for the human-made fracture seen in these satellite images is a ship channel.

In the austral summer, usually in January, an icebreaker rams a path through the fast ice—a type of sea ice that is anchored to the shore—that often covers McMurdo Sound. This annual effort allows cargo ships to reach McMurdo Station, a research base operated by the United States Antarctic Program. The U.S. Coast Guard Cutter Polar Star completed the task in January 2026, arriving after breaking a path through several miles of ice between the Ross Sea and an ice pier at McMurdo. Most of the channel was cut between January 19 and 20.

Seven satellite images captured in January 2026 show a stepwise lengthening of a ship channel in sea ice flanking the coast of Ross Island. The channel spans diagonally across the image, from an area of dark open water on the bottom-right to a research base on the top-left.

January 2 – January 27, 2026

The animation above, made of images captured by the OLI (Operational Land Imager) on Landsat 8 and 9, offers satellite views of the icebreaker’s work. Images were captured on January 2, 7, 19, 20, 23, 25, and 27. The nearly 120-meter (400-foot) vessel weighs 13,500 tons and has thick steel-plated hulls. With 75,000 shaft horsepower, it’s the world’s most powerful non-nuclear icebreaker.

The ship sometimes conducts search-and-rescue missions as well. On January 17, the day marking its 50th year of service, the Polar Star responded to a call from an Australian cruise ship in the Ross Sea hampered by thick, pack ice—a type of sea ice unattached to the shoreline that drifts. After making two close passes to break up the ice and clear a path, the Polar Star escorted the cruise ship 4 nautical miles (7 kilometers) to open water in the Ross Sea, according to the U.S. Coast Guard.

A reference map of Antarctica shows the continent in white surrounded by light blue ocean. Labels identify the Weddell Sea, Amundsen Sea, Ross Ice Shelf, Ronne Ice Shelf, West Antarctica, and the Antarctic Peninsula. A small boxed area near the Ross Ice Shelf marks the “Area of Landsat images." This boxed area is centered on sea ice in McMurdo Sound near McMurdo Station.

Established in 1955, McMurdo Station is the southernmost point on Earth accessible by ship. With a population that swells to 1,200 in the summer, it is the largest research station in Antarctica, hosting a harbor, two airfields, and a helicopter pad. Though once powered by a portable nuclear reactor known as “Nukey Poo,” the base now runs on energy from diesel electric generators and a wind farm on Crater Hill.

With the ship passage open, McMurdo Station is slated to receive two large deliveries this summer. The Stena Polaris, a tanker, arrived on January 20 with 5 million gallons of diesel fuel. Plantijngracht, a cargo ship, will arrive later with food, supplies, and parts of a new floating pier that will replace the traditional ice pier that military engineers have constructed each winter to give ships somewhere to unload cargo.

The U.S. National Science Foundation manages McMurdo Station and much of the science conducted there. NASA has also been involved in several projects at the base over the years. For instance, NASA’s McMurdo Ground Station, a Near Space Network facility, is used to download data from polar-orbiting satellites such as Landsat 9 and SMAP. The agency also flew its Operation Ice Bridge airborne campaign from McMurdo in 2013 and regularly launches research balloons from the station as part of its scientific ballooning program.

The Polar Star typically remains at McMurdo through March to keep the ship passage clear and returns to its home port of Seattle in April.

NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.