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With one glance at a particular 12-mile stretch of Lake Huron’s shoreline, it’s clear there’s a pattern. Small islands outlined by tan beaches and bright, shallow water align in a remarkably parallel orientation. The claw-mark-like appearance of this Great Lakes locale is evident in this image, acquired with the OLI (Operational Land Imager) on the NASA-USGS Landsat 9 satellite in July 2026.

The Les Cheneaux Islands are a group of 36 islands near the shore of Michigan’s Upper Peninsula, about 20 miles (32 kilometers) northeast of the Straits of Mackinac. The archipelago contains coastal marshes, rock and sand beaches, peat bogs, and forests full of pine and cedar. Parts of several islands are set aside as nature preserves, including a substantial portion of Marquette Island, which is only accessible by boat or over ice. The islands are interspersed with sheltered waters that inspired their name; the French “Les Cheneaux” roughly translates to “the channels.”

The Les Cheneaux Islands, like many landforms in the Great Lakes region, look the way they do because of glaciers that carved the landscape during the Wisconsin Ice Age before retreating around 10,000 years ago. Their elongated shapes indicate many of them are drumlins: mounds of glacial debris that run parallel to the direction of the ice’s movement. 

The glacial topography has helped give rise to a distinct local maritime culture. In contrast with the Great Lakes’ vast open expanses, the waters around the Les Cheneaux Islands are relatively protected from the infamous storms that can otherwise roil the upper Midwest lakes. This creates opportunities for paddling, as well as fishing in quiet alcoves for species such as smallmouth bass, northern pike, yellow perch, and lake trout. The town of Cedarville boasts an annual antique wooden boat show, a boat-building school, and museums highlighting how people, from the area’s earliest inhabitants to today’s residents, have used the islands and waterways.

On land, the much older geology of the area is revealed in a couple of brightly colored quarries. The bedrock here is dolomite, a modified form of limestone. It was deposited in the Silurian period more than 400 million years ago in a shallow, tropical sea before the movement of tectonic plates brought it up north. Michigan is home to several large dolomite and limestone mines, and Port Dolomite, east of Cedarville, ships millions of tons of the material every year.

NASA Earth Observatory image by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Lindsey Doermann.

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July 23, 2026

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References & Resources

• Aldo Leopold Festival (2021) Les Cheneaux Geology Tour. Accessed August 20, 2026.
• Les Cheneaux Historical Association (2026) Welcome to The Les Cheneaux Historical Association. Accessed August 20, 2026.
• Les Cheneaux Islands Chamber of Commerce (2026) Visitor Information. Accessed August 20, 2026.
• National Park Service (2018, February 22) Drumlins. Accessed August 20, 2026.
• Schaetzl, R., Sedimentary Rock Sequence in the Michigan Basin. Accessed August 20, 2026.

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The Moon joins a tea party… Venus cranks up the brightness… the seasons officially change… and the Harvest Moon meets up with some planetary neighbors.

That’s What’s Up for September.

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Though invisible to the eye, sporadic E layers make their presence known to the radio signals we rely on for long-distance communication. When present, sporadic E can send those signals ping-ponging off in unexpected directions, rendering the technology temporarily unreliable.

Scientists have long sought a fuller understanding of these radio-disrupting clouds, but until recently, they had only sampled them one narrow slice at a time. The rocket, called the sporadic E Electrodynamics Demonstration, or SpEED Demon for short, launched from NASA’s Wallops Flight Facility in Virginia on Aug. 24, 2022, and demonstrated the first concurrent, multi-point view inside sporadic E.  Its results, from a team led by Embry-Riddle Aeronautical University, are described in a new study in the Journal of Geophysical Research: Space Physics.

Sporadic E layers form in the ionosphere, a region of the upper atmosphere beginning around 40 miles (60 kilometers) up where the neutral gases begin to transform into plasma, or ionized gas. Some of the particles there come from meteors, which burn up and leave behind traces of iron, magnesium, and other metals. These metals occasionally clump into dense, cloud-like sheets — the sporadic E layers — that reflect radio waves.

“Sporadic E layers are, in one sense, giant mirrors of radio frequency waves in the sky,” said Aroh Barjatya, the mission’s principal investigator and a professor of engineering physics at Embry-Riddle in Daytona Beach, Florida.

When a sporadic E layer forms, signals meant to travel out to space can ricochet back toward the ground. Air traffic controllers and marine radio users may pick up distant transmissions as though they were nearby, and radars scanning beyond the horizon can register so-called “ghosts,” or false targets. The effects reach everyday technology, too.

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Because sporadic E layers hover around 60 miles (100 kilometers) up—too high for weather balloons, too low for satellites — and form and dissipate unpredictably, they have long been the province of sounding rockets, which can be launched on short notice to catch one in the act. But a single rocket flies a single path, taking measurements only along a line. Barjatya likens the situation to viewing a scene through a crack in a wall. One can only observe what is happening along that narrow slit, missing out on the crucial context of whatever is occurring to the left or right of one’s view.

The SpEED Demon mission changed that. The mission was the first to deploy ejectable probes, called dropsondes, inside a sporadic E layer. Once inside, the rocket released four dropsondes that flew away from the main payload and from one another, each measuring the plasma along its own track and beaming its measurements back to ground stations. Together with the main payload, the probes sampled the layer in a total of five places at the same moment.

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After years of study, sporadic E layers are no longer as unpredictable as they once were. “They have a seasonality to them, with peak occurrence happening in the local summer,” Barjatya said.

Questions about how and when they form are increasingly fine-grained. The new deployable multi-point rocket sensor methodology, along with ground-based measurements, is likely to bring the picture even closer to completion. “The science community as a whole is now in its final stretches of fully understanding these giant radio frequency mirrors in the sky,” Barjatya said.

By Miles Hatfield 
NASA’s Goddard Space Flight Center, Greenbelt, Md. 

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