On 15 April 1928, the dirigible Italia lifted off from Milan, Italy, hoping to be the second airship ever to reach the North Pole. Over a month later, on 24 May, expedition leader Umberto Nobile sent a triumphant radio message to a ship anchored at the airship’s base camp near Ny-Ålesund, in the Norwegian archipelago of Svalbard: The mission was a success. It would be the last message the base camp would ever receive from the Italia.
Ten days later, a young Russian with a homemade radio picked up a desperate SOS signal originating 1,900 kilometers (1,180 miles) away. The Italia had crashed on sea ice north of Svalbard on its return journey, leaving nine surviving crew members who had been attempting desperately to contact the base ship to send help. The shipwrecked crew could pick up a news station from Rome, 4,000 kilometers (2,485 miles) away, but no matter what frequency they tried, their cries for help could not reach their camp on the other side of the Svalbard Islands. The stranded crew were eventually rescued after weeks on the ice.
“This was completely mysterious to them, I’m sure,” said Delores Knipp, former editor in chief of Space Weather and a research professor at the University of Colorado Boulder. “They could not understand how they could receive a signal from Rome—very distant—but not be able to contact what appeared to be a very close-by potential rescue ship.”
Unbeknownst to the Italia’s crew, their plight was caused by an unlucky confluence of space weather disturbances, according to a new retrospective analysis by a team of Italian researchers published this month in Space Weather. The crew had crash-landed in what is known as a radio skip zone, where radio signals can’t be received, during a period of turbulent solar and geomagnetic activity that prevented the signal from getting through.
“This is a history lesson that could replay during other explorations such as lunar or interplanetary travels, so possible communication issues due to disturbed space weather conditions must be taken in due consideration even more nowadays,” said Ljiljana Cander, a visiting scientist at the Rutherford Appleton Laboratory in the United Kingdom and a coauthor of the study.
A Different Kind of Storm
High-frequency radio communication takes advantage of a layer of the atmosphere ionized by solar radiation, which extends from 50 to 1,000 kilometers above Earth’s surface. Space weather is the term for the phenomena—often solar and electromagnetic disturbances—that affect this layer.
In 1928, radio was still a nascent technology and one that had been used largely at midlatitudes. Few had attempted to reach the North Pole, and fewer still had succeeded. Explorers knew that the poles were capable of brutal terrestrial weather events with howling winds and icy conditions. But they had no real concept of space weather or any idea that it behaved dramatically differently at northern latitudes as well.
“Our midlatitude regions are pretty well behaved. We have to have really severe space weather storms to disrupt high-frequency radio communication,” Knipp said. But at the transition from midlatitude to polar regions, the ionosphere gets “turbulent.” It fluctuates more day to day and is more heavily affected by geomagnetic activity. This causes both longer-term radio disruptions and shorter-term blackouts.
Skip zones, or silent zones, are areas where the radio signal cannot reach the ground, meaning that a radio transmission can’t be received within the skip area. These silent zones occur near all radio transmitters, but their size is influenced by the electron density of the ionosphere, which fluctuates more at the poles. Polar latitudes also have unique ionosphere disturbances like polar cap absorption resulting from solar eruptions and auroral radio absorption caused by fluxes in energetic electron activity from the magnetosphere.
An Expedition on Thin Ice
As some of the first polar explorers, the crew of Italia became unwitting participants in the earliest-known demonstration of what happens when several of these absorption events conspire to disrupt a signal at the same time. When the airship crashed on the ice, the nine survivors immediately attempted to contact the base ship using a portable high-frequency radio. Signals fluctuated between the 9.1- and 9.4-megahertz frequencies, to no avail.
The dirigible had crash-landed in a silent zone for those particular frequencies, which extended across most of the Svalbard islands and made it impossible for the crew to contact their base. A geomagnetic storm flared up for several days after the crash, potentially further restricting the range of radio frequencies that could get through.
“The combination of the two—a lowering of usable frequencies and an increase of the absorption—might have caused either a narrowing of the usable frequency spectrum or even a blackout that lasted for a few days, preventing the survivors from being heard,” said Michael Pezzopane, a researcher at the Istituto Nazionale di Geofisica e Vulcanologia and a coauthor of the study.
To the North Pole and Beyond
The plight of the Italia crew is still relevant today. Space weather as a discipline has been officially recognized only since the 1990s, and our understanding of space weather still lags behind our understanding of traditional weather patterns. Analyzing key space weather events from the past using modern technology and understanding can help us avoid similar pitfalls in the future.
“I do think these historical reconstructions are useful, especially from the point of view of generating awareness for space weather and how it can either adversely or positively affect what we do here on Earth,” said Nathaniel Frissell, an assistant professor in the Physics and Engineering Department at the University of Scranton in Pennsylvania who was not involved in the study.
“The people who were involved in this event were very much explorers and frontiers people,” Knipp said. “We can draw a parallel with that now for humanity as we try to go back and establish some kind of base on the Moon and as we reach out to cross to a new planet—Mars.”
—Rachel Fritts (@rachel_fritts), Science Writer