🔭 astrophysics

The Amerigo Vespucci as a traveling laboratory for studying the cosmic-ray fluxes at sea level

During the 2023–2025 global tour of the Italian Navy training vessel Amerigo Vespucci, researchers utilized a plastic scintillator detector to measure sea-level cosmic-ray flux across a wide latitude range, observing a 16% variation between the lowest rate near 7° N and the highest rate in Trieste due to the Earth's geomagnetic field configuration.

Original authors: Davide Cerasole, Federica Cuna, Gaia De Palma, Riccardo Di Tria, Leonardo Di Venere, Fabio Gargano, Mario Giliberti, Francesco Licciulli, Antonio Liguori, Pierpaolo Loizzo, Francesco Loparco, Leonarda

Published 2026-07-07

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CC BY 4.0

Original authors: Davide Cerasole, Federica Cuna, Gaia De Palma, Riccardo Di Tria, Leonardo Di Venere, Fabio Gargano, Mario Giliberti, Francesco Licciulli, Antonio Liguori, Pierpaolo Loizzo, Francesco Loparco, Leonarda Lorusso, Mario Nicola Mazziotta, Giuliana Panzarini, Roberta Pillera, Davide Serini

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the Earth is wrapped in a giant, invisible magnetic force field, like a protective bubble. This bubble acts as a bouncer at a very exclusive club: it decides which high-speed space particles (called cosmic rays) get to enter our atmosphere and which ones get turned away.

This paper tells the story of how scientists used a historic Italian Navy sailing ship, the Amerigo Vespucci, as a giant, moving laboratory to test this "bouncer" and see how the space weather changes as you sail around the world.

Here is the breakdown of their adventure:

The Mission: A Floating Lab

The Amerigo Vespucci is a beautiful, tall-masted ship used to train young naval officers. In late 2024, scientists strapped a special "cosmic-ray detector" to the ship. Think of this detector as a high-tech rain gauge, but instead of catching water, it catches invisible particles raining down from space.

The ship set sail from Darwin, Australia, and traveled all the way to Trieste, Italy, and then continued through the Mediterranean to Genoa. This journey took them across a wide range of latitudes, from the hot equator up to the cooler northern seas.

The "Bouncer" Effect (Latitude)

The main discovery was about how the Earth's magnetic field changes depending on where you are.

The Equator is a Tough Bouncer: Near the equator (around 7° North latitude, near places like Singapore and Phuket), the Earth's magnetic field is strongest against incoming particles. It's like a very strict bouncer who only lets the strongest, most energetic particles through. As a result, the detector saw the lowest number of particles here.
The Poles are a Lenient Bouncer: As the ship sailed north toward Italy, the magnetic "bouncer" became more relaxed. It let more particles through. By the time the ship reached Trieste (the northernmost point), the detector was counting about 16% more particles than it did near the equator.

The scientists found that once you get past a certain latitude (about 40° North), the "bouncer" stops changing his mind, and the particle count levels off.

The "Solar Storms" (Forbush Decreases)

While sailing, the Sun was having a very active period (Solar Cycle 25). The Sun occasionally shoots out huge clouds of magnetic energy and particles, called Coronal Mass Ejections.

When these solar clouds hit Earth, they push the cosmic rays away, like a strong wind blowing rain clouds aside. The scientists called these events "Forbush decreases."

They spotted seven major solar storms during the trip.
Every time a storm hit, the detector saw a sudden, sharp drop in the number of cosmic rays.
Interestingly, the drop was much smaller on the ship (about 1–4%) compared to a stationary detector in Finland (about 3–12%). This suggests that the particles hitting the ship (mostly muons) are tougher and come from higher-energy sources than the ones hitting the Finnish detector.

The Tools and the "Weather"

To make sure their measurements were accurate, the scientists didn't just count particles; they also monitored the ship's environment.

Temperature and Pressure: Just like weather affects rain, air pressure affects how many particles reach the sea level. They corrected their data for this, ensuring that a drop in particle count wasn't just because the air pressure changed.
The Ship's Tilt: Since the ship rocks on the waves, the detector tilts. The scientists mathematically corrected for this "rocking" to ensure they were counting particles coming straight down, not just from the side.

The Conclusion

By the time the Amerigo Vespucci finished its journey in Genoa in June 2025, the scientists had confirmed what they suspected:

Location matters: You get fewer cosmic rays near the equator and more near the poles because of Earth's magnetic shield.
The Sun matters: Solar storms can temporarily clear the sky of cosmic rays.
The detector works: A simple, plastic-scintillator detector on a moving ship can provide precise, high-quality data that matches what we see with massive, stationary detectors on land.

In short, the ship acted as a giant, moving ruler, measuring the invisible "rain" of cosmic rays and proving that Earth's magnetic shield is a dynamic, changing force that depends entirely on where you stand on the map.

Technical Summary: The Amerigo Vespucci as a Traveling Laboratory for Studying Cosmic-Ray Fluxes at Sea Level

Problem and Context
Cosmic rays (CRs), primarily high-energy protons and atomic nuclei, interact with the Earth's atmosphere to produce secondary particle cascades, including muons and electrons, which reach sea level. The intensity of these particles at the Earth's surface is modulated by two primary factors: the geomagnetic field and solar activity. The geomagnetic field acts as a shield, deflecting lower-energy charged particles; the minimum momentum required for a particle to reach a specific location is known as the "geomagnetic cutoff." This cutoff varies with latitude, being highest near the magnetic equator and lowest near the poles. Additionally, solar activity, characterized by the 11-year solar cycle, solar flares, and coronal mass ejections (CMEs), influences CR flux through transient decreases known as "Forbush decreases."

Historically, the latitude effect on CRs was established in the 1930s through expeditions by J. Clay and later by Arthur Compton. However, the geomagnetic field evolves over time, altering cutoff rigidities. Furthermore, while neutron monitors (NMs) have provided extensive data on the nucleonic component of CRs, measurements of the muonic component at sea level across a continuous, wide range of latitudes during periods of high solar activity remain valuable for comparative analysis. This study addresses the need for continuous, high-precision measurements of secondary CR fluxes at sea level across varying geomagnetic latitudes and solar conditions.

Methodology
The authors utilized the Amerigo Vespucci, a training vessel of the Italian Navy, as a mobile laboratory to measure cosmic-ray fluxes during its 2023–2025 global tour. The study was divided into two main campaigns:

World Tour (Darwin to Trieste): From October 4, 2024, to March 4, 2025, covering a geographic latitude range from 12.47°S to 45.63°N.
Mediterranean Tour (Trieste to Genova): From March 7, 2025, to June 11, 2025.

Detector System:
The instrument consisted of two overlapping 1 cm thick plastic scintillator tiles (15 × 15 cm²), read out by silicon photomultipliers (SiPMs). The system required a 4-fold coincidence (two signals from each tile) within a 50 ns window to trigger an event, with a discrimination threshold of approximately 0.75 MeV. The detector was equipped with a comprehensive sensor suite to monitor environmental and positional variables, including:

Position and Orientation: GPS (L80-M39) and a Sense HAT board (LSM9DS1) for yaw, pitch, roll, and local magnetic field.
Environmental Conditions: Temperature (DS18B20, BME280), pressure (LPS25H, BME280), and humidity (HTS221).
Data Acquisition: A Raspberry Pi 4 managed data collection in 10-minute runs, storing data locally and transmitting it to the INFN Bari computer center.

Data Analysis and Corrections:
Raw count rates were corrected for:

Inclination: Adjusted based on the vessel's motion and the detector's off-axis angle.
Barometric Effect: Corrected using a coefficient ( $\beta$ ) determined in Darwin ( $\beta = 1.52 \pm 0.48 \times 10^{-3} \text{ hPa}^{-1}$ ) to account for atmospheric pressure variations.
Solar Activity: The Oulu Neutron Monitor (NM) data served as a reference to identify and model Forbush decreases. The authors fitted the Vespucci data using a phenomenological model (Eq. 1) that combined a latitude-dependent term and a Forbush decrease term. The latitude term was modeled as a function of the vertical geomagnetic cutoff rigidity ( $R_c$ ) using the Dorman function (Eq. 5).

Key Results

Latitude Dependence: The study confirmed a clear latitude effect. The lowest CR rate was observed at a geographic latitude of approximately 7°N (near Singapore, Belawan, and Phuket), where the geomagnetic cutoff is maximal. This minimum rate was approximately 16% lower than the maximum rate measured at Trieste (45.63°N), the northernmost point of the journey.
Saturation: The data indicated that the CR rate begins to saturate above 40° latitude (corresponding to a vertical cutoff rigidity below ~5 GV).
Forbush Decreases: Seven distinct Forbush decreases were identified during the Darwin-Trieste leg, corresponding to solar activity peaks in Solar Cycle 25. The amplitude of these decreases in the Vespucci muon detector ranged from 1.1% to 4%, significantly lower than the 3.1% to 12.3% observed in the Oulu NM. This discrepancy highlights that muons are sensitive to higher-energy primary CRs than neutrons.
Mediterranean Campaign: The second leg (Trieste to Genova) showed consistent results, with a 5% rate decrease observed between the northernmost (Trieste) and southernmost (La Valletta) points, aligning with the global tour data. A Forbush decrease in late May 2025 was also recorded, with a similar amplitude reduction (~8%) compared to the Oulu NM.
Model Fitting: The experimental data were well-described by the Dorman function relating rate to vertical geomagnetic cutoff. The fitted parameters were $A = 9.21 \pm 0.22$ and $k = 0.575 \pm 0.007$ . The value of $k$ was found to be lower than values typically derived from NM data, further supporting the observation that the nuclear component of CRs is attenuated more rapidly by the atmosphere than the muon component.

Significance and Claims
The paper claims that the Amerigo Vespucci expedition provided a unique, continuous dataset of cosmic-ray fluxes at sea level across a wide range of latitudes (15°S to 45°N) during a period of maximum solar activity (Solar Cycle 25). The study validates historical findings regarding the latitude effect and the location of the cosmic-ray equator (around 7°N).

The authors emphasize that the use of a single, stable instrument over a long duration allowed for a precise dataset with reduced systematic effects. The comparison between the Vespucci muon counter and the Oulu neutron monitor provides empirical evidence of the different energy sensitivities of these detectors, demonstrating that muons are less affected by Forbush decreases and atmospheric attenuation than neutrons. The results are consistent with previous expeditions (e.g., Compton, Millikan, JARE, and icebreaker surveys) and contribute to the ongoing understanding of the Earth's magnetospheric structure and solar-terrestrial interactions.

The Mission: A Floating Lab

The "Bouncer" Effect (Latitude)

The "Solar Storms" (Forbush Decreases)

The Tools and the "Weather"

The Conclusion

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