On April 23, 2019, the night sky over central Costa Rica was illuminated by a spectacular fireball, marking the arrival of a significant extraterrestrial visitor. This event, witnessed by many and captured on various cameras, culminated in a meteorite shower near the town of Aguas Zarcas. The event quickly garnered national and international attention, leading to a rapid recovery effort that secured a rare and valuable sample.
The Fall and Initial Recovery
The meteorite’s descent on April 23, 2019, at 9:07 PM local time, created a bright flash detected by orbiting satellites. It entered Earth’s atmosphere from the west-northwest at about 14.6 kilometers per second, at a near-vertical angle. Despite intense atmospheric entry causing some vaporization, the main body fragmented little until it shattered at about 25 kilometers (15.5 miles) above the Earth’s surface.
Fragments scattered across the districts of Aguas Zarcas and La Palmera in San Carlos. An estimated 27 to 30 kilograms (60 to 66 pounds) of material were recovered, making it the largest fall of its kind since the Murchison meteorite in 1969. Swift recovery efforts, often by local residents, contributed to the pristine state of the samples. Many fragments, some with a blue iridescence on their fusion crust, remained intact. They landed in soft jungle and grassy terrain during a prolonged dry season, preventing significant damage or dissolution.
A Window into the Early Solar System
The Aguas Zarcas meteorite is classified as a CM2 carbonaceous chondrite. It is a primitive meteorite, rich in carbon compounds and water-bearing minerals. These meteorites are remnants from the early solar system, preserving their original chemical, isotopic, and mineralogical composition from the first few million years of its formation.
Often described as a “mudball,” the meteorite contains high levels of water-rich minerals, primarily serpentine, and organic compounds. It is also a breccia, composed of coalesced fragments of different rock types (lithologies). These different lithologies show varying degrees of aqueous alteration and heating. The presence of hydrocarbons, carboxylic acids, dicarboxylic acids, sugar alcohols, and sugar acids provides insights into early solar system organic synthesis. This contributes to understanding prebiotic compounds potentially available on early Earth.
Connecting to Asteroid Missions
Studying the Aguas Zarcas meteorite informs and helps interpret data from ongoing asteroid sample-return missions. Its pristine condition and similarity to target asteroids make it an important “ground truth” for scientists. Researchers use detailed analyses of Aguas Zarcas to understand samples returned by NASA’s OSIRIS-REx mission from asteroid Bennu and JAXA’s Hayabusa2 mission from asteroid Ryugu.
Both OSIRIS-REx and Hayabusa2 collect samples from carbonaceous asteroids, thought to be unaltered remnants from the solar system’s formation. Understanding the mineralogy and chemistry of meteorites like Aguas Zarcas allows scientists to validate or refine models based on remote sensing data from these asteroids. This comparison helps decipher the complex organic chemistry and hydrated minerals in returned asteroid samples, providing a more complete picture of conditions and materials during planetary formation.
Unveiling a Resilient Past
Research on the Aguas Zarcas meteorite revealed a detail about its journey through space. Scientists determined the meteorite spent an unusually long time, about two million years, in orbit without significant collisions before impacting Earth. This was determined by measuring radioactive elements within the rock, which indicate how long its inner layers were exposed to cosmic rays since breaking off from a larger asteroid.
This extended period in space without major impacts challenges previous assumptions about the fragility of carbonaceous chondrites, which are often described as “mudballs” and thought to be more susceptible to damage. The meteorite’s strength and its steep entry trajectory into Earth’s atmosphere contributed to a large fraction of its mass surviving to the ground. This discovery provides new insights into the orbital dynamics and survival mechanisms of these meteorites within the asteroid belt, suggesting they are more durable than previously considered.