Watch a Blue-Green Comet Illuminate Skies Over Spain and Portugal

The colorful fireball mesmerized onlookers—and its unexpected appearance surprised astronomers who are hoping to better predict when space rocks enter Earth’s atmosphere

a bright green streak in the sky next to some clouds makes the entire night sky appear green
A bright green fireball is captured on camera over Cáceres, Spain, by the European Space Agancy. Officials say the object was a comet and likely broke up over the Atlantic Ocean. ESA / PDO / AMS82 - AllSky7 via ESA Operations

Late on Saturday night, a cosmic projectile turned the skies over Spain and Portugal a magnificent aquamarine. For a few ethereal moments, the near-midnight hues above parts of Iberia changed from the usual deep blue-black to a bright blue-green and back again. 

The sight sparked ripples of wonder among concert goers in the city of Barcelos in Portugal as the sky lit up and attendees caught a glimpse of the sudden light. Bernardo Taborda, a Lisbon resident, was out for a walk with friends when the object passed overhead, he tells Reuters Catarina Demony and Ana Cantero.

“It almost looked like daylight … we all looked back and saw it,” Taborda says to the publication. “It felt like a movie. We all looked at each other, and we were stunned.”

At first, astronomers had trouble identifying the object. Hurtling at roughly 28 miles per second, the cool-colored fireball passed far too quickly to be an asteroid, and it moved with an odd trajectory. The European Space Agency (ESA) captured footage of the object with its “fireball camera” in Cáceres, Spain, near the Portuguese border.

Though it initially called the mysterious object a “stunning meteor,” the agency later corrected itself: The fireball was actually a fragment of a comet—a so-called “dirty snowball” made of ice, dust and other organic matter that orbits the sun. According to NASA, material in comets likely dates to some 4.6 billion years ago, when our solar system was formed.

The Spanish Observatorio de Calar Alto came to the same conclusion as the ESA, saying the “object had a cometary origin,” writes Forbes Eric Mack.

Some comets pass by Earth on routine schedules, even though it may take many decades for them to reappear. Halley’s Comet, perhaps the most famous, is visible once every 76 years on average, and  it isn’t due to be back again until 2061. Other comets have expected return dates and are tracked by astronomers. But by all accounts, no one knew this comet was coming.

“It’s an unexpected interplanetary fireworks show,” Meg Schwamb, an astrophysicist at Queen’s University Belfast in Northern Ireland, tells the New York Times Robin George Andrews.

The comet’s striking color was emitted as it burned up, the air around it heating due to friction as it sped through Earth’s atmosphere. The blue-green hue is indicative of the comet’s chemical composition, according to’s Robert Lea, and means it likely had a high concentration of magnesium.

The ESA estimates the comet fully broke up 37 miles above Earth, somewhere over the Atlantic Ocean. It is unlikely, the agency says, that any bits will be recoverable on land.

Still, the comet’s brief and spectacular performance could hold lessons for astronomers involved with planetary defense. Space agencies aim to track celestial objects that could potentially collide with Earth in hopes that they could deflect them.

In the past, some space rocks have escaped detection: In 2013, the unpredicted explosion of an approximately 65-foot meteor above Chelyabinsk, Russia, injured more than 1,000 people.

Saturday’s comet—its size still unspecified—was also not detected ahead of its arrival. The ESA shared on social media that its experts are currently reviewing “precovery” information—trying to retrospectively find the comet in existing data.

“It would have been great to detect the object prior to colliding with the Earth,” Juan Luis Cano, an aeronautical engineer with the ESA’s Planetary Defense Office, tells the New York Times.

Get the latest stories in your inbox every weekday.