On Saturday, revelers across Spain and Portugal braved the balmy spring evening in hopes of a night to remember. No one expected a visitor from outer space to explode over their heads.
At 11:46 p.m., a fireball flew across the sky in Portugal, leaving behind a smoldering trail of incandescent graffiti. Footage shared on social media shows jaws dropping as the dark night briefly turns to day, erupting in shades of snowy white, otherworldly green and arctic blue.
Rocky asteroids cause cloud streaks when they self-destruct in the Earth’s atmosphere with a certain frequency. But over the weekend, the projectile hurtled toward Earth at an extraordinary speed — about 100,000 miles per hour, more than double the expected speed of a typical asteroid. Experts say it had a strange trajectory that doesn’t match the usual trajectory of nearby space rocks.
That’s because the intruder wasn’t an asteroid. It was a fragment of a comet – an icy object that may have formed at the dawn of the solar system – lost its battle with our planet’s atmosphere 37 miles above the Atlantic Ocean. The European Space Agency said none of the objects likely reached the ground.
“This is an unexpected interplanetary firework,” said Meg Schwamb, a planetary astronomer at King’s University in Belfast.
It is not uncommon for comets to produce shooting stars. “Throughout the year, we have notable meteor showers that are the result of debris clouds from certain comets crossing Earth,” Dr. Schwamb said. For example, the Perseids that occur every August are the result of our world sweeping up the debris left behind by Comet Swift-Tuttle.
These meteor showers and a lone shard over the weekend are lighting up the sky in a similar way. The air in front of the objects is compressed and heated, which boils, erodes, splits and destroys the debris. This destructive process releases light – and, if the projectile is large enough, a powerful shock wave as it releases its enormous kinetic energy into the sky.
“The weekend chunk is probably a little bit bigger than a good fraction of the meteors we see in meteor showers, so it just made a bigger light show,” Dr Schwamb said.
In addition to the striking features, the breakup of the comet fragment served as a wake-up call for experts hoping to protect the planet from large killer asteroids.
One of the principles of protecting the planet is to find space rocks before they find us; that way the defenders of the planet can try to do something about them. But the shard over Portugal and Spain was not seen until his death.
“It would be great to detect an object before it collides with Earth,” said Juan Luis Cano, a member of the European Space Agency’s Planetary Defense Office.
The worry is that the object, slightly larger than Saturday’s missile, could again elude detection and explode with deadly effect over an unsuspecting, unwarning city. For example, the tiny 55-foot meteor that exploded over the Russian city of Chelyabinsk in 2013 was also not identified before it arrived—and its aerial blast, equivalent to nearly 500,000 tons of TNT, caused widespread damage that injured at least 1,200 a person
But with improvements in technology on the ground and in space, there’s hope that even tiny, innocuous objects from across the solar system (like the icy visitor over the weekend, which experts estimated was several feet across) can be spotted, providing practice To protect the planet, researchers search the heavens for common but elusive rocks the size of a football field that could destroy a city.
Fortunately, a series of next-generation observatories are scheduled to come online in the next few years — including one named after an American astronomer, the Vera K. Rubin Observatory in Chile, which will detect millions of faint and previously undiscovered asteroids.
For now, the spectacle in Spain and Portugal reminds us that Earth is a participant in the Solar System’s never-ending game of planetary billiards, and that the task of finding as many killer space rocks as possible is a task of the utmost importance.