On Saturday, revelers across Spain and Portugal ventured into the temperate spring evening hoping for a night to remember. No one expected a visitor from outer space to explode over their heads.
At 11:46 p.m., a fireball shot across the sky in Portugal, leaving a smoldering trail of glowing graffiti. Footage shared on social media shows jaws dropping as the dark night briefly turns into day, glowing in shades of snow white, otherworldly green and arctic blue.
Rocky asteroids cause sky-high streaks because they self-destruct in Earth’s atmosphere with some frequency. But over the weekend, the projectile plunged toward Earth at a remarkable speed — about 100,000 miles per hour, more than twice as fast as expected from a typical asteroid. Experts say it had a strange trajectory, unlike the kind that nearby space rocks normally take.
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 beginning of the solar system – that lost its battle with our planet’s atmosphere 60 kilometers above the Atlantic Ocean. According to the European Space Agency, none of the objects are believed to have reached the ground.
“It’s an unexpected interplanetary fireworks display,” said Meg Schwamb, a planetary astronomer at Queen’s University Belfast.
It is not uncommon for comets to form shooting stars. “We have remarkable meteor showers throughout the year, which are the result of Earth passing through debris clouds of certain comets,” said Dr. Sponge. For example, the Perseids, which occur every August, are the result of debris left behind by Comet Swift-Tuttle that floods our world.
These meteor showers and the weekend’s lone shard are lighting up the sky in a similar way. The air in front of the objects is compressed and heated, causing the debris to cook, erode, burst and destroy. This destructive process releases light – and, if the projectile is large enough, a powerful shockwave as it releases its immense kinetic energy into the sky.
“The chunk from the weekend is probably a little bit larger than a good portion of the meteors we see in meteor showers, so it just made for a bigger light show,” said Dr. Sponge.
In addition to its eye-catching achievement, the comet fragment’s disintegration served as a test run for experts hoping to protect the planet from large killer asteroids.
A tenet of planetary defense is to find space rocks before they find us. This way the planet’s protectors can try to do something about it. But the shard over Portugal and Spain was not spied on before its sinking.
“It would have been great to detect the object before it collided with Earth,” said Juan Luis Cano, a member of the European Space Agency’s Planetary Defense Office.
The concern is that an object only slightly larger than Saturday’s rocket could again escape detection and explode with deadly effect over an unsuspecting, unprepared city. The skinny, 55-foot-tall meteor that exploded over the Russian city of Chelyabinsk in 2013 was also not identified before its arrival — and its aerial blast, equivalent to nearly 500,000 tons of TNT, caused widespread damage that injured many people and at least 1,200 people.
But with improved technology on the ground and in space, the hope is that even tiny, harmless objects from around the solar system (like the weekend’s icy visitor, which experts estimate was only a few meters across) can be detected, which could be seen as an exercise could be used to defend the planet Researchers are searching the skies for the common but elusive stones the size of a football field that could destroy a city.
Fortunately, a number of next-generation observatories will come online in the next few years – including one named after an American astronomer, the Vera C. Rubin Observatory in Chile, which will discover millions of faint and previously undiscovered asteroids.
For now, the spectacle in Spain and Portugal reminds us that Earth is involved in the solar system’s endless game of planetary billiards, and that finding as many killer space rocks as possible is a task of paramount importance.