On Saturday, revelers in Spain and Portugal ventured into the balmy 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. in Portugal, a fireball tore through the sky, leaving a smoldering trail of red-hot graffiti in its wake. Footage shared on social media showed jaws hanging as the dark night briefly turned into day ablaze in shades of snow white, ethereal green and arctic blue.
Rocky asteroids cause sky-high streaks as they self-destruct in Earth’s atmosphere with some frequency. But over the weekend, the projectile was hurtling toward Earth at a remarkable speed — about 100,000 miles per hour, more than twice the speed expected from a typical asteroid. Experts say it had a strange trajectory that did not match the usual for 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 — that lost its battle with our planet’s atmosphere 37 miles above the Atlantic Ocean. None of the objects are likely to have reached earth, the European Space Agency said.
“It’s an unexpected interplanetary fireworks show,” said Meg Schwam, a planetary astronomer at King’s University Belfast.
It is not uncommon for comets to create shooting stars. “We have remarkable meteor showers throughout the year that are the result of the Earth passing through clouds of debris from certain comets,” Dr Schwamb said. For example, the Perseids that appear every August are the result of our world being swept through the debris left by Comet Swift-Tuttle.
These meteor showers and the weekend’s lone debris lit up the sky in a similar fashion. The air in front of the objects is compressed and heated, which cooks, erodes, opens and obliterates the debris. This destructive process releases light—and, if the projectile is large enough, a powerful shock wave—as it delivers its massive kinetic energy into the sky.
“The weekend patch is probably a bit bigger than a lot of the meteors we see during meteor showers, so it just made a bigger light show,” Dr Schwamb said.
In addition to its brilliant performance, the breakup of the comet fragment served as a test for experts hoping to protect the planet from large killer asteroids.
One principle of planetary defense is to find space rocks before they find us; thus, the defenders of the planet can try to do something about them. But the fragment over Portugal and Spain was not spied before his death.
“It would be great to detect the 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 an object slightly larger than Saturday’s missile could again go undetected and explode with deadly effect over an unaware, unwarned city. The meager, 55-foot meteor that exploded over the Russian city of Chelyabinsk in 2013, for example, was also not identified before its arrival—and its aerial explosion, equivalent to nearly 500,000 tons of TNT, caused widespread damage that injured the most a little over 1,200 people.
But with improved technology on the ground and in space, the hope is that even small, harmless objects from across the solar system (like the weekend’s icy visitor, which experts say was several feet across) can be spotted, providing practice for protecting the planet explorers searching the skies for the common but elusive rocks the size of a football field that could destroy a city.
Fortunately, a series 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 spot 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.
