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On Saturday, revelers across Spain and Portugal ventured into the temperate springtime evening, hoping for a memorable night. None were expecting a visitor from outer space exploding above their heads.<\/p>\n
At 11:46 p.m. in Portugal, a fireball streaked across the sky, leaving a smoldering trail of incandescent graffiti in its wake. Footage shared on social media shows jaws dropping as the dark night briefly turns into day, blazing in shades of snowy white, otherworldly green and arctic blue.<\/p>\n
Rocky asteroids cause sky-high streaks as they self-destruct in Earth\u2019s atmosphere with some frequency. But over the weekend, the projectile was plunging toward Earth at a remarkable speed \u2014 around 100,000 miles per hour, more than twice that expected by a typical asteroid. Experts say it had a strange trajectory, not matching the sort normally taken by nearby space rocks.<\/p>\n
That\u2019s because the interloper wasn\u2019t an asteroid. It was a fragment of a comet \u2014 an icy object that may have formed at the dawn of the solar system \u2014 that lost its battle with our planet\u2019s atmosphere 37 miles above the Atlantic Ocean. None of the object is likely to have made it to the ground, the European Space Agency said.<\/p>\n<\/div>\n<\/div>\n
\u201cIt\u2019s an unexpected interplanetary fireworks show,\u201d said Meg Schwamb, a planetary astronomer at Queen\u2019s University Belfast.<\/p>\n
It is not rare for comets to create shooting stars. \u201cWe have notable meteor showers throughout the year, which are the result of the Earth crossing debris clouds of specific comets,\u201d Dr. Schwamb said. For example, the Perseids, which occur every August, are the result of our world\u2019s sweeping through litter left behind by Comet Swift-Tuttle.<\/p>\n
These meteor showers, and the lone shard over the weekend, light up the sky in a similar manner. Air in front of the objects is compressed and heats up, which cooks, erodes, cracks open and obliterates the debris. That destructive process releases light \u2014 and, if the projectile is big enough, a powerful shock wave when it surrenders its immense kinetic energy into the sky.<\/p>\n
The weekend\u2019s \u201cchunk is likely a bit bigger than a good fraction of the meteors we see during meteor showers, so this just made a bigger light show,\u201d Dr. Schwamb said.<\/p>\n
In addition to its flashy performance, the comet fragment\u2019s breakup served as a dry run for experts hoping to defend the planet from large killer asteroids.<\/p>\n<\/div>\n<\/div>\n
One tenet of planetary defense is to find space rocks before they find us; that way, the planet\u2019s protectors can try to do something about them. But the shard over Portugal and Spain was not spied before its demise.<\/p>\n
\u201cIt would have been great to detect the object prior to colliding with the Earth,\u201d said Juan Luis Cano, a member of the Planetary Defence Office at the European Space Agency.<\/p>\n
The worry is that an object just a little larger than Saturday\u2019s missile could again escape detection and explode with lethal effect over an unaware, unwarned city. The meager, 55-foot meteor that exploded above the Russian city of Chelyabinsk in 2013, for example, wasn\u2019t identified before its arrival, either \u2014 and its airborne blast, equivalent to nearly 500,000 tons of TNT, caused widespread damage, which injured at least 1,200 people.<\/p>\n
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\u2019s icy visitor, which experts estimate was a few feet across) can be spotted, providing practice for planetary defense researchers searching the heavens for the common but elusive football-field-size rocks that could destroy a city.<\/p>\n
Fortunately, a series of next-generation observatories are set to come online in the next few years \u2014 including one named after an American astronomer, the Vera C. Rubin Observatory in Chile, which will spot millions of faint and previously undiscovered asteroids .<\/p>\n
For now, the spectacle in Spain and Portugal reminds us that Earth is a participant in the solar system\u2019s never-ending game of planetary billiards, and that working to find as many killer space rocks as possible is a task of the utmost importance.<\/p>\n<\/div>\n<\/div>\n