It’s been a momentous May for skywatchers around the world. First the big auroral event of May 10-11, next a flaming space rock entering over Spain and Portugal. The inbound object was captured by ground-based cameras and the MeteoSat Third Generation Imager in geostationary orbit.
The incoming meteor dazzled viewers across both countries as it sped across the skies at 160,000 km/hour. Of course, social media came alive with speculation about what was burning up in the atmosphere. Most people thought it was a piece of space rock from an asteroid. European Space Agency members of the Planetary Defence Office immediately began analyzing images and data to figure out the composition of the impactor. Now it seems more likely the chunk of space debris came from a comet. They used other data about the energy released as the fragment flew through the atmosphere to determine the size of the object. It was likely about 1 meter across with a mass of between 500 to 1,000 kg.
On 18 May, the meteor burned up in the night sky over Spain and Portugal – as seen by the fireball camera in Cáceres, Spain, operated by ESA’s Planetary Defence OfficeThis is pretty small, which makes it hard to spot on the way in. Also, the object approached from the direction of the sky crowded with stars, making it doubly difficult to see as it spun into our planet’s atmosphere. It explains why planetary defense telescopes or observers didn’t detect the meteor.
To most observers, the meteor over Portugal and Spain looked blue-green and very bright. Those colors are created as various elements in the meteor get heated up by friction with our atmosphere. That vaporizes them and we see the “fiery” aspect light up the sky. If it was a piece of a comet, then the colors also indicate the materials it contained. Most comets contain water, carbon dioxide, ammonia, and methane ice. Other comet “stuff” consists of silica dust, carbon, various metals, and organic molecules. The metals, in particular, could show spectacular colors as they heat up and vaporize.
It’s not known which comet supplied the chunk that broke up and vaporized that night. Earth’s orbit crosses the orbit of several different comets. As they travel through space, particularly as they get close to the Sun, comets shed pieces of themselves. That cometary debris stays in the original orbit around the Sun. Occasionally, Earth’s orbit intersects that cometary path. Its particles particles eventually end up in our atmosphere. The best-known path creates the Orionid Meteor Shower and we can thank Comet Halley for that show from late September to mid-November.
As planetary scientists learn more about the near-Earth environment and its population of asteroids and other space debris, they’ve formed observation groups within NASA and ESA. There’s a network of ground-based observers and facilities that watch the sky each night, looking for incoming impactors. Most of the time, their search is limited to objects larger than the Portugal/Spain object. In addition, satellites such as MeteoSat can pick up these intruders. MeteoSat was launched by ESA to monitor weather conditions and detect lightning strikes. The instrument has four cameras covering Europe, Africa, the Middle East, and parts of South America. Each can capture up to a thousand images per second, allowing the satellite to monitor lightning continuously from space.
ESA’s Planetary Defence Office is in charge of monitoring the positions and approaches of near-Earth objects that could pose a threat to any portion of our planet. It does regular observing campaigns to search for bits of asteroids and comets. NASA operates the Center for Near Earth Object Studies (CNEOS) to do similar searches for possibly dangerous rocks. The Near-Earth objects it’s most concerned about are asteroids and comets with orbits that bring them to within 195 million kilometers of the Sun. Their orbits can move through our planet’s neighborhood. Most of these small bodies are asteroids as small as a few meters wide to nearly 40 kilometers across.
Artist’s concept of the path that a space rock can take that might bring it near Earth. Planetary defense facilities around the planet try to track these objects and warn of their close approach whenever possible. Courtesy: ESA – P.Carril.
The office uses data from observatories around the world—both professional and amateur. Much of this data comes from larger facilities, including Pan-STARRS, the Catalina Sky Survey, and NASA’s NEOWISE mission. In addition, there’s a significant program of planetary radar measurements that contribute data to the NEO observations effort. All of these skywatching campaigns contribute to increased awareness and predictions of near-Earth objects that could pose a threat to our planet.
