Key details about a large meteor's fiery passage over the Russian city of Chelyabinsk in February were inadvertently captured by environmental satellites originally tasked to study Earth's weather, scientists say. (See pictures of the Russian meteorite.)
The results, published in this week's issue of the Proceedings of the National Academy of Sciences, suggest that dozens of orbiting and geostationary satellites currently operating in space could be drafted to study potentially dangerous near-Earth objects, or NEOs.
"Sometimes we can use these Earth-viewing meteorological satellites in unconventional ways," said study first author Steven Miller, an atmospheric scientist at Colorado State University.
"In this case, we used the debris trail left in the atmosphere by a large meteor to infer the direction from which it came and provide some insight on where it came from."
Largest Since Tunguska
Miller was home watching television on February 15 when footage of the Chelyabinsk meteor streaking across an early morning sky began appearing on the news.
"I had to rewind and play it back a few times just to confirm that what I was seeing was truly what it was," he recalled.
Miller had good reason to be astonished: About the size of a small house, the Chelyabinsk meteor was the largest known natural object to enter the Earth's atmosphere since the 1908 Tunguska event—widely believed to have also been a meteor—that flattened a wide swath of forest in Siberia.
"We've all seen shooting stars, but this was something above and beyond that," Miller said.
Looking at the early videos and photographs of the meteor, Miller noted the bright debris trail as it broke apart in midair. The residual track reminded him of the condensation trails created by airplanes. (Related: "Giant Chunk of Russian Meteor Recovered.")
"As satellite meteorologists, we see airplane contrails all the time. So the thought was, well, one of these satellites may have been able to capture [this meteor event], so we immediately started looking," Miller said.
Many Eyes in the Sky
As it turned out, more than one satellite was watching. The researchers found that the meteor's dramatic entry into the atmosphere and its eventual breakup was captured by at least seven geostationary satellites.
These satellites are situated above the equator at altitudes that allow them to fly at speeds that match the planet's rotation, so they effectively hover in place.
The event was also observed by a defense weather satellite that just happened to be passing nearby in a lower altitude orbit at the time of the meteor's arrival, providing a particularly stellar view of the meteor trail within just a few minutes of impact.
"We were lucky," Miller said.
Collectively, the satellites captured images of the meteor taken from several different vantage points and from a variety of different sensors, including visible and infrared light.
Using the multiview satellite data, the scientists were able to glean key details about the Chelyabinsk meteor, including its trajectory. The team's estimates agreed well with those inferred from photographs and amateur videos. (Also see "Exploding Asteroids Pose Greater Threat Than Direct Hits.")
Jorge Zuluaga, an astronomer at the University of Antioquia in Colombia, said he was initially skeptical about using weather satellites in this way, but is now convinced that it is possible.
"Now I see how all possible sources of information are key to underpinning the secrets of this wonderful phenomenon," said Zuluaga, who was not directly involved in Miller's study but whose team reconstructed the Chelyabinsk meteor's flight path using amateur videos and photographs.
Josep Trigo-Rodriguez, head of the Meteorite and Minor Body Planetary Sciences Group at the Institute of Space Sciences (CSIC-IEEC) in Barcelona, Spain, said that when it comes to searching for incoming meteors, satellites have several advantages over ground-based monitoring systems, such as the Spanish Fireball Network that he coordinates.
For one thing, the coverage areas of terrestrial surveys are relatively small, he explained.
But "from space it is possible to [watch over a much larger] atmospheric area or even a full
hemisphere without weather interferences," said Trigo-Rodriguez, who also did not directly participate in Miller's study.
Miller thinks environmental satellites could prove especially useful for studying meteors that enter over remote areas not well monitored from the ground. Scientists think the bulk of midsize meteors, also known as meteoroids, that strike our planet fall into this category.
"Only about half a percent of [incoming midsize meteors] are known about," he said. "The 99.5 percent of the remaining objects flying around out there are not being tracked."
In certain cases, environmental satellites could even serve as a limited early warning system, Miller added. For example, scientists tracing the trajectory of an object entering the atmosphere might discover that it's part of a cluster of incoming impactors.
"If a Chelyabinsk-like event was indeed a harbinger of a series of objects sharing a similar orbit, then perhaps by noting its exact direction of travel there would be an opportunity to focus attention on that specific direction and see if other—and potentially larger—objects are coming," Miller said. (Also see "Asteroid Impacts: 10 Biggest Known Hits.")
Even just a few hours of advance warning could be enough time to enable people to find shelter and avoid the worst effects of the blast wave that a striking meteor generates, Trigo-Rodriguez said.
"For larger bodies it would be better to have several days [lead time] to promote an ordered evacuation," said Trigo-Rodriguez, who also leads NEO follow-ups by using the Joan Oró Robotic Telescope at Montsec Astronomical Observatory in Spain.
No Replacement for a Dedicated Telescope
But as useful as they might be for observing incoming objects, the current suite of weather satellites do have important drawbacks, scientists say.
For example, because they were designed to study Earth's weather, the bulk of the satellites' sensors are aimed at the Earth and are not configured or coordinated to provide rapid response to such events.
This limits their ability to proactively scan the skies for incoming objects, such as the recently discovered asteroid 2013 TV135, which scientists think will pass close to Earth in 2032.
"If we really want to tackle this problem, we need to do what many experts have suggested," Miller said: "Put a dedicated space telescope for tracking smaller objects in orbit so it can see what's coming and not what has already entered the atmosphere."
That would be in addition to resources capable of deflecting the orbit of inbound hazards well in advance.
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