Inner Workings: Networks of cameras are tracking meteorites with unprecedented precision

Around the globe, networks of camera lenses are trained upward. They scan the night skies, aiming to catch streaks of bright light: meteorites as they fall to Earth. Searching for these space rocks is not new. But the precision and resolution with which increasingly expansive networks of Earth-bound cameras are tracking meteorites is starting to offer insights into both where these bodies go and where they came from.

Networks of cameras are trained on the skies in hopes of gathering meteorite samples—from events such as the Perseid Meteor Shower shown here—that can help researchers understand the rocks' origins, frequency, and composition. Image courtesy of NASA/JPL.

For astronomers, catching sight of a meteor is more than a stroke of luck. It represents a potentially valuable research sample that has fallen to Earth. “These are samples of heavenly bodies reaching us decades before we might actually go there,” says Phil Bland, planetary scientist at Curtin University and director of the Desert Fireball Network (DFN) in Australia. His network is one of several high-tech attempts to track and gather meteorites in the hopes of understanding their origins, frequency, and composition.

Eyes on the Sky

Bland and others want to map out the paths of space rocks by determining precise orbits, and gleaning which asteroids or near-earth region of space from which the rocks emanate. Those participating in these networks are photographing, tracking, and hunting down meteorites.

The DFN consists of 52 autonomous digital cameras placed in the hot, dry Nullarbor desert, with another dozen cameras scattered in multiple countries. Waterproof containers help the cameras survive the Australian outback; inbuilt fans keep the cameras cool through the day. The project is a collaboration between Imperial College London, Ondrejov Observatory in the Czech Republic, Curtin University in Western Australia, and the Western Australian Museum.

To help achieve a high-resolution view of the skies, the network also enlists citizen scientists. According to the project’s website, more than 26,000 people in 88 countries have downloaded the app “Fireballs in the Sky.” Users point their phones to the place in the sky where they saw a fireball start, tap to start the trail, trace the path until the point in the sky where they saw the fireball disappear, and tap again. Options allow users to “fine-tune” the appearance of the fireball, its brightness, duration, shape, and color, and to note whether they heard a sonic boom. The DFN team uses the information to track where the rock may have come from and may have fallen to Earth. If a sighting is corroborated by multiple users, researchers check to confirm the reports. If the DFN team receives enough information, they let users know where the rock they sighted originated in the solar system.

Other meteor-spotting networks opt for a different emphasis. Some, like Bland’s, are meant to spot and help scientists recover fallen meteorites. Others, such as the Cameras for Allsky Meteor Survey (CAMS), curated by Peter Jenniskens of the Search for Extraterrestrial Intelligence (SETI) Institute and sponsored by NASA, focus on searches for new meteor showers and trace them to their original orbits. The network’s 263 cameras are positioned in California in the United States, as well as Belgium, the Netherlands, the United Arab Emirates, and several other nations.

Nearly 5-years-old, the CAMS network has provided the first overview of which meteor streams hit the Earth throughout the year. The network has also discovered more than 100 new showers, with more waiting to be confirmed (1). “It’s basically video surveillance of the night sky,” says Jenniskens. “You film the meteors that appear and you do that from two or more sites, triangulate the track, and determine from where the meteors are coming and at what speed.”

Cameras such as this one (Left), located in Fowlers Gap in New South Wales Australia, help astronomers track and retrieve meteorites such as this one (Right), which researchers found in Kati Thanda–Lake Eyre in Australia. Image courtesy of Desert Fireball Network.

Space Rock, Data Packet

Big strides have been made in the field in recent years. “When I was an amateur [astronomer] 20 years ago, looking at the night sky, there was really no understanding of what was going on,” Jenniskens says, recalling his use of pen and paper to plot the tracks with star charts. Low-light video cameras have been a boon for observers, he says.

Surprising findings from CAMS suggest that meteor showers can shift; the point in the sky that they radiate from can change. The well-known Perseid shower, for example, radiates from the constellation of Perseus during the meteor showers’ mid-August peak (2). But when the meteors first appear in early July, the camera network detected them in Cassiopeia. By early September, the meteors were radiating from the constellation Camelopardalis. These showers are captured in a stunning visualization on the SETI website (see www.seti.org/warped-meteor-shower-hits-earth-at-all-angles).

Already, the creation of meteor shower maps, built upon the observations from networks like CAMS and DFN, has helped astronomers make predictions about when meteor showers will occur. Tracking and forecasting meteor impacts helps ensure the safety of spacecraft and astronauts (3).

That tracking can also, potentially, have real consequences on the ground. In 2013, the Chelyabinsk meteor hit Russia, causing the hospitalization of more than a thousand people (4). Jenniskens traveled to the site in the months after the impact to participate in a Russian Academy of Science field study of the meteorite’s impact. When the meteor whizzed by, glass didn’t just shatter, observers told him, it turned into spray. They didn’t just feel the ground shake, they were knocked off their feet.

The fact that a rock only 20 meters in diameter could cause so much damage was a shock to many astronomers. Generally, smaller rocks weren’t considered a problem. Meteors of this size are pretty common, Jenniskens says, and hit the planet fairly frequently, every 40 years or so. [Chelyabinsk could have suffered more damage if the meteor had entered at a steeper angle and had not fractured into small pieces (5).]

However, meteors can be far smaller than the one at Chelyabinsk, or a breadbox, or a tube of lipstick, and still cause trouble, especially for anyone in space. At NASA’s Meteoroid Environments Office at the Marshall Space Flight Center in Huntsville, Alabama, established in 2004, the mission is more safety than science oriented. Its aim: to generate meteor shower forecasts for the International Space Station and other spacecraft: “So they know when to batten down the hatches,” says office director Bill Cooke. The minute objects he is concerned with are more common that those meteorites strewn across the atmosphere, and more likely to cause trouble for space station astronauts.

The NASA All Sky Fireball Network, started by the NASA Meteoroid Environment Office, consists of 15 cameras, set up in schools, science centers, planetariums, and observatories. Most of the cameras are in the Southern and Eastern United States. Six are in the area surrounding Huntsville. Four are in the northern Ohio and Pennsylvania area. The rest are in southern New Mexico and Arizona.

The office also collaborates with the University of Western Ontario in Canada, which operates the Canadian Meteor Orbit Radar, now in its second iteration. The Canadian Meteor Orbit Radar can see particles down to a 10th of a millimeter and spots between 4,000 and 5,000 individual meteoroid orbits daily.

Fireball Cartographers

Direct sampling of comets and asteroids is likely to happen in the coming years. The OSIRIS-REx mission, launched in September 2016, is now heading for a near-Earth asteroid called Bennu (6, 7). If all goes according to plan, the mission will collect a sample and return it to Earth in 2023 for study.

Bland lauds the effort, but cites the cost of such missions: OSIRIS-REx has a price tag of about $800 million. “A fireball network,” he says, “is the cheap way of getting to that [space rock] map.” The networks attempt to link space rocks to their original orbits using cameras, computers, trucks, and occasionally a plane. No spacecraft is needed.

Even so, setting up networks to cover the night sky comprehensively isn’t a simple endeavor. Hoping to improve capabilities, Eleanor Sansom, a former doctorate student in Bland’s laboratory, has developed a novel, automated method for estimating the mass and origin of bright fireballs detected with the digital cameras that are part of the Desert Fireball Observatories (8). Her method effectively updates the standard way of using equations of flight through the atmosphere to calculate mass as a result of deceleration (with brightness used as a kind of proxy for the fireball’s starting mass).

Traditionally, these interpretations would be based on a series of photographic plates and calculated by hand (9). Instead, her system continually updates the flight equations, using data captured by the cameras to estimate the fireball’s distance traveled, mass, and velocity. Finding the rock on the ground is then essentially a matter of triangulation. When they’re lucky the researchers can actually retrieve it. So far they’ve recovered 4 rocks and know where to look for about another 15. The researchers are finding they have about a 33% success rate, which Bland says is “a lot

“We can use a probabilistic model to roll back those orbits further back in time so we can see where an object originated from in the main belt.”

—Phil Bland

better than anyone has managed before,” although he sees plenty of potential for improvement.

Estimating the rock’s origin entails, in essence, projecting into the past. “We can use a probabilistic model to roll back those orbits further back in time so we can see where an object originated from in the main belt,” says Bland. “Did it come from the innermost part of the belt? Did it come from a specific resonance, where it got thrown out into the inner solar system?” The DFN’s automated method calculates a rock’s origins without lots of manpower. Sansom’s flightpath update technique should allow them to more accurately trace the rock back to its origins.

Most meteorites seen on Earth, astronomers are finding, probably come from asteroid families categorized by their orbits and color spectra. The meteorites generally get thrown toward Earth as a result of disruption events or big impacts between asteroids or asteroid families in the belt. “If you can match meteorites up to one of those,” says Bland, “then you’re then seeing into the interior of an asteroid.”

Such models should only improve as these networks expand and boost their visual acuity—allowing for an even better, high-definition view of these streaks of light as they fall to Earth.