Sandia LabNews

Oct. 9 meteor event adds to understanding of atmospheric phenomena


EYE ON THE SKY Ñ Dale Jackson (5737) checks out a Sentinel network all-sky video camera system prior to installation at SandiaÕs LAZAP facility. A Sentinel system consists of a small, inexpensive black-and-white video camera equipped with a fisheye lens, with digitized video fed to a PC. Almost 100 Sentinel systems are deployed and monitored by volunteers in 11 states and five Canadian provinces. SandiaÕs Sentinel camera and a unit in Lamy, N.M., recorded a significant meteor event in the early hours of Oct. 9. (Photo by Randy Montoya)

You probably didn’t see it, but a couple of instruments in the Sandia-established Sentinel network did. What they saw — and you likely missed — was a marvelous nighttime light show.

In the early morning hours of Oct. 9 — at around 2 a.m. MDT — a meteor came streaking into the atmosphere over the western US. Its trail, an unusually bright and persistent slash across the dark sky, was picked up by at least two Sentinel skywatch systems, one at Sandia and one maintained by serious amateur astronomer Tom Ashcraft near Lamy, N.M.

The meteor, visually striking enough to generate local media interest, came out of the northwest sky and — according to early estimates by Sandia astrophysicist Dale Jackson (5737) — likely impacted somewhere in the rough country south and east of Glorieta, N.M. Dale says that as he and colleague Dick Spalding (5730) refine and analyze the data collected that night, they’ll get a better handle on the size and trajectory of the meteor and may even be able to pinpoint the impact location with some precision.

Using a Google Maps application written specifically for the purpose in the summer of 2008 by student intern Leandra Boucheron (1344 now; 5737 last year), Dale and Dick plotted the meteor’s flight path as seen from the Sandia instrument and from Tom Ashcraft’s instrument in Lamy. With those two frames of reference, they used the software to generate a Google Map overlay showing the initial estimate of the meteor track.

Dick is in the process of polling other members of the Sentinel network to find out if any other systems detected the meteor that night. As with GPS data, the more different frames of reference they have to work with, the more accurately Dick and Dale can refine the trajectory and impact point.

Despite a media-published estimate that the Oct. 9 meteor might be as large as a small car, Dick and Dale think it’s likely it was about the size of a beach ball — big enough to make a pretty impressive streak across the sky, but not that unusual. Dick, who’s been watching the skies for a long time as part his work at Sandia, says that about once a year there’s a meteor event in the Albuquerque skies on the scale of the one seen on Oct. 9.

Space junk or meteor?

Was it maybe not a meteor at all, but space junk?

Dale and Dick can rule that out with confidence. For one thing, the object was traveling too fast: Space junk — most of which is coming out of low Earth orbit — enters the atmosphere at roughly 17,000 miles per hour. A meteor enters the atmosphere at speeds of 25,000 mph or higher.

Also, as the Oct. 9 object swept across the sky in its downward arc, it displayed a flaring phenomenon characteristic of meteors and not seen in space junk reentries.

The flaring happened in rapid pulses; it’s quite evident in video of the event and shows up as strikingly obvious spikes in a light curve plot of the meteor’s transit of the sky.

The flares interest Dale and Dick because the mechanism that causes the phenomenon is not well understood. Conventional theory would hold that the flares are caused by a thermodynamic process — the heating and ablation of meteor material. (That’s how heat shields worked on the Mercury/ Gemini/Apollo spacecraft.) But the flares recorded on Oct. 9 happened way too fast to be the result of a heating process, says Dick.

“There’s some other emission mechanism at work here,” he asserts.

Dick subscribes to an idea proposed in a paper published last year by Czech researchers: The flaring detected in meteors is contended to be an electrical phenomenon. According to their theory, as a meteor enters the outer edges of the atmosphere it encounters triboelectric charging, which builds up and discharges over and over again very rapidly. The discharges can be substantial — those are the flares you see in the recordings, Dick says.

Dale, the astrophysicist, agrees that conventional explanations for the flaring phenomenon don’t cut it.

“I challenge anyone to reproduce the curve we see here, demonstrating these effects, using the standard [thermodynamic] model,” Dale says.

Understanding the flare-causing mechanism is of more than academic interest. First, Dale notes, a better understanding is needed to ensure safe spacecraft reentry. While the flaring phenomenon and its electrical implications hasn’t specifically been associated with spacecraft, it would be the unwise scientist or engineer who would dismiss the concern out of hand.

Also, adds Dick, it’s important that the nation’s skywatchers understand what they see when they see it. When you see a pattern of unusual flaring behavior in the sky — whether you’re seeing it from a space-based or ground-based platform — it’s critical to understand what’s causing it. Is it that triboelectric phenomenon associated with meteor activity? Or is it a rogue test of a nuclear device?

Understanding the difference is vitally important, Dick says.

The real issue, says Dale, is that there isn’t a lot of data available about atmospheric phenomena similar to this.

“There just aren’t a lot of resources invested in monitoring the atmosphere,” he says.

What is the Sentinel network?

The Sentinel network was conceived of about a decade ago by Sandia senior engineer Dick Spalding (5730) and colleague George Alder (ret.). It was established specifically to record transient light events such as the Oct. 9 meteor. It’s designed to monitor the skies more or less automatically, with little need for hands-on maintenance.

Today, there are nearly 100 Sentinel systems deployed in 11 US states and five Canadian provinces; there’s even an outlier system in Ireland. They are mostly maintained by knowledgeable and dedicated amateur volunteers. (Astronomy is one area of science where amateurs still make valued, important, and frequent contributions to the body of knowledge.)

A Sentinel system consists of a small, inexpensive black-and-white video camera equipped with a fisheye lens, with digitized video fed to a PC. The camera sees the entire sky and any time a light event occurs that meets certain software-defined characteristics, the camera starts recording whatever is in the video. Thus, whenever a bright light event happens — like the Oct. 9 meteor event over Albuquerque — the Sentinel system captures a precise video record of it.

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