While amateur astronomers enjoy the spectacular sky show the Perseids meteor shower is putting on this month, scientists at Western University are using this “sky laboratory” to learn more about what happens as small rocks interact with the atmosphere.
The university has a network of cameras stretching from southern Ontario to southern Quebec looking at the meteor shower – which runs until Aug. 12 – in wavelengths ranging from optical to radar. Western also uses microphones to pick up the occasional sounds these meteors produce, and this data-gathering only represents the beginning of Perseids and meteor research.
“Because the weather’s so good [in August] and there are so many bright Perseids, it’s a unique laboratory for us to study – using many different kinds of instruments – how meteors interact with the atmosphere, how they burn up and what their structure is like,” said Peter Brown, the Canada Research Chair in Planetary Small Bodies at Western.
“We look at the Perseids with radar, and we look at the electrons in the plasma that’s produced,” he added, as meteorites move through the atmosphere.
“Believe it or not,” he continued, “some of the brighter Perseids can penetrate deep enough that they produce a sonic boom. We use that information from the shockwave, together with the light production to figure out energy gets distributed – how much [energy] goes into the shockwave and how much goes into plasma production. That feeds back into things like models of how metal ions get deposited in the upper atmosphere, and that can lead back to trying to understand bigger things hitting the Earth.”
Brown joked that his only regret is his team doesn’t need to look at the sky with their own eyes, because the network of instruments they have is so extensive – and records the information in so many ways – that the human time is better used in analyzing the results and making sure the instruments are running well. Here is how Western looks for meteorite information:
The Global Fireball Observatory: Western is a participant in this multi-institutional network that stretches around the world. On Western’s side, the university has eight stations in southern Quebec and southern Ontario as part of the Southern Ontario Meteor Network, Brown said. Western detects fireballs using 20 video cameras, recording at 30 frames a second. “They [the cameras] are very sensitive, and they record meteors like the Perseids – as bright as Jupiter,” Brown said. The cameras automatically record the orbits and trajectories of the meteors, and the optical data can also guide radar observations, he said.
The Canadian Automated Meteor Observatory (CAMO): This system uses prototype cameras that track meteors using mirrors, Brown said. Using image intensifiers, the cameras examine a 20-by-20-degree patch of sky and record it at 100 frames a second. Whenever a meteor is detected, a computer finds the meteor, locates the position and slews the mirrors to within a few milliseconds of the meteor’s position. Telescopes can then track the meteor (at two stations) with roughly three-meter resolution, Brown said; one research project using the CAMO mirror system was recently published in Icarus. “We use that information … to work out exactly how the object breaks up, the debris that comes off and the grain sizes that come off” as the meteor streaks through the atmosphere, Brown explained. The Perseids, he said, usually produce dozens of events – and the researchers are in the early stages of figuring out the chemistry of the individual meteors through examining their spectra, Brown added.
Electron-Multiplied CCDs (EMCCDs): These are extremely sensitive cameras Western uses that can detect meteors down to 100 microns in size. “They [the cameras] give us fluxes of the very smallest things that would be most germane, say to satellite impacts,” Brown said. In other words, this research helps evaluate the threat of a meteor shower to satellites. In August 1993, for example, Brown said the European Space Agency’s Olympus-1 communications technology demonstration satellite was likely damaged and had to be decommissioned due to Perseid activity. “The cosmonauts onboard the Mir space station also reported hearing impacts and outside the space station,” Brown added, saying the noises were never explained but were coincident with the peak of the Perseids. The shower was quite strong in August 1993 – seven months after their parent comet, 109P/Swift-Tuttle, made its closest approach to the sun in December 1992.
Radar: Western’s radar system sends out pulses of radiofrequency energy at about 500 times a second. “When it [the radar] hits perpendicular to the trail of electrons – set up by the meteorite when it’s bleeding into the atmosphere – we get a big pulse that gets sent back to the radar, and we can detect the meteors through this sort of ‘specular reflection’,” Brown explained. The radar has two unique features Brown identified.
- It records in three frequencies: 17, 29 and 38 megahertz. “When we probe the meteor and its echo, we actually can calibrate for a whole bunch of different effects that are wavelength dependent,” Brown explained. The different wavelengths allow the researchers to calibrate the system to improve their ability to spot different fluxes.
- The network is spread out over a region between about Kitchener, Ont. and London, Ont.; the cities are roughly an hour and 15 minutes apart by driving distance. The span of the network allows the transmitting radar beam to hit a meteor, and the receiver sites that are spread around the region can pick up the radar reflection – with a time delay. “Based on that time delay, we can figure out the orientation of the meteor, its speed and its orbit,” Brown explained. The system automatically measures meteor orbits to predict items such as how often meteoroids that are bigger than a few 100 microns hit the upper atmosphere. That data is sent to NASA to help them make predictions for meteor shower activity, Brown added.
Machine learning: Like many other observatories, Western is using algorithms to crunch the “big data” it receives, especially because this information is often delivered in high-quality 4K resolution across large swaths of sky. Machine learning, Brown said, “facilitates our ability to quickly find things. We’re also using machine learning to take models where you have millions and millions of combinations of a model input; machine learning is really good at telling you, ‘These are the ones that are allowable.’ “
Interdisciplinary research: For all of the above data and modelling, Western is also working on ways of “fusing” it to create a “coherent picture” for each meteor event like the annual Perseids, Brown said. “We’re trying to get radar data and optical data, and then put all that together with ablation models to truly constrain what’s going on in the physics of these things [meteors] as they get in the atmosphere. That tells us something about their structure and chemistry.” Brown added that the researchers can also use such data to relate the meteors back to the parent bodies from which they came.
Looking ahead: Comet Swift-Tuttle’s stream of debris (visualized in spectacular form here) subtly changes position over time due to perturbations from Jupiter and Saturn, which creates a 12- to 13-year cycle to the Perseids in terms of their intensity. (This planetary effect on the Perseids was the subject of Brown’s Ph.D. research 25 years ago, he added.) The next big show is expected in 2028, due to influence from Saturn, Brown said. As for 2021, the show will be “pretty normal”, Brown noted. That said, the moon will be at a crescent or new phase for the next week, allowing skywatchers to get a clear view of the meteor shower with a minimum of natural light pollution. As for Comet Swift-Tuttle’s next closest approach, we’ll be waiting more than a century until it returns in 2125.