When you look into the night sky and see a shooting star, it might look like something very big, but the odds are that it's a meteor the size of a dust mote. A team of scientists led by Ryou Ohsawa from the Institute of Astronomy at the University of Tokyo have now combined observations from radar and optical telescopes to learn more about this interplanetary dust as it burns up in the Earth's atmosphere.
It's estimated that every day over a metric tonne of this interplanetary dust falls on the Earth. These meteors are of great interest to astronomers because the spectrographs of the light they give off as they burn can give valuable insights into the nature of the solar system. This is because these particles are the remnants of asteroids and comets that have either disintegrated or have had debris break off due to collisions and thermal stresses.
The problem is that telescopes have a very narrow field of view and can only study meteors if the instrument happens to be pointing in the right direction at the right time. On the other hand, radar can scan large areas of the sky, allowing it to easily detect meteors even before they burn up. Unfortunately, radar can only reveal that a meteor is there and not much about its mass or composition.
But by analyzing the observations of these two methods, the University of Tokyo team sought the best of both worlds. They did this in 2009, 2010, and 2018 by using the Middle and Upper Atmosphere (MU) Radar facility in Shigaraki, Shiga Prefecture, and the Kiso Observatory on the Nagano Prefecture side of Mount Ontake.
According to the team, these two sites are 107 miles (173 km) apart. The MU points straight up, but the telescope was set at an angle so it could be aimed at a point 62 miles (100 km) above the radar site. During the study, the Tomo-e Gozen wide-field camera mounted on the Kiso Schmidt Telescope captured over a million images per night, which were analyzed by special software to recognize faint meteors. This combination allowed the scientists to observe a statistically reliable 228 meteors by both radar and optical observations.
"We thought that if you could observe enough meteors simultaneously with both radar and optical facilities, details of the meteors in the optical data may correspond to previously unseen patterns in the radar data too," says Ohsawa. "I am pleased to report this is in fact the case. We recorded hundreds of events over several years and have now gained the ability to read information about meteor mass from subtle signals in radar data."
The team says this will allow radar, with its much wider field of view, to make observations previously only possible using optical telescopes.
The research was published in Planetary and Space Science.
Source: University of Tokyo
