Weighing space dust with radar
Researchers give radar new abilities using optical data about meteors


Date:
November 10, 2020
Source:
University of Tokyo
Summary:
It is thought that over 1,000 kilograms of so-called interplanetary
dust falls to Earth every day. This dust is essentially an untold
number of small faint meteors, discarded remnants of asteroids and
comets that pass by the Earth. Two ways to study faint meteors
are radar and optical observations, each with advantages and
limitations. Astronomers have combined specific observations
with both methods, and can now use radar to make the kinds of
observations that previously only optical telescopes could make.



FULL STORY ==========================================================================
It is thought that over 1,000 kilograms of so-called interplanetary dust
falls to Earth every day. This dust is essentially an untold number
of small faint meteors, discarded remnants of asteroids and comets
that pass by the Earth. Two ways to study faint meteors are radar and
optical observations, each with advantages and limitations. Astronomers
have combined specific observations with both methods, and can now use
radar to make the kinds of observations that previously only optical
telescopes could make.


==========================================================================
Our solar system is a busy place -- in addition to the large bodies we are
all familiar with exist an uncountably large number of rocky asteroids
and icy comets. These mostly stay put in their orbits far from Earth
but many also roam around the solar system. As they do, they shed some
material due to collisions, deformations or heating. Due to this, the
Earth is surrounded by small particles we call interplanetary dust. By investigating the size and composition of the interplanetary dust,
astronomers can indirectly investigate the activity and makeup of the
parent bodies.

"When in space, interplanetary dust is practically invisible. However,
around 1,000 kilograms falls to Earth every day in the form of
tiny meteors which appear as bright streaks in the night sky," said
astronomer Ryou Ohsawa from the Institute of Astronomy at the University
of Tokyo. "We can observe these with ground-based radar and optical instruments. Radar is useful as it can cover wide areas and gather vast readings, but optical telescopes can give more detailed information
useful for our studies. So we set out to bridge this gap to boost our observational capacity." Ground-based radar is very good at detecting
the motion of meteors, but it does not reveal much information about
the mass or composition of the meteors.

Optical telescopes and sensors can infer those details based on
the light given off by falling meteors due to interaction with the
atmosphere. However, telescopes have a limited field of view and until
recently lacked the sensitivity to see faint meteors at all. Ohsawa and
his team wished to imbue radar observatories with the powers of optical
ones. After a few years, they have finally succeeded.

"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,"
said 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."
In 2009, 2010 and 2018, the team used the Middle and Upper Atmosphere (MU) Radar facility, operated by Kyoto University and located in Shigaraki,
Shiga Prefecture, and the Kiso Observatory, operated by the University
of Tokyo, on the Nagano Prefecture side of Mount Ontake. They are 173 kilometers apart, which is important: the closer the facilities, the
more accurately the data from them can be correlated. MU points directly upwards, but Kiso can be angled, so it was pointed 100 km above the
site of MU. The team saw 228 meteors with both facilities and this was
plenty to derive a statistically reliable relationship to connect radar
and optical observations.

"Data analysis was laborious," said Ohsawa. "A sensitive instrument
called the Tomo-e Gozen wide-field camera mounted to the Kiso telescope captured over a million images a night. This is too much for us to
analyze manually so we developed software to automatically recognize faint meteors. From what we've learned here we hope to extend this project and
begin using radar to investigate the composition of meteors. This could
help astronomers explore comets and aspects of solar system evolution
like never before."

========================================================================== Story Source: Materials provided by University_of_Tokyo. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Ryou Ohsawa, Akira Hirota, Kohei Morita, Shinsuke Abe, Daniel
Kastinen,
Johan Kero, Csilla Szasz, Yasunori Fujiwara, Takuji Nakamura,
Koji Nishimura, Shigeyuki Sako, Jun-ichi Watanabe, Tsutomu Aoki,
Noriaki Arima, Ko Arimatsu, Mamoru Doi, Makoto Ichiki, Shiro Ikeda,
Yoshifusa Ita, Toshihiro Kasuga, Naoto Kobayashi, Mitsuru Kokubo,
Masahiro Konishi, Hiroyuki Maehara, Takashi Miyata, Yuki Mori,
Mikio Morii, Tomoki Morokuma, Kentaro Motohara, Yoshikazu Nakada,
Shin-ichiro Okumura, Yuki Sarugaku, Mikiya Sato, Toshikazu
Shigeyama, Takao Soyano, Hidenori Takahashi, Masaomi Tanaka,
Ken'ichi Tarusawa, Nozomu Tominaga, Seitaro Urakawa, Fumihiko Usui,
Takuya Yamashita, Makoto Yoshikawa. Relationship between radar
cross section and optical magnitude based on radar and optical
simultaneous observations of faint meteors. Planetary and Space
Science, 2020; 194: 105011 DOI: 10.1016/j.pss.2020.105011 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/11/201110190938.htm

--- up 11 weeks, 1 day, 7 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)