menu bar: storm - science - researcher - images - ILW - *news


Leonid MAC

View the shower
Mission Brief
Science Update
Media Brief

LEONID DAILY NEWS: November 1, 2000

Leonid meteoroid cloud in space Figure right: Diffuse glow of scattered sunlight from Leonid meteoroids by Ryosuke Nakamura and colleages.


Unsettling as it may sound, Leonid meteoroids are all but invisible when in the vast expanse of space between the planets. The tiny grains are too far dispersed and too large to scatter sunlight effectively. Until now, the only way to detect the grains in space was from their thermal infrared emission. In this manner, many short-period comets were found to have dust trails in their orbit.

Now, in the recent September 10 issue of the Astrophysical Journal, Ryosuke Nakamura of Kobe University, Japan, and his co-workers report on the discovery of a faint glow of scattered sunlight from the dust trail of the Leonid parent comet 55P/Tempel-Tuttle. While inside the dust trail of comet 55P/Temple-Tuttle, a faint glow was seen in the direction of approach of the particles, just above the body of the constellation "Leo" (figure right). Such "meteoroid clouds" were known before only from a few anecdotes of eye witnesses of past meteor storms.

The glow was first detected during the November 1998 Leonid shower, in a conserted airborne and ground-based effort involving the 1998 Leonid MAC mission and the Mauna Kea observatory in Hawaii. It was not seen a month later in December, when the Earth had moved away from the dust trail (figure below).

This detection provides a unique cross-section of the dust complex, which measures about 0.02 AU across (2 percent of the Earth-Sun distance), and is elongated in the comet orbital plane. The brightness of the cloud is approximately 2-3 percent of the background zodiacal light and represents all of Tempel-Tuttle's meteoroid complex, not just the part of the dust trail responsbible for the 1998 Leonid shower (Full paper - PDF).

This year, the last quarter Moon will make further observations all but impossible in the direction of approach. Southern hemisphere observers, however, may be able to see the trail in the opposite direction on the sky, where the meteoroids move away from Earth, in the evening hours when the Moon (and the Leonid shower) do not distract.

Figures below: The diffuse glow seen during the Leonid shower and one month later. Left: A graph showing how the dust trail would look like as seen from Earth.

Leonid cloud in space model Leonid meteoroid cloud

Previous news items:
Nov. 01 - Leonids approaching Earth
Oct. 31 - Prospects for Moon Impact Studies
Oct. 30 - Comet dust crumbled less fine

These and other results of Leonid storm research will appear in a special issue of the peer-reviewed journal "Earth, Moon and Planets", published by Kluwer Academic Publishers, the Netherlands.

Top of Page - Text/Image Use Guidelines

Science Update Storm Science Researcher Images ILW News