An international team of astronomers has used the Low Frequency Receiver onboard the twin Solar TErrestrial RElations Observatory (STEREO) to learn more about the interplanetary nanodust – nanometer-scale particles created by asteroid collisions and the evaporation of comets.
Zodiacal light scattered from dust grains in our Solar System is seen rising diagonally up to the left in this image, as the plane of the Milky Way rises up to the right (Tunc Tezel / TWAN / APOD).
These particles are abundant in our Solar System. They are the source of the zodiacal light, a diffuse glow in the night sky that extends along the ecliptic and which is seen from Earth stretching along the zodiac, most easily after sunset or before sunrise.
The gravity of the planets affects the distribution of these dust particles. The Earth, for example, collects dust in a series of patches which lie in a ring along the Earth’s orbit.
A grain of nanodust is smaller than a wavelength of optical light, and unlike the roughly ten times larger grains responsible for the zodiacal light, nanodust is too small to efficiently scatter sunlight and can only be detected using space instruments.
When a grain of nanodust impacts a spacecraft, it creates an expanding cloud of ionized gas which can lead to a voltage pulse between a spacecraft’s body and its antenna, and which can then be sensed.
Nanodust can be accelerated by the interplanetary magnetic field to the speed of the solar wind – significantly faster than the orbital speeds of heavier dust grains. Because the electrical signal induced by a dust grain depends more strongly on its impact speed than on its mass, nanodust produces a strong signal despite its being lightweight.
Dr Gaetan Le Chat, who is a lead author of a paper reporting the results in the journal Solar Physics (arXiv.org), with his colleagues have used the two STEREO spacecraft to deduce the characteristics of nanodust.
The spacecraft are in solar orbits with one ahead of the Earth and one trailing behind. On average, the spacecraft recorded about fifty nanodust impacts every second, with occasional bursts of up to a thousand hits.
The team analyzed over seven hundred thousands measurements to conclude that nanodust is a significant contributor to the total mass of material in interplanetary space, in agreement with earlier estimates, and to begin to characterize its properties.
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Bibliographic information: G. Le Chat et al. 2013. Interplanetary Nanodust Detection by the Solar Terrestrial Relations Observatory/WAVES Low Frequency Receiver. Solar Physics, vol. 286, no. 2, pp. 549-559; doi: 10.1007/s11207-013-0268-x
