[meteorite-list] Ulysses Sees Galactic Dust On The Rise

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:28 2004
Message-ID: <200308041940.MAA19660_at_zagami.jpl.nasa.gov>

ESA Science News
http://sci.esa.int

01 Aug 2003

Ulysses sees Galactic Dust on the rise

Since early 1992 Ulysses has been monitoring the stream of stardust flowing
through our Solar System. The stardust is embedded in the local galactic cloud
through which the Sun is moving at a speed of 26 kilometres every second. As a
result of this relative motion, a single dust grain takes twenty years to
traverse the Solar System. Observations by the DUST experiment on board Ulysses
have shown that the stream of stardust is highly affected by the Sun’s magnetic
field.

In the 1990s, this field, which is drawn out deep into space by the out-flowing
solar wind, kept most of the stardust out. The most recent data, collected up to
the end of 2002, shows that this magnetic shield has lost its protective power
during the recent solar maximum. In an upcoming publication in the Journal of
Geophysical Research ESA scientist Markus Landgraf and his co-workers from the
Max-Planck-Institute in Heidelberg report that about three times more stardust
is now able to enter the Solar System.

The reason for the weakening of the Sun’s magnetic shield is the increased solar
activity, which leads to a highly disordered field configuration. In the
mid-1990s, during the last solar minimum, the Sun’s magnetic field resembled a
dipole field with well-defined magnetic poles (North positive, South negative),
very much like the Earth. Unlike Earth, however, the Sun reverses its magnetic
polarity every 11 years. The reversal always occurs during solar maximum. That’s
when the magnetic field is highly disordered, allowing more interstellar dust to
enter the Solar System. It is interesting to note that in the reversed
configuration after the recent solar maximum (North negative, South positive),
the interstellar dust is even channelled more efficiently towards the inner
Solar System. So we can expect even more interstellar dust from 2005 onwards,
once the changes become fully effective.

While grains of stardust are very small, about one hundredth the diameter of a
human hair, they do not directly influence the planets of the Solar System.
However, the dust particles move very fast, and produce large numbers of
fragments when they impact asteroids or comets. It is therefore conceivable that
an increase in the amount of interstellar dust in the Solar System will create
more cosmic dust by collisions with asteroids and comets. We know from the
measurements by high-flying aircraft that 40,000 tonnes dust from asteroids and
comets enters the Earth’s atmosphere each year. It is possible that the increase
of stardust in the Solar System will influence the amount of extraterrestrial
material that rains down to Earth.

For further information please contact:
      SciTech.editorial_at_esa.int

IMAGE CAPTIONS:

[Image 1:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=33620]
The Sun and the nearest stars move through filaments of galactic clouds.
Copyright: P. C. Frisch, University of Chicago

[Image 2:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=33619]
The pictures above show cut-aways of where interstellar dust is concentrated in
the Solar System -- high concentration: red/yellow, low concentration:
blue/green (the planets are not shown). During solar minimum (top picture) most
interstellar dust can be found above or below the Sun, while at the solar
maximum (bottom picture) the dust is concentrated close to the Sun in the plane
of the planets' orbits. Copyright: ESA

[Image 3:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=33482]
SWOOPS image of solar wind at solar minimum and solar maximum. Copyright: D. McComas
Received on Mon 04 Aug 2003 03:40:42 PM PDT