ESA sees stardust storms heading for Solar System (Forwarded)

European Space Agency
Science News Release SNR 13-2003
Paris, France 18 August 2003

ESA sees stardust storms heading for Solar System

Until ten years ago, most astronomers did not believe stardust could enter our
Solar System. Then ESA's Ulysses spaceprobe discovered minute stardust particles
leaking through the Sun's magnetic shield, into the realm of Earth and the other
planets. Now, the same spaceprobe has shown that a flood of dusty particles is
heading our way.

Since its launch in 1990, Ulysses has constantly monitored how much stardust
enters the Solar System from the interstellar space around it. Using an on-board
instrument called DUST, scientists have discovered that stardust can actually
approach the Earth and other planets, but its flow is governed by the Sun's
magnetic field, which behaves as a powerful gate-keeper bouncing most of it
back. However, during solar maximum -- a phase of intense activity inside the
Sun that marks the end of each 11-year solar cycle -- the magnetic field becomes
disordered as its polarity reverses. As a result, the Sun's shielding power
weakens and more stardust can sneak in.

What is surprising in this new Ulysses discovery is that the amount of stardust
has continued to increase even after the solar activity calmed down and the
magnetic field resumed its ordered shape in 2001.

Scientists believe that this is due to the way in which the polarity changed
during solar maximum. Instead of reversing completely, flipping north to south,
the Sun's magnetic poles have only rotated at halfway and are now more or less
lying sideways along the Sun's equator. This weaker configuration of the
magnetic shield is letting in two to three times more stardust than at the end
of the 1990s. Moreover, this influx could increase by as much as ten times until
the end of the current solar cycle in 2012.

The stardust itself is very fine -- just one-hundredth of the width of a human
hair. It is unlikely to have much effect on the planets but it is bound to
collide with asteroids, chipping off larger dust particles, again increasing the
amount of dust in the inner Solar System. On the one hand, this means that the
solar panels of spacecraft may be struck more frequently by dust, eventually
causing a gradual loss of power, and that space observatories looking in the
plane of the planets may have to cope with the haze of more sunlight diffused by
the dust.

On the other hand, this astronomical occurrence could offer a powerful new way
to look at the icy comets in the Kuiper Belt region of the outer Solar System.
Stardust colliding with them will chip off fragments that can be studied
collectively with ESA's forthcoming infrared space telescope, Herschel. This
might provide vital insight into a poorly understood region of the Solar System,
where the debris from the formation of the planets has accumulated.

Back down on Earth, everyone may notice an increase in the number of sporadic
meteors that fall from the sky every night. These meteors, however, will be
rather faint.

Astronomers still do not know whether the current stardust influx, apart from
being favoured by the particular configuration of the Sun's magnetic field, is
also enhanced by the thickness of the interstellar clouds into which the Solar
System is moving. Currently located at the edge of what astronomers call the
local interstellar cloud, our Sun is about to join our closest stellar neighbour
Alpha Centauri in its cloud, which is less hot but denser.

ESA's Ulysses data make it finally possible to study how stardust is distributed
along the path of the Solar System through the local galactic environment.
However, as it takes over 70 thousand years to traverse a typical galactic
cloud, no abrupt changes are expected in the short term.

Notes to editors

The results of this investigation will appear in the October 2003 issue of
Journal of Geophysical Research. The investigation has been conducted by a team
lead by Markus Landgraf of ESA's European Space Operation Centre in Darmstadt
(Germany) and including Harald Krüger, Nicolas Altobelli, and Eberhard Grün of
the Max Planck Institute for Nuclear Physics in Heidelberg (Germany).

Ulysses is the first mission to study the environment of space above and below
the Sun's poles. It is a joint mission with NASA and has been in space since
1990, after a mission extension agreed in 2000. Launched from the Space Shuttle
Discovery in October 1990, Ulysses has now completed two orbits, passing both
the Sun's north and south pole on each occasion. Its data gave scientists their
first look at the variable effect that the Sun has on the space that surrounds it.

The Ulysses DUST experiment provides direct observations of dust grains weighing
less than a millionth of a gram in interplanetary space as Ulysses moves along
an orbit that takes it periodically away from the Sun and from the plane of the
planets -- a disc known as the ecliptic. DUST measures the mass, speed, flight
direction, and electric charge of individual dust particles.

Astronomers wanted to know what portion of dust is provided by comets and
asteroids and what, instead, comes directly from interstellar space. By taking
measurements when Ulysses was farthest from the Sun and high above the ecliptic,
in regions where cometary dust can hardly reach, scientists were able to detect
and isolate particles of stardust entering the Solar System from the outer
space. To confirm that these dust grains are indeed of interstellar origin,
Landgraf and his collaborators verified that the dust had the same flight
direction and speed as the atoms of helium which are known to come exclusively
from interstellar space.

For further information, please contact:

Markus Landgraf, Mission Analyst
ESA - ESOC (European Space Operations Centre, Germany)
Tel: + 49 6151 90 3627
Fax: + 49 6151 90 2625
E-mail:

ESA Science Programme Communication Service
Tel: + 31 71 565 3273
Fax: + 31 71 565 4101

ESA Media Relations Service
Tel: + 33 1 5369 7155
Fax: + 33 1 5369 7690

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/export/esaCP/SEMD..._index_1.html]
SOHO image of the Sun. SOHO is a project of international cooperation between
ESA and NASA. SOHO's EIT (Extreme ultraviolet Imaging Telescope) images the
solar atmosphere at several wavelengths and, therefore, shows solar material at
different temperatures. In the images taken at 304 Angstroms, the bright
material is at 60 000 to 80 000K. In those taken at 171, at 1 million Kelvin.
195 Angstrom images correspond to about 1.5 million Kelvin. The hotter the
temperature, the higher you look in the solar atmosphere. Photo: SOHO Instrument
Consortium

[Image 2:
http://asimov.esrin.esa.it/export/im...ironment_l.jpg (36KB)]
The Sun's galactic environment. The Sun and the nearest stars move through
filaments of galactic clouds. Credits: P.C. Frisch, University of Chicago

[Image 3:
http://www.esa.int/export/esaCP/SEMD...html#subhead2]
Artist's impression of Ulysses. Ulysses has made fundamental contributions to
our understanding of the Sun, the heliosphere, and our local interstellar
neighbourhood. Credits: David Hardy

Hi Andrew, I've been following this story for a few weeks now and have
a couple of questions I can't seem to get an answer for.

What is the average density of of this cloud?

What is the majority of the dust made of?

What velocity are the particles in the cloud traveling at relative to
us?

What will happen to the heliopause and the termination shock? will
they change shape or reduce in size?


When I look at the SOHO site I get information like this,

Current solar wind velocity 551 km/s

Current density 5.90 p/cm^3

400-800 km/sec electron-proton plasma velocity


What is the density of our solar system out at the heliopause?