[meteorite-list] ESA Sees Stardust Storms Heading For Solar System
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:34 2004
European Space Agency
Science News Release SNR 13-2003
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
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
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
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
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
The Sun's galactic environment. The Sun and the nearest stars move through
filaments of galactic clouds. Credits: P.C. Frisch, University of Chicago
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
Flip a Sun's pole for more dust
European Space Agency
20 August 2003
Astronomers once thought they understood how the Sun worked. A
large ball of gas, generating energy by nuclear fusion, it also created a
magnetic field enclosing Earth and the other planets in a gigantic
This bubble protected us from the dusty cosmic debris that shoots
through space beyond the Solar System. Thanks to ESA's solar
polewatcher Ulysses, that picture is changing...
Ulysses has revealed a complexity to the Sun's magnetic field that astronomers
had never imagined. The Sun's magnetic field consists of a north pole, where the
field flows out of the Sun and a south pole, where the field reenters. Usually,
these line up, more-or-less, with the rotation axis of the Sun. Every 11 years
the Sun reaches a peak of activity that triggers the magnetic poles to exchange
places. The reversal was thought to be a rapid process but, thanks to Ulysses,
astronomers now know it is gradual and could take as much as seven years to
During this slow-motion reversal, the line connecting the poles - known as the
magnetic axis - comes close to the Sun's equator and is swept through space
like the beam of a light house. Eventually it passes through this region and lines
up with the opposite pole.
Imagine if this happened on Earth! Compasses would
become useless, given that they rely on the fact that
Earth's magnetic axis is roughly coincident with its
rotation axis, which passes through the North and
South geographic Pole. Although it seems surprising,
magnetic pole reversals have happened on Earth
also. The last time was about 740 000 years ago.
After studying magnetic rocks, scientists conclude
that field reversals on Earth take place once every
5000 to 50 million years (but are impossible to
predict). Reversals on the Sun, however, are almost
as regular as clockwork - every 11 years, with its
magnetic axis changing position for most of that time.
More shooting stars
Earth's magnetic field is more stable because it arises in the metal-dominated
regions in the deep interior of the planet. The Sun's field, however, comes from a
high-temperature, electrified gas called plasma so it is a much more volatile
thing. Loops of the magnetic field can burst through the surface of the Sun and
when they do, they create the dark patches known as sunspots.
Astronomers are still studying the precise reasons behind the Sun's 11-year
magnetic flips. However, using Ulysses, they have now shown that, when the
Sun's magnetic axis points near its equator, it allows much more cosmic dust to
enter the Solar System than normal. What does that mean for us?
If there is more dust in the Solar System, more of it will fall on Earth also.
Scientists estimate that in the coming years, about 40 000 tonnes of dust could
fall on Earth every day. However, most of it will be so small that it will burn up
in the atmosphere before reaching the ground. This will certainly increase the
number of faint shooting stars during the next 11 years, but fortunately the Earth
will not become a dustier place!
Received on Wed 20 Aug 2003 03:11:21 PM PDT