Ulysses: the science legacy (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 12 Jun 2008 19:20:27 -0400
ESA News
http://www.esa.int
12 June 2008
Ulysses: the science legacy
During its 17.5 years in space, Ulysses has rewarded scientists with the
unprecedented depth and breadth of its results. These have not just been
about the Sun and its influence on nearby space. The mission has also
provided surprising insights into the nature of our galaxy and even the fate
of the Universe.
The joint ESA/NASA mission was designed to study the solar wind -- a
constant stream of particles emitted by the Sun, and the magnetic field that
this carries through space. Because the Sun rotates, scientists believed
that the magnetic field would wind up into a spiral.
Ulysses showed that the actual magnetic field is much more complex in shape
and extent. This allows particles emitted by solar storms at low latitudes
to climb up to higher latitudes, and vice-versa. This is very important as
regions of the Sun not previously considered as possible sources of
hazardous particles for astronauts and satellites must now be taken into
account and carefully monitored.
Scientists originally thought that speed of the solar wind was typically
400km/s, with higher speed gusts. Ulysses soon showed that for much of the
sunspot cycle, it is a fast wind emitted from the solar magnetic poles that
dominates. The slow wind, whose origin remains somewhat mysterious, is a
minor player.
When the mission was extended beyond the original goal of one orbit of the
Sun, scientists were able to watch how the solar wind changed with time. "We
designed the mission to give us a 3-D view of the solar wind, but we got the
fourth dimension of time, as well," says Richard Marsden, ESA Ulysses
Project Scientist.
The Sun does not emit solar wind steadily, but the emission varies through a
cycle of magnetic activity lasting approximately 11 years. The cycle
culminates in the reversal of the direction of the Sun's magnetic field.
Ulysses saw that on a large scale, the complexity of the magnetic field near
the solar surface simplifies into a field created by a bar magnet inside the
Sun. When solar activity is at a minimum, this bar magnet is aligned with
the rotation poles. Six years later, at maximum, the bar magnet has moved to
lie at 90 deg to the rotation poles. It then continues moving so that by the
time of the next minimum, it is aligned with the rotational pole again, but
in the opposite orientation.
The Sun's magnetic field creates a sphere of influence known as the
heliosphere. "Prior to Ulysses, this was thought to be impenetrable to dust
from deep space," says Ed Smith, NASA Ulysses Project Scientist; Ulysses
showed that this was not true.
The spacecraft carried a superb instrument for diagnosing these invading
particles. It found 30 times more dust from deep space in the vicinity of
the Solar System than astronomers had previously expected.
Ulysses also detected heavy atomic nuclei racing into the Solar System.
Known as cosmic rays, these are thought to have been accelerated by the
explosion of high-mass stars. Ulysses estimated that the average age of a
cosmic ray entering the Solar System is 10-20 million years and they have
spent their lives streaming through the galaxy's outer regions before
finding their way into the Solar System.
Ulysses collected rare samples of interstellar helium isotopes. These are
especially interesting to cosmologists because theory predicts that their
abundance was more or less fixed within a few minutes of the Big Bang.
Ulysses measured these isotopes, supplying evidence to support the idea that
the Universe will expand forever because insufficient matter was created in
the Big Bang to halt its outward march.
Ulysses has been a big scientific effort, with many pay-offs, spread across
Europe and America. "There must have been 150 to 200 scientists working on
the instrument teams," estimates Smith. In addition, large numbers of
scientists have accessed the mission's archived data, which is made
available via the Internet. Around 1500 papers have been published so far
using Ulysses data.
This rich treasure of unprecedented observations will keep the mission alive
long after the actual spacecraft has died.
For more information:
ESA Media Relations Office
Tel: +33 1 5369 7155
Fax: +33 1 5369 7690
Email: media @ esa.int
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMKFTUG3HF_index_1.html ]
.
- Prev by Date: Sun to set on Ulysses solar mission on 1 July (Forwarded)
- Next by Date: Ulysses: the engineering challenge (Forwarded)
- Previous by thread: Sun to set on Ulysses solar mission on 1 July (Forwarded)
- Next by thread: Ulysses: the engineering challenge (Forwarded)
- Index(es):
Relevant Pages
|
