Cosmic Rays

Science Highlights from the First Solar Orbit

Cosmic Rays
A fundamental question that has been answered by Ulysses relates to the presence of large-scale directional fluctuations in the polar heliospheric magnetic field. Prior to the launch of Ulysses, it was suggested that the classical picture of smooth, near-radial polar magnetic field lines would be modified by the effects of random walk of the field foot points resulting from super-granulation motion in the photosphere. This stochastic motion would lead to large-scale transverse fluctuations in the polar fields, which in turn would impede the access of cosmic ray particles to the inner heliosphere over the poles.

The data from Ulysses' first polar passes have confirmed both the existence of the field fluctuations, and the absence of large latitudinal gradients in the fluxes of cosmic ray particles. Of particular interest is the latitude distribution of the so-called anomalous cosmic ray component (ACR), generally thought to be singly-charged interstellar ions that have been accelerated to MeV energies at the solar wind termination shock. Ulysses results show a modest positive latitudinal gradient for ACR oxygen, nitrogen and neon, qualitively in agreement with models in which the acceleration takes place largely at the poles of the heliosphere, the ACR subsequently diffusing

Ulysses

Named after the hero of Greek legend, Ulysses is a joint
mission between ESA and NASA which aims to explore the unknown space
above the poles of the sun. The spacecraft was provided by ESA which
also manages the mission operations. NASA provided the Space Shuttle
Discovery to get the craft into orbit around the Sun and the power
generator for the spacecraft.


launch

Ulysses
was launched by the space shuttle Discovery in October 1990 and reached
Jupiter in February 1992. The probe then used Jupiter’s gravity to
slingshot to a 6.2-year orbit above the Sun’s poles. Ulysses passed
over the North Pole of the Sun in 1995 and 2001 and the South Pole in
1994 and 2000.
Objectives

There are 11 scientific instruments
on board Ulysses, investigating phenomena ranging from the solar wind
to cosmic dust and gamma-ray bursts. Ultimately the data will enable
scientists to better understand the Sun and its heliosphere and perhaps
the Sun’s influence on the Earth’s climate.



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