The Ulysses Interstellar Neutral Gas Experiment

Principal Investigator (PI)

Dr. Manfred Witte
Max-Planck-Institut fur Aeronomie
Max-Planck-Strasse 2
D-37191 Katlenburg-Lindau
Image of GAS instrument

PI reference article |  Key References |  PI website ]


The Ulysses GAS dataset consists of pixel map data called skymap and quicklook plots of skymaps derived from the first direct measurement of neutral Helium particles or UV photons (see brief description section below).

All GAS data are available on the Ulysses Final Archive, including

  • Skymaps data files derived from the measure of celestial UV intensities, available in the folder full_sky
  • Skymaps data files based on the measure of neutral Helium particles, available in the folder is_helium
  • Skymaps data files measured during Jupiter flybys, available in the folder jupiter
  • Skymaps data files containing at least a star in its field of view, available in the folder stars
  • A brief user guide
  • A text file describing the data format

​This archive also contains a Skymap images browser with a calendar view

Data coverage: full mission (1990-2007)


Brief description

The GAS-Instrument on ULYSSES provides angular distributions of count rates from interstellar neutral Helium particles (in the NG-mode) or from celestial UV-intensities (UV-mode), i.e. UV photons. The angular distributions of these count rates are mapped in an ecliptic coordinate system centered in the spacecraft, to form skymaps. In this system, the positions of the Sun and the planets vary with time and with the position of the spacecraft along its trajectory. However, the positions of stars remain fixed. The actual positions of the Sun, the Earth, and Jupiter are indicated by yellow, green and white dots, respectively. The area around the Sun is excluded from observation to avoid damaging intensities from direct sunlight. The intensities obtained in the UV-mode (the housekeeping parameter HV given in the bottom line of each map, has a positive value) are color coded in the range 10 to 1000 counts/s, in the NG-mode (HV has a negative value) in the range 0.1 to 10 counts/s. Read more here.

As an example, please find below an annoted sky map image derived from interstellar Helium neutral particles count rates measured between 09 and 10 April 1992, during the first Jupiter flyby by Ulysses.



Skymap browser

Please note that all sky maps images can be easily browsed on the Ulysses Final Archive (select the Plots tab on top). For GAS, several options are proposed in the "Select Instrument" drop down menu on the left side of the Ulysses Final Archive (UFA)  web application. Every plot can be downloaded in low resolution GIF file or high resolution PDF file (see top right of the page). Here is a an animated gif showing how neutral Helium skymaps recorded on August 2002 are displayed finshing off with a composite image gathering all images from that month (see bottom left of the composite image).