Voyager Planetary Encounter Dates

Jupiter

1979-03-05 (day 64) Voyager 1 flies by Jupiter, passing within 280,000 km of the cloud tops

1979-07-09 (day 189) Voyager 2 flies by Jupiter, passing within 650,000 km of the cloud tops

Saturn

1980-11-12 (day 317) Voyager 1 flies by Saturn, passing within 130,000 km of the cloud tops.

1981-08-26 (day 236) Voyager 2 flies by Saturn, passing within 100,000 km of the cloud tops

Uranus

1986-01-24 (day 24) Voyager 2 is first spacecraft to fly by Uranus, passing within 82,000 km of the planet.

Neptune

1989-08-25 (day 237) Voyager 2 is first spacecraft to fly by Neptune, passing within 5,000 km of the cloud tops.

Coordinate Systems

In planetocentric coordinates, the z-axis points toward the north pole of the reference body. The x-axis is defined by the intersection of the equator and prime meridian of the body. The origin is at the center of the body.

Let P be a point in space, and let V be the position vector from the origin of the planetocentric frame to P.

The planetocentric latitude of P is the angle between the equator and V. North latitudes are positive, south latitudes are negative.

The planetocentric longitude of P is the angle between the x-axis and the projection of V onto the x-y plane, positive from x toward y.

The planetocentric radius of P is the distance from the center of the reference body to P (the magnitude of V).

Jupiter Planetocentric

The Jupiter System III (1965) coordinate system follows the definition of Dr. Alex Dessler in Appendix B of 'Physics of the Jovian Magnetosphere' [DESSLER1983]. This coordinate system is the accepted standard for analysis of data from the jovian system. System III is a spherical, planetographic coordinate system where the planetary rotation rate of (9h, 55m, 29.71s) is based on the rate of rotation of Jupiter's magnetic field. The prime meridian is defined as the sub-Earth meridian at 00:00:00 UT on Jan 1, 1965. Range is measured from the Jupiter center of mass. Longitude for standard System III is measured west. This direction choice causes the coordinate system to be left-handed and to a stationary or distant observer, longitude increases with time.

Jovicentric cartesian (Jupiter fixed) coordinates

X - points along the Jupiter-Sun line in the solar equatorial plane (positive towards the Sun)

Y - completes the right handed set

Z - points along the jovian spin axis, positive

Jovicentric System III (1965) spherical coordinates

R - Jupiter to spacecraft range (positive away from Jupiter) in Jovian radii (1 Rj = 71942 km)

LAT - latitudinal component completes the left handed, orthogonal set

LON - System III (1965) east longitude (with longitude increasing eastward from a specific jovian prime meridian)

Jovicentric System III (1965) magnetic (B) field vectors

Br - radial B-field component (along the Jupiter to spacecraft line) positive away from Jupiter

Btheta - North/South (SYS3) B-field component, positive southward

Bphi - azimuthal (SYS3) B-field component, positive eastward. SYS3 position, is given in a left-handed spherical system. Longitude (i.e. West longitude) is defined such that it appears to increase with time for a stationary observer [DESSLER1983].

[DESSLER1983] Dessler, A.J., Physics of Jovian Magnetosphere Coordinate Systems, Physics of the Jovian Magnetosphere, 1983.

Saturn Planetocentric

The Kronographic (L1) coordinates is a Saturn centered spherical system, based on the Saturn Longitude System [DESCH&KAISER1981]. In this coordinate system, longitude increases with time as viewed by a stationary remote observer.

Saturn-centric cartesian coordinates

X - points along the Saturn-Sun line in the solar equatorial plane (positive towards the Sun)

Y - completes the right handed set

Z - points along the Saturn's spin axis, positive

Saturn-centric spherical coordinates

R - Saturn to spacecraft range (positive away from Saturn) in Saturn radii (1 Rs = 60330 km)

LAT - latitudinal component completes the left handed, orthogonal set

LON - east longitude (with longitude increasing eastward from a specific Saturnian prime meridian)

Saturn-centric magnetic field vectors

Br - radial B-field component (along the Saturn to spacecraft line) positive away from Saturn

Btheta - North/South (L1) B-field component, positive southward

Bphi - azimuthal (L1) B-field component, positive eastward Trajectory is left handed and based upon the Saturn Longitude System [DESCH&KAISER1981].

[DESCH&KAISER1981] Voyager Measurements of the Rotation Period of Saturn's Magnetic Field, Desch and Kaiser, JGR, 8, 253, 1981

Uranus Planetocentric

The U1 coordinate system is a non-inertial spherical coordinate system that rotates with Uranus with a period of 17.24 hours. The prime meridian of the this system is defined such that at 1986-01-24T18:00:00.000 the Voyager 2 spacecraft was at 302 degrees west longitude (58 degrees east longitude).

Uranus-centric cartesian coordinates

X - lies in the equatorial plane of Uranus, positive away from the planet, and through the prime meridian at the reference epoch.

Y - Z x X (righthanded)

Z - parallel to the Uranus spin axis, positive in the southern hemisphere in ecliptic (orbital) coordinates.

The Cartesian coordinate system does not rotate with the planet.

Uranus-centric spherical coordinates

R - Radial distance in units of Ru (1 Ru= 25,600 km) along the Uranus-S/C line, positive away from Uranus

Theta - colatitudinal component in degrees

Phi - west longitudinal component in degrees

Uranus-centric magnetic field vectors

Br - radial component

Btheta - colatitudinal component in degrees

Bphi - longitudinal component in degrees

Neptune Planetocentric

The NLS or Neptune West Longitude System coordinate system is a planetocentric system fixed to Neptune which is rotating with a 16.11 hour period. The prime meridian of the this system is defined such that at 1989-08-25T03:56:00.000 the Voyager 2 spacecraft was at 167.7 degrees west longitude.

NLS coordinate system

X lies in the equatorial plane of Neptune, positive away from the planet, and through the prime meridian.

Y is X x Z (lefthanded)

Z is parallel to the Neptune spin axis

Neptune-centric spherical coordinates

R - Spacecraft radial distance in units of Rn (1 Rn = 24,765 km)

Theta - colatitudinal component in degrees

Phi - west longitudinal component in degrees

Neptune-centric magnetic field vectors

Br - radial component

Btheta - colatitudinal component in degrees

Bphi - longitudinal component in degrees

USERS ARE ENCOURAGED TO READ CAREFULLY THE DISCUSSION IN THE NEPTUNE SPECIAL ISSUE OF JGR REGARDING MODEL PARAMETER RESOLUTION AND USE OF THE MODEL COEFFICIENTS.

Connerney, J. E. P., M. H. Acuna, and N. F. Ness, 'The magnetic field of Neptune', J. Geophys. Res., vol. 96, Supplement, 19023-19042, 1991.