The Magellan spacecraft was launched on May 4, 1989, arrived at Venus on August 10, 1990 and was inserted into a near-polar elliptical orbit with a periapsis altitude of 294 km at 9.5 deg. N. Radio contact with Magellan was lost on October 12, 1994. The primary objectives of the Magellan mission were to map the surface of Venus with a synthetic aperture radar (SAR) and to determine the topographic relief of the planet. At the completion of radar mapping 98% of the surface was imaged at resolutions better than 100 m, and many areas were imaged multiple times. The image at the top of the page shows the 30-km diametar crater Adivar, with a jet-like streak extending off to the left. The streak, which measures over 500 km in length, is probably the result of the initial crater-forming impact. (This image is from C1-MIDR 15N077;1, framelet 52, Magellan CD-ROM MG_0019.) The mission was divided up into "cycles", each cycle lasted 243 days (the time necessary for Venus to rotate once under the Magellan orbit - i.e. the time necessary for Magellan to "see" the entire surface once.) The mission proceeded as follows:
04 May 1989 - Launch 10 Aug 1990 - Venus orbit insertion and spacecraft checkout 15 Sep 1990 - Cycle 1: Radar mapping (left-looking) 15 May 1991 - Cycle 2: Radar mapping (right-looking) 15 Jan 1992 - Cycle 3: Radar mapping (left-looking) 14 Sep 1992 - Cycle 4: Gravity data acquisition 24 May 1993 - Aerobraking to circular orbit 03 Aug 1993 - Cycle 5: Gravity data acquisition 30 Aug 1994 - Windmill experiment 12 Oct 1994 - Termination experiment - loss of signal 13 Oct 1994 - Presumed loss of spacecraft
More detailed information about the cycles is available. A total of 4225 usable SAR imaging orbits was obtained by Magellan. Each orbit typically covered an area 20 km wide by 17,000 km long, at a resolution of 75 m/pixel. This raw SAR data was processed into image strips called full-resolution basic image data records (F-BIDRs). Adjacent F-BIDRs were then assembled into full-resolution mosaicked image data records (F-MIDRs). These images were then compressed once (by a factor of 3), twice (9), or 3 times (27), to give C1-, C2-, and C3-MIDRs. The MIDRs are available on the Magellan MIDR CD-ROMs from NSSDC. More details about using Magellan CD-ROM's are also available, as are answers to frequently asked questions about the CD-ROMs and MIDRs. In addition, a CD-ROM Browser is available courtesy of the PDS Microwave Subnode. Other data was also collected by Magellan and is available at the NSSDC. Altimetry and radiometry composite data records (ARCDR) are available on the ARCDR CD-ROMs. Magellan also collected radar emissivity, radar reflectivity, slope, and topographic data, available on the GxDR CD-ROMs, and gravity and radio occultation data. The USGS has also produced a set of full-resolution mosaics called FMAPs. All the Magellan CD-ROMs mentioned above have been produced under the auspices of the Planetary Data System, and have PDS formats and labels. Below is shown a global map of radar reflectance.
The Magellan mission scientific objectives were to study land forms and
tectonics, impact processes, erosion, deposition, chemical
processes, and model the interior of Venus.
Magellan showed us an Earth-sized planet with no evidence of Earth-like plate
tectonics. At least 85% of the surface is covered with volcanic flows, the
remainder by highly deformed mountain belts. Even with the high surface
temperature (475 C) and high atmospheric pressure (92 bars), the
complete lack of water makes erosion a negligibly slow process, and
surface features can persist for hundreds of millions of years. Some
surface modification in the form of wind streaks was observed. Over 80%
of Venus lies within 1 km of the mean radius of 6051.84 km. The mean
surface age is estimated to be about 500 My. A major unanswered question
concerns whether the entire surface was covered in a series of large events
500 My ago, or if it has been covered slowly over time. The gravity field of Venus
is highly correlated with the surface topography, which indicates the
mechanism of topographic support is unlike the Earth, and may be controlled
by processes deep in the interior. Details of the global tectonics on Venus
are still unresolved.
Shown here is a section of a Magellan radar image of a 40 x 60 km
"petal" type volcano in eastern Aphrodite Terra, centered at 7.5 S, 200.5.
This image is taken from F-MIDR 10S200, framelets 6 and 7, CD-ROM MG_0027.
Clicking on the image will give the full-resolution view as it appears
on the F-MIDR.
Other views of Venus are available at the NSSDC Image Catalog and Photo Gallery.