venus landing-sites – where we have been and where we want to go 1st vep landing-sites workshop,...

Venus Landing-Sites – Where we have been

and where we want to go

1st VEP Landing-Sites Workshop, November 14-15, 2006, Vienna, Austria

J. J. Leitner, Dept. of Astronomy, Univ. of Vienna, Austria

?Venus before the space-age:

In 1961, before the first spacecraft reached Venus, different descriptions about planet Venus exist in literature (Colin, 1983):

Cool, Earth-like, with surface water and a dense atmosphere, or

Cold, polar regions with 10-km-thick icecaps and a hot equatorial region with temperatures far above the water boiling point, or

A moist, swampy and teeming with life planet, or

Warm, encased by a global carbonic acid ocean, or

Warm, massive clouds consisting of water and intensive lighting, or

Hot and dusty, dry, windy, a global dessert, or

Extremely hot, cloudy, molten lead and zinc puddles at the equator, seas of bromine, butyric acid and phenol at the poles.

History of the space exploration of Venus:

Sputnik 7 represents the first (Soviet’s) approach to send a spacecraft to Venus (with the goal to impact on the planetary surface)

Successfully launched into Earth orbit in Feb. 1961 (a launch platform and the probe).

Probably due to a faulty timer, the probe remained in Earth orbit and never starts towards Venus.

Originally it was thought to be Venera 1, but due to its failure the name Sputnik was given.


Venera 1, launched 8 days later, was intended to fly-by Venus.

7,500,000 km away from Earth, the contact with the probe was lost.

It is assumed that the probe flyby Venus at a distance of 100,000 km, but no data were returned.

Payload: magnetometer (operates during the first days), micrometeorite detectors, ion traps cosmic radiation counters.


Mariner 1, launched in July 1962, was the first U.S. mission to Venus.

290 seconds after its launch the probe was destroyed by the mission command, because of a trajectory error and the chance to crash into an inhabited area on Earth.

Payload: microwave and infrared radiometer, a magnetometer, an electrostatic analyzer and two instruments to investigate the cosmic dust and the cosmic ray ionization during the craft’s travel to Venus.


Sputnik 19, a Venera-like spacecraft was launched in August 1962 and was intended to be Venera 2.

It was designed to land on the surface of Venus.

Due to a technical fault in the escape stage from the launch rocket, the probe remained in Earth orbit and burned out in the atmosphere.


Mariner 2, launched in August 1962, was the first successful planetary exploration probe (at all, not only for Venus) and performed a Venus flyby mission.

After a 109 days lasting journey the probe flybys Venus at a distance of 34,833 km.

It measured the radiation temperature of small areas of Venus in a region between 200 K and 600 K in two different wavelengths.

By orbit tracking of Mariner 2 the value for the Venusian mass was improved.

Most important scientific discovery: complete absence of charged particles associated with the planet at a distance of the craft’s closest approach no magnetosphere

First atmospheric measurements: mainly CO2 and detection of a continuous cloud cover without any breaks and a cloud top altitude of about 60 km.


Sputnik 20, was launched in September 1962 and was concepted as a Venus landing mission.

It endured the same fate than Sputnik 19 and reenters Earth atmosphere 5 days after its launch.

Because of the mission design and its purpose it is very probable, that the craft was intended to be second probe of the Venera series.


Sputnik 21, was also launched in September 1962 (11 days after Sputnik 20) and was an attempted Venus flyby mission.

It was destroyed in Earth orbit, after the third rocket stage exploded.


Cosmos 21, presumably was a technology test for the Venera series, or (and this is up to now not known) an attempted Venus flyby mission.

It was successfully launched into Earth orbit in November 1963, but for whatever reasons it never left it.

It is known that the designation “Cosmos” since the beginning of 1963 was given to spacecrafts, which remained in Earth orbit regardless their originally scheduled destinations (e.g. engine burn problems).

But the Cosmos designation was also used for spacecrafts, which had only military tasks or served as communications satellites. As a consequence of this, it was easy for the mission control to veil the original function of a craft by the use of the Cosmos name (a tactic of blur, which was often used in the era of the cold war).

Today it is assumed that about 50 % of all the Cosmos crafts (more than 2300) had been used from the former Soviets military for their purposes.

A clue for this assumption is that nearly all of the Cosmos crafts had an orbit inclination between 88° and 99°, which is very useful to obtain a maximum view on Earth and thus it is often used for espionage satellites.


Venera 1964A and Venera 1964B (launched in February and March 1964) were planned as a bipartite Venus flyby mission.

Due to faults in their launching phases, the crafts were destroyed and did never reach Earth orbit.

Cosmos 27 presumably likewise was projected as a Venus flyby mission, which already reached successfully Earth orbit but did never start to Venus.

Presumably it was a new try to make Venera 2.


Zond 1 reached successfully Venus after its launch in April 1964.

The contact with the spacecraft was lost in May 1964.

The official mission aims were ultraviolet observations of Venus and space research consisting of measurements of the energetic particles in the interplanetary medium and to perform tests of the probe systems with the ulterior motivation to improve the Venera space mission designs.


The real Venera 2, launched in November 1965 passed the planet Venus in February 1966 at distance of 24,000 km.

Unfortunately the communication systems of the probe had already stopped to work before the probe the planet was reached.

The main mission task was to obtain photos from the Venusian surface after performing a soft-landing.

But at least after a long series of mission faults, a Soviet spacecraft had arrived again at Venus.

The only data returned to Earth were measurements about the energetic particles during the craft’s journey to the planet (like Zond 1).


Venera 3 (also launched in November 1965) main mission task also was to land on the surface of Venus, but the communication with the probe was lost shortly before it started to descent the atmosphere.

Nevertheless Venera 3 was the first spacecraft, which impacted on the surface of another planet.

Cosmos 96 probably was intended as a Venus lander of similar design than Venera 3. It reached successfully Earth orbit, but an explosion after the separation phase from the rocket body finished the plan to execute the first successful soft-landing on the Venusian surface.

Presumably this mission was part of a bipartite mission together with Venera 1965A, which was launched three days later, but not successful due to a fault in the launching phase.


Venera 4 (launched in June 1967) represents the first really successful atmospheric descent probe. In contrast to its predecessors the probes communication systems operated accurately all the obtained data were transmitted back to Earth.

Mission aims: cosmological investigations during its flight, to probe the planetary vicinity and to penetrate deep into the atmosphere in order to determine its physical and chemical characteristics.

The craft consists of two different parts: an interplanetary and an descending unit. After Venus was reached the two units were separated and the descent unit began its 93 min lasting way through the Venusian atmosphere.

The probe measured at different altitudes the pressure and the temperature in the atmosphere and performed first gas analyses. The mean temperature gradient in the atm. was found to be roughly linear with about 10 K km-1.

Measurements of the magnetic field of the planet showed that it did not exceed 0.0003-times the magnetic field of the Earth at its surface.


Mariner 5 (launched in June 1967, 2 days after Venera 4) was the second NASA mission to Venus and flyby’s it successfully at a distance of 3,320 km.

The craft determined the magnetic field, atmospheric turbulences, the interaction of the solar wind with the atmosphere and the wind velocity.

A very high concentration of CO2 (about 90 %) and a content of N2 lower than 10 % was measured.

In general, Mariner 5 confirms the measurements of Venera 4 spacecraft.

Orbit tracking of the spacecraft allows to determine the Venusian planetary radius to be between 6079 and 6105 km, but closer to 6079 km.


Cosmos 167, constructed very similar to Venera 4 was also launched in June 1967.

But as it is the fate of Venus “Cosmos” missions it was damaged in Earth orbit and reentered Earth’s atmosphere 8 days after its launch.

Because of its launch date (5 days after Venera 4) it seems reasonable, that the craft was intended to be a companion of Venera 4 with a planned designation Venera 5.


Venera 5 and Venera 6 (launched in January 1969 with a difference of 5 days) main mission aims of their descent probes was to continue the success of Venera 4 by obtaining more atmospheric data of Venus.

Their design have been improved (greater structural strength, reduced parachute area, improved instruments).

In addition to the measurements also done by Venera 4, Venera 5 and 6 also measured solar wind fluxes and ions with energies greater that 50 eV. The probes measured more than 70 times the pressure and more than 50 times the temperature during their descents and determined also the atmospheric composition from an altitude of 55 km down to 19 km.

Venera 5 returned data from the atmosphere for 53 min and Venera 6 for 51 min. Both missions we owe a much better knowledge about the composition of the atmosphere, better thermal and pressure gradients.


Venera 7 (launched in August 1970 with a difference of 5 days) was regarding its design similar to Venera 5 and 6, but modified to tolerate a pressure of about 180 atm and an outside temperature of about 800 K.

Its main mission goal was to perform a soft-landing on the surface.

The craft entered successfully the atmosphere and after a 35 min lasting descent (with returned atmospheric data from a height of 55 km down to the surface) it successfully performed a soft-landing on the night side of the surface, about 2000 km away from the sunrise terminator.

From its landing area it transmitted back data for 23 min, which made Venera 7 to the first spacecraft that returned data from the surface of another planet.

The temperature was found to be 747 ± 20 K, the pressure to be between 86 and 97 atm.

The improved value for the planetary radius was 6050 ± 5 km.


Cosmos 359 (launched in August 1970), launched 5 days after Venera 7, presumably was scheduled to be Venera 8 with the intention to company the previous probe.

Due to a fault in the escape stage of the launch-rocket, the engine did not last the necessary time to leave Earth orbit toward Venus (about 4 min).

The spacecraft remained in Earth orbit for 410 days until its orbit decayed and the craft burnt up in the terrestrial atmosphere.

By orbit tracking of Cosmos 359 during its life-span, valuable information about the terrestrial atmospheric rotations speed and the atmospheric density at altitudes near 200 km was obtained.


Venera 8 (launched in March 1972), also executed a successful soft-landing on the Venusian surface. It transmitted back data during its 56 min lasting descent about the pressure, temperature and the downward light flux from an altitude of 50 km down to ground. Thereby it experienced a sharp decrease in the illumination level between 35 and 30 km (maybe as a consequence of different amounts of aerosols in the atmosphere).

Further: composition of the atmosphere, cloud structure and the cloud layers, measurements about aerosols, wind speeds, rotation of the upper clouds, etc.

Its landing-site is dominated by volcanic plains, steep-sided domes and shield fields. The site is composed of a mosaic of radar-light and radar-dark spots, crossed by radar-bright lineaments in N-W orientation (open fractures) and with a pancake structure at the northern edge of the landing-site (Abdrakhimov 2001; Basilevsky et al., 2001).

It survived 50 min at the surface and transmitted back data about temp., pressure and performed the first gamma-ray spectroscopic analysis of the surface of another planet. Based on this experiment the rocks were interpreted to be either alkaline basalts or some more evolved subalkaline and alkaline intermediate rocks (perhaps andesite, trachyte), resembling to the composition of terrestrial continental crust and in a good agreement with the assumed composition of the near pancake-structure (Basilevsky et al., 1991, 1992, 1997).

The light level at the surface was found to be similar to the amount of illumination in Moscow at noon on an overcast winter day with a visibility of about 1 km.


Cosmos 482 (launched in March 1972), was originally thought to be Venera 9.

It was very similar in design to Venera 8, but after its successful launch into Earth orbit, an error in the launch phase (a too short engine burn) let it remain in Earth orbit.


Mariner 10 (launched in November 1973) primarily was a Mercury probe, but on its journey to the planet it encountered Venus at a distance of 5,768 km.

It was the first spacecraft that visited two planets and thereby used the first gravity-assist maneuver.

The Venus flyby was used to study the ionosphere and upper atmosphere for a time period of 8 days. It observes emissions from the upper atmosphere and confirmed the 4-days rotation period of the atmosphere.

Further: measurements about thermal emissions of the atmosphere, interaction between the solar wind and the atmosphere.

Orbit tracking


Venera 9 and 10 (launched in June 1975): Each spacecraft consists of two different parts: an orbiter and a lander. The probes performed similar measurements about the atmospheric parameters than the earlier Venera probes.

Venera 9 lands in the Beta regio uprise and transmitted back data to Earth for a period of 53 min. Thereby the very first photo from the surface of another planet was received.

The investigated rocks at this site were very shape-edged without features, which would indicate the presence of geochemically evolved lavas. Due to their shape the rocks are called “slaps”. The adjacent surface, in which the rocks were ingrained, consists of a fine-grained matrix with a very low albedo.

Gamma-ray spectroscopic measurements indicates contents of K, U, Th similar to that of tholeiitic basalts on Earth.


Venera 10 landed in a distance of about 2,000 km away from Venera 9, in the southeastern edge of Beta regio. The area is dominated by wrinkle-ridged plains. Tessera terrain of heavily deformed material of unknown nature was located close to its landing-site.

It transmitted back data for 65 min about temp., pressure, one photo and wind velocity measurements.

Venera 10 performed the first direct density measurements of Venusian rocks were found in a good agreement with the conception of a basaltic composition of the crust (2800 ± 100 km m-3).

The radioactive contents of the investigated rocks were somewhat lower than that at the Venera 9 site, but again in a good agreement with a basaltic composition (in a transitional zone between tholeiitic and alkaline basalts).


The Pioneer Venus 1 (Orbiter) was launched in May 1978) and operated at a distance between 150 km and 66,900 km away from the Venusian surface.

One of its main tasks was a radar investigation of the surface of the planet and the detection of the gravity field. Beside this also: cloud layers, ionosphere, solar wind and atmosphere interaction, magnetic field, mass and density distribution, etc. better models of the interior and specification of the amount of isostatic compensation of the Venusian topography and crust.

It performed the first radar and altimetry mapping of the surface (93 %) with resolutions between 150 and 200 m.

Roughly characterization of the surface: Uplands, 65 % of the surface Highlands, ~ 8 % of the surface three radar-bright extremes: Ishtar-, Aphrodite- and Beta Regio Lowlands, 27 % of the surface, mainly covered by younger basaltic lava


PV surface map of Venus:


Pioneer Venus 2 Multiprobe (launched in August 1978) consisted of a large entry bus, a large probe and three smaller probes allows simultaneous investigations of the atmosphere in different areas.

Measurements about the atmospheric structure, composition, particle size, radiation, solar flux, winds, turbulences, etc.

The probes did not have parachutes to perform a soft landing. Regardless this lack one of the probes returned data for a period of 67 min after its impact.

Ultraviolet image of Venus cloud patterns


Venera 11 and 12 (launched in September 1978, with a delay of 5 days) consisted again of an orbiter and descent/landing unit.

Measurements about the solar wind composition, observation of gamma-ray bursts, investigation of the ultraviolet radiation and the electron and proton density in the ionosphere of Venus.

Studies of the characteristics and the composition of the atmosphere Detection of a very high 36Ar/40Ar ratio, and evidences for lighting and thunder.

After their soft-landing the probes transmitted back for 95 and 110 min, but unfortunately some instruments fail (no pictures were returned to Earth, if they have carried cameras, not really known, because in the Soviet literature there are no clues about it.


Venera 13 and 14 (launched in October/November 1982, with a delay of 5 days) consisted again of an orbiter and descent/landing unit.

The probes performed similar measurements than the earlier Venera probes, but had working imaging systems. The landers carried along x-ray spectrometer and instruments to perform chemical, isotopic and mechanical measurements of surface samples.

Venera 13 returned data for 127 min, the landing-site at all was similar to that of Venera 10. Taken soil samples manifest themselves as weakly differentiated melanocratic alkaline gabbroid with high MgO, a low silica and with a content of about 4 % K2O.

The load capacity of the soil was found to be between 2.6 and 10 kg cm-2.

Venera 14 lands on a basaltic plain and about 800 km southeast of Venera 13. Its site is dominated by lava flows arising from the nearby volcano with lengths between tens and hundreds of kilometers (Basilevsky et al., 1992).

The soil sample was again found to be similar to oceanic tholeiitic basalts.


Venera 15 and 16 (launched in June 1983, with a delay of 5 days) were each part of a common Venus radar mapping mission to study the surface properties of the planet.

Together they imaged about 25 % of the planet’s surface, but offers in contrast to Pioneer Venus also images of the northern polar region consisted again of an orbiter and descent/landing unit.

From the available data more than 150 impact craters have been identified.

First identification of Corona structures (clues were available also from PV).


Vega 1 and 2 (launched in December 1984, with a delay of 6 days) primarily were designed to investigate comet Halley, which in 1986 returned to the Sun’s environment during its 76 years period.

The Venusian experiments were executed from two balloons (at similar latitudes north and south of the equator), which were ejected by the Vega crafts. During the descent of the balloons, their courses were tracked for 47 hours good record of the atmospheric winds and gusts along them atmospheric parameters have been determined.

Small landers were dropped out, which successfully reached the surface and confirms in the first line the older measurements.

X-ray spectrometer and mass spectrographs, but no imaging systems.


NASA Magellan (launched in May 1983) was implemented to obtain detailed knowledge about the Venusian surface and its mechanisms.

The mission offered a nearly global radar imaging survey of the surface with a very high resolution and high accuracy gravity data. Its radiometer allowed to obtain temperature, pressure and density values of the whole atmosphere.

At the end of the mission 98 % of the surface have been mapped and gravity data for 95 % of the planet were available.

Large number of different structures have been discovered based on its datasets.

Up to now the Magellan datasets are the basis for any work related to the surface of Venus.


Hemispheric view of Venus (produced by Magellan):

After Magellan only flybys have taken place until 2006 (Cassini, Galileo) (as VEX reached Venus), but no other Venus missions were performed.

Summarizing the previous landing-sites:

VEP landing-sites:

Main question now:

Where to go with the VEP descent probes?

To which structures, altitudes, etc.

Only two restrictions at the moment:3 dayside, 1 nightside (close to antisolar point)

wide latitudinal distribution

venus landing-sites – where we have been and where we want to go 1st vep landing-sites workshop,...

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