Venera

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Short description: Soviet program that explored Venus with multiple probes
Position of Venera landing sites. Red points denote sites returning images from the surface, black central dots sites of surface sample analysis. Map based on mapping from Pioneer Venus Orbiter and Magellan.

The Venera (Russian: Вене́ра, pronounced [vʲɪˈnʲɛrə], which means "Venus" in Russian) program was the name given to a series of space probes developed by the Soviet Union between 1961 and 1984 to gather information about the planet Venus.

Thirteen probes successfully entered the Venusian atmosphere, including the two Vega program and Venera-Halley probes. Ten of those successfully landed on the surface of the planet. Due to the extreme surface conditions on Venus, the probes could only survive for a short period on the surface, with times ranging from 23 minutes to two hours.[1]

The Venera program established a number of precedents in space exploration, among them being the first human-made devices to enter the atmosphere of another planet (Venera 3 on 1 March 1966), the first to make a soft landing on another planet (Venera 7 on 15 December 1970), the first to return images from another planet's surface (Venera 9 on 8 June 1975), the first to record sounds on another planet (Venera 13 on 30 October 1981), and the first to perform high-resolution radar mapping scans (Venera 15 on 2 June 1983).

The Venera probes

Venera 1 and 2

Main pages: Astronomy:Venera 1 and Astronomy:Venera 2
Full-scale model of the Venera 1 in the Memorial Museum of Cosmonautics

The first Soviet attempt at a flyby probe to Venus was launched on 4 February 1961, but failed to leave Earth orbit. In keeping with the Soviet policy at that time of not announcing details of failed missions, the launch was announced under the name Tyazhely Sputnik ("Heavy Satellite"). It is also known as Venera 1VA.[2]

As with some of the Soviet Union's other planetary probes, the later versions were launched in pairs, with a second vehicle launched soon after the first.

Venera 1 and Venera 2 were intended to fly past Venus without entering orbit. Venera 1 was launched on 12 February 1961. Telemetry on the probe failed seven days after launch. It is believed to have passed within 100,000 km (62,000 mi) of Venus and remains in heliocentric orbit. Venera 2 launched on 12 November 1965, but also suffered a telemetry failure after leaving Earth orbit.

Several other failed attempts at Venus flyby probes were launched by the Soviet Union in the early 1960s,[3][4] but were not announced as planetary missions at the time, and hence did not officially receive the "Venera" designation.

Venera 3 to 6

Main pages: Astronomy:Venera 3, Astronomy:Venera 4, Astronomy:Venera 5, and Astronomy:Venera 6
Venera station liquid based engine.

The Venera 3 to 6 probes were similar. Weighing approximately one ton, and launched by the Molniya-type booster rocket, they included a cruise "bus" and a spherical atmospheric entry probe. The probes were optimised for atmospheric measurements, but not equipped with any special landing apparatus. Although it was hoped they would reach the surface still functioning, the first probes failed almost immediately, thereby disabling data transmission to Earth.

Venera 3 became the first human-made object to impact another planet's surface as it crash-landed on 1 March 1966. However, as the spacecraft's data probes had failed upon atmospheric penetration, no data from within the Venusian atmosphere were retrieved from the mission.

On 18 October 1967, Venera 4 became the first spacecraft to measure the atmosphere of another planet. This spacecraft first showed the major gas of Venus's atmosphere to be CO2.[5] While the Soviet Union initially claimed the craft reached the surface intact, re-analysis, including atmospheric occultation data from the American Mariner 5 spacecraft that flew by Venus the day after its arrival, demonstrated that Venus's surface pressure was 75–100 atmospheres, much higher than Venera 4's 25 atm hull strength, and the claim was retracted.

Realizing the ships would be crushed before reaching the surface, the Soviets launched Venera 5 and Venera 6 as atmospheric probes. Designed to jettison nearly half their payload prior to entering the planet's atmosphere, these craft recorded 53 and 51 minutes of data, respectively, while slowly descending by parachute before their batteries failed.

Around that time it became increasingly known that Venus was unlikely to have liquid bodies of water, however the designs for the Soviet Venera probes still considered the possibility of a water landing as late as 1964.[6]:xiii

Venera 7

Main page: Astronomy:Venera 7
Space probe Venera on Venus's surface (artist recreation).

The Venera 7 probe, launched in August 1970, was the first one designed to survive Venus's surface conditions and to make a soft landing. Massively overbuilt to ensure survival, it had few experiments on board, and scientific output from the mission was further limited due to an internal switchboard failure that stuck in the "transmit temperature" position. Still, the control scientists succeeded in extrapolating the pressure (90 atm) from the temperature data with 465 °C (869 °F), which resulted from the first direct surface measurements. The Doppler measurements of the Venera 4 to 7 probes were the first evidence of the existence of zonal winds with high speeds of up to 100 metres per second (330 ft/s, 362 km/h, 225 mph) in the Venusian atmosphere (super rotation). Along with the pressure and temperature data acquired Venera 7 also measured atmospheric composition.[7][5]

Venera 7's parachute failed shortly before landing very close to the surface. It impacted at 17 metres per second (56 ft/s) and toppled over, but survived. This caused antenna misalignment making the radio signal very weak, but it was detected (with temperature telemetry) for 23 more minutes before its batteries expired. Thus, it became, on 15 December 1970, the first human-made probe to transmit data from the surface of Venus.

Venera 8

Main page: Astronomy:Venera 8

Venera 8, launched in 1972, was equipped with an extended set of scientific instruments for studying the surface (gamma-spectrometer etc.). The cruise bus of Venera 7 and 8 was similar to that of earlier ones, with the design ascending to the Zond 3 mission. The lander transmitted data during the descent and landed in sunlight. It measured the light level but had no camera. It transmitted data for almost an hour.

Venera 9 to 12

Main pages: Astronomy:Venera 9, Astronomy:Venera 10, Astronomy:Venera 11, and Astronomy:Venera 12

Following the failed Kosmos 482, the 1975 Venera 9 and 10 probes and 1978 Venera 11 and 12 probes were of a different design. They weighed approximately five tons and were launched by the powerful Proton booster. They included a transfer and relay bus that had engines to brake into Venus orbit (Venera 9 and 10, 11 and 12) and to serve as receiver and relay for the entry probe's transmissions. The entry probe was attached to the top of the bus in a spherical heat shield. The probes were optimized for surface operations with an unusual design that included a spherical compartment to protect the electronics from atmospheric pressure and heat for as long as possible. Beneath this was a shock-absorbing "crush ring" for landing. Above the pressure sphere was a cylindrical antenna structure and a wide, dish-shaped structure that resembled an antenna but was actually an aerobrake. They were designed to operate on the surface for a minimum of 30 minutes. Instruments varied on different missions, but included cameras and atmospheric and soil analysis equipment. All four landers had problems with some or all of their camera lens caps not releasing.

The Venera 9 lander operated for at least 53 minutes and took pictures with one of two cameras; the other lens cap did not release.

The Venera 10 lander operated for at least 65 minutes and took pictures with one of two cameras; the other lens cap did not release.

The Venera 11 lander operated for at least 95 minutes but neither cameras' lens caps released.

The Venera 12 lander operated for at least 110 minutes but neither cameras' lens caps released.

Venera 13 and 14

Main pages: Astronomy:Venera 13 and Astronomy:Venera 14
Model of a Venera lander

Venera 13 and 14 (1981–82) each had a descent craft/lander that contained most of the instrumentation and electronics, and a flyby spacecraft that was used as a communications relay. The design was similar to the earlier Venera 9–12 landers. They carried instruments to take scientific measurements of the ground and atmosphere once landed, including cameras, a microphone, a drill and surface sampler, and a seismometer. They also had instruments to record electric discharges during its descent phase through the Venusian atmosphere.

The two descent craft landed about 950 km (590 mi) apart, just east of the eastern extension of an elevated region known as Phoebe Regio. The Venera 13 lander survived for 127 minutes, and the Venera 14 lander for 57 minutes, where the planned design life was only 32 minutes. The Venera 14 craft had the misfortune of ejecting the camera lens cap directly under the surface compressibility tester arm, and returned information for the compressibility of the lens cap rather than the surface. The descent vehicles transmitted data to the buses, which acted as data relays as they flew by Venus.

Venera 15 and 16

Main pages: Astronomy:Venera 15 and Astronomy:Venera 16
Radar topography obtained by Venera 15/16

The 1983 Venera 15 and 16 spacecraft were orbiter missions; similar to previous probes, but the entry probes were replaced with surface imaging radar equipment. Radar imaging was necessary to penetrate the dense cloud of Venus and both missions included identical synthetic aperture radar (SAR) and radio altimeter systems. The SAR system was crucial in the mapping efforts of the mission and featured an 8-month operational tour to capture Venus's surface at a resolution of 1 to 2 kilometers (0.6 to 1.2 miles).[8] When the system was switched to radio altimeter mode the antenna operated at wavelength band of 8 centimeters to send and receive signals off of the Venusian surface over a period of 0.67 milliseconds.

The results were a detailed map of the reflectivity distribution over the surface of the Venusian Northern Hemisphere. The linear distance measurements that were taken ranged from 91 to 182 kilometers. The twin Soviet spacecraft flew in near-polar elliptical orbits and succeeded in mapping the top half of the northern atmosphere (from the north pole to 30 degrees N latitude, about 115 million square kilometers or 71 million square miles) by the end of the main mission. An altimeter provided topographical data with a height resolution of 50 m (164 feet), and an East German instrument mapped surface temperature variations.[9]

VeGa probes

Main page: Astronomy:Vega program

The VeGa (Cyrillic: ВеГа) probes to Venus and comet 1/P Halley launched in 1984 also used this basic Venera design, including landers but also atmospheric balloons which relayed data for about two days. "VeGa" is an agglutination of the words "Venera" (Venus in Russian) and "Gallei" (Halley in Russian).

Future

Venera-D

Main page: Astronomy:Venera-D

Venera-D is a proposed mission to Venus that would include a highly capable orbiter and a lander. From the standpoint of total mass delivered to Venus, the best launch opportunities occur in 2026 and 2031;[10] however, as of March 2021, Venera-D is planned for launch no earlier than November 2029.[11] Venera-D could incorporate some NASA components, including balloons, a subsatellite for plasma measurements, or a long-lived (24 hours) surface station on the lander.[12][13][14]

Scientific findings

First view of Venus' surface or any other planet other than Earth. The first clear panoramic image taken by Venera 9 lander. This image was sent back in the lander's 53-minute lifetime 22 October 1975. Although it was intended to be a 360-degree image, the second camera's lens cap did not open resulting in this 180-degree panorama.

There were many scientific findings from the data retrieved by the Venera probes making them pivotal in our understanding of Venus. The Venera probes provided direct data regarding Venus' surface and atmosphere while also providing important information on electronics lifetime under Venus' harsh conditions. Venera 4 was the first successful probe, and showed that CO2 is the main component in Venus' atmosphere.[15][5] Venera 7 found the temperature and pressure data as well as the atmospheric composition.[5][16] Venera 8 measured the K, U, and Th on the surface through gamma-ray analysis.[5] Venera 9 provided the first images of the surface of Venus as well as more gamma-ray analysis.[17] By sending the first images of Venus' surface back to Earth the Venera missions provided scientists with the ability to relay the achievements with the public. Venera 13 provided the first color images and X-ray fluorescence data of the surface of the planet. After analyzing the radar images returned from Venera 15 and 16, it was concluded that the ridges and grooves on the surface of Venus were the result of tectonic deformations.[18] This was found by radar imaging while in orbit. Even with their short lifetimes, the Venera missions each added significant understanding of our sister planet.

Types of Venera probes

Venera program probe types[19]
Model Type First Launch Last Launch Missions
(success / total)		 Launch Vehicle Mass Equipment
1VA Impact 4 February 1961 12 February 1961 0/2 Molniya 643.5 kg (1,419 lb) 5 scientific instruments
2MV-1 Flyby and Atmospheric probe 25 August 1962 1 September 1962 0/2 Molniya 1,097 kg (2,418 lb) 11 scientific instruments
2MV-2 Flyby 12 September 1962 12 September 1962 0/1 Molniya 890 kg (1,960 lb) 10 scientific instruments
3MV-1 and 1A Flyby 19 February 1964 2 April 1964 0/3 Molniya 800 kg (1,800 lb) (1A) and 948 kg (2,090 lb) 10 scientific instruments
3MV-4 Flyby 12 November 1965 23 November 1965 0/2 Molniya-M 963 kg (2,123 lb) 11 scientific instruments
3MV-3 Atmospheric probe and Lander 16 November 1965 16 November 1965 0/1 Molniya-M 958 kg (2,112 lb) 10 scientific instruments
1V Atmospheric probe and Lander 12 June 1967 17 June 1967 1/2 Molniya-M 1,106 kg (2,438 lb) 8 scientific instruments
2V Atmospheric probe and Lander 5 January 1969 10 January 1969 2/2 Molniya-M 1,130 kg (2,490 lb) 8 scientific instruments
3V Atmospheric probe and Lander 17 August 1970 31 March 1972 2/4 Molniya-M 1,180 kg (2,600 lb) 5 or 9 scientific instruments
4V-1 and 1M Orbiter and Lander 22 October 1975 4 November 1981 6/6 Proton-K 4,363 kg (9,619 lb) 5,033 kg (11,096 lb) 16 and 21 scientific instruments
4V-2 Orbiter 2 June 1983 7 June 1983 2/2 Proton-K 5,250 kg (11,570 lb) 5,300 kg (11,700 lb) 7 scientific instruments with radar

Flight data for all Venera missions

Name Model Mission Launch Arrival Survival time min Results Image Lander coordin.
Venera 1VA No. 1 1VA No. 1 Flyby 4 February 1961 N/A N/A Failed to leave earth orbit N/A
Venera 1 1VA No. 2 Flyby 12 February 1961 N/A N/A Communications lost en route to Venus
Venera 1 (a) (Memorial Museum of Astronautics).JPG
 N/A
Venera 2MV-1 No.1 2MV-1 No.1 Atmospheric probe 25 August 1962 N/A N/A Escape stage failed; Re-entered three days later
Sputnik19.gif
 N/A
Venera 2MV-1 No.2 2MV-1 No.2 Atmospheric probe 1 September 1962 N/A N/A Escape stage failed; Re-entered five days later N/A
Venera 2MV-2 No.1 2MV-2 No.1 Flyby 12 September 1962 N/A N/A Third stage exploded; Spacecraft destroyed N/A
Venera 3MV-1 No.2 3MV-1 No.2 Flyby 19 February 1964 N/A N/A Did not reach parking orbit N/A
Kosmos 27 3MV-1 No.3 Flyby 27 March 1964 N/A N/A Escape stage failed N/A
Venera 2 3MV-4 No.4 Flyby 12 November 1965 N/A N/A Communications lost just before arrival
Zond 2.jpg
 N/A
Venera 3 3MV-3 No.1 Atmospheric probe 16 November 1965 N/A N/A Communications lost just before atmospheric entry. This was the first manmade object to land on another planet on 1 March 1966 (crash). Probable landing region: -20° to 20° N, 60° to 80° E. N/A
Kosmos 96 3MV-4 No.6 Atmospheric probe 23 November 1965 N/A N/A Failed to leave Earth orbit and reentered the atmosphere. Believed by some researchers to have crashed near Kecksburg, Pennsylvania, USA on 9 December 1965, an event which became known as the "Kecksburg Incident" among UFO researchers. All Soviet spacecraft that never left Earth orbit were customarily renamed "Kosmos", regardless of the craft's intended mission. The name is also given to other Soviet/Russian spacecraft that are intended to—and do reach Earth orbit. N/A
Venera 4 4V-1 No.310 Atmospheric probe 12 June 1967 18 October 1967 N/A The first probe to enter another planet's atmosphere and return data. Although it did not transmit from the surface, this was the first interplanetary transmission of any probe. Landed somewhere near latitude 19° N, longitude 38° E.
Venera 4 (MMA 2011) (1).JPG
 N/A
Kosmos 167 4V-1 No.311 Atmospheric probe 17 June 1967 N/A N/A Escape stage failed; Re-entered eight days later N/A
Venera 5 2V (V-69) No. 330 Atmospheric probe 5 January 1969 16 May 1969 53* Successfully returned atmospheric data before being crushed by pressure within 26 kilometres (16 mi) of the surface. Landed at 3° S, 18° E. N/A
Venera 6 2V (V-69) No.331 Atmospheric probe 10 January 1969 17 May 1969 51* Successfully returned atmospheric data before being crushed by pressure within 11 kilometres (6.8 mi) of the surface. Landed at 5° S, 23° E. N/A
Venera 7 4V-1 No. 630 Lander 17 August 1970 15 December 1970 23 The first successful landing of a spacecraft on another planet, and the first transmission from another planet's surface. Survived for 23 minutes before succumbing to heat and pressure.
Venera-7 spuskaemiy apparat.jpg
 [ ⚑ ] 5°S 351°E / 5°S 351°E / -5; 351
Kosmos 359 3V (V-70) Lander 22 August 1970 N/A N/A Escape stage failed; Ended up in an elliptical Earth orbit N/A N/A
Venera 8 4V-1 No.670 Lander 27 March 1972 22 July 1972 50 Landed within a 150-kilometre (93 mi) radius of 10.70° S, 335.25° E.
Nave espacial Venera 8.jpg
 [ ⚑ ] 10°S 335°E / 10°S 335°E / -10; 335
Kosmos 482 3V (V-72) no. 671 Probe 31 March 1972 N/A N/A Escape stage exploded during Trans-Venus injection; Some pieces re-entered and others remained in Earth orbit N/A N/A
Venera 9 4V-1 No. 660 Orbiter and Lander 8 June 1975 22 October 1975 53 Sent back the first (black and white) images of Venus' surface. Landed within a 150-kilometre (93 mi) radius of 31.01° N, 291.64° E.
Venera 9 Space Probe 01.jpg
 [ ⚑ ] 31°N 291°E / 31°N 291°E / 31; 291
Venera 10 4V-1 No. 661 Orbiter and Lander 14 June 1975 25 October 1975 65 Landed within a 150-kilometre (93 mi) radius of 15.42° N, 291.51° E.
"Венера-10".jpg
 [ ⚑ ] 15°42′N 291°51′E / 15.7°N 291.85°E / 15.7; 291.85
Venera 11 4V-1 No. 360 Flyby and Lander 9 September 1978 25 December 1978 95 The lander arrived, but the imaging systems failed. [ ⚑ ] 14°S 299°E / 14°S 299°E / -14; 299
Venera 12 4V-1 Flyby and Lander 14 September 1978 21 December 1978 110 The lander recorded what is thought to be lightning. [ ⚑ ] 7°S 294°E / 07°S 294°E / -07; 294
Venera 13 4V-1 no.760 Flyby and Lander 30 October 1981 1 March 1982 127 Returned the first colour images of Venus' surface, and discovered leucite basalt in a soil sample using a spectrometer. [ ⚑ ] 07°05′S 303°00′E / 7.083°S 303°E / -7.083; 303
Venera 14 4V-1 No. 761 Flyby and Lander 14 November 1981 5 March 1982 57 A soil sample revealed tholeiitic basalt (similar to that found on Earth's mid-ocean ridges). [ ⚑ ] 13°25′S 310°00′E / 13.417°S 310°E / -13.417; 310
Venera 15 4V-2 No. 860 Orbiter 2 June 1983 10 October 1983 N/A Mapped (along with Venera 16) the northern hemisphere down to 30 degrees from North (resolution 1–2 km) N/A
Venera 16 4V-2 Orbiter 7 June 1983 14 October 1983 N/A Mapped (along with Venera 15) the northern hemisphere down to 30 degrees from North (resolution 1–2 km) N/A
Vega 1 5VK No. 902 Flyby and Lander 15 December 1984 11 June 1985 N/A Part of the Vega program. The vessel was en route to Halley's Comet. During entry into atmosphere, the surface instruments began work early, and the lander failed. Vega model - Udvar-Hazy Center.JPG [ ⚑ ] 07°05′N 177°07′E / 7.083°N 177.117°E / 7.083; 177.117
Vega 2 5VK No. 901 Flyby and Lander 21 December 1984 15 June 1985 56 Part of the Vega program. The vessel was en route to Halley's Comet. Vega model - Udvar-Hazy Center.JPG [ ⚑ ] 08°05′S 177°07′E / 8.083°S 177.117°E / -8.083; 177.117

See also

References

  1. ↑ "NASA Solar System Exploration: Venus". https://solarsystem.nasa.gov/planets/venus/exploration/. 
  2. ↑ Wade, Mark. "Venera 1VA". Encyclopedia Astronautica. http://www.astronautix.com/v/venera1va.html. 
  3. ↑ NSSDC Chronology of Venus Exploration, Dave Williams, 28 October 2021, NASA Goddard Space Flight Center; see also NSSDC Tentatively Identified (Soviet) Missions and Launch Failures, Dave Williams, 22 February 2022, NASA Goddard Space Flight Center
  4. ↑ "Venus Exploration Atlas". Ultimax Group. 1 April 2003. http://www.ultimax.com/resource/venumore.html. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Fegley, B. (2014). "2.7 – Venus" (in en). Treatise on Geochemistry (2 ed.). Elsevier. pp. 127–148. doi:10.1016/b978-0-08-095975-7.00122-4. ISBN 978-0-08-098300-4. https://linkinghub.elsevier.com/retrieve/pii/B9780080959757001224. 
  6. ↑ Dozois, Gardner (3 March 2015). "Return to Venusport". in Martin, George R. R. (in en). Old Venus: A Collection of Stories. Random House Publishing Group. ISBN 978-0-8041-7985-0. https://books.google.com/books?id=oJBoBAAAQBAJ&dq="The+Long+Rain"+"All+Summer+in+a+Day""+Bradbury+Venus+-wikipedia&pg=PT8. 
  7. ↑ Marov, M.Ya. (1972). "Venus: A perspective at the beginning of planetary exploration" (in en). Icarus 16 (3): 415–461. doi:10.1016/0019-1035(72)90094-2. Bibcode: 1972Icar...16..415M. https://linkinghub.elsevier.com/retrieve/pii/0019103572900942. 
  8. ↑ "Venera 15 & 16". https://solarviews.com/eng/venera16.htm. 
  9. ↑ "In Depth | Venera 15". https://solarsystem.nasa.gov/missions/venera-15/in-depth.  This article incorporates text from a publication now in the public domain:
  10. ↑ Development of the Venera-D Mission Concept, from Science Objectives to Mission architecture. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083).
  11. ↑ Zak, Anatoly (5 March 2021). "New promise for the Venera-D project". RussianSpaceWeb. http://www.russianspaceweb.com/venera-d-2021.html. 
  12. ↑ Wall, Mike (17 January 2017). "Russia, US Mulling Joint Mission to Venus". Space. https://www.space.com/35333-russia-nasa-venus-mission-venera-d.html. 
  13. ↑ Greicius, Tony, ed (7 August 2017). "NASA Studies Shared Venus Science Goals with Russian Space Institute". NASA. https://www.nasa.gov/feature/jpl/nasa-studying-shared-venus-science-objectives-with-russian-space-research-institute. 
  14. ↑ Senske, D.; Zasova, L. (31 January 2017). Venera-D: Expanding our horizon of terrestrial planet climate and geology through the comprehensive exploration of Venus (Report). Venera-D Joint Science Definition Team. http://iki.rssi.ru/events/2017/venera_d.pdf. 
  15. ↑ The Venus Atmosphere. Gordon and Breach. 1969. https://pubs.giss.nasa.gov/abs/ra04300u.html.  Papers from the Second Arizona Conference on Planetary Atmospheres, previously published in Journal of the Atmospheric Sciences; Mariner 5 reports, previously published in Science; and selected post-conference reports.
  16. ↑ Marov, M.Ya. (1972). "Venus: A perspective at the beginning of planetary exploration" (in en). Icarus 16 (3): 415–461. doi:10.1016/0019-1035(72)90094-2. Bibcode: 1972Icar...16..415M. https://linkinghub.elsevier.com/retrieve/pii/0019103572900942. 
  17. ↑ Hunten, Donald M.; Colin, Lawrence; Donahue, Thomas M.; Moroz, Vassily I. (4 January 2022), "Preface", Venus (University of Arizona Press): pp. vii–viii, doi:10.2307/j.ctv25c4z16.4, http://dx.doi.org/10.2307/j.ctv25c4z16.4, retrieved 2022-05-04 
  18. ↑ Basilevsky, A. T.; Pronin, A. A.; Ronca, L. B.; Kryuchkov, V. P.; Sukhanov, A. L.; Markov, M. S. (1986). "Styles of tectonic deformations of Venus – Analysis of Venera 15 and 16 data". Journal of Geophysical Research (Journal of Geophysical Research 30 March 1986, p. D399-D411) 91: 399. doi:10.1029/JB091iB04p0D399. ISSN 0148-0227. Bibcode: 1986JGR....91D.399B. https://adsabs.harvard.edu/full/1986LPSC...16..399B. 
  19. ↑ Huntress et al. p. 49-266 op. cit. Link needs repairing

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