Mapping Venus

Oleg Rzhiga of the Soviet Institute of Radio Engineering and Electronics (IRE) explained in 1988 why Venus had to be mapped by radar: in visible, infrared and ultraviolet light an observer sees the cloud tops 65 to 70 km up, while radio waves pass through the atmosphere and reflect from the solid surface. Telescope observers drew markings all the same. Francesco Bianchini's Hesperi et Phosphori nova phaenomena of 1728 showed dusky patches on the partly lit disc, markings that the Linda Hall Library calls illusory (the imagined Venus page follows that thread). The real map began with radar echoes in 1961 and was completed from orbit by Pioneer Venus Orbiter, Venera 15 and 16 and Magellan.

It opened with a wrong answer. MIT's Lincoln Laboratory announced radar echoes from Venus in 1958, and Jodrell Bank said in September 1959 that it had validated them; both implied an astronomical unit, the mean distance from Earth to the Sun, of 149,467,000 km, and Lincoln could not repeat its own result. JPL pointed its Goldstone radars at Venus on 10 March 1961, and that July W. K. Victor and R. Stevens announced in Science a value of 149,599,000 km, give or take 1,500 km, more than 100,000 km larger. Andrew Butrica's NASA history of planetary radar, To See the Unseen, calls this the first unambiguous detection, while noting that Lincoln later found an echo of 6 March 1961 on its own tapes; Lincoln, Jodrell Bank and an RCA group all published 1961 values within a few thousand kilometres of JPL's. MIT's obituary of Gordon Pettengill, who aimed Lincoln's Millstone radar at Venus in 1961, says the recalibrated unit proved instrumental in navigating Mariner 2 in 1962.

Vladimir Kotelnikov, IRE's director, led the Soviet attempt from the deep space communications centre near Yevpatoria in Crimea, using, Rzhiga wrote, the centre's transmitting antenna built to command spacecraft. The team observed Venus from 18 to 26 April 1961, and on 12 May Pravda and Izvestia printed a preliminary astronomical unit that Butrica gives as 149,457,000 km. IRE's full analysis, published in Radiotekhnika i elektronika in 1962, gave 149,599,300 km with a maximum error of 2,000 km, and a footnote explained the slip: the first reports had resolved an ambiguity with older astronomical values that had proved wrong, 'therefore the value of the astronomical unit given in the newspapers is also wrong'.

Radar also showed how Venus turns. The Soviet 1962 paper found a narrow spike in the echo plus a broad component up to 400 Hz wide, and offered two readings: a day of about 11 Earth days if the broad part came from the whole rotating surface, or more than 100 days if Venus scattered like the Moon and the broad part came from something else. Butrica reads the group as having persistently favoured about 11 days until its 1962 data pointed to a retrograde period of 200 to 300 days, by which time JPL and Lincoln had found the backward spin. Lincoln's William B. Smith found retrograde motion in echoes from 1961, but his supervisor had him tone it down, and his abstract of February 1963 said only 'very slow or possibly retrograde'. At Goldstone, Roland Carpenter suggested a retrograde period of about 150 days in an internal report of 1 May 1962; near-daily observations late that year then showed an echo detail that persisted and drifted, which he attributed to 'an actual physiographic feature on the surface of Venus', and he and Goldstein stated the retrograde spin in Science on 8 March 1963. The modern figures are on the Venus time page.

The Yevpatoria radar also sent words. IRE's account says three of its scientists, Morozov, Rzhiga and Vladimir Dubrovin, beamed Morse code at Venus to test and demonstrate the new planetary radar: MIR (peace, or world) on 19 November 1962, and LENIN and SSSR on 24 November, at 769 MHz. IRE calls the transmission a forerunner of interstellar radio messages. Butrica and the Soviet 1962 paper both give 700 MHz for the 1961 radar; no source consulted says whether that figure is rounded or the equipment changed by 1962.

The first surface features came out of the echo spectra in 1964. JPL's Richard Goldstein found two spots drifting with the rotation and named them Alpha, in the south, and Beta, in the north. At Arecibo the Cornell student Raymond Jurgens, urged by Tommy Gold, named features after pioneers of electromagnetism: Gauss, Hertz, Faraday and Maxwell. The first three matched Goldstein's regions, but Maxwell, seen in Arecibo images of 4 September 1967, matched nothing recorded before. Soviet observers saw the same kind of detail: Rzhiga reproduces 39 cm spectra from the conjunctions of June 1964 and January 1966 in which radio-bright regions move with the spin.

Earth-based radar had a blind side. At each inferior conjunction, Rzhiga explained, Venus turns nearly the same hemisphere towards Earth; the other hemisphere comes round three months later, when the planet is three times farther away and the echo almost a hundred times weaker, and the poles cannot be seen at all. Rzhiga credits Arecibo's 300 m dish at 13 cm with images at 10 to 20 km resolution in 1975 to 1977 showing Lakshmi, Maxwell, Beta and Alpha, and Butrica says Donald Campbell's images reached 1 to 3 km in 1983 and 1.5 km in 1988, then stopped because Magellan's radar frequency was close to Arecibo's. Arecibo's 305 m telescope collapsed on 1 December 2020, according to the US National Science Foundation.

Pioneer Venus Orbiter, in orbit from the end of 1978, carried a 17 cm radar altimeter that, Rzhiga explains, took a height about every 120 km along the track, with tracks 150 to 160 km apart at the equator. Its 1980 topographic map covered 65 degrees south to 75 degrees north and showed continents; ridges, craters and rifts were too small to register. MIT's obituary of Pettengill, the radar's principal investigator, calls it 'the first near-global topographic map of any planet'. The June 1980 edition already carries names: Ishtar and Aphrodite Terrae, Maxwell, Sappho, Lise Meitner and, inside Alpha Regio beside the zero meridian, a spot marked Eve.

Names were being chosen alongside. The IAU's Working Group for Planetary System Nomenclature, formed in 1973, gave Venus a task group chaired by Pettengill, with Goldstein, the USGS geologist Harold Masursky and the Soviet scientist M. Ya. Marov, Butrica records. At its Moscow meeting of 14 to 18 July 1975 the working group set two themes: the 'feminine mystique long associated with Venus', which put the goddesses of love Ishtar and Aphrodite on the highland continents, and deceased radio, radar and space scientists. Alpha was admitted as an exception for helping to define the origin of the official longitude system, and by August 1979 Beta and Maxwell had been approved too. The gazetteer's entry for Maxwell cites a 'list of radar scientists provided by G. H. Pettengill'.

Venera 15 and 16 turned orbital radar into cartography. Rzhiga, the experiment's scientific leader, dates the idea to IRE in the autumn of 1972 and the first survey to 16 October 1983. By 1984 the pair had imaged the north from the pole to 30 degrees north, a quarter of the planet. Drawing the maps by hand would have taken at least ten years, so IRE and the cartographic institute TsNIIGAiK built all 27 sheets by computer, which Rzhiga describes as the first time every step of making a map had been done digitally. IRE's institutional history calls the resulting Atlas of the Surface of Venus (1989, chief editor Kotelnikov) the first in the history of science. Data crossed the Cold War line both ways: Soviet tapes went to the Americans through the Interkosmos council, and the Soviet side received all of Pioneer Venus's radar data.

The survey also wrote words onto Venus. Rzhiga records that its nomenclature, more than 250 names prepared with Soviet specialists, was approved by the IAU General Assembly in Delhi in November 1985, with Russian women's names and women's names from the peoples of the USSR and socialist countries widely represented; the first printed sheet, Lakshmi Planum, carried craters for Yekaterina Dashkova, Anna Akhmatova, Polina Osipenko and Eugénie Cotton. All four are in today's gazetteer, which dates 224 names to 1985, a gap with Rzhiga's count that neither source explains. Two terms came from the same images: tessera, from the word for tile (Greek in Rzhiga's account, Latin in a 1990 NASA caption), and 'crown' for ring structures 200 to 600 km across; a NASA Magellan caption later said that coronae were first identified in Soviet radar images. In 1988 Rzhiga also wrote that nobody knew whether Cleopatra, the double crater on Maxwell's eastern slopes, came from an eruption or an impact; the Magellan caption calls it a double-ring impact basin about 100 km across (95 km for the outer ring in Rzhiga, 105 km in the gazetteer).

Magellan finished the job, imaging more than 98 percent of Venus at about 100 m resolution in radar passes between 1990 and 1992. The familiar globe is a composite, and NASA's caption for the hemisphere centred on 0 degrees says how: Magellan mosaics as the base, gaps filled with Arecibo images near 0 degrees latitude and longitude and with a neutral tone near the south pole, missing heights filled from Venera and Pioneer Venus altimetry, and colour for elevation. Names followed the images. The gazetteer dates 491 approvals to 1994 and 760 to 1997, then a trickle; the latest ten were approved on 5 May 2023.

The rules sit in the IAU's table of themes. Craters over 20 km honour women who made outstanding or fundamental contributions to their field, and smaller ones take common female first names; coronae are fertility and earth goddesses, chasmata goddesses of hunt and the Moon, terrae goddesses of love, tesserae goddesses of fate and fortune, planitiae mythological heroines, farra (pancake-like structures) water goddesses. Two rows carry caveats: montes are 'goddesses, miscellaneous (also one physicist)', who is Maxwell, and regiones 'giantesses and Titanesses (also two Greek alphanumeric)', Alpha and Beta. The IAU's general rules add that names must avoid political, military or religious significance (political figures before the 19th century excepted), that nobody is commemorated until dead for at least three years, and that selection should be equitable across ethnic groups, countries and gender. Mead, 270 km across and named for the anthropologist Margaret Mead, is the gazetteer's widest crater.

The long valleys are the planet naming itself: channels 400 km or longer carry the word for Venus in a world language, and shorter ones river goddesses. In the current file 38 of the 72 valles are named this way, from Baltis Vallis, the Syrian word and at 6,000 km the longest valley in the gazetteer, through Citlalpul (Aztec), Utrenitsa (Old Russian), Kinsei (Japanese) and Ikhwezi (Zulu). The edges are loose: Kinsei Vallis is listed at 375 km, below the threshold, while Saga and Sinann Valles, above it, carry river goddess names.

Zero longitude has moved with the maps. Goldstein put his zero on Alpha, and in 1988 Rzhiga still wrote that meridians on Venus are counted from Alpha. Today the gazetteer fixes zero at the central peak of Ariadne, a 23.6 km crater at 43.9 degrees north; the feature once called Eve (crater) is now Eve Corona, 330 km across. The rotation model in NASA's NAIF planetary constants kernel matches a sidereal period of 243.0185 days, fitted to Magellan images by Merton Davies and colleagues in 1992 (Rzhiga had quoted an IAU-adopted 243.01 days). In 2012 ESA reported that Venus Express had found surface features up to 20 km from where that period put them, as if the day averaged 6.5 minutes longer, and a 2021 study led by Jean-Luc Margot, with Campbell among its authors, used Earth-based radar speckle observations to measure an average of 243.0226 days for 2006 to 2020, with the length of day varying by about 20 minutes.

The summit has had several addresses. Rzhiga gives the highest point from the January 1984 Venera survey as 11.5 km above a 6,051 km sphere at 65.9 degrees north, 2.3 degrees east, and Pioneer Venus's as 11.1 km some 220 km farther south; NASA's Magellan caption puts Maxwell almost 11 km above the mean radius, and the top value in Magellan's 1997 topography is 11,687 m above 6,051.0 km. The reference spheres and sampling differ, so the figures need not agree. From 1994 the gazetteer also carried Skadi Mons at 64.0 degrees north, 4.0 degrees east inside Maxwell Montes, and Guinness World Records listed it as the tallest mountain on Venus. On 17 December 2025 the name was dropped 'because topographic data analysis has shown there is no mons feature at this location'. Guinness, checked on 4 November 2026, credits an unnamed cluster of peaks in Maxwell, provisionally called the Western Pinnacles by the researcher Jim Singh, at 10,690 m above the mean radius, and notes that a strip of missing Magellan data crosses it; that name has no IAU standing.

Ishtar Terra in the north, named for the Babylonian goddess of love, holds Lakshmi Planum, a plateau 2.5 to 5 km high (Rzhiga) named for the Indian goddess of love and war and ringed by Maxwell, Akna and Freyja Montes and the scarp of Vesta Rupes. Most of Maxwell returns radar strongly; NASA's Magellan caption suggests a reflective mineral such as pyrite, stable only within a band of altitude. Along the equator, Aphrodite Terra runs 10,000 km, with Ovda Regio, named for a Marijian Titaness, in its western part, and Diana Chasma, one of the steep-sided troughs the IAU calls chasmata, to the east. Artemis Corona, 2,600 km across and the widest corona in the gazetteer, takes its name from Artemis Chasma. In the far south Lada Terra, named in 1982 for the Slavic goddess of love, holds Quetzalpetlatl Corona, named for an Aztec fertility goddess. Addams, 87 km across at 56.2 degrees south, honours the social reformer Jane Addams.

Alpha Regio is the planned descent target of DAVINCI (NASA mission page, updated 14 July 2026). Beta Regio holds the landing areas of Venera 9 and 10 in its north-eastern and south-eastern parts, according to geological mapping by A. M. Abdrakhimov of the Vernadsky Institute, who places Venera 13 and 14 on Navka Planitia east of Phoebe Regio and Vega 1 and 2 in Rusalka Planitia, named for a Russian mermaid.

In Atla Regio, Robert Herrick and Scott Hensley reported in Science in 2023 a vent of about 2.2 square kilometres associated with Maat Mons that changed shape between February and October 1991. The rift across Atla is officially Ganis Chasma, for a western Lapp forest maiden; ESA's 2015 material on Venus Express hot spots calls it Ganiki Chasma, a name absent from the gazetteer, where Ganiki is a plain. In Eistla Regio stands Sif Mons. In 2024 Davide Sulcanese, Giuseppe Mitri and Marco Mastrogiuseppe read radar changes on Sif's western flank and in western Niobe Planitia as new lava flows; on 22 April 2026 Nature Astronomy published a comment by Bhiravarasu and colleagues arguing that differing viewing geometry explains the changes, with a reply in which the original authors hold that geometry alone cannot, so the question is open. Farther south, Idunn Mons in Imdr Regio was mapped in 2017 by Piero D'Incecco and colleagues as a site of 'recently active lava flows', and Themis Regio was studied in 2016 by Ellen Stofan and colleagues for recent volcanism in Venus Express VIRTIS data. The newest find is underground: on 9 February 2026 Leonardo Carrer, Elena Diana and Lorenzo Bruzzone of the University of Trento reported in Nature Communications a conduit beside a skylight in the Nyx Mons region, which they hypothesise is a lava tube about 1 km across; they traced it at least 300 m from the skylight and infer from aligned pits that it runs 45 km or more. The volcanoes on Venus page has the detail.

The next remapping has not flown. India's Venus Orbiter Mission is to carry a mapping radar, and the Trento release notes that VERITAS and EnVision are both to carry imaging radars; none had launched by 4 November 2026, and their pages give their status. Until one of them arrives, the 1,985 names sit on a map built almost entirely from data gathered before 1995, and each new study of old Magellan data, from Skadi Mons to Nyx Mons, still edits it.