Venus Express

From April 2006 to November 2014 the European Space Agency's Venus Express circled the planet, a near copy of Mars Express rebuilt for a world where sunlight is four times as strong as at Mars. ESA's own FAQ explains the name by the speed of the project, promising less than three years from approval to launch; lift-off came three years and four days after the final go-ahead of November 2002. Planned for 500 days, it worked for eight and a half years, was sent on a deliberate dive through the upper atmosphere as its propellant ran low, and fell silent in the winter of 2014 to 2015.

The mission was proposed in March 2001 to reuse the Mars Express design on strict terms: the same equipment and industrial teams, ready for the 2005 launch window. ESA's Science Programme Committee agreed unanimously on 11 July 2002 to start work, but that autumn Italy, responsible for part of the payload, could not fully commit its funding by the October deadline. On 4 and 5 November 2002 the committee endorsed a rescue: Italy would supply spare parts of the VIRTIS and PFS experiments, and ESA would add 8.5 million euros to integrate the Italian hardware and fill the gaps. Science director David Southwood told scientists and industry to 'go to work to go to Venus!'

Copying a Mars spacecraft for Venus meant turning its thermal design inside out. ESA enlarged the radiators and halved the solar arrays, whose cells alternate with strips of mirror so the panels would not peak at 250 °C. Seen from Venus, Earth can lie in any direction relative to the Sun, so a second high-gain antenna from the Rosetta design faced the opposite way to the main dish. Sources give the launch mass as 1,240 kg or 1,270 kg.

Seven instruments flew: SPICAV, an ultraviolet and infrared spectrometer led from France by Jean-Loup Bertaux, with a new solar-occultation channel, SOIR (ESA lists Belgian and Russian institutes as co-leads); VIRTIS, an imaging spectrometer led by Giuseppe Piccioni in Rome and Pierre Drossart in Paris; PFS, the Planetary Fourier Spectrometer; ASPERA-4, for escaping ions and energetic neutral atoms; the magnetometer MAG; VeRa, which used the radio link itself to sound the atmosphere; and the camera, VMC, from the Max Planck Institute for Solar System Research (MPS). Two lost capability. NSSDCA records PFS as not operational from launch (the Planetary Society reported in July 2007 that its scanner mirror was stuck in the launch position), the loss of the VIRTIS-M infrared channel when its cryocooler failed in October 2008, and a drop in S-band signal level at the end of 2006.

The launch, planned for 26 October 2005 at the opening of a window that closed on 24 November, was postponed because of contamination of the fairing, NSSDCA records. A Soyuz-FG with a Fregat upper stage finally lifted off from Baikonur on 9 November 2005 at 03:33:34 UT. The next day ESA's new deep-space antenna at Cebreros, west of Madrid, received its first X-band signal, from Venus Express, and ESA dates the start of the station's operations from that signal.

Venus Express reached Venus on 11 April 2006, 153 days and 400 million km after launch. Its main engine started at 07:10:29 UT spacecraft time, according to NASA's mission page; NSSDCA gives 07:17:14 UT, the moment the signal reached Earth. ESA said that morning that the burn of about 50 minutes had slowed the craft relative to Venus from 29,000 to about 25,000 km/h. Further burns took it from a capture orbit of about nine days to its working orbit on 7 May 2006: polar, 24 hours long, from about 250 km above the north polar region to 66,000 km over the south pole. Routine science began on 4 June.

Far out over the south pole the instruments could watch for hours; near pericentre they gained detail, though ESA notes the craft passed too close to the north pole for detailed imaging of the vortex there. Correcting the orbit against the Sun's pull every 40 to 50 days used propellant, and ESA warned in 2010 that it would run out in 2015 unless drag could be used to lower the orbit. The first extension came on 23 February 2007, moving the end from September 2007 to early May 2009; CNES records later ones to the end of 2014, and ASI mentions one to the end of 2016. Counts differ: CNES says four, NASA five and INAF six.

Between 12 and 19 April 2006, still in the capture orbit, VIRTIS imaged a double-eyed vortex over the south pole. Years of follow-up showed its core changing shape within a day, from an S or a figure of eight to near chaos, and ESA's summary calls it more variable than any comparable polar vortex known in the Solar System. Studies of VMC images led by Igor Khatuntsev in Moscow and Toru Kouyama in Japan found average cloud-top winds between 50 degrees north and south rising from about 300 km/h in 2006 to 400 km/h over six Earth years, and ESA said in 2013 that no one could explain why. Nils Müller of DLR found surface features seen by VIRTIS displaced by up to 20 km from where Magellan's rotation period placed them, as if the day were on average 6.5 minutes longer (how long a day lasts on Venus). ESA wrote in 2014 that any link between faster winds and slower spin remained unknown.

In October 2006 Bertaux told ESA's French service that he did not expect to find ozone on Venus in any notable quantity, because it would have been detected already. Five years later SPICAV found it, in the tenuous amounts his remark allowed for, by watching stars set through the planet's limb; ESA announced the thin night-side layer on 6 October 2011, with Franck Montmessin as lead scientist. The 2011 release placed it at about 100 km, four times higher than Earth's and a hundred to a thousand times less dense; ESA's 2014 summary gives 90 to 120 km and a thickness of 5 to 10 km. In the models ESA cited, sunlight splits carbon dioxide on the day side and winds carry the oxygen to the night side, where some recombines as ozone without any biology.

Other results filled in the chemistry of the upper atmosphere. SOIR's solar occultations, analysed over five years by Arnaud Mahieux, revealed a permanent temperature minimum near 125 km along the day-night line, around minus 175 °C and at some heights below the freezing point of carbon dioxide, although Mahieux cautioned in 2012 that bright patches which could be ice might have other causes. ASPERA found hydrogen escaping from the night side at about twice the rate of oxygen, the proportions of water, while deuterium is enriched high up because it escapes less easily (oceans and the greenhouse). Lightning is less settled: ESA's May 2014 summary described bursts identified by their electromagnetic signature, but a 2018 critical review by Ralph Lorenz called the claimed detections and non-detections qualitatively contradictory, while concluding that the preponderance of observations supports some kind of frequent electrical activity.

On volcanoes the evidence accumulated without closing the case. A 2010 study led by Sue Smrekar of JPL used VIRTIS emissivity data at three hotspots, Imdr, Themis and Dione Regiones, to identify little-weathered lava flows, which ESA has aged three ways: a few hundred thousand to 2.5 million years (its Italian release), no more than 2.5 million years and possibly much less (the 2014 end-of-mission release), and perhaps a few thousand to a few tens of thousands of years (its highlight page). Sulfur dioxide above the clouds rose sharply after arrival and then fell to about a tenth over six years, Emmanuel Marcq of LATMOS reported in 2012; sunlight destroys the gas within days, so it must have been lifted recently, and his team left open whether eruptions or the circulation did it, noting that Pioneer Venus had seen a similar decline. In 2015 Eugene Shalygin of MPS reported four transient hotspots in VMC images along a rift near Ozza and Maat Montes, one estimated at about 1 square km and 830 °C. ESA and the paper call the rift Ganiki Chasma, a name missing from the IAU gazetteer, which has Ganis Chasma there and the plain Ganiki Planitia to the north. In 2022 J. Brossier and colleagues read low Magellan radar emissivity along Ganis Chasma as geologically recent volcanism matching the transient anomalies, and suggested activity there for at least the last few decades.

The spacecraft also served as an instrument. In drag passes between 2008 and 2010, down to 175 km, ground stations tracked its deceleration, and ESA reported in 2010 that the polar atmosphere at those heights was about 60 percent thinner than predicted. Routine science ended on 15 May 2014 and the aerobraking experiment began: the pericentre was allowed to sink from 190 km, and from 18 June to 11 July the craft skimmed the atmosphere at 131 to 135 km, with small burns lowering it further. ESA's release of 11 July expected 129.1 km the next day; its November summary gives a minimum of 129.2 km on 11 July, and the December release rounds the campaign to 130 to 135 km. Fifteen burns from 12 July raised the pericentre to about 460 km. ESA wrote in 2016 that aerobraking had never before been used on any of its planetary missions.

At those depths the atmosphere proved more variable than expected and about four times denser by day than by night. In April 2016 a team led by Ingo Müller-Wodarg of Imperial College London reported in Nature Physics that the polar atmosphere at 130 to 140 km averaged minus 157 °C, up to 70 degrees colder than the reference model built from Pioneer Venus data, and 22 to 40 percent less dense. ESA's factsheet for EnVision, read on 26 September 2026, plans 11 months of aerobraking to reach that mission's science orbit.

Afterwards the pericentre sank again, and ESA planned raising burns for 23 to 30 November 2014, assuming some propellant was left. Full contact was lost on 28 November; the partial, unstable links that followed showed the craft losing attitude control, most likely because the propellant ran out about halfway through the burns, said mission manager Patrick Martin. ESA declared the mission over on 16 December. Controllers kept listening for the bare carrier: around 15:00 UTC on 18 January 2015 its level jumped by more than 30 dB for about a minute, and the last intermittent detection came on 19 January. Martin said on 23 January that the signal was gone, while the spacecraft might continue orbiting under conditions that did not allow a signal to be received. No observation of its entry exists, so this page gives it no point on the globe (what we left at Venus).

Radio telescopes outside ESA's network also listened. The PRIDE experiment recorded its X-band carrier with VLBI dishes in China, Russia, Australia and Japan in five occultation sessions, four in 2012 and one on 23 March 2014, according to a 2019 study by T. M. Bocanegra-Bahamon and colleagues. In 2014 China's 65 m Tianma telescope held the signal through a complete occultation behind Venus (China and Venus).

A naming trap waits for anyone moving between ESA's two Express missions. On Venus Express, VMC is the Venus Monitoring Camera, a wide-angle camera imaging in four wavelengths, led by Wojciech Markiewicz of MPS. On Mars Express, VMC is the Visual Monitoring Camera, an engineering camera fitted to confirm the separation of Beagle 2 and later used for outreach as the Mars webcam. This page's cloud images and 2015 hotspots come from the Venus camera.

Giuseppe Piccioni summed up the mission for INAF's news service on 17 December 2014: the team had squeezed the spacecraft and every instrument aboard for the greatest possible scientific return. ESA wrote in November 2014 that it had sent back more data than all previous missions to Venus combined, and the EnVision factsheet names Venus Express among the missions it builds on, alongside the Venera programme, Pioneer Venus and Magellan, and says it will also use findings from Akatsuki.