159-798: This article provides a timeline of the Cassini–Huygens mission (commonly called Cassini ). Cassini was a collaboration between the United States ' NASA , the European Space Agency ("ESA"), and the Italian Space Agency ("ASI") to send a probe to study the Saturnian system, including the planet, its rings , and its natural satellites . The Flagship -class uncrewed robotic spacecraft comprised both NASA's Cassini probe, and ESA's Huygens lander which
318-455: A Mariner Mark II mission and generically. Cassini-Huygens was a Flagship -class mission to the outer planets. The other planetary flagships include Galileo , Voyager , and Viking . Cassini had several objectives, including: Cassini–Huygens was launched on October 15, 1997, from Cape Canaveral Air Force Station 's Space Launch Complex 40 using a U.S. Air Force Titan IV B/ Centaur rocket. The complete launcher
477-596: A dust ring-cloud , with a suspected origin either from Venus–trailing asteroids, interplanetary dust migrating in waves, or the remains of the Solar System's original circumstellar disc that formed the planetary system . Earth and Venus have a near orbital resonance of 13:8 (Earth orbits eight times for every 13 orbits of Venus). Therefore, they approach each other and reach inferior conjunction in synodic periods of 584 days, on average. The path that Venus makes in relation to Earth viewed geocentrically draws
636-457: A pentagram over five synodic periods, shifting every period by 144°. This pentagram of Venus is sometimes referred to as the petals of Venus due to the path's visual similarity to a flower. When Venus lies between Earth and the Sun in inferior conjunction, it makes the closest approach to Earth of any planet at an average distance of 41 million km (25 million mi). Because of
795-408: A runaway greenhouse effect evaporated any water and turned Venus into its present state. The rotation of Venus has been slowed and turned against its orbital direction ( retrograde ) by the currents and drag of its atmosphere. It takes 224.7 Earth days for Venus to complete an orbit around the Sun, and a Venusian solar year is just under two Venusian days long. The orbits of Venus and Earth are
954-399: A synthetic aperture radar mapper, a charge-coupled device imaging system, a visible/ infrared mapping spectrometer , a composite infrared spectrometer, a cosmic dust analyzer, a radio and plasma wave experiment, a plasma spectrometer, an ultraviolet imaging spectrograph, a magnetospheric imaging instrument, a magnetometer and an ion /neutral mass spectrometer . Telemetry from
1113-444: A working group to investigate future cooperative missions. Two European scientists suggested a paired Saturn Orbiter and Titan Probe as a possible joint mission. In 1983, NASA's Solar System Exploration Committee recommended the same Orbiter and Probe pair as a core NASA project. NASA and the European Space Agency (ESA) performed a joint study of the potential mission from 1984 to 1985. ESA continued with its own study in 1986, while
1272-605: A "mission of firsts" that has revolutionized human understanding of the Saturn system, including its moons and rings, and our understanding of where life might be found in the Solar System . Cassini ' s planners originally scheduled a mission of four years, from June 2004 to May 2008. The mission was extended for another two years until September 2010, branded the Cassini Equinox Mission . The mission
1431-412: A "mission of firsts", that has revolutionized human understanding of the Saturnian system, including its moons and rings , and our understanding of where life might be found in the Solar System . Cassini ' s primary mission lasted for four years, from June 2004 to May 2008. The mission was extended for another two years until September 2010, under the name of Cassini Equinox Mission . The mission
1590-451: A 4" telescope. Although naked eye visibility of Venus's phases is disputed, records exist of observations of its crescent. When Venus is sufficiently bright with enough angular distance from the sun, it is easily observed in a clear daytime sky with the naked eye, though most people do not know to look for it. Astronomer Edmund Halley calculated its maximum naked eye brightness in 1716, when many Londoners were alarmed by its appearance in
1749-414: A Venusian year (243 versus 224.7 Earth days). Slowed by its strong atmospheric current the length of the day also fluctuates by up to 20 minutes. Venus's equator rotates at 6.52 km/h (4.05 mph), whereas Earth's rotates at 1,674.4 km/h (1,040.4 mph). Venus's rotation period measured with Magellan spacecraft data over a 500-day period is smaller than the rotation period measured during
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#17327723946911908-459: A change that would have occurred over the course of billions of years. The rotation period of Venus may represent an equilibrium state between tidal locking to the Sun's gravitation, which tends to slow rotation, and an atmospheric tide created by solar heating of the thick Venusian atmosphere. The 584-day average interval between successive close approaches to Earth is almost exactly equal to 5 Venusian solar days (5.001444 to be precise), but
2067-574: A depression. These features are volcanic in origin. Most Venusian surface features are named after historical and mythological women. Exceptions are Maxwell Montes, named after James Clerk Maxwell , and highland regions Alpha Regio , Beta Regio , and Ovda Regio . The last three features were named before the current system was adopted by the International Astronomical Union , the body which oversees planetary nomenclature . The longitude of physical features on Venus
2226-456: A diameter of 15 to 20 km. 30 December 2000 10:05 UTC − Gravity-assisted flyby of Jupiter . Cassini was at its closest point (9.7 million kilometres, 137 Jovian radii) to Jupiter at this date, and performed many scientific measurements. It also produced the most detailed global color portrait of Jupiter ever produced (seen on the right); the smallest visible features are approximately 60 km (37 mi) across. 30 May 2001 – During
2385-480: A distance of 1,010 km (630 mi), the closest flyby and only visit to the moon during the primary mission. 27 July 2006 – NASA confirms the presence of hydrocarbon lakes in Titan's northern polar region. Cassini%E2%80%93Huygens Cassini–Huygens ( / k ə ˈ s iː n i ˈ h ɔɪ ɡ ən z / kə- SEE -nee HOY -gənz ), commonly called Cassini , was a space-research mission by NASA ,
2544-401: A distance of 9 million kilometers from Saturn, the last major firing of the main engine took place to adjust the next closest approach and avoid the particles in the ring system. The 51 minute burn increased the velocity of the probe by 325 meters per second, moving the orbital periapsis point about 300,000 km farther away from Saturn than its smallest distance during SOI. At the same time,
2703-467: A dynamo at its core. A dynamo requires three things: a conducting liquid, rotation, and convection . The core is thought to be electrically conductive and, although its rotation is often thought to be too slow, simulations show it is adequate to produce a dynamo. This implies that the dynamo is missing because of a lack of convection in Venus's core. On Earth, convection occurs in the liquid outer layer of
2862-553: A million, with the data still supporting Einstein's theory. 27 February 2004 – A new, high-resolution picture of Saturn taken by Cassini on 9 February was released, and it was noted that mission scientists were puzzled by the fact that no "spokes" in Saturn's ring are visible. These dark structures in the "B" section of the ring had been discovered in pictures taken by the Voyager probe in 1981. Another picture, in infrared light, taken on 16 February shows cloud height differences and
3021-537: A minimum distance of about 1,025 kilometers was executed at 19:12 UTC. This was the closest flyby up to this date, and provided the opportunity to obtain more detailed data on the constituents in the upper atmosphere of Titan. The first analysis of that data showed a large range of complex carbon molecules . On 25 April a mass plot was published that demonstrates the existence of these molecules. 3 May 2005 – Cassini begins Radio occultation experiments on Saturn's Rings , to determine ring particle size distribution, on
3180-449: A more massive primary atmosphere from solar nebula have been proposed to explain the enrichment. However, the atmosphere is depleted of radiogenic argon, a proxy for mantle degassing, suggesting an early shutdown of major magmatism. Studies have suggested that billions of years ago, Venus's atmosphere could have been much more like the one surrounding the early Earth, and that there may have been substantial quantities of liquid water on
3339-403: A number of risky passes through the gaps between Saturn and its inner rings. This phase aimed to maximize Cassini 's scientific outcome before the spacecraft was intentionally destroyed to prevent potential contamination of Saturn's moons if Cassini were to unintentionally crash into them when maneuvering the probe was no longer possible due to power loss or other communication issues at
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#17327723946913498-535: A picture of Huygens taken from Cassini two days after its release. It reported that the analysis of that picture shows that the probe is on the correct course within the expected error range. These checks were necessary in order to place Cassini in the correct orientation to receive the data from Huygens when it entered Titan's atmosphere. 28 December 2004 – OTM-10 was executed at 03:00 UTC in Spacecraft Event Time . This maneuver, also called
3657-491: A radio link between Huygens and Cassini provided by Probe Data Relay Subsystem (PDRS). As the probe's mission could not be telecommanded from Earth because of the great distance, it was automatically managed by the Command Data Management Subsystem (CDMS). The PDRS and CDMS were provided by the Italian Space Agency (ASI). After Cassini 's launch, it was discovered that data sent from
3816-510: A result, Cassini became more specialized. The Mariner Mark II series was cancelled. The combined orbiter and probe is the third-largest uncrewed interplanetary spacecraft ever successfully launched, behind the Phobos 1 and 2 Mars probes, as well as being among the most complex. The orbiter had a mass of 2,150 kg (4,740 lb), the probe 350 kg (770 lb) including 30 kg (66 lb) of probe support equipment left on
3975-585: A series of calibration photos. On January 23, 2000, Cassini performed a flyby of the asteroid 2685 Masursky at around 10:00 UTC. It took photos in the period five to seven hours before the flyby at a distance of 1.6 × 10 ^ km (0.99 × 10 ^ mi) and a diameter of 15 to 20 km (9.3 to 12.4 mi) was estimated for the asteroid. Cassini made its closest approach to Jupiter on December 30, 2000, at 9.7 million kilometers, and made many scientific measurements. About 26,000 images of Jupiter, its faint rings , and its moons were taken during
4134-572: A set of "clumps" moving along the "F" ring. 26 March 2004 – The Cassini science team published the first sequence of pictures of Saturn showing clouds moving at high speed around the planet. Using a filter to better see water haze on top of the dense cloud cover, motions in the equatorial and southern regions are clearly visible. The pictures were taken during the days from 15 to 19 February. 8 April 2004 – The first "long-term" observation of cloud dynamics in Saturn's atmosphere were published by mission scientists. A set of pictures shows two storms in
4293-622: A successful Titan flyby, with new regions of its surface scanned by radar . Cassini ' s mapping radar acquired a picture that shows a large crater on Titan, with an estimated diameter of 440 km (270 mi). 17 February 2005 – The first close flyby of Enceladus was executed and the first closeup images were sent back to Earth. The flyby distance was about 1,180 km (730 mi). 17 March 2005 – The Cassini probe revealed that Saturn's moon Enceladus has an atmosphere. It has been described as "substantial" by its discoverers. 16 April 2005 – The fifth planned flyby of Titan with
4452-589: A way that, at closest approach to Saturn, it was only 3,000 km (1,900 mi) above the planet's cloudtops, below the inner edge of the D ring . This sequence of "proximal orbits" ended when its final encounter with Titan sent the probe into Saturn's atmosphere to be destroyed. Cassini–Huygens ' s origins date to 1982, when the European Science Foundation and the American National Academy of Sciences formed
4611-422: Is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen . The surface pressure is 9.3 megapascals (93 bars ), and the average surface temperature is 737 K (464 °C; 867 °F), above the critical points of both major constituents and making the surface atmosphere a supercritical fluid out of mainly supercritical carbon dioxide and some supercritical nitrogen. The Venusian surface
4770-540: Is a rocky body like Earth. It is similar to Earth in size and mass and is often described as Earth's "sister" or "twin". Venus is close to spherical due to its slow rotation. Venus has a diameter of 12,103.6 km (7,520.8 mi)—only 638.4 km (396.7 mi) less than Earth's—and its mass is 81.5% of Earth's, making it the third-smallest planet in the Solar System . Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere
4929-405: Is currently volcanically active, specifically the detection of olivine , a volcanic product that would weather quickly on the planet's surface. This massive volcanic activity is fuelled by a superheated interior, which models say could be explained by energetic collisions from when the planet was young. Impacts would have had significantly higher velocity than on Earth, both because Venus's orbit
Timeline of Cassini–Huygens - Misplaced Pages Continue
5088-487: Is expressed relative to its prime meridian . The original prime meridian passed through the radar-bright spot at the centre of the oval feature Eve, located south of Alpha Regio. After the Venera missions were completed, the prime meridian was redefined to pass through the central peak in the crater Ariadne on Sedna Planitia . The stratigraphically oldest tessera terrains have consistently lower thermal emissivity than
5247-636: Is far from certain. Studies reported on 26 October 2023 suggest for the first time that Venus may have had plate tectonics during ancient times and, as a result, may have had a more habitable environment , possibly one capable of sustaining life . Venus has gained interest as a case for research into the development of Earth-like planets and their habitability . Much of the Venusian surface appears to have been shaped by volcanic activity. Venus has several times as many volcanoes as Earth, and it has 167 large volcanoes that are over 100 km (60 mi) across. The only volcanic complex of this size on Earth
5406-576: Is faster due to its closer proximity to the Sun and because objects would require higher orbital eccentricities to collide with the planet. In 2008 and 2009, the first direct evidence for ongoing volcanism was observed by Venus Express , in the form of four transient localized infrared hot spots within the rift zone Ganis Chasma , near the shield volcano Maat Mons . Three of the spots were observed in more than one successive orbit. These spots are thought to represent lava freshly released by volcanic eruptions. The actual temperatures are not known, because
5565-462: Is formed by sulphur dioxide and water through a chemical reaction resulting in sulfuric acid hydrate. Additionally, the clouds consist of approximately 1% ferric chloride . Other possible constituents of the cloud particles are ferric sulfate , aluminium chloride and phosphoric anhydride . Clouds at different levels have different compositions and particle size distributions. These clouds reflect, similar to thick cloud cover on Earth, about 70% of
5724-456: Is induced by an interaction between the ionosphere and the solar wind , rather than by an internal dynamo as in the Earth's core . Venus's small induced magnetosphere provides negligible protection to the atmosphere against solar and cosmic radiation . The lack of an intrinsic magnetic field on Venus was surprising, given that it is similar to Earth in size and was expected to contain
5883-404: Is most likely at least partially liquid because the two planets have been cooling at about the same rate, although a completely solid core cannot be ruled out. The slightly smaller size of Venus means pressures are 24% lower in its deep interior than Earth's. The predicted values for the moment of inertia based on planetary models suggest a core radius of 2,900–3,450 km. This is in line with
6042-432: Is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide ( galena ). Although Venus has no seasons, in 2019 astronomers identified a cyclical variation in sunlight absorption by the atmosphere, possibly caused by opaque, absorbing particles suspended in the upper clouds. The variation causes observed changes in the speed of Venus's zonal winds and appears to rise and fall in time with
6201-863: Is recent evidence of lava flow on Venus (2024), such as flows on Sif Mons, a shield volcano, and on Niobe Planitia, a flat plain. There are visible calderas . The planet has few impact craters , demonstrating that the surface is relatively young, at 300–600 million years old. Venus has some unique surface features in addition to the impact craters, mountains, and valleys commonly found on rocky planets. Among these are flat-topped volcanic features called " farra ", which look somewhat like pancakes and range in size from 20 to 50 km (12 to 31 mi) across, and from 100 to 1,000 m (330 to 3,280 ft) high; radial, star-like fracture systems called "novae"; features with both radial and concentric fractures resembling spider webs, known as " arachnoids "; and "coronae", circular rings of fractures sometimes surrounded by
6360-510: Is remarkable how startling it is to see these images for the first time." 2 July 2004 – Cassini ' s first flyby of Titan was executed and first close up pictures were sent back to Earth. Due to the planning of the initial orbit, Cassini was passing over the south pole of the moon and from a larger distance than in later flybys. Regardless, during a press conference on 3 June, mission scientists presented pictures that were already causing them to rethink previous theories. It now seems that
6519-406: Is speculation on the possibility that life exists in the upper cloud layers of Venus, 50 km (30 mi) up from the surface, where the atmospheric conditions are the most Earth-like in the Solar System, with temperatures ranging between 303 and 353 K (30 and 80 °C; 86 and 176 °F), and the pressure and radiation being about the same as at Earth's surface, but with acidic clouds and
Timeline of Cassini–Huygens - Misplaced Pages Continue
6678-420: Is that the absence of a late, large impact on Venus ( contra the Earth's "Moon-forming" impact) left the core of Venus stratified from the core's incremental formation, and without the forces to initiate/sustain convection, and thus a "geodynamo". The weak magnetosphere around Venus means that the solar wind is interacting directly with its outer atmosphere. Here, ions of hydrogen and oxygen are being created by
6837-465: Is the Big Island of Hawaii. More than 85,000 volcanoes on Venus were identified and mapped. This is not because Venus is more volcanically active than Earth, but because its crust is older and is not subject to the same erosion process. Earth's oceanic crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years, whereas
6996-500: Is visible in dark skies long after sunset. As the brightest point-like object in the sky, Venus is a commonly misreported " unidentified flying object ". As it orbits the Sun, Venus displays phases like those of the Moon in a telescopic view. The planet appears as a small and "full" disc when it is on the opposite side of the Sun (at superior conjunction ). Venus shows a larger disc and "quarter phase" at its maximum elongations from
7155-417: Is −4.14 with a standard deviation of 0.31. The brightest magnitude occurs during the crescent phase about one month before or after an inferior conjunction. Venus fades to about magnitude −3 when it is backlit by the Sun. The planet is bright enough to be seen in broad daylight, but is more easily visible when the Sun is low on the horizon or setting. As an inferior planet , it always lies within about 47° of
7314-487: The Magellan spacecraft imaged a highly reflective substance at the tops of the highest mountain peaks, a " Venus snow " that bore a strong resemblance to terrestrial snow. This substance likely formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gaseous form to higher elevations, where it is cooler and could precipitate. The identity of this substance
7473-684: The Cassini Telemetry Dictionary. Out of these 67 lower complexity mini-packets, 6 mini-packets contained the subsystem covariance and Kalman gain elements (161 measurements), not used during normal mission operations. This left 947 measurements in 61 mini-packets. A total of seven telemetry maps corresponding to 7 AACS telemetry modes were constructed. These modes are: (1) Record; (2) Nominal Cruise; (3) Medium Slow Cruise; (4) Slow Cruise; (5) Orbital Ops; (6) Av; (7) ATE (Attitude Estimator) Calibration. These 7 maps cover all spacecraft telemetry modes. The Huygens probe, supplied by
7632-688: The Cassini mission from the three candidates at hand and promising that NASA would commit to the mission as soon as ESA did. At the time, NASA was becoming more sensitive to the strain that had developed between the American and European space programs as a result of European perceptions that NASA had not treated it like an equal during previous collaborations. NASA officials and advisers involved in promoting and planning Cassini–Huygens attempted to correct this trend by stressing their desire to evenly share any scientific and technology benefits resulting from
7791-541: The Cassini orbiter was powered by three GPHS-RTG radioisotope thermoelectric generators , which use heat from the decay of about 33 kg (73 lb) of plutonium-238 (in the form of plutonium dioxide ) to generate direct current electricity via thermoelectrics . The RTGs on the Cassini mission have the same design as those used on the New Horizons , Galileo , and Ulysses space probes, and they were designed to have very long operational lifetimes. At
7950-456: The Cassini orbiter's high-gain radio antenna , with the incorporation of a low-gain antenna (to ensure telecommunications with the Earth for the entire duration of the mission), a compact and lightweight radar , which also used the high-gain antenna and served as a synthetic-aperture radar , a radar altimeter , a radiometer , the radio science subsystem (RSS), and the visible -channel portion VIMS-V of VIMS spectrometer . NASA provided
8109-410: The European Space Agency (ESA) and named after the 17th century Dutch astronomer who first discovered Titan, Christiaan Huygens , scrutinized the clouds, atmosphere, and surface of Saturn's moon Titan in its descent on January 15, 2005. It was designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory down to the surface. The probe system consisted of
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#17327723946918268-414: The European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, including its rings and natural satellites . The Flagship -class robotic spacecraft comprised both NASA's Cassini space probe and ESA's Huygens lander , which landed on Saturn's largest moon, Titan . Cassini was the fourth space probe to visit Saturn and
8427-496: The Huygens probe to Cassini orbiter (and then re-transmitted to Earth) would be largely unreadable. The cause was that the bandwidth of signal processing electronics was too narrow and the anticipated Doppler shift between the lander and the mother craft would put the signals out of the system's range. Thus, Cassini 's receiver would be unable to receive the data from Huygens during its descent to Titan. A work-around
8586-467: The Sun . Venus "overtakes" Earth every 584 days as it orbits the Sun. As it does so, it changes from the "Evening Star", visible after sunset, to the "Morning Star", visible before sunrise. Although Mercury, the other inferior planet, reaches a maximum elongation of only 28° and is often difficult to discern in twilight, Venus is hard to miss when it is at its brightest. Its greater maximum elongation means it
8745-494: The asteroid 2685 Masursky , and Jupiter (December 2000). The probes entered orbit on 1 July 2004, and the mission ended on 15 September 2017, when Cassini flew into Saturn's upper atmosphere in order to prevent any risk of contaminating Saturn's moons, some of which have active environments that could potentially bear life. The mission is widely perceived to have succeeded beyond expectations. Cassini-Huygens has been described by NASA's Planetary Science Division Director as
8904-454: The coast phase between Jupiter and Saturn, it was noticed that "haze" became visible in the pictures taken by the narrow-angle camera of Cassini . This was first seen when a picture of the star Maia in the Pleiades was taken after a routine heating period. 23 July 2002 – In late January, a test was performed to remove the "haze" from the narrow-angle camera lens by heating it. Warming
9063-401: The decreasing eccentricity of Earth's orbit , the minimum distances will become greater over tens of thousands of years. From the year 1 to 5383, there are 526 approaches less than 40 million km (25 million mi); then, there are none for about 60,158 years. While Venus approaches Earth the closest, Mercury is more often the closest to Earth of all planets. Venus has
9222-422: The dissociation of water molecules from ultraviolet radiation. The solar wind then supplies energy that gives some of these ions sufficient velocity to escape Venus's gravity field. This erosion process results in a steady loss of low-mass hydrogen, helium, and oxygen ions, whereas higher-mass molecules, such as carbon dioxide, are more likely to be retained. Atmospheric erosion by the solar wind could have led to
9381-423: The solar wind . Internal heat escapes through active volcanism , resulting in resurfacing instead of plate tectonics . Venus is one of two planets in the Solar System , the other being Mercury , that have no moons . Conditions perhaps favourable for life on Venus have been identified at its cloud layers. Venus may have had liquid surface water early in its history with a habitable environment , before
9540-497: The 16-year period between the Magellan spacecraft and Venus Express visits, with a difference of about 6.5 minutes. Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury 's 176 Earth days — the 116-day figure is close to the average number of days it takes Mercury to slip underneath
9699-646: The ASI/NASA Cassini orbiter, named for the Italian astronomer Giovanni Domenico Cassini , discoverer of Saturn's ring divisions and four of its satellites; and the ESA-developed Huygens probe , named for the Dutch astronomer, mathematician and physicist Christiaan Huygens , discoverer of Titan. The mission was commonly called Saturn Orbiter Titan Probe (SOTP) during gestation, both as
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#17327723946919858-615: The American astronaut Sally Ride , in her influential 1987 report NASA Leadership and America's Future in Space , also examined and approved of the Cassini mission. While Ride's report described the Saturn orbiter and probe as a NASA solo mission, in 1988 the Associate Administrator for Space Science and Applications of NASA, Len Fisk, returned to the idea of a joint NASA and ESA mission. He wrote to his counterpart at ESA, Roger Bonnet, strongly suggesting that ESA choose
10017-578: The ESA $ 500 million (15%), and the ASI $ 160 million (5%). However, these figures are from the press kit which was prepared in October 2000. They do not include inflation over the course of a very long mission, nor do they include the cost of the extended missions. The primary mission for Cassini was completed on July 30, 2008. The mission was extended to June 2010 ( Cassini Equinox Mission). This studied
10176-558: The Earth in its orbit [the number of days of Mercury's synodic orbital period]). One Venusian year is about 1.92 Venusian solar days. To an observer on the surface of Venus, the Sun would rise in the west and set in the east, although Venus's opaque clouds prevent observing the Sun from the planet's surface. Venus may have formed from the solar nebula with a different rotation period and obliquity, reaching its current state because of chaotic spin changes caused by planetary perturbations and tidal effects on its dense atmosphere,
10335-458: The Earth. It took 68 to 84 minutes for radio signals to travel from Earth to the spacecraft, and vice versa. Thus ground controllers could not give "real-time" instructions for daily operations or for unexpected events. Even if response were immediate, more than two hours would have passed between the occurrence of a problem and the reception of the engineers' response by the satellite. Instruments: Cassini ' s instrumentation consisted of:
10494-609: The Orbit Deflection Maneuver (ODM), took Cassini off of a Titan-impacting trajectory and on to a flyby trajectory with the required altitude to receive data from the Huygens probe as it plunged into Titan's thick atmosphere. 31 December 2004 – Cassini ' s flyby of Iapetus occurred at 18:45:37 UTC at an altitude of 122645 kilometers. First raw pictures were available the next day. 14 January 2005 – Huygens entered Titan's atmosphere at 09:06 UTC and landed softly on its surface about two hours later. This
10653-483: The SED (Spin/Eject device), which provided a relative separation speed of 0.35 metres per second (1.1 ft/s) and a spin rate of 7.5 rpm. It returned data to Earth for around 90 minutes, using the orbiter as a relay. This was the first landing ever accomplished in the outer Solar System and the first landing on a moon other than Earth's Moon. At the end of its mission, the Cassini spacecraft executed its "Grand Finale":
10812-551: The Saturn system in detail during the planet's equinox , which happened in August 2009. On February 3, 2010, NASA announced another extension for Cassini , lasting 6 1 ⁄ 2 years until 2017, ending at the time of summer solstice in Saturn's northern hemisphere ( Cassini Solstice Mission). The extension enabled another 155 revolutions around the planet, 54 flybys of Titan and 11 flybys of Enceladus . In 2017, an encounter with Titan changed its orbit in such
10971-487: The Sun and thus receives only 25% of Mercury's solar irradiance , of 2,600 W/m (double that of Earth). Because of its runaway greenhouse effect , Venus has been identified by scientists such as Carl Sagan as a warning and research object linked to climate change on Earth. Venus's atmosphere is rich in primordial noble gases compared to that of Earth. This enrichment indicates an early divergence from Earth in evolution. An unusually large comet impact or accretion of
11130-477: The Sun's 11-year sunspot cycle . The existence of lightning in the atmosphere of Venus has been controversial since the first suspected bursts were detected by the Soviet Venera probes . In 2006–07, Venus Express clearly detected whistler mode waves , the signatures of lightning. Their intermittent appearance indicates a pattern associated with weather activity. According to these measurements,
11289-422: The Sun, and appears at its brightest in the night sky. The planet presents a much larger thin "crescent" in telescopic views as it passes along the near side between Earth and the Sun. Venus displays its largest size and "new phase" when it is between Earth and the Sun (at inferior conjunction). Its atmosphere is visible through telescopes by the halo of sunlight refracted around it. The phases are clearly visible in
11448-792: The VIMS infrared counterpart, as well as the Main Electronic Assembly, which included electronic sub-assemblies provided by CNES of France. On April 16, 2008, NASA announced a two-year extension of the funding for ground operations of this mission, at which point it was renamed the Cassini Equinox Mission. The round of funding was again extended in February 2010 with the Cassini Solstice Mission . The mission consisted of two main elements:
11607-460: The Venusian surface is covered by smooth, volcanic plains, consisting of 70% plains with wrinkle ridges and 10% smooth or lobate plains. Two highland "continents" make up the rest of its surface area, one lying in the planet's northern hemisphere and the other just south of the equator. The northern continent is called Ishtar Terra after Ishtar , the Babylonian goddess of love, and is about
11766-590: The Venusian surface is estimated to be 300–600 million years old. Several lines of evidence point to ongoing volcanic activity on Venus. Sulfur dioxide concentrations in the upper atmosphere dropped by a factor of 10 between 1978 and 1986, jumped in 2006, and again declined 10-fold. This may mean that levels had been boosted several times by large volcanic eruptions. It has been suggested that Venusian lightning (discussed below) could originate from volcanic activity (i.e. volcanic lightning ). In January 2020, astronomers reported evidence that suggests that Venus
11925-431: The areas of net-rising atmospheric motion on Jupiter, [so] the net motion in the zones has to be sinking". Venus Venus is the second planet from the Sun . It is a terrestrial planet and is the closest in mass and size to its orbital neighbour Earth . Venus has by far the densest atmosphere of the terrestrial planets, composed mostly of carbon dioxide with a thick, global sulfuric acid cloud cover. At
12084-496: The asteroid 2685 Masursky , and Jupiter (December 2000). The mission ended on September 15, 2017, when Cassini ' s trajectory took it into Saturn's upper atmosphere and it burned up in order to prevent any risk of contaminating Saturn's moons, which might have offered habitable environments to stowaway terrestrial microbes on the spacecraft. The mission was successful beyond expectations – NASA's Planetary Science Division Director, Jim Green , described Cassini-Huygens as
12243-495: The atmosphere and surface. The spacecraft successfully skimmed the hazy, smoggy atmosphere of Titan, coming within 1,176 kilometers of Titan's surface. The flyby was the closest that any spacecraft has ever come to Titan. The pictures, spectra, and radar data revealed a complex, puzzling surface. The only glitch during the "Titan-A" event involved the CIRS instrument. During playback, the instrument team observed corrupted data. A decision
12402-411: The atmosphere before reaching the ground. Without data from reflection seismology or knowledge of its moment of inertia , little direct information is available about the internal structure and geochemistry of Venus. The similarity in size and density between Venus and Earth suggests that they share a similar internal structure: a core , mantle , and crust . Like that of Earth, the Venusian core
12561-478: The atmosphere of Venus. On 29 January 2013, ESA scientists reported that the ionosphere of Venus streams outwards in a manner similar to "the ion tail seen streaming from a comet under similar conditions." In December 2015, and to a lesser extent in April and May 2016, researchers working on Japan's Akatsuki mission observed bow-shaped objects in the atmosphere of Venus. This was considered direct evidence of
12720-443: The atmosphere. Later research attributed the spectroscopic signal that was interpreted as phosphine to sulphur dioxide, or found that in fact there was no absorption line. Thermal inertia and the transfer of heat by winds in the lower atmosphere mean that the temperature of Venus's surface does not vary significantly between the planet's two hemispheres, those facing and not facing the Sun, despite Venus's slow rotation. Winds at
12879-434: The camera to 4 degrees Celsius (39 degrees Fahrenheit) for eight days produced positive results. Later, the heating was extended to 60 days, and a picture of the star Spica showed an improvement of more than 90 percent compared to before the heating period. On 9 July, a picture showed that the removal procedure was completed successfully, which was announced on 23 July. 10 October 2003 – The Cassini science team announced
13038-517: The carbon dioxide air. Venus's atmosphere could also have a potential thermal habitable zone at elevations of 54 to 48 km, with lower elevations inhibiting cell growth and higher elevations exceeding evaporation temperature. The putative detection of an absorption line of phosphine in Venus's atmosphere, with no known pathway for abiotic production, led to speculation in September 2020 that there could be extant life currently present in
13197-628: The closest approach to the Moon at 377,000 km, and took a series of calibration images. The spacecraft flew past Earth at a distance of 1,171 kilometers (728 mi), passing most closely above the eastern South Pacific at 23°30′S 128°30′W / 23.5°S 128.5°W / -23.5; -128.5 . Cassini received a 5.5-kilometer-per-second (about 12,000-mile-per-hour) boost in velocity. 23 January 2000 – flyby of Asteroid 2685 Masursky around 10:00 UTC. Cassini took images 5 to 7 hours before at 1.6 million km distance and estimated
13356-408: The closest between any two Solar System planets, approaching each other in synodic periods of 1.6 years. Venus and Earth have the lowest difference in gravitational potential of any pair of Solar System planets. This allows Venus to be the most accessible destination and a useful gravity assist waypoint for interplanetary flights from Earth. Venus figures prominently in human culture and in
13515-412: The communications antenna and other special transmitters (an S-band transmitter and a dual-frequency K a -band system) was also used to make observations of the atmospheres of Titan and Saturn and to measure the gravity fields of the planet and its satellites. The HSP channel is designed to observe starlight that passes through Saturn's rings (known as stellar occultations) in order to understand
13674-420: The core because the bottom of the liquid layer is much higher in temperature than the top. On Venus, a global resurfacing event may have shut down plate tectonics and led to a reduced heat flux through the crust. This insulating effect would cause the mantle temperature to increase, thereby reducing the heat flux out of the core. As a result, no internal geodynamo is available to drive a magnetic field. Instead,
13833-552: The crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust. Venusian craters range from 3 to 280 km (2 to 174 mi) in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed so much by the atmosphere that they do not create an impact crater. Incoming projectiles less than 50 m (160 ft) in diameter will fragment and burn up in
13992-619: The darker and brighter albedo features on the surface do represent different materials. But in contrast to expectation, the icy regions seem to be darker than the areas where other (possibly organic) matter is mixed in with the ice. 16 August 2004 – Mission scientists announce the discovery of two new moons of Saturn, and with it the successful start of one of the programs of Cassini : Locating small and yet unknown moons. Later named " Methone " (S/2004 S 1) and " Pallene " (S/2004 S 2), these objects are small compared to other moons and they orbit between Mimas and Enceladus . 23 August 2004 – At
14151-418: The data to make more concrete conclusions. 16 June 2004 – TCM-21 took place with a 38-second main engine burn. It was planned as the last correction of the trajectory of Cassini before SOI. A few days later the final TCM-22 tentatively scheduled for 21 June was canceled. 1 July 2004 – The Saturn Orbit Insertion burn was successfully executed. At 7:11 p.m. PDT (10:11 p.m. EDT), Cassini crossed
14310-412: The daytime with overcast clouds". Strong 300 km/h (185 mph) winds at the cloud tops go around Venus about every four to five Earth days. Winds on Venus move at up to 60 times the speed of its rotation, whereas Earth's fastest winds are only 10–20% rotation speed. The surface of Venus is effectively isothermal ; it retains a constant temperature not only between the two hemispheres but between
14469-540: The daytime. French emperor Napoleon Bonaparte once witnessed a daytime apparition of the planet while at a reception in Luxembourg . Another historical daytime observation of the planet took place during the inauguration of the American president Abraham Lincoln in Washington, D.C., on 4 March 1865. A transit of Venus is the appearance of Venus in front of the Sun, during inferior conjunction . Since
14628-507: The dynamics of the ring system, because their orbits are close enough that they interact with each other in a chaotic manner. They have a history of defying predictions of their orbits. One of Cassini's missions will be to monitor the movements of these bodies closely. 18 May 2004 – Cassini entered the Saturn system. The gravitational pull of Saturn began to overtake the influence of the Sun. 20 May 2004 – The first picture of Titan with better resolution than any Earth-based observation
14787-578: The early solar system orbital dynamics have shown that the eccentricity of the Venus orbit may have been substantially larger in the past, reaching values as high as 0.31 and possibly impacting early climate evolution. All planets in the Solar System orbit the Sun in an anticlockwise direction as viewed from above Earth's north pole. Most planets rotate on their axes in an anticlockwise direction, but Venus rotates clockwise in retrograde rotation once every 243 Earth days—the slowest rotation of any planet. This Venusian sidereal day lasts therefore longer than
14946-529: The end of its operational lifespan. The atmospheric entry of Cassini ended the mission, but analysis of the returned data will continue for many years. Scientists and individuals from 27 countries made up the joint team responsible for designing, building, flying and collecting data from the Cassini orbiter and the Huygens probe . NASA 's Jet Propulsion Laboratory in the United States, where
15105-611: The end of the nominal 11-year Cassini mission, they were still able to produce 600 to 700 watts of electrical power. (Leftover hardware from the Cassini RTG Program was modified and used to power the New Horizons mission to Pluto and the Kuiper belt , which was designed and launched later. ) Power distribution was accomplished by 192 solid-state power switches , which also functioned as circuit breakers in
15264-442: The equator and the poles. Venus's minute axial tilt —less than 3°, compared to 23° on Earth—also minimizes seasonal temperature variation. Altitude is one of the few factors that affect Venusian temperatures. The highest point on Venus, Maxwell Montes , is therefore the coolest point on Venus, with a temperature of about 655 K (380 °C; 715 °F) and an atmospheric pressure of about 4.5 MPa (45 bar). In 1995,
15423-424: The event of an overload condition. The switches used MOSFETs that featured better efficiency and a longer lifetime as compared to conventional switches, while at the same time eliminating transients . However, these solid-state circuit breakers were prone to erroneous tripping (presumably from cosmic rays), requiring them to reset and causing losses in experimental data. To gain momentum while already in flight,
15582-415: The existence of perhaps the largest stationary gravity waves in the solar system. Venus orbits the Sun at an average distance of about 0.72 AU (108 million km ; 67 million mi ), and completes an orbit every 224.7 days. Although all planetary orbits are elliptical , Venus's orbit is currently the closest to circular, with an eccentricity of less than 0.01. Simulations of
15741-621: The first observation-based estimate of 3,500 km. The principal difference between the two planets is the lack of evidence for plate tectonics on Venus, possibly because its crust is too strong to subduct without water to make it less viscous . This results in reduced heat loss from the planet, preventing it from cooling and providing a likely explanation for its lack of an internally generated magnetic field . Instead, Venus may lose its internal heat in periodic major resurfacing events. In 1967, Venera 4 found Venus's magnetic field to be much weaker than that of Earth. This magnetic field
15900-400: The first soft landing on another planet by Venera 7 in 1970. These probes demonstrated the extreme surface conditions, an insight that has informed predictions about global warming on Earth. This finding ended the theories and then popular science fiction about Venus being a habitable or inhabited planet. Venus is one of the four terrestrial planets in the Solar System, meaning that it
16059-492: The first to enter its orbit, where it stayed from 2004 to 2017. The two craft took their names from the astronomers Giovanni Cassini and Christiaan Huygens . Launched aboard a Titan IVB/Centaur on October 15, 1997, Cassini was active in space for nearly 20 years, with 13 years spent orbiting Saturn and studying the planet and its system after entering orbit on July 1, 2004. The voyage to Saturn included flybys of Venus (April 1998 and July 1999), Earth (August 1999),
16218-474: The following 200 years , but most were determined to be stars in the vicinity. Alex Alemi's and David Stevenson 's 2006 study of models of the early Solar System at the California Institute of Technology shows Venus likely had at least one moon created by a huge impact event billions of years ago. About 10 million years later, according to the study, another impact reversed
16377-429: The heat from the core is reheating the crust. One possibility is that Venus has no solid inner core, or that its core is not cooling, so that the entire liquid part of the core is at approximately the same temperature. Another possibility is that its core has already been completely solidified. The state of the core is highly dependent on the concentration of sulphur , which is unknown at present. Another possibility
16536-472: The history of astronomy. Orbiting inferiorly (inside of Earth's orbit), it always appears close to the Sun in Earth's sky, as either a "morning star" or an "evening star". While this is also true for Mercury , Venus appears more prominent, since it is the third brightest object in Earth's sky after the Moon and the Sun. In 1961, Venus became the target of the first interplanetary flight, Venera 1 , followed by many essential interplanetary firsts , such as
16695-399: The hypothesis of a spin-orbit resonance with Earth has been discounted. Venus has no natural satellites. It has several trojan asteroids : the quasi-satellite 524522 Zoozve and two other temporary trojans, 2001 CK 32 and 2012 XE 133 . In the 17th century, Giovanni Cassini reported a moon orbiting Venus, which was named Neith and numerous sightings were reported over
16854-402: The lightning rate is at least half that on Earth, however other instruments have not detected lightning at all. The origin of any lightning remains unclear, but could originate from clouds or Venusian volcanoes . In 2007, Venus Express discovered that a huge double atmospheric polar vortex exists at the south pole. Venus Express discovered, in 2011, that an ozone layer exists high in
17013-492: The loss of most of Venus's water during the first billion years after it formed. However, the planet may have retained a dynamo for its first 2–3 billion years, so the water loss may have occurred more recently. The erosion has increased the ratio of higher-mass deuterium to lower-mass hydrogen in the atmosphere 100 times compared to the rest of the solar system. Venus has a dense atmosphere composed of 96.5% carbon dioxide , 3.5% nitrogen—both exist as supercritical fluids at
17172-470: The lowest gravitational potential difference to Earth than any other planet, needing the lowest delta-v to transfer between them. Tidally Venus exerts the third strongest tidal force on Earth, after the Moon and the Sun, though significantly less. To the naked eye , Venus appears as a white point of light brighter than any other planet or star (apart from the Sun). The planet's mean apparent magnitude
17331-496: The material's radioactive decay was turned into electricity. Huygens was supported by Cassini during cruise, but used chemical batteries when independent. The probe contained a DVD with more than 616,400 signatures from citizens in 81 countries, collected in a public campaign. Until September 2017 the Cassini probe continued orbiting Saturn at a distance of between 8.2 and 10.2 astronomical units (1.23 × 10 and 1.53 × 10 km ; 760,000,000 and 950,000,000 mi ) from
17490-522: The mission. In part, this newfound spirit of cooperation with Europe was driven by a sense of competition with the Soviet Union , which had begun to cooperate more closely with Europe as ESA drew further away from NASA. Late in 1988, ESA chose Cassini–Huygens as its next major mission and the following year the program received major funding in the US. The collaboration not only improved relations between
17649-550: The new course will bring Cassini very close to Titan on its next flyby. 14 September 2004 – Final checks of the Huygens lander were completed successfully. 26 October 2004 – The second flyby of Titan (called "Titan-A") was successfully executed. Data started to arrive at the JPL mission center at 01:30 UTC, 27 October, and included the highest resolution pictures ever taken of the surface of that moon. Additionally, first high-resolution infra-red spectra and pictures were taken from
17808-560: The new moon's presence and its orbital distance from Saturn after last July's sighting of a set of peculiar spiky and wispy features in the Keeler gap's outer edge. 14 July 2005 – The closest flyby of Enceladus with a distance of 175 km (109 mi) was executed successfully. First raw pictures were published. 7 September 2005 – Flyby of Titan at a distance of 1,075 km (668 mi), data gathered partially lost due to software problem. 26 September 2005 – Flyby of Hyperion at
17967-404: The orbit of Venus is slightly inclined relative to Earth's orbit, most inferior conjunctions with Earth, which occur every synodic period of 1.6 years, do not produce a transit of Venus above Earth. Consequently, Venus transits above Earth only occur when an inferior conjunction takes place during some days of June or December, the time where the orbits of Venus and Earth cross a straight line with
18126-505: The orbiter was assembled, managed the mission. The European Space Research and Technology Centre developed Huygens . The centre's prime contractor, Aérospatiale of France (part of Thales Alenia Space from 2005), assembled the probe with equipment and instruments supplied by many European countries (including Huygens ' batteries and two scientific instruments from the United States). The Italian Space Agency (ASI) provided
18285-547: The orbiter. With the launch vehicle adapter and 3,132 kg (6,905 lb) of propellants at launch, the spacecraft had a mass of 5,600 kg (12,300 lb). The Cassini spacecraft was 6.8 meters (22 ft) high and 4 meters (13 ft) wide. Spacecraft complexity was increased by its trajectory (flight path) to Saturn, and by the ambitious science at its destination. Cassini had 1,630 interconnected electronic components , 22,000 wire connections, and 14 kilometers (8.7 mi) of cabling. The core control computer CPU
18444-405: The planet underwent a global resurfacing event 300–600 million years ago, followed by a decay in volcanism. Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens
18603-421: The planet's spin direction and the resulting tidal deceleration caused the Venusian moon gradually to spiral inward until it collided with Venus. If later impacts created moons, these were removed in the same way. An alternative explanation for the lack of satellites is the effect of strong solar tides, which can destabilize large satellites orbiting the inner terrestrial planets. The orbital space of Venus has
18762-581: The planet's surface with a density 6.5% that of water —and traces of other gases including sulphur dioxide . The mass of its atmosphere is 92 times that of Earth's, whereas the pressure at its surface is about 93 times that at Earth's—a pressure equivalent to that at a depth of nearly 1 km ( 5 ⁄ 8 mi) under Earth's ocean surfaces. The density at the surface is 65 kg/m (4.1 lb/cu ft), 6.5% that of water or 50 times as dense as Earth's atmosphere at 293 K (20 °C; 68 °F) at sea level. The CO 2 -rich atmosphere generates
18921-616: The potential environmental impact a launch failure might have (because of its plutonium power source) attempted to derail it through protests and lawsuits until and past its 1997 launch. The spacecraft was planned to be the second three-axis stabilized, RTG -powered Mariner Mark II , a class of spacecraft developed for missions beyond the orbit of Mars , after the Comet Rendezvous Asteroid Flyby (CRAF) mission, but budget cuts and project rescopings forced NASA to terminate CRAF development to save Cassini . As
19080-414: The probe itself which descended to Titan, and the probe support equipment (PSE) which remained attached to the orbiting spacecraft. The PSE includes electronics that track the probe, recover the data gathered during its descent, and process and deliver the data to the orbiter that transmits it to Earth. The core control computer CPU was a redundant MIL-STD-1750A control system. The data were transmitted by
19239-537: The probe to collide with the Earth, NASA's complete environmental impact study estimated that, in the worst case (with an acute angle of entry in which Cassini would gradually burn up), a significant fraction of the 33 kg of nuclear fuel inside the RTGs would have been dispersed into the Earth's atmosphere so that up to five billion people (i.e. almost the entire terrestrial population) could have been exposed, causing up to an estimated 5,000 additional cancer deaths over
19398-411: The results of a test of Einstein 's theory of gravity , using radio signals from the Cassini probe. The researchers observed a frequency shift in the radio waves to and from the space craft, as those signals traveled close to the Sun . Past tests were in agreement with the theoretical predictions with an accuracy of one part in one thousand. The Cassini experiment improved this to about 20 parts in
19557-425: The ring plane between Saturn's F and G rings. Its antenna was oriented forward acting as a shield against small ring particles. At 7:36 p.m. PDT (10:36 p.m. EDT), the spacecraft began a critical 96-minute main engine burn to cut its velocity by 626 meters per second and permit a 0.02 x 9 million kilometer Saturn orbit. Right after that burn, pictures of the rings were taken and sent back to mission scientist as
19716-477: The same disturbance visible throughout the 1990s in Hubble Space Telescope images. 12 March 2004 – Pictures taken on 23 February do show a feature discovered by Voyager : Clumps in the outer "F"-ring. What could not be ascertained at the time was the exact lifetime of these clumps, and it is hoped that Cassini will provide conclusive data about this question. The first set of pictures shows
19875-418: The scale of centimeters. 10 May 2005 – At the beginning of a period of focussed observation of the ring system of Saturn, slated to take until September, mission scientists announced the discovery of a new moon in the " Keeler gap " inside the "A" ring. Provisionally named S/2005 S 1 and later named Daphnis , it was first seen in a time-lapse sequence of images taken on 1 May. Imaging scientists had predicted
20034-400: The six-month flyby. It produced the most detailed global color portrait of the planet yet (see image at right), in which the smallest visible features are approximately 60 km (37 mi) across. A major finding of the flyby, announced on March 6, 2003, was of Jupiter's atmospheric circulation. Dark "belts" alternate with light "zones" in the atmosphere, and scientists had long considered
20193-479: The size of Australia. Maxwell Montes , the highest mountain on Venus, lies on Ishtar Terra. Its peak is 11 km (7 mi) above the Venusian average surface elevation. The southern continent is called Aphrodite Terra , after the Greek mythological goddess of love, and is the larger of the two highland regions at roughly the size of South America. A network of fractures and faults covers much of this area. There
20352-528: The size of the hot spots could not be measured, but are likely to have been in the 800–1,100 K (527–827 °C; 980–1,520 °F) range, relative to a normal temperature of 740 K (467 °C; 872 °F). In 2023, scientists reexamined topographical images of the Maat Mons region taken by the Magellan orbiter. Using computer simulations, they determined that the topography had changed during an 8-month interval, and concluded that active volcanism
20511-484: The southern latitudes merge during a period from 19 to 20 March. Both storms had a diameter of about 1,000 km (620 mi) before they merged. 15 April 2004 – NASA announced that two moons discovered by Voyager 1 were sighted again by Cassini in pictures taken on 10 March: Prometheus and Pandora . These are no ordinary moons, but their gravitational effects on the "F" ring led scientists to call them " shepherd moons ". They fascinate all researchers interested in
20670-411: The space probe with enough momentum to travel all the way out to the asteroid belt , while the Sun's gravity pulled the space probe back into the inner Solar System. On August 18, 1999, at 03:28 UTC, the craft made a gravitational-assist flyby of the Earth. One hour and 20 minutes before closest approach, Cassini made its closest approach to the Earth's Moon at 377,000 kilometers, and it took
20829-518: The spacecraft approached within 19,980 kilometers (12,400 miles) from the cloud tops. Scientists were surprised by the clarity and detail of the pictures and will be poring over them for quite some time. "We won't see the whole puzzle, only pieces, but what we are seeing is dramatic," said Dr. Carolyn Porco , Cassini imaging team leader, Space Science Institute, Boulder, Colo. "The images are mind-boggling, just mind-boggling. I've been working on this mission for 14 years and I shouldn't be surprised, but it
20988-586: The spacecraft on course for its second Venus flyby in 1999. The engine burn slowed the spacecraft by close to 450 meters per second (about 1,006 miles per hour) relative to the Sun. Cassini ' s speed went from 67,860 kilometers per hour (42,168 miles per hour) at the start of the maneuver to 66,240 kilometers per hour (41,161 miles per hour) at the end of the engine firing. 24 June 1999 13:30 PDT – Gravity-assisted flyby of Venus at 623 km. 18 August 1999 03:28 UTC − Gravity-assisted flyby of Earth. An hour 20 minutes before closest approach, Cassini made
21147-410: The strongest greenhouse effect in the Solar System, creating surface temperatures of at least 735 K (462 °C; 864 °F). This makes the Venusian surface hotter than Mercury 's, which has a minimum surface temperature of 53 K (−220 °C; −364 °F) and maximum surface temperature of 700 K (427 °C; 801 °F), even though Venus is nearly twice Mercury's distance from
21306-497: The structure and optical depth of the rings. Stellar occultation data from both the HSP and FUV channels confirmed the existence of water vapor plumes at the south pole of Enceladus, as well as characterized the composition of the plumes. Because of Saturn's distance from the Sun, solar arrays were not feasible as power sources for this space probe. To generate enough power, such arrays would have been too large and too heavy. Instead,
21465-410: The subsequent decades (0.0005 per cent, i.e. a fraction 0.000005, of a billion cancer deaths expected anyway from other causes; the product is incorrectly calculated elsewhere as 500,000 deaths). However, the chance of this happening were estimated to be less than one in one million, i.e. a chance of one person dying (assuming 5,000 deaths) as less than 1 in 200. NASA's risk analysis to use plutonium
21624-443: The sunlight that falls on them back into space, and since they cover the whole planet they prevent visual observation of Venus's surface. The permanent cloud cover means that although Venus is closer than Earth to the Sun, it receives less sunlight on the ground, with only 10% of the received sunlight reaching the surface, resulting in average daytime levels of illumination at the surface of 14,000 lux , comparable to that on Earth "in
21783-459: The surface are slow, moving at a few kilometres per hour, but because of the high density of the atmosphere at the surface, they exert a significant amount of force against obstructions, and transport dust and small stones across the surface. This alone would make it difficult for a human to walk through, even without the heat, pressure, and lack of oxygen. Above the dense CO 2 layer are thick clouds, consisting mainly of sulfuric acid , which
21942-413: The surface it has a mean temperature of 737 K (464 °C; 867 °F) and a pressure 92 times that of Earth's at sea level. These extreme conditions compress carbon dioxide into a supercritical state at Venus's surface. Internally, Venus has a core , mantle , and crust . Venus lacks an internal dynamo, and its weakly induced magnetosphere is caused by atmospheric interactions with
22101-503: The surface. After a period of 600 million to several billion years, solar forcing from rising luminosity of the Sun and possibly large volcanic resurfacing caused the evaporation of the original water and the current atmosphere. A runaway greenhouse effect was created once a critical level of greenhouse gases (including water) was added to its atmosphere. Although the surface conditions on Venus are no longer hospitable to any Earth-like life that may have formed before this event, there
22260-420: The surrounding basaltic plains measured by Venus Express and Magellan , indicating a different, possibly a more felsic , mineral assemblage. The mechanism to generate a large amount of felsic crust usually requires the presence of water ocean and plate tectonics , implying that habitable condition had existed on early Venus with large bodies of water at some point. However, the nature of tessera terrains
22419-449: The trajectory of the Cassini mission included several gravitational slingshot maneuvers: two fly-by passes of Venus , one more of the Earth, and then one of the planet Jupiter . The terrestrial flyby was the final instance when the probe posed any conceivable danger to human beings. The maneuver was successful, with Cassini passing by 1,171 km (728 mi) above the Earth on August 18, 1999. Had there been any malfunction causing
22578-622: The two space programs but also helped Cassini–Huygens survive congressional budget cuts in the United States. Cassini–Huygens came under fire politically in both 1992 and 1994, but NASA successfully persuaded the United States Congress that it would be unwise to halt the project after ESA had already poured funds into development because frustration on broken space exploration promises might spill over into other areas of foreign relations. The project proceeded politically smoothly after 1994, although citizens' groups concerned about
22737-410: The zones, with their pale clouds, to be areas of upwelling air, partly because many clouds on Earth form where air is rising. But analysis of Cassini imagery showed that individual storm cells of upwelling bright-white clouds, too small to see from Earth, pop up almost without exception in the dark belts. According to Anthony Del Genio of NASA's Goddard Institute for Space Studies , "the belts must be
22896-605: Was a redundant system using the MIL-STD-1750A instruction set architecture . The main propulsion system consisted of one prime and one backup R-4D bipropellant rocket engine. The thrust of each engine was 490 N (110 lbf ) and the total spacecraft delta-v was 2,352 m/s (5,260 mph). Smaller monopropellant rockets provided attitude control. Cassini was powered by 32.7 kg (72 lb) of nuclear fuel, mainly plutonium dioxide (containing 28.3 kg (62 lb) of pure plutonium ). The heat from
23055-442: Was a subject of speculation until some of its secrets were revealed by planetary science in the 20th century. Venera landers in 1975 and 1982 returned images of a surface covered in sediment and relatively angular rocks. The surface was mapped in detail by Magellan in 1990–91. The ground shows evidence of extensive volcanism, and the sulphur in the atmosphere may indicate that there have been recent eruptions. About 80% of
23214-451: Was confirmed by the reception of the carrier wave emitted by the probe during its descent and touchdown. At 16:19 UTC, the Cassini orbiter started to relay the scientific data received from the probe to Earth. The first picture was released at 19:45 UTC, showing a view from about 16 km above the surface. A second picture taken from the probe at rest on the surface was released a short time later. 15 February 2005 – Cassini executed
23373-479: Was designed to land on Saturn's largest moon, Titan . Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. The craft were named after astronomers Giovanni Cassini and Christiaan Huygens . Launched aboard a Titan IVB/Centaur on 15 October 1997, Cassini had a nearly 20-year life span, with 13 of these years spent orbiting Saturn. The voyage to Saturn included flybys of Venus (April 1998 and June 1999), Earth (August 1999),
23532-524: Was destroyed. The atmospheric entry of Cassini effectively ended the mission, although data analysis and production is still ongoing. 15 October 1997 01:43 Pacific Daylight Time (PDT) – Cassini launched at 08:43 UTC inside Titan IVB / Centaur rocket at Cape Canaveral . 26 April 1998 06:52 PDT – Gravity-assisted flyby of Venus at 284 km, receiving a boost in speed of about 7 kilometers per second. 3 December 1998 22:06 PST – Cassini fired its main rocket engine for 90 minutes, setting
23691-478: Was developed from the ground up, due to the spacecraft using a more modern set of computers than previous missions. Therefore, Cassini was the first spacecraft to adopt mini-packets to reduce the complexity of the Telemetry Dictionary, and the software development process led to the creation of a Telemetry Manager for the mission. There were around 1088 channels (in 67 mini-packets) assembled in
23850-407: Was extended a second and final time with the Cassini Solstice Mission , lasting another seven years until September 15, 2017, on which date Cassini was de-orbited to burn up in Saturn's upper atmosphere. The Huygens module traveled with Cassini until its separation from the probe on December 25, 2004; Huygens landed by parachute on Titan on January 14, 2005. The separation was facilitated by
24009-409: Was extended a second and final time with the Cassini Solstice Mission , lasting until the spacecraft's destruction in September 2017. The Huygens module traveled with Cassini until its separation from the probe on 25 December 2004; it was successfully landed by parachute on Titan on 14 January 2005. It successfully returned data to Earth for around 90 minutes, using the orbiter as a relay. This
24168-466: Was found to recover the mission. The trajectory of Cassini was altered to reduce the line of sight velocity and therefore the doppler shift. Cassini' s subsequent trajectory was identical to the previously planned one, although the change replaced two orbits prior to the Huygens mission with three, shorter orbits. The Cassini space probe performed two gravitational-assist flybys of Venus on April 26, 1998, and June 24, 1999. These flybys provided
24327-434: Was made to power the instrument off to reboot it. CIRS was powered back on within 24 hours and returned to its nominal state. 23 November 2004 – The last in-flight checks of the Huygens probe before separation were completed successfully. 13 December 2004 – The "Titan-B" flyby was executed successfully. 25 December 2004 – Huygens probe separated from Cassini orbiter at 02:00 UTC. 27 December – NASA published
24486-526: Was made up of a two-stage Titan IV booster rocket , two strap-on solid rocket engines , the Centaur upper stage, and a payload enclosure, or fairing. The total cost of this scientific exploration mission was about US$ 3.26 billion , including $ 1.4 billion for pre-launch development, $ 704 million for mission operations, $ 54 million for tracking and $ 422 million for the launch vehicle. The United States contributed $ 2.6 billion (80%),
24645-514: Was mainly designed to change Cassini's velocity by 34.7 m/s (78 mph), setting up a flyby of the moon Phoebe 11 June. 11 June 2004 – Cassini flew by the moon Phoebe at 19:33 UT in Spacecraft Event Time at 2068 kilometers distance. All of the eleven onboard instruments operated as expected and all data was acquired. Scientists plan to use the data to create global maps of the cratered moon, and to determine Phoebe's composition, mass and density. It took scientists several days to pore over
24804-470: Was publicly criticized by Michio Kaku on the grounds that casualties, property damage, and lawsuits resulting from a possible accident, as well as the potential use of other energy sources, such as solar and fuel cells, were underestimated. The Cassini spacecraft was capable of transmitting in several different telemetry formats. The telemetry subsystem is perhaps the most important subsystem, because without it there could be no data return. The telemetry
24963-485: Was released. It was taken 5 May from a distance of 29.3 million kilometers (18.2 million miles). 27 May 2004 – TCM-20, the Phoebe approach TCM (Trajectory Correction Maneuver) was executed at 22:26:00 UTC. This was a 5-minute and 56 second burn of the main engine, which was not used since December 1998. It therefore doubled as a "dress rehearsal" for the 96 minute burn during "Saturn Orbit Insertion" (SOI). However, TCM-20
25122-458: Was the cause. Almost a thousand impact craters on Venus are evenly distributed across its surface. On other cratered bodies, such as Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, whereas on Earth it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates
25281-400: Was the first landing ever accomplished in the outer Solar System and the first landing on a moon other than our own. At the end of its mission, the Cassini spacecraft executed the "Grand Finale" of its mission: several risky passes through the gaps between Saturn and Saturn's inner rings. The purpose of this phase was to maximize Cassini 's scientific outcome before the spacecraft
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