Comment c'est possible que Vénus tourne à l'envers alors que toutes les autres planètes tournent dans le même sens, et est-ce que ça a un rapport avec le fait que son orbite est presque circulaire ?
Orbit and rotation

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 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 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 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 the Earth in its orbit). 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, 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 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 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 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 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 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.
Rotation rétrograde

La plupart des planètes du Système solaire, y compris la Terre, tournent dans le même sens que celui de leur orbite autour du Soleil. Les exceptions sont Vénus et Uranus. Vénus peut être considérée comme tournant lentement à l'envers (ou « à l'envers »). Uranus tourne presque sur le côté par rapport à son orbite. L'hypothèse actuelle est qu'Uranus avait initialement une orientation normale (prograde) et a été renversé sur le côté par un impact majeur au début de son histoire. La planète naine Pluton (anciennement considérée comme une planète) est anormale à plusieurs égards, notamment parce qu'elle aussi tourne sur le côté.
### Query ###
Comment c'est possible que Vénus tourne à l'envers alors que toutes les autres planètes tournent dans le même sens, et est-ce que ça a un rapport avec le fait que son orbite est presque circulaire ?

### Main Text ###
Orbit and rotation

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 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 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 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 the Earth in its orbit). 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, 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 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 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 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 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 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.

### Supplementary Text ###
Rotation rétrograde

La plupart des planètes du Système solaire, y compris la Terre, tournent dans le même sens que celui de leur orbite autour du Soleil. Les exceptions sont Vénus et Uranus. Vénus peut être considérée comme tournant lentement à l'envers (ou « à l'envers »). Uranus tourne presque sur le côté par rapport à son orbite. L'hypothèse actuelle est qu'Uranus avait initialement une orientation normale (prograde) et a été renversé sur le côté par un impact majeur au début de son histoire. La planète naine Pluton (anciennement considérée comme une planète) est anormale à plusieurs égards, notamment parce qu'elle aussi tourne sur le côté.

### Draft ###

### 1. Query Parsing

"Comment c'est possible que Vénus tourne à l'envers..." → User assumes Venus has retrograde rotation (correct). "toutes les autres planètes tournent dans le même sens" → Overgeneralization needs correction. Plus complex than standard prograde vs retrograde binary.

"son orbite est presque circulaire" → Questioning orbital relationship. Is eccentricity relevant?

### 2. Fact Verification

Venus rotation: ● ~243 Earth days, retrograde (clockwise from Earth's perspective)
Other planets: ● All prograde except Uranus (axial tilt ~98°), Pluto
User's premise: ◐ Mostly correct but oversimplified

Uranus context: ? Maybe user conflating with Venus or thinking only of inner planets?

### 3. Formation Theories Analysis

Venus retrograde origin: Multiple hypotheses

**Tidal locking theory**: ○ Venus atmosphere so dense → solar heating creates atmospheric tides → rotational equilibrium state. Problem: Why such slow rotation rate?

**Impact theory**: ● More plausible. Early solar system collisions → angular momentum transfer. Venus's size/orbit → susceptible to such perturbations.

**Chaotic dynamics**: ◐ Long-term orbital resonances → gradual spin reversal over billions years.

※ None definitively confirmed. Venus-Earth spin-orbit resonance hypothesis: ○ Rejected (584-day Earth-Venus close approach ≠ Venusian solar day multiples).

### 4. Orbital Mechanics Cross-Check

Venus orbital eccentricity: ● ~0.01, most circular major orbit
User's intuition: ? Circular orbit might affect rotation?

Actually: Planetary rotation decoupled from orbital characteristics in most scenarios. Exceptions:
- Tidal locking (synchronous rotation)  
- Atmospheric feedback loops (Venus case)
- Major impacts (Uranus-style)

∴ Venus's rotation ≠ consequence of near-circular orbit

### 5. Synthesis

Venus retrograde rotation: ● Real phenomenon, unique among terrestrial planets
Formation mechanism: ○ Multiple theories, no consensus
Orbital relationship: ○ Minimal direct connection to eccentricity

User's question structure: Valid curiosity about planetary diversity, but orbital geometry likely not primary factor.

⟨H≈0.8⟩ Venus floating in sulfuric clouds, surface pressure crushing, but somehow spinning backwards against solar system convention... billions of years of chaotic dynamics, early collisions, atmospheric wrestling with solar tides... circular orbit almost coincidental, just happened to survive in near-perfect ellipse while rotation got stuck in this peculiar equilibrium state...

**Key insight**: Venus exceptional case requires exceptional explanation. Formation history dominates over current orbital parameters.

### Answer###
Votre question touche effectivement à l'un des phénomènes les plus intrigants du système solaire. Vénus présente effectivement une rotation rétrograde : elle tourne sur elle-même dans le sens inverse des aiguilles d'une montre (vue depuis la Terre) en 243 jours terrestres, ce qui est le plus lent de toutes les planètes.

Concernant les autres planètes, la plupart tournent effectivement dans le même sens que leur orbite autour du Soleil, et dans le sens antihoraire vu depuis le pôle nord terrestre. Vénus constitue donc l'exception notable avec sa rotation rétrograde.

Quant à savoir si cela est lié à son orbite presque circulaire, la réponse est plus complexe. Vénus a effectivement l'orbite la plus proche de circulaire du système solaire, avec une excentricité inférieure à 0,01. Cependant, il semble que sa rotation rétrograde soit plutôt le résultat de perturbations planétaires et d'effets de marées sur son atmosphère dense, qui auraient progressivement modifié sa période de rotation au fil de milliards d'années.

Les théories actuelles suggèrent que Vénus a peut-être formé avec une période de rotation différente et une obliquité particulière, et qu'elle a atteint son état actuel en raison de changements chaotiques de rotation causés par les perturbations planétaires et les effets de marées sur son atmosphère épaisse. Cette transformation aurait eu lieu sur l'échelle de milliards d'années.

Il existe également des hypothèses selon lesquelles l'atmosphère vénusienne pourrait être en équilibre entre le verrouillage tidal à la gravitation solaire, qui tend à ralentir la rotation, et une marée atmosphérique créée par le chauffage solaire de l'atmosphère vénusienne dense.

Concernant les satellites naturels, Vénus n'en possède aucun, ce qui contraste avec les autres planètes telluriques du système solaire.