Venus and Mercury March 2025
Mercury Background: Mercury is the first planet from the Sun and the smallest in the Solar System.
It is a terrestrial planet with a heavily cratered surface due to overlapping impact events. These features are well preserved since the planet has no geological activity and an extremely
tenuous atmosphere called an exosphere.
Despite being the smallest planet in the Solar System with a mean diameter of 4,880 km (3,030 mi), 38% of that of Earth,
Mercury is dense enough to have roughly the same surface gravity as Mars.
Mercury has a dynamic magnetic field with a strength about 1% of that of Earth's and has no natural satellites.
According to current models, Mercury may have a solid silicate crust and mantle overlying a solid outer core, a deeper liquid core layer, and a solid inner core.
Having almost no atmosphere to retain heat, Mercury has surface temperatures that change wildly during the day, ranging from 100 K (−173 °C; −280 °F) at night to 700 K (427 °C; 800 °F)
during sunlight across the equator regions.
At Mercury's poles there are large reservoirs of water ices that are never exposed to direct sunlight, which has an estimated mass of about 0.025–0.25% the Antarctic ice sheet.
Because Mercury is very close to the Sun, the intensity of sunlight on its surface is between 4.59 and 10.61 times the Sun's typical energy received by the Earth: the solar constant.
Mercury orbits the Sun in a 3:2 spin–orbit resonance, meaning that relative to the background stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun.
Counterintuitively, due to Mercury's slow rotation, an observer on the planet would see only one Mercurian solar day (176 Earth days) every two Mercurian solar years (88 Earth days each).
Mercury's axis has the smallest tilt of any of the Solar System's planets, about 1⁄30 of a degree, and its orbital eccentricity is the largest of all known planets in the Solar System.
It is named after the Roman god Mercurius (Mercury), god of commerce, communication and the messenger of gods.
Like Venus, Mercury orbits the Sun within Earth's orbit, making it appear in Earth's sky only as a "morning star" or "evening star" that is relatively close to the Sun.
Mercury can only be viewed about 45 minutes after sunset of ~45 minutes before sunrise. Mercury appears as a 'star' just above the horizon
Venus Background: The ancient Romans could easily see seven bright objects in the sky: the Sun, the Moon, and the five brightest planets: Mercury, Venus, Mars, Jupiter, and Saturn.
They named the objects after their most important gods. Venus is named for the ancient Roman goddess of love and beauty, who was known as Aphrodite to the ancient Greeks.
Most features on Venus are named for women. It’s the only planet named after a female god.
Venus is the second planet from the Sun, and Earth's closest planetary neighbor.
Venus is the third brightest object in the sky after the Sun and Moon. Venus spins slowly in the opposite direction from most planets.
Venus is similar in structure and size to Earth, and is sometimes called Earth's evil twin. Its thick atmosphere traps heat in a runaway greenhouse effect,
making it the hottest planet in our solar system with surface temperatures hot enough to melt lead. Below the dense, persistent clouds, the surface has volcanoes and deformed mountains.
Venus has by far the densest atmosphere of the terrestrial planets, composed mostly of carbon dioxide with a thick, global sulfuric acid cloud cover.
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 the closest between any two Solar System planets, approaching each other in synodic periods of 1.6 years.
Venus is the easiest destination to reach from Earth because of the low delta-v needed, and is a useful gravity assist waypoint for interplanetary flights from Earth.
Venus is very close to spherical due to its slow rotation. It 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.
Venus and Mercury
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