The Ice Giants
When NASA’s Voyager 2 (1977 – approx. 2025) completed its mission exploring Jupiter and Saturn, the spacecraft was re-tasked to continue on, stopping at both Uranus and Neptune before traveling beyond the heliosphere. Though the ice giants have since been studied in depth by ground-based observatories, Voyager 2 is the only spacecraft to ever visit the outer planets.
Voyager 2 arrived at Uranus in 1986 after a five-year journey and surprisingly found that the third largest planet in the solar system was tipped on its side. Ten new satellites were discovered as well as a ring system. In contrast to the icy rings of Saturn, scientists theorize that the ones around Uranus consist of rock and metal and were formed by the collision of asteroids or a small moon.
With a gravity assist from Uranus, Voyager continued on for another three years to Neptune. Five new moons and a sparse ring system were discovered. As with Uranus, the atmosphere of Neptune was believed to contain high levels of methane, causing the planets to appear blue-green. Voyager relayed information about the magnetic field of Neptune and the levels of solar radiation that exist 4.5 billion kilometers from the sun.
The Huygens lander, part of NASA’s Cassini mission, bounced and tumbled on the surface of Titan in January 2005 and then transmitted data through the Cassini orbiter and back to earth for about 90 minutes.
Scientists found that the geography and weather patterns on Saturn’s largest moon are somewhat similar to earth, though in place of breathable oxygen and a water cycle, the rivers and lakes of Titan are filled with methane. The “air” at its surface is a mixture of nitrogen and other elements that envelops the moon in a hazy atmosphere.
In recent years, China, Japan, India, the ESA, and NASA have all been exploring the moon. They’ve conducted flybys, placed spacecraft in orbit, and the Chang’e 3 was the first lander on the moon since 1976.
The Lunar Reconnaissance Orbiter is a NASA mission launched in June 2009. The LRO arrived at the moon after a four day journey and was placed in orbit approximately 30 miles (50 km) above the surface. With specialized equipment, NASA has been creating a 3D map of the landscape while collecting data about the effects of the sun’s radiation in space and searching for water ice at the north and south pole.
Using images from the LRO, NASA has created a tour of the moon with an overview of its largest impact craters and evidence that volcanos erupted at the surface of the moon billions of years ago.
Mapping the Sky
In the 1920’s, the International Astronomical Union established the precise coordinates of the 88 constellations.
The most ancient constellations were observed more than 5,000 years ago. They each tell a story about the civilization that first put into writing their view of the stars, the phases of the moon, and the seasonal changes that influenced their planting and harvesting.
Centuries later, the Greeks and then the Romans adapted these same star groupings to represent tales of love, hate, lust, and war among deadly creatures and legendary warriors. Relying solely on the sharpness of their eyesight, these early astronomers mapped the night sky with incredible accuracy.
When the first refracting telescopes were aimed at the stars in the 1700’s, new constellations were being “discovered” by explorers as they navigated the oceans near the North and South Pole, completing the map of the night sky.
About four and a half billion years ago, the gravitational pull of the newly formed sun influenced the location of the planets within the solar system. Each one eventually settled into a stable orbit, traveling on paths that range from near circular to oval.
A circular pathway through the solar system, such as the one Venus travels on, means that a planet is orbiting the sun at a constant distance and speed. Planets with an elliptical orbit, like that of Mercury, were formed with a speed and trajectory that is continually changing.
At perihelion (nearest the sun) Mercury speeds up and then “sling shots” away, slowing down at aphelion (farthest from the sun) before being pulled in again by gravity.
Volcanoes on Venus
Venus and the Earth are similar in that they both have a molten core that erupts at the planet’s surface. On Earth, the most familiar type of volcanoes are the composite type, the cone-shaped structures that explosively spew lava, ash, and hot gases from a chamber of molten rock beneath the surface. They’re usually located along fractures in the earth’s crust where tectonic plates are clashing, such as the “ring of fire” that includes Mt. St. Helens in the northwest. Shield volcanoes, in contrast, are like the ones found in the Hawaiian Islands, characterized by a continuous and steady flow of lava that cools to reshape the landscape.
Because of Venus’ heavy atmosphere and lack of tectonic plates, its volcanoes are the shield type from which molten rock slowly and uneventfully flows to create the lava plains and “pancake” domes that cover the planet.