With the New Horizons spacecraft on its way to Pluto, and scheduled to flyby the dwarf planet in 2015, there is a growing interest in this distant world. Much of this focuses on aspects of the planet that might be important for the flyby. A while back I talked about how computer simulations of Pluto and its largest moon Charon showed that they likely formed through a large collision, and as a result New Horizons should find additional plutonian moons.
Kepler’s Hypothesis
One of the common misconceptions presented in science is that it occurs in revolutionary steps. For example, the idea that Copernicus developed the heliocentric (sun-centered) model of the solar system, then Kepler showed that planets moved in ellipses and introduced Kepler’s laws, then Newton introduced the law of gravity that proved Kepler’s laws to be true. Each revolutionary idea replacing the previous one. But the real history is not quite so clean. Take for instance the development of Kepler’s laws.
Twist and Shout
Orbital dynamics, that is, the motion of planets and stars about each other, is deeply dependent on computational modeling. The basic motion of one planet or star about another (the so-called two body problem) is fairly simple, and can be summarized by Kepler’s laws of planetary motion, the motion of multiple planets and stars is extraordinarily complex. In fact while the two-body problem is almost trivial to solve, the three-body problem has no exact general solution. As soon as you have three or more masses in your system, the motion can be highly chaotic.
Water World
Venus and Earth are quite similar in many ways. The diameter of Venus is about 95% of Earth’s, its mass is about 80% of Earth’s, it has a similar geological make up, and surface gravity. Where they differ greatly is in their surface temperature. Venus has a surface temperature of over 800 degrees Fahrenheit, while Earth’s average temperature is around 57 degrees (460 C vs 14 C for you science types). They also differ in the amount of water they have. Venus has almost no water, while Earth is a watery world.
Moving Heaven and Earth
We know that our solar system formed during the Sun’s youth, when it still had a protoplanetary disk. Such a disk contains gas and dust left over from the star’s formation, and over time the planets coalesced from that material. We can see such protoplanetary disks today around young stars, such as those forming in the Orion nebula.
Oddly Satisfying
Besides Earth, there are seven planets in our solar system (poor Pluto). If you were to line them up end to end, could they fit between the Earth and the Moon?
Spot On
In 1665 Gian Domenico Cassini observed a feature on Jupiter. It was described as an oval about 1/7 the width of the planet itself, and since it appeared reddish in color it became known as the Great Red Spot. Since then the spot has been observed over the years by both professional and amateur astronomers. It has been Jupiter’s most prominent feature for nearly four centuries.
That’s No Space Station
Mimas is a small moon of Saturn, about 400 km in diameter. It’s surface is dominated by Herschel crater, which gives the moon a passing resemblance to a fictional space station. For this reason it is often used in memes and jokes, but Mimas is actually an interesting puzzle.
Invariable Plane
One aspect of our solar system is that it is essentially a closed system. The stars are so widely separated that it would be rare for a stray asteroid or other object from beyond the Oort cloud to enter our solar system. This means that nearly all the rocky material orbiting the Sun now was also part of the solar system billions of years ago. This has a few consequences, one of which is the tendency for the solar system to lie in a plane.