Eccentric Universe

February 8, 2011

In our solar system, the Moon is the most massive satellite in the solar system relative to the size of the planet that it orbits. Because the Moon is so big compared to other satellites, its gravity tugs our oceans into areas of high and low tides, depending on the interactions of the Sun, the Moon and the Earth. Areios has three small moons, which makes their interaction with life on the planet interesting. We experience areas of high tide to the side facing the moon, and when the moon is at its farthest approach, we experience areas of low tide. If we didn’t have a moon, the Sun’s gravity on Earth would still cause some tides to occur, but not nearly as pronounced. Not only does the moon interact with the Earth’s oceans, the moon’s orbit has been slowing down the rotation of the Earth. The moon’s orbit has been growing wider and wider, too. In the next few billion years, the moon will fall into a closer orbit around the earth and get torn apart by the Earth’s gravity.

Our planet Areios has three moons, two of which were created from an impact event similar to the one that created Earth’s moon. The middle moon was an asteroid captured during the Late Heavy Bombardment era. Of Areios’ three moons, the innermost and outermost moons will wander out of Areios’ gravitational pull one day, but the middle moon will collide with the planet’s Roche Limit at some point, forming a ring of debris that could get dislodged and rain fragments down down Areios, spelling doom for anything unfortunate enough to be caught in the crossfire down below. Earth’s moon stabilizes the earth orbit, keeping the axial tilt of the planet in check, unlike Mars. Because Mars has two smaller moons, its axial tilt is out of control and the climate fluctuates wildly with each season without a massive moon to keep it in check. Areios experiences seasonal fluctuations more akin to Mars than Earth because its three moons all orbit with a different period and angle, only coming into alignment once every few hundred years. This would cause wild changes in weather leading to bitterly cold era of winter and longer blazing hot era of summer. These mood swings in climate could be challenging for any life on the planet to adjust to and such an unpredictable climate might lead to a higher rate of extinction during some epochs, and this would free up niches in the environment for new evolutionary forms to exploit, essentially increasing the turnover rate for species, so to speak.

On Earth, Milankovitch cycles caused by interactions with the gravitational fields of the other astronomical objects in the solar system with the Earth triggers regular perturbations in the Earth’s orbit, but these mild events happen like clockwork that a Serbian astronomer deduced their recurrence. Precession is any change in rotational axis or orbital path of a planet and both the Earth and Areios go through regular patterns of precession over geologic time. The Earth’s axis completes one full cycle of precession the orientation of Earth’s axis of rotation shifts slightly approximately every 26,000 years, creating a wobbling effect like a spinning top. At the same time the elliptical orbit rotates more slowly because of Jupiter or Saturn‘s gravity tugging at the Earth‘s orbit. The combined effect of the two precessions leads to a 21,000-year period between the seasons and the orbit. The angle between the Earth’s rotational axis and a perpendicular plane is call obliquity (or axial tilt), and the Earth moves from 22.1 degrees to 24.5 degrees and back again on a 41,000-year cycle. Areios goes through similar orbital changes but the most pronounced processional change is the obliquity in its rotational axis. Its axial tilt will vary up to a couple degrees every 35,000 years or so. Because the axial tilt is so extreme, Areios would experience different seasons and more extreme changes in weather.

Areios is very peculiar in that it rotates on its axis like Uranus, with the poles tilted very nearly onto the plane of revolution it has around Hemera. This gives it polar ice caps around the East and West instead of North and South. This strange arrangement was brought up briefly in the discussion of precession, but the impact that formed Areios’ two moons are also responsible for its off-kilter tilt of about 90 degrees. That means that the northern hemisphere is in constant light for weeks or months on end at one point and the other one is in constant darkness. Half an orbit later the roles are reversed. And halfway between those times, the rotational axis is perpendicular to the Sun’s direction, making day and night alternate in a way similar to what the Earth experiences at equinox. Any organism living on the planet would have to adapt with wildly-dramatic seasons that would vary from frigid temperatures in the winter to sweltering temperatures in the summers. Some creatures might adapt by burrowing into the ground to avoid the climate extremes and some may go into hibernation. We’ll discuss how animals survive such a harsh environment, but for now it will suffice to say that because these creatures have to live in an environment far different from what we find on Earth, a whole new set of morphological adaptations would be present on Areios to help them survive a solid month of perpetual sunlight or darkness.

This is a diagram of Uranus' 90 degree axial rotation.

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