October 23, 2017

14.04.10: Milankovitch Cycles…On Titan?

 

(Credit: NASA/JPL/University of Arizona).

(Credit: NASA/JPL/University of Arizona).

An amazing sight; sunlight reflected off the Kraken Mare caught by Cassini! 

   NASA’s Cassini spacecraft has revealed an elusive mystery on the surface of Titan; namely, why does the northern hemisphere of the large moon contain numerous lake basins, while in the south they’re relatively scarce? Now, scientists at Caltech working with JPL think they may have an answer. These lakes show up as bright (empty) and dark (filled) patches as the Cassini spacecraft pings them with its Synthetic Aperture Radar (SAR). Of course, on Titan, the hydrologic chemical of choice is liquid ethane and methane, and it is thought that some transport mechanism results in a net flow imbalance between the two hemispheres. Seasons on Titan last roughly 15 years as it dances around Saturn in its 29.5 year orbit about the Sun. But simple seasonal drainage of about a meter per year couldn’t empty the 100 meter-plus deep basins in a single season. This also doesn’t account for the overall disparity in number of basins seen, both filled and unfilled. Instead, scientists point towards the eccentricity of Saturn’s orbit as the possible cause. Saturn’s eccentricity is 0.055, or a little over 5% deviation from a perfect circle. This would make for periodic inequalities in the seasons, much like what occurs on Earth. For example, the perihelion of Earth actually occurs in northern hemisphere winter, somewhat ameliorating the severity of the seasons. But the variation of eccentricity coupled with the obliquity of the planetary spin axis and the precession of the equinoxes can vary over geologic time scales, causing variations in the climate. This is known as the Milankovitch cycle, and is thought to be a major contributing factor to the onset of Ice Ages. On Titan, a similar process is thought to occur, resulting in a net imbalance over thousands of years in the methane flow cycles between the two hemispheres. We may now simply be observing Titan during an epoch when seasonal methane pooling favors the northern hemisphere. Whatever the case, Titan is proving to be a fascinating and changing world deserving of further scrutiny.

Review: The Cosmic Connection by Jeff Kanipe

Cosmic catastrophe seems to be trending today, much unlike the currently pallid 11-year sunspot cycle. Without a doubt, the next killer asteroid will top your Tweetdeck, although whether it will bump #TGIF and Paris Hilton remains to be seen. The Cosmic Connection: How Astronomical Events Impact Life on Earth, by Jeff Kanipe and out by Prometheus Books comes as a sort of impromptu trilogy of reviews, as fans of this space will remember our recent review of Death from the Skies! And our forthcoming review of Heavens Touch, due out next month. Do not confuse this title with Sagan’s Cosmic Connection: An Extraterrestrial Perspective from 1973, which was complete with the trippy space age cover designed to pull in UFO buffs, but was Sagan all the way!

The Cosmic Connection shows how we are intimately related to the continual celestial goings-on all around us, and that we’re ultimately not immune to our stellar environs. I always like to point this out to the astrologically minded; the universe does indeed influence human affairs but not in the mundane way your newspaper horoscope might suggest. Instead, solar activity, supernovae, and even the evolving tilt of our own planet form a continuing ballet, and we’re all along for the ride!

The book opens with a deconstruction of our planet’s own complicated orbital behavior. Cycles such as the precession of the equinoxes the variation of the obliquity and fluctuation of our axial tilt all add up to a very complex affair, and that’s just for starters. Its hard to imagine that the “Goldilocks” epoch that we live in just happens to be stable and “just right” for us to thrive, and that this won’t always be so.

Even our own star, the Sun, is exposed for the notorious side it can sometimes exhibit. Its role in climate change is discussed; we thought that the “exorcism” of the Chamonix glacier, which was prone to advancing 100 acres per day in 1610, was an especially unique tale. The infamous solar season of 1859-1860 is also discussed; we have yet in modern technological times  to see a season quite as active as this one!

Think we know our own cosmic back yard? The Cosmic Connection will give you pause to think again. The chapter …At any time delves into the state and history of Near Earth Object (NEO) detection. For example, did you know that astronomers estimate that there remains perhaps 20,000 Near Earth Asteroids (NEAs) of the 140 meter or greater class to be discovered? In a timely fashion, the book makes mention of the October 5th 2008 impact in Sudan, the first time we’ve been able to spot an asteroid before impact. The author also lays out a template for increased funding and efforts towards detection. Of all the cosmic disaster death scenarios, killer space rocks are one of the few that we possess any means to do something about!

And as mentioned, I’ll bet that doomsday asteroid will trend on Twitter…

Even our place and epoch in the galactic scheme of things is addressed. True, a death dealing potential supernova candidate currently doesn’t lurk nearby in our local galactic neighborhood.The currently accepted “kill zone” is a radius of about 25 light years, and Spica and Betelgeuse, at distances of 260 and 425 light years, respectively are the nearest potential candidates. However, as we continue our 225 million year circuit about the galaxy, this will not always be the case. In addition, we bob up and down around the galactic plane, through largely unknown mediums of intergalactic dust. Our overall motion about the center of our galaxy is oblong, with our motion towards the solar apex in the constellation Hercules at about 12 miles per second. About 20 “Galactic Years” have passed since the formation of our solar system, and less than a hundredth of the past GY since the dawn of humanity. The author also points out that we may owe our placid existence to our current placement just outside of whats termed as the Local Bubble, an expanse of 300 light years across in the Orion Arm carved out by ancient supernovae.

All in all, its pretty remarkable to note the cosmic ingredients that go into an Earth as we know it; we live on a planet that orbits a relatively stable star, within its habitable zone, with a Moon to stabilize our tilt, in a supernovae free zone of our galaxy in just the right epoch. Of course, the Drake Equation has been given treatment, as it has here at Astroguyz… the sentiment echoes a recent controversial book, Rare Earth, which posits that our circumstances make life here unique. Of course, we are talking about life that know, as in carbon based, water-loving life…

In the end, the author presents a very convincing argument as to how our existence is intimately related to our evolving place in the cosmos. Consider it a sort of “volume two” in our cosmic review trilogy, Death From the Skies! being first and Heavens Touch to be forth coming. And next clear night, (we do our review reading on the cloudy ones!) be sure to check out the summer Milky Way (if you don’t suffer from light pollution) and thank your lucky stars that we’re here at all to appreciate our privileged place in space and time!