Day: November 7, 2016

We’re all familiar with the Moon, Earth’s cosmic companion. So familiar with it in fact, that we probably all think we know the theory behind how it got to be where it is – the result of a “giant impact” far back in Earth’s early history. However, a new study, published on October 31st in Nature, suggests what actually led to the creation of the Moon was possibly a lot  more elegant than previously realised.

The Moon is actually quite unique among the solar system’s satellites. It’s relatively large when compared to its parent planet, and it is a made of pretty much the same stuff, minus some more volatile compounds that evaporated long ago. Other moons tend to be a lot more chemically diverse when compared to one another and their parent worlds.

The accepted theory of lunar formation has it that not long after primordial Earth formed, a Mars-sized object grazed it, throwing off a mass of material from which the Moon subsequently condensed. This impact set the angular momentum for the Earth-moon system, and gave the early Earth a five-hour day. Then, over the aeons, the Moon slowly receded from the Earth (as it continues to do so to this day), and Earth’s rotation has slowed to our current 24-hour day.

It’s a theory all worked out be a combination on mathematics based on the moon’s current orbit, the angular momentum of the Earth-Moon system, the influence of various tidal forces, a little bit of guesswork, etc.  However, it does have a couple of holes in it.

The first is that if the Moon was formed as a result of material set free during a slight collision between Earth and another body, then that material should have been a mix of debris from both Earth and the other body, giving rise to a lunar composition that should be at least somewhat different to that of Earth. The second is that if the Moon condensed from a disk of material rotating around Earth’s equator, it should be in orbit over the equator – but instead, its orbit is tilted 5 degrees off the equator.

Both of these issues have previously been explained in terms of “intervening steps” between what we see today and the original  “giant impact”. However, a team of scientists led by Sarah Stewart, professor of earth and planetary sciences at the University of California, have posited an alternative explanation, which requires no “intervening steps”, but always natural mechanics to explain everything.

In their model, the “giant impact” still occurs –  but it completely destroys the nascent Earth and whatever hit it, leaving a mass of vaporised and molten material  orbiting the Sun, which eventually condenses to form a “new” Earth and the Moon – thus giving them similar chemical compositions. Initially, the Earth would have likely been tipped so its axis was pointing towards the Sun while spinning in a two-hour day.

Then, as angular momentum was dissipated through tidal forces, the Moon started receding from Earth, eventually reaching a point called the “LaPlace plane transition”. At this point the forces from the Earth on the Moon became less important than gravitational forces from the sun, resulting in some of the angular momentum of the Earth-Moon system transferring to the Earth-Sun system, causing the Earth to tip “upright”, while leaving the Moon in a very highly inclined orbit relative to Earth’s equator. However, as the Moon continued to slowly and naturally recede from the Earth, it eventually reached the Cassini transition, gradually reducing the Moon’s angle of inclination relative to the Earth’s equator, bringing it to the five-degree offset we see today.

Thus, with this model, no exotic intermediary steps are required to account for the Moon’s composition or why it is where it is today; everything can be explained through the application of mathematics and planetary mechanics, offering a compelling alternative to the accepted theory of lunar evolution.

China Launches the Long March 5 Heavy Lifter

China’s newest and biggest heavy-lift rocket, the Long March 5 (Chang Zheng-5) lifted-off from the Wenchang launch centre on Hainan Island, off China’s southern coast, at 12:43:14 UT or 20:43 Beijing time on Thursday, November 3rd, carrying an experimental satellite designed to test electric-propulsion technology.

With a 25 tonne low Earth orbit payload capacity, the Long March 5 stands on a par with the current crop of heavy lift launch vehicles in operation around the world. The product of two decades of research and development, it is destined to become a centrepiece of China’s growing space ambitions.

Among its may missions, the Long March 5 will play a leading role in the construction of China’s upcoming space station, starting with the launch of the core Tianhe (“Harmony of the Heavens”) module in 2018. When completed in 2022, the 60-tonne station will comprise the core module supported by the Wentian (“Quest for the Heavens”) and Mengtian (“Dreaming of the Heavens”) pressurised experiments modules, all of which will be linked by a multi-port adaptor / EVA airlock.

Continue reading “Space Sunday: of moons, storms and rockets” →