Monthly Archives: August 2018

The Moon’s Bombardment and Volcanism Combo

The Earth’s surface is subject to great change over geological time periods, due to the movement of tectonic plates, and volcanic activity, as well as long-term weathering and erosion.  As a result, craters caused by meteorite, asteroid and comet bombardment long ago is gradually eradicated.  We therefore look to the Moon’s cratered surface to provide clearer evidence of the bombardment history of the Earth/Moon binary.  That cratering history is then compared to other planets and objects in the inner solar system, allowing astronomers to discern patterns in cratering over long time periods.  One of the most significant events is the late, heavy bombardment.  Following  a period of relative quiet after the formation of the planets, this mass bombardment was thought to have occurred about 3.9 billion years ago:

“Competing models of meteorite-impact rate for the first 2 billion years (Ga) of Earth and Moon history. Note that Earth is believed to have formed about 4.55 Ga before present. Two hypotheses are shown: exponential decay of impact rate (dashes); and cool early Earth–late heavy bombardment (solid curve).” [see right-hand graph] (1).

More recently however, there has been a gradual realisation that this was not a sudden, dramatic event, but rather a sustained period of impacts by what were some colossal bodies:

“Recent high-resolution orbital data and images, more refined techniques for studying small lunar, terrestrial, and other impact samples and a better understanding of their ages, and improved dynamical models based on orbital and sample data have caused a paradigm shift in how we think about the lunar impact rate … The long-held idea of a “lunar cataclysm” at ~3.9 Ga is being replaced by the idea of an extended lunar bombardment from ~4.2 Ga to 3.5 Ga.” (3)  Read More…

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Proximal Planet Formation

Somehow or other (and it’s by no means clear how), some exoplanet gas giants whizz around their stars at great proximity.  The hottest of these objects so far discovered is an exoplanet named Kelt-9b.  It is a sub-brown dwarf of ~3 Jupiter masses.  It’s so close to its parent star that its rotation is tidally locked, and orbits the star in just 36 hours.  The temperature of its ‘dayside’ is over 4000 degrees C.  This remarkably high temperature is likely due to the immense amount of stellar radiation Kelt-9b is subjected to.  This temperature and stellar irradiation is driving off huge amounts of hydrogen from Kelt-9b’s atmosphere, creating an extended envelope of atomic hydrogen gas (1).  Other similar tailed gas giants have been studied before (2,3).  One can only imagine how spectacular this must look – a gas giant ‘comet’ streaming out a tail from near to or even within its parent star’s extended corona.

New analysis of Kelt-9b’s atmosphere has confirmed the presence of iron and titanium atoms within the planet’s atomic chemical soup (4).  It’s known that brown dwarfs can have cloudy atmospheres containing liquid iron rain, as well as other atmospheric dusts (5).  These dusty, cloudy atmospheres tend to form below 2,500 degrees Celsius, and then clear when the brown dwarf drops its temperature below about 1,500 degrees C.  Read More…

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