Sunday, August 30, 2015

Geosonnet 31

Gyrations of a topsy-turvy world
Could spur migration of the cryosphere
No snowball Earth, just poles and tropics whorled
The data which support this are unclear.
Precambrian magnetic fields suggest
That tropics, poles exchanged with frightful speed.
Magnetic hysteresis is the test
Anorthosite and feldspar crystals need.
A shaky witness cross-examination
The steep magnetic field begins to fray
Faced with a single crystal refutation
The polar history has gone away.
   The Ediacaran poles didn't roam.
   Emerging life was blessed with stable home.

Geology 43 132

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Saturday, August 29, 2015

Hard rock men and soft rock girls

Readers with short attention spans who waste too much time on social media may have noticed that Brian Romans has been complaining over on twitter about the hardrock/ softrock divide. This being a blog, I will whinge in more depth below:

For those of you who grew up on a carbonaceous chondrite, there is a historical cultural divide between hardrock- the study of high temperature processes as recorded in crystalline rocks, and softrock- the study of low temperature processes which can be recorded in sediments.

I’m not sure where in the fossil record this division first appeared, but my experience of it goes back to teachers who were trained in the Apollo era. Back in the 60’s and 70’s, the moon race injected lots of cash into the study of (dead, high temperature) moon rocks and associated meteorites. A generation later, from the 90’s on, there has been an increasing push to understand climate, presumably in hope that we can learn something about it before it kills us all. One result of this change in focus is an unnecessary cultural divide, premised on lazy assumptions that in some cases are decades out of date.

For example, one of the strengths of the 20th century hardrock push was the elevation of petrology beyond a simple descriptive science to a thermodynamically constrained, math-based quantitative science. The calculations done with thermocalc or MELTS or any of the other equilibrium simulators are of course trivial compared to what goes into climate models or organic geochemistry or genetics, but some of the older, out-of-touch hardrock evangelists haven’t quite caught on to these developments yet. Similarly, researchers who have used the surge in climatological research funding to tackle new fields of research have sometimes been labeled as too soft to make it in hard rock, while in many cases they feel that their former fields of study have either had the interesting questions answered, or degenerated into untestable speculating.

In reality, the advancement in modern analytical, conceptual, and computational techniques means that the separation between hardrock and softrock is largely a psychological or historical one. As you carbonaceous chondrite dwellers surely appreciate, we have moved on from isotopic anomalies in presolar grains to organic cosmochemistry, the origin of chirality and life, and other burning questions that require understanding the interaction between low and high temperature processes in active planets. Even bread-and-butter questions like continental crust formation are increasingly having to deal with the effects of weathering (and how it changes as the atmosphere evolves), in order to explain increasingly detailed analyses. As a community, we should have realized way back when subduction was discovered that it is futile to separate aqueous and thermal processes on a planet whose thermal engine is driven by downgoing oceanic slabs.

Having met a lot of scientists over the years, the ones who use their skills to address a variety of questions across outdated subdisciplinary boundaries seem to be happier and more productive than those who choose to wave an archaic banner from a lost tribe of geoscience. From the 21st century, the hardrock / softrock divide seems as old fashioned as the Billy Joel song parodied below:

Softrock Girl

Softrock girl,
She’s been living in her softrock world.
I bet she’s never had a mantle guy
I bet her momma never told her why.

I’m gonna try for a softrock girl
She’s been living in her climate world
As long as anyone with magma can
and now she’s looking for a hard rock man

And when she knows what she wants from deep ti-i-ime
And when she wakes up and makes up her mi-i-ind
She’ll see I’m not so tough
Just because
I’m in love
With a softrock girl.

You know I’ve seen her in her soft rock world,
She’s getting tired of her plankton toys
and her presents from her soft rock boys
She’s got a choice.

Softrock girl
You know I can’t abide to study pearls
But maybe someday when my ship comes in
Drilling MOHO through the MORB so thin
and then I’ll win.

And when she’s walking on sand grains so fi-i-ine.
And when she’s drilling, she yearns for a mi-i-ine.
She’ll say I’m not so tough
Just because
I’m in love with a softrock girl
She’s been living in her climate world
As long as anyone with magma can
and now she’s looking for a hard rock man
That’s what I am
Softrock girl
She’s my softrock girl.
You know I’m in love with a
Softrock girl
My softrock girl.
You know I’m in love with a
Softrock girl
My softrock girl.

Thursday, August 06, 2015

A one-way ticket to an unsuspecting Kepler 452b?

There has been a bit in the science press about the newly discovered exoplanet, Kepler 452b. This related to the observation that it is in the “habitable zone” of a sun-like star.  The big news, as always, is that this planet is completely unlike anything in our solar system. If it is solid, it has three times the mass than every rocky body in our solar system combined. If it is not solid, then it is one of the sub-neptune planets common everywhere but around our star.  But there are two points in particular which have been ignored- or at least not appreciated, which I would like to expound on.

Firstly, we can see them, but they can’t see us.  There are two main techniques used for detecting planets around stars: Radial velocity, and transits.  The motion of the planet around the star pulls the star backwards and forwards, in proportion to their relative masses.

With the radial velocity method measures the very small Doppler shift in the light of the star created by this pull. However, in order to see this motion, the orbit of the planet around the star needs to be somewhat edge-on as seen from earth. If we are looking town down on the orbit, then the star doesn’t move towards or away from us; it just goes in a circle (or ellipse). And sideways motion in the sky is much harder to detect that motion towards of away from Earth.

With transit detection, the crossing of the planet across the face of the star (as seen from Earth) causes the light from the start to dim a little bit in a periodic fashion. This requires Earthly observers to be in the same plane as the orbit of the planet- For a Earth-like planet orbiting a sun-like star, the planet will only transit if the Earth is within a half degree of the planet’s orbital plane.  The Kepler mission is a transit mission; all the planets it detects are systems which are edge-on as seen from Earth.

For aliens trying to detect us using the transit method, they need to be viewing us from a star that lies in the ecliptic. Basically, if they want to see the Earth pass in front of the sun, to detect its transit, then from our point of view, the sun needs to cross in front of their star.

However, the Kepler primary mission* field of view is nowhere near the ecliptic. It is, fore the most part, more than 60 degrees from the ecliptic. This makes transit detection of the Earth in front of the sun impossible from any star systems in the original Kepler field of view. And due to the high angle, radial velocity measurements of the Earth’s pull on the sun will be less than half as effective as our radial velocity measurements of their planets.

So the Kepler mission isn’t just a telescope.  It is a spy satellite, peering down on a thousand planets circling hundreds of distance star, all of whom are blissfully unaware of our planet’s existence.  If there are aliens on Kepler 452b- or any other planet Kepler discovers, they aren’t waving at us, because assuming technological parity, they can’t possibly know that we are here.

Of course, we know that they are there.  And it might be that one day,. given a modest technological advancement, someone could sent a colony ship on a hundred thousand year mission to visit them.  However, the visit could easily overstay its welcome.

Kepler 452b is probably not an Earthlike planet. However, if it does have an Earthlike composition, then it is a gigantic hunk of rock and metal three times more massive than every rocky-metal planet in our solar system combined. Due to gravitational self-compression, this planet would have a mass six times that of Earth.  At 36 hellagrams, it is just under half the mass of Uranus. The surface gravity would be a crushing 2.3 times greater than on Earth.  No rocket we currently have could even leave the launch pad under suck crashing gravity.  And even if it did, the velocity required to achieve orbital velocity, 15.5 km/s, is almost twice what is required on Earth.

Although technology is sure to advance if we are to get the ability to launch colony ships, such a huge planet would trap any rocket conceivable with current technology.  Kepler 452b is, in essence, a gigantic Hotel California, from which no-one can ever leave.  As a result, any short-lived visitation attempt would inevitably become a permanent stay.

So don’t be too disappointed if the locals on Kepler 452b don’t wave back.  They are blissfully unaware that we are staring at them.  And if they did know, the fact that we would wear out our welcome upon visiting by a factor of infinity is unlikely to cheer them up.

 * The secondary mission, however, is observing on the ecliptic.