September 5, 2017 | Henry Richter

Facing Reality About Life on Other Planets: Geophysics

by Dr Henry Richter

This is a continuation of my discussion on the requirements to allow life to exist on a planet elsewhere in the universe. My discussion moved from our position in the galaxy, our position in the solar system, and then focused on the earth, looking at the influence of our moon, our planetary motion, and our atmosphere. This article will look at the gross characteristics of our earth, its rotation rate, structure from interior to surface, and the existence and value of our magnetic field.

Rotation Rate

In my last article in this series, the importance of a small inclination of the spin axis was examined. Looking at the spin of the earth – one rotation in twenty-four hours – allows for what I would call a reasonable night-to-day ratio. This could also be considered rest-to-work-time ratio. We could consider the situation of a fast spin – say a one-hour day. I suppose a living organism could adapt to a short cycle such as this, but it would not allow time for a metabolic process to quickly change from “on” to “slow.” We are used to decent periods of activity, and then recovery through resting. It probably would not affect plants much, but animals which move around and engage in activities would not be able to pursue much in the way of a productive schedule. A spin rate of once every one hour might lessen the effect of gravity a bit through centrifugal force, but not much. It might change the earth’s core and affect the magnetic field. A fast spin might throw off some of our gaseous atmosphere.

Credit: Illustra Media

A spin rate of, say, three hundred hours to the day would be a long stretch between activity and rest. It would require much energy storage in the individual to keep active for one-hundred-fifty hours in a day, even though there would be one-hundred-fifty hours to replenish the energy supply. A slow spin might not prohibit the development and existence of life, but it would sure change the physical form.

Elemental Composition

I have mentioned the composition of the earth. The earth has a hot liquid iron-nickel core which churns in constant motion. The churning may be caused by the slow loss of heat to the surface, with resulting convection currents moving the liquid. I feel certain that the structure and composition of the earth helps produce a result that allows life, but I cannot pinpoint specifics so cannot conclusively add the composition or structure  to the list of absolute requirements. We do know that the earth’s magnetic field results from the nature and activity of the molten metallic core.

Magnetic Field

Having now mentioned the magnetic field, I believe this is an absolute necessity to protect the earth. The earth rides through space in a magnetic  bubble which wards off different types of particles which would be destructive if they reached the earth’s atmosphere or surface. The sun gives off several  types of particles in the form of the solar wind, coronal eruptions, and solar flares. The particles consist of both electrons and ions. The electrons, being lighter, are confined to the sun’s magnetic field lines, and often decay into x-rays which can be detected at the earth. The ions consist mainly of protons, with a smattering of heavier element ions.

A NASA report  from the Goddard Space Flight Center states:

We cannot observe the way the distant universe accelerates cosmic rays or produces energetic photons, but acceleration processes also occur on our Sun, though on a much more moderate scale.

Starting in 1942, Geiger counters and other detectors, set up to monitor cosmic rays, have occasionally seen sudden increases in the intensity of the radiation, associated with outbursts on the Sun, mostly with visible flares. The cosmic ray intensity returns to normal within minutes or hours, as the acceleration process ends and as accelerated ions disperse throughout interplanetary space.

On the scale of cosmic radiation, solar-produced ions have relatively low energies, generally below 1 Gev (=billion electron volts) and rarely above 10 Gev. That is why such events are often missed by cosmic ray detectors near the equator, where the lowest energies are excluded by the Earth’s magnetic field. The best detectors for observing solar particles are therefore those sensitive to the lowest energies of the cosmic radiation.

These solar particles are destructive to tissues and materials. They are deflected by the earth’s magnetic field lines, or trapped into the magnetic field lines and become part of the Van Allen belts. They occasionally slide down the magnetic field lines into the polar regions making the spectacular aurora (northern lights). The auroras are particularly prominent after solar storms or corona magnetic ejection events. But these are particles that would reach the earth were they not deflected or trapped by the magnetic field. So the magnetic field is absolutely crucial to protecting life. Were it not there, over time the solar wind and particle flux would strip away the earth’s atmosphere.

The sun emits a wide range of particles of different energies. These are known to cause a variety of damages to materials. The range of parameters and types of damage are shown in the following table from the European Spacecast website, which monitors emissions harmful to satellites:

The table shows the varieties of damage that exposure to these solar ejecta and emissions can cause. These are present bombarding the earth at all times, although they vary in intensity depending on the solar activity. A planet without a sizable magnetic field would not retain an atmosphere for any length of time as the solar wind would slowly (or maybe rapidly) blast the atoms and molecules into space. A few collisions of energetic particles with atmospheric molecules would send them flying like billiard balls in various directions, but many would end up sailing out into space.

CME takes aim at Earth. Credit: SOHO/NASA

It has been known for some time that the magnetic field affected cosmic rays impinging the earth. That is why cosmic ray measurements have been made at a wide range of longitudes. Not much was known about the solar wind until earth satellites were developed and measurements outside the earth’s atmosphere became possible. Measurements by rocket-borne detectors were made outside the atmosphere, but it was mainly measurements in the polar regions, where the magnetic field was lowest, that many measurements of the solar wind were made.

So, among the criteria of conditions crucial to life on an exoplanet, the existence of a suitable magnetic field is high on the list. The strength of the field is important: strong enough to produce a magnetic bubble of the right size, but not too strong to affect surface processes.

Obviously any exoplanet must have a host star to orbit. Any star being fueled by thermonuclear reactions will produce radiation and will eject particles; thus, the need for planetary protection like that afforded by our magnetic field: another “coincidence” that turned out just right at earth.

Dr Henry Richter, a contributing science writer to Creation-Evolution Headlines, was a key player at NASA/JPL in the early days of the American space program. With a PhD in Chemistry, Physics and Electrical Engineering from Caltech), Dr Richter brings a perspective about science with the wisdom of years of personal involvement. His book America’s Leap Into Space: My Time at JPL and the First Explorer Satellites (2015), chronicles the beginnings of the space program based on his own records and careful research into rare NASA documents, providing unequaled glimpses into events and personnel in the early days of rocketry that only an insider can give. His next book, Spacecraft Earth: A Guide for Passengers, is due out later in 2017. For more about Dr Richter, see his Author Profile.

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