Saturday, November 7, 2015
Did The Solar Wind Really Rip Away Mars' Atmosphere?
Artist's depiction of solar wind shredding Mars' atmosphere.
According to new findings made by the MAVEN spacecraft on Mars, that neighbor planet's atmosphere was ripped away over billions of years by a ferocious solar wind. This is an audacious new hypothesis that needs to be thoroughly tested, and for sure is different from earlier theories.
When I took astronomy at USF the standard theory for Martian loss of atmosphere was based on the escape of particles due to reaching escape velocity from thermal effects. Calculations show, in fact, that if the mean molecular speed is as much as one-third the planet's velocity of escape (or 1.7 km/sec for Mars) the planet will lose one half of its atmospheric gas in only a few weeks.
If the mean molecular speed is even one fifth of escape velocity (1.02 km/sec for Mars) the gas will disperse into space in a few hundred million years. To hold a gas of sufficient atmospheric density to allow standing water-for billions of years - would necessitate a velocity of escape 6-8 times the mean molecular speed of the gas in question. This is simply not the case for Mars, where one can easily work out the mean molecular speed of oxygen, say from:
v = Ö( (3 k T/m)
where k is Boltzmann's constant (1.38 x 10 -23 J/K), T is the absolute temperature applicable in degrees K, and m is the mass of a single gas molecule. Then compare it to Mars' escape velocity of ~ 5.1 km/sec, as well as to one -third values and one -fifth values of that velocity.
Now fast forward some forty-odd years: MAVEN's probing appears to have revealed at least one other culprit: "winds" generated by bursts of gas and magnetic energy from the Sun. Maven evidently detected recent solar winds stripping away the planet's atmospheric gases bit by bit, grabbing ions and dispatching them into space. Maven's detectors show typical solar activity, without storms, can remove Mars' atmospheric gases at a rate of about 100 grams, or a quarter-pound, of particles every second. In the distant past this may have been up to 100 times as much. (The MAVEN team determined that when a storm hits Mars today, it increases the rate of removal of ions by a factor of 10 to 20 — a rate and speed of particle loss greater than initially anticipated.) Clearly enough to remove the atmosphere over billions of years.
But is this agency really needed?
I would argue that we need to parse far more data, over extended periods of time. Also, it should be feasible to at least partly replicate the mechanism in terms of near Earth experiments - such as those conducted and observed using the aurora at the Geophysical Institute, University of Alaska, Fairbanks. This would be in conjunction with HAARP (High Frequency Active Auroral Research Program). As noted in the Wiki article on the program:
"According to the HAARP team, this (research) will advance the study of basic natural processes that occur in the ionosphere under the natural but much stronger influence of solar interaction,"
In other words, it is plausible that the MAVEN data - used in conjunction with HAARP data for processes of solar wind interaction near Earth - could shed more light on the basic physical processes whereby the solar wind lurches particles from the atmosphere.
One point wifey raised in connection to the findings is: How could a Martian atmosphere even have formed in the first place if the solar wind was so powerful?
Well, the only explanation is that from its origin Mars must have had an intact magnetosphere (like Earth does now) .shielding it from the much greater solar wind. This must have required the existence of an iron core in order to generate a magnetic field strong enough for a viable magnetosphere. How or when this iron core formed ought to be a serious future field for planetary astronomers,
To be sure, astronomers estimate that Mars' magnetic field disappeared about 4.2 billion years ago, although they're not sure why. But again, the real issue and question is twofold: 1) Was there in fact a Martian molten iron core, and 2) What mechanism would have led it to cease activity and the derivative magnetosphere to collapse?
NASA's InSight lander, which will launch early next year to study Mars' interior, might solve some of that mystery.