The habitable zone as seen through the atmosphere
University of Victoria
The dominant paradigm in assigning "habitability" to terrestrial planets
is to define a circumstellar habitable zone: the locus of orbital radii
in which the planet is neither too hot nor too cold for life as we know
it. I'll review the atmospheric physics that has led to hard boundaries
being set for the habitable zone and show recent work which shows multiple
stable states and challenges these boundaries.
The width of the habitable zone is turns out to be determined by the
atmospheric inventories of di-nitrogen and carbon dioxide. Yet Earth
teaches us that these abundances are very heavily influenced (perhaps even
controlled) by biology. This is paradoxical: the habitable zone seeks
to define the region a planet should be capable of harbouring life; yet
whether the planet is inhabited determines these boundaries. This matters,
because future life detection missions may use habitable zone boundaries
in mission design.
I propose that we must amend the paradigm of habitability to acknowledge
that habitability depends on inhabitance; for life as we know it is a
planetary scale -- and planet dominating -- phenomenon.
|Date: ||Tuesday, 10 November 2015|
|Where: ||McGill University|
| ||Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103)|
|Contact: ||Robert Rutledge|