[ExI] kepler study says 8.8e9 earthlike planets

[BillK]

On Wed, Nov 13, 2013 at 8:32 AM, Kelly Anderson  wrote:
> There is no debate (that I know of) that mars has a very weak magnetosphere.
> That is the issue that most affects life at this point. It probably did have
> one in the distant past.
>
> So nobody knows NASA's definition of goldilocks planets well enough to know
> if mars would count as one of the eight billion or not?
>
>

I think the confusion is between 'habitable zone' and 'habitable planet'.
A goldilocks planet must be in the habitable zone, but for other
reasons (like being too small) may not be habitable.
Quote:
In astronomy and astrobiology, the circumstellar habitable zone (CHZ)
(or simply the habitable zone), colloquially known as the Goldilocks
zone, is the region around a star within which planetary-mass objects
with sufficient atmospheric pressure can support liquid water at their
surfaces.
------------

But there is even some dispute about the size of Sol's habitable zone.
Quote:
Given the large spread in the masses of planets within a circumstellar
habitable zone, coupled with the discovery of super-Earth planets
which can sustain thicker atmospheres and stronger magnetic fields
than Earth, circumstellar habitable zones are now split into two
separate regions—a "conservative habitable zone" in which lower-mass
planets like Earth or Venus can remain habitable, complemented by a
larger "extended habitable zone" in which super-Earth planets, with
stronger greenhouse effects, can have the right temperature for liquid
water to exist at the surface.
----------

See:
<https://en.wikipedia.org/wiki/Habitable_zone>
<http://phl.upr.edu/projects/habitable-exoplanets-catalog>


BillK