> On Feb 25, 2017, at 1:21 PM, Phil Pugliese (via tml list) <xxxxxx@simplelists.com> wrote:
>
>
> I just saw some animations of TRAPPIST-1 on a network news prg & it showed all seven planets alongside the Earth.
>
> All of them appear to be smaller than the Earth.

Per the Nature article their radii vary from 1.13 to .72 times Earth’s, so the animation was wrong.

<http://dbdev2.pharmacy.arizona.edu/miscjunk/nature21360.pdf> See Table 1. Radius is expressed as ratio to Earth’s.

>
> Made me wonder if any of those planets could maintain a breathable atmo.
> How much smaller could a planet otherwise similar to Earth be & still have an atmo thick enough for us to breathe w/o assist?
> (I imagine a Venus-size planet could. But could a Mars-sized one?)

Mars lost it’s atmosphere largely because it has a cold iron non-spinning core, meaning no magnetic field, and so the solar wind pretty much blew away the atmosphere over time. We know that Mars had enough atmosphere at one point to have considerable liquid running on the surface. Titan is only .4 the diameter of Earth, smaller than Mars, but atmospheric pressure on the surface is almost one and a half times Earths.

--
Bruce Johnson
University of Arizona
College of Pharmacy
Information Technology Group

Institutions do not have opinions, merely customs