What is the minimum mass of a habitable planet?

Mars is not habitable now (7 mbar atmosphere) but once upon a time
Mars had flowing rivers, steady dendritic drainage and occasional
outburst floods.

What was the atmospheric pressure on Mars back then?

How much more massive than Mars would a planet have to be to keep
atmosphere breathable for people? Assuming that the planet is also
warmer than Mars, in Earth´s orbit more vulnerable to atmospheric
escape?

Does this depend on what is defined as "breathable"?

It is alleged that Venus and Mars have less atmospheric escape because
they have cold exosphere, and exosphere is cold because carbon dioxide
radiates heat. Whereas nitrogen and oxygen exosphere of Earth (just
0,03 %% carbon dioxide) tends to heat and escape.

Carbon dioxide is poisonous.

However, the Earth´s 0,3 mbar is far less than the poisonous amount to
people. People have 50 mbar carbon dioxide in lungs. In submarines,
there is normally 10 to 20 mbar carbon dioxide, which is perceivable
but quite tolerable.

"Crown-Horned Snorkack" wrote in message
news:73c10a24-c4ee-474b-9ac8-e1ca2ab7ec13@m36g2000hse.googlegroups.com...
What is the minimum mass of a habitable planet?

Mars is not habitable now (7 mbar atmosphere) but once upon a time
Mars had flowing rivers, steady dendritic drainage and occasional
outburst floods.

What was the atmospheric pressure on Mars back then?

How much more massive than Mars would a planet have to be to keep
atmosphere breathable for people? Assuming that the planet is also
warmer than Mars, in Earth

Crown-Horned Snorkack wrote:

In addition to being massive, Mars would need a magnetic field.

Bob Kolker

On 15 mai, 13:11, "Robert J. Kolker" comcast.net> wrote:

Mercury has magnetic field. Venus has none, but nevertheless possesses
a massive atmosphere.

How much less massive than Venus would a nonmagnetic planet need to be
to lose atmosphere?

On May 14, 11:22 pm, Crown-Horned Snorkack
wrote:

Titan manages a 1.5 bar pressure despite being smaller than Mars.
Granted, it's cold.

Can you even have a pure oxygen atmosphere without anything else?
Don't plants need to convert atmosphere to oxygen?

In message
<14850294-86ae-4d97-a6d3-1240f0bba5cf@p25g2000pri.googlegroups.com>,
MWillMartin@gmail.com writes

Oxygen gas is so reactive that it's unlikely to be found free except
where there is a process that continually generates it.

It turned out to be a really bad idea in the Apollo capsule fire.
A pure oxygen atmosphere has a boundless enthusiasm for
oxidizing, really rapidly, anything vaguely burnable given a
start.

On May 15, 12:59 pm, "Anthony Buckland"
telus.net> wrote:

The fact that the capsule while sitting on the pad was held
at 1 full atmosphere was also part of the problem. I'm under
the impression that in flight, the pressure was considerably
reduced. I suspect this would also reduce the firehazard.

pt

On May 15, 6:11 am, "Robert J. Kolker" comcast.net> wrote:

The magnetic field reduces the solar radiation flux in the
upper atmosphere. In the case of Mars, the lack of a
magnetic field is thought to have allowed the radiation
to dissociate water molecules. The hydrogen escaped
into space, and the oxygen reacted with iron in the soil.
Thus, Mars dried out.

On May 15, 1:33 pm, petert...@gmail.com wrote:

No. Photons are most certainly non-magnetic :)

Um, again, planetary magnetic fields actually have zero effect on
solar radiation. Charged particles, yes, but water is disassociated by
solar UV.

In fact, the only point I can think of in favor of a magnetic field is
to possibly prevent atmospheric stripping by the solar wind over time
(one factor thought to contribute to Mars' low surface pressure).
Venus maintains an atmosphere just fine without it, as would Earth,
and those atmospheres are nicely thick from the standpoint of
radiation shielding as well (in other words, you again don't need a
planetary magnetic field).