Radiation & Habitable-zone Planets

[Chris Peterson]

The way I read that Wikipedia article, astronomers believed that Venus had a magnetic field, and models showed that it ought to have a magnetic field, but observations showed that it did not have one.

I think the astronomers were right. Venus is like Earth, and it probably did have a magnetic field. Likewise for Mars. And both could easily have developed life, and we might find evidence of that someday.

Earth probably is typical in many ways of rocky planets. One thing that probably make it less typical is its stability, provided in part by the Moon, and perhaps by its complex biosystem, as well.

My expectation is that life is common on terrestrial planets in habitable zones (which I think are much wider than typically suggested). But in many cases, we may find that the period that life exists on a planet is only a few hundred million years, not the several billion as in Earth's case. Most life is probably equivalent to simple bacteria and plants, not complex animals.

[mjimih]

Seems that it would be best if we could tell if Kepler candidates slated for closer inspection had magnetic fields or not, as those with it may be more likely to have a life friendly surface? Will we be able to make an instrument in the future which could detect a magnetic field presence around these distant orbs? Probably a tough nut to crack right, but if ever possible it should narrow the search a bit.
Is it safe to assume most super Earths would have internal dynamo's, and hence have healthy magnetic fields? Most of these candidates to research further are going to be larger than the Earth somewhat, should they all have internal dynamos just because of their sheer size? How dependent is Earth's magnetic field on the Moon-creating collision having created it? Are we going to... wait! hold the presses!! Sulfur?! What's Sulfur got to do with it?
(too many questions)
Yoda knows...
"The --magnetic- Force Is My Ally"

Click to play embedded YouTube video.

[Chris Peterson]

Seems that it would be best if we could tell if Kepler candidates slated for closer inspection had magnetic fields or not, as those with it may be more likely to have a life friendly surface?

I wouldn't assume that planets with magnetic fields are all that much more likely to have life.

Will we be able to make an instrument in the future which could detect a magnetic field presence around these distant orbs?

Magnetic fields leave a record in photons, so it is entirely possible we'll one day have tools for measuring magnetic fields around distant planets.

Is it safe to assume most super Earths would have internal dynamo's, and hence have healthy magnetic fields?

It's a reasonable assumption. It's also one that is likely to have exceptions.

[mjimih]

I wouldn't assume that planets with magnetic fields are all that much more likely to have life.

But isn't a magnetic field a principal protector of an atmosphere from the ravages of a Solar wind? With a more stable atmosphere as a result, allowing surface life to take hold.

I was referring to just surface life too. Life in an ocean, or cave, isn't nearly as affected, or isn't affected at all, by solar radiation is it?

[Chris Peterson]

I wouldn't assume that planets with magnetic fields are all that much more likely to have life.

But isn't a magnetic field a principal protector of an atmosphere from the ravages of a Solar wind? With a more stable atmosphere as a result, allowing surface life to take hold.

I was referring to just surface life too. Life in an ocean, or cave, isn't nearly as affected, or isn't affected at all, by solar radiation is it?

To the extent that a magnetic field is necessary to preserve an atmosphere, it becomes a matter of time. What we know from Earth is that life developed early, and quickly. A rocky planet is likely to have a magnetic field for at least the first one or two billion years of its existence- more than enough time for life to develop. And even a planet like Mars has enough of an atmosphere to support life... Earth life. I don't see that the gradual loss of atmosphere has to pose an extinction threat to life.

Again, when I say life I'm talking about something very simple. To evolve complex life I think you need much more stable conditions, and therefore this is something that will exist in only a small percentage of cases (still a lot in absolute numbers, though).

[mjimih]

If science is leaning towards life on Earth being seeded by comets and the like...

Science is leaning pretty hard against that view. Rather, these kinds of bodies are seen as possibly providing some of the organic ingredients that were incorporated by the first life.

http://www.bbc.co.uk/news/science-environment-23872765
28 August 2013
Earth life 'may have come from Mars'

"The evidence seems to be building that we are actually all Martians; that life started on Mars and came to Earth on a rock," he commented.

"It’s lucky that we ended up here, nevertheless - as certainly Earth has been the better of the two planets for sustaining life. If our hypothetical Martian ancestors had remained on Mars, there may not have been a story to tell."

[Chris Peterson]

http://www.bbc.co.uk/news/science-environment-23872765
28 August 2013
Earth life 'may have come from Mars'

"The evidence seems to be building that we are actually all Martians; that life started on Mars and came to Earth on a rock," he commented.

Translation: the evidence has gone from zero to an extremely small amount.

[saturno2]

It seems that on Mars was there ever elemental life
Earth conditions are unique and Earth life emerged here, I think

[Doum]

TOWARDS THE MINIMUM INNER EDGE DISTANCE OF THE HABITABLE ZONE

We find that the inner edge
of the Habitable Zone for hot desert worlds can be as close as 0.38 AU around a solar-like star, if the
greenhouse effect is reduced (∼ 1% relative humidity) and the surface albedo is increased.

here is the article. It's interesting.

http://arxiv.org/pdf/1304.3714.pdf

[miliksitek]

Yeah, these all facts give us some certainty that there used to be(is) life on Mars.

[Chris Peterson]

Yeah, these all facts give us some certainty that there used to be(is) life on Mars.

Well, actually they do no such thing. All they do is slightly enhance the possibility... maybe.

In any case, there are dozens of different theories about the range of habitable zones around stars, and most of them already place Mars in the Sun's habitable zone, so yet another theory does not change much.

[mjimih]

I'm trying to get at the survivability rate of HZ planets' atmospheres? What types of destructive forces on a viable atmosphere, would there be, say, on Earth-candidates nearer the inner edge of a habitable zone? Does size matter? Are super Earths more likely to have safe surfaces for life bc of strong magnetic fields & thick atmospheres (protection from Radiation)? Mars is/was too light to be a good candidate for instance.

Mark

[Chris Peterson]

I'm trying to get at the survivability rate of HZ planets' atmospheres? What types of destructive forces on a viable atmosphere, would there be, say, on Earth-candidates nearer the inner edge of a habitable zone? Does size matter? Are super Earths more likely to have safe surfaces for life bc of strong magnetic fields & thick atmospheres (protection from Radiation)? Mars is/was too light to be a good candidate for instance.

I'd argue that Mars is still habitable, and still has an ample atmosphere after more than 4 billion years to support life.