h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: The Habitable Zone - A45726933
Author: Galaxy Babe - U128652

Anyone for porridge?


GB

Toast and jam please GB!


Another little lesson for me on astronomy? Oh goodie!

isn't a lot of it dependant on atmosphere??

venus is too hot due to runaway greenhouse effect

mars is too cold because the atmosphere is too thin

Porridge? move along folks, nowt to see here, no typos, no spelling errors.


BMT Scout

I don't like the first sentence. It seems to suggest that every planet has a habitable zone. The habitable zone is a region of space around a star in which conditions would be suitable for life if there were a planet there. There should be some nice way of saying that.


Why is 55 Cancri A a "likely candidate" if all its planets are gas giants?

I've reworded that first sentence.

55 Cancri A = any rocky moons? I've added that

'is considered'? The other five bullet points are complete sentences.

There's a comma missing somewhere, but let's not be too picky.

The presence of water (H2O) in liquid form, considered essential for living creatures by most botanists.

changed to

The presence of water (H2O) in liquid form is considered essential for living creatures by most botanists.

thanks

isn't liquid water considered the universal solvent?? for the purposes of life

Yep, that's why I've linked to A596450

Substances can be divided into polar and non-polar. Water is the universal polar solvent, but it doesn't dissolve non-polar substances such as oil. Detergents are substances which mix polar and non-polar together, allowing non-polar substances to be dissolved in water.

Habitability and life supporting potential is influenced by more than stellar constant and orbital dynamics.

A couple of other important factors influencing habitability are presence of a magnetic field, preventing by means of magnetic trap effects atmospheric radicals like atomic oxygen, nitrogen and hydrogen generated by exposure to stellar radiation in the exosphere from being carried away by the stellar wind, shielding the planets' surface from stellar wind radiation events and also, a survivable diurnal period.

If the Earth had a diurnal period like Venus, it would probably be uninhabitable, constantly swept with hurricane force winds at temperatures between 300 C and 400 C. On the other hand, if Mars had a 48 hour day, its day time temperatures would probably be quite comfortable, though night time temperatures without moderating atmospheric and oceanic heat sinks might still drop to temperatures approaching -70 C.

The effect is the same effect that makes daytime temperatures increase well into the afternoon and makes the hour before the dawn the coldest time of day, a consequence of heat absorbed during the day being radiated back into space during the night.

This is an important factor which opens up the possibility of having more than one potentially life supporting world in the stellar constant range that allows liquid water and can disallow the possibility even given ideal orbital dynamics.

I'd make the term 'botanist' 'biologist', be as generalized as possible.

changed 'botanist' to 'biologist'

I had already mentioned the importance of the presence of a magnetic field in the bullet points, but I have added "a survivable diurnal period"

Thanks everyone

I like it! It seems to me, though, that you might do better combining it with your PR entry 'The Possibility of Finding Alien Life' since they do seem to overlap quite a bit.

"A rocky planet-finder project is underway and astronomers have a list of likely candidate stars within 50 light years that they'd like to check out, including 55 Cancri A, which is home to the most planets3 that we know of at the time of writing, and the Gliese 581 (HO Librae) planetary system which is the closest."

You've updated the first mention of Gliese 581 but you should probably uopdate it here too, because they have looked at it.

I hadn't realised that as I wrote them at different times. I'm happier with this one than the other entry, so I'll remove that and combine the two here. Will report back when updated, as usual.

How about trace gases in the atmosphere, like carbon dioxide, which are essential for life?

I could have sworn I'd already mentioned CO2

Updated

I also have an idea that a stable axial tilt is necessary for sufficient diverity and seasons to maintain a global wholesomness. That only happens when the planet has a moon. Just a hunch!