What is "Earth-like"?

[Forty Two]

It may be that the chance of life forming in the universe is one in 9 septillion.

Or, it may be one in 1 trillion.

Or, it may be one in 1 billion.

Is there any reason, based on what we know now, to settle on a probability closer to one of those numbers than the others?

[Hermit]

For the third time: The probability is not calculable on empirical grounds. Haven't we agreed on this some time ago?

[Brian Peacock]

Aye, the Drake Equation is a thought experiment, an exercise in probabilistic logic, not the expression of an empirical fact. Still, given it's premises it does carry more than a little rational force - though it's main impact is emotional I think: there's both an element of comfort and dread to be found in the thought that "We are not alone!"

[JimC]

Don't forget, aliens could turn out to be a kind of galactic Mormon...

[rainbow]

At this stage we have no data point of an earth-like planet that does not contain life forms.

Venus.

[pErvinalia]

Average temperature on Venus: 462 deg C. Very Earth-like...

[rainbow]

The search for exoplanets is largely motivated by answering the question: Is our solar system common? Venus and Earth formed under very similar conditions and probably had water delivered to their surfaces in the same way. However, at some point in their histories, the evolution of their surfaces and atmospheres diverged dramatically! To understand the history of the Earth, we must also understand the tenuous gap that separates the Earth from a runway greenhouse, such as that which exists on Venus. That understanding will come from determining the frequency of Venus-like planets as well as possible habitable planets like the Earth.

http://hzgallery.org/venus.html

[pErvinalia]

Venus had large coal reserves and its former inhabitants burned it all and caused the greenhouse effect that led to their extinction.

[Hermit]

At this stage we have no data point of an earth-like planet that does not contain life forms.

Venus.

Seriously? You seem to be working with a definition of "earth-like" I had not hitherto encountered. There certainly are similarities between the two planets. Both are round, both orbit a star, but with 96% of the atmosphere consisting of carbon dioxide, no presence of water, nor even hydrogen and, as rEv mentioned, a mean temperature of 462 °C, I would not describe it as earth-like in the sense of being a planet capable of supporting life, much less, a planet capable of supporting intelligent life.

[JimC]

At this stage we have no data point of an earth-like planet that does not contain life forms.

Venus.

Seriously? You seem to be working with a definition of "earth-like" I had not hitherto encountered. There certainly are similarities between the two planets. Both are round, both orbit a star, but with 96% of the atmosphere consisting of carbon dioxide, no presence of water, nor even hydrogen and, as rEv mentioned, a mean temperature of 462 °C, I would not describe it as earth-like in the sense of being a planet capable of supporting life, much less, a planet capable of supporting intelligent life.

Agreed, but rainbow brings up an interesting point that relatively similar planets in relatively similar orbits can dramatically diverge in surface conditions, precluding "life as we know it" in some cases. I'm sure I remember reading speculation that it was (at least partly) the absence of a moon that was a factor...

[rainbow]

At this stage we have no data point of an earth-like planet that does not contain life forms.

Venus.

Seriously? You seem to be working with a definition of "earth-like" I had not hitherto encountered. There certainly are similarities between the two planets. Both are round, both orbit a star, but with 96% of the atmosphere consisting of carbon dioxide, no presence of water, nor even hydrogen and, as rEv mentioned, a mean temperature of 462 °C, I would not describe it as earth-like in the sense of being a planet capable of supporting life, much less, a planet capable of supporting intelligent life.

Point being is that it is within a zone that could've, and probably at one stage had liquid water. If we came across such a planet in a nearby solar system, it would be described as "Earth-like".

Did you not even bother reading the OP at the beginning of this thread:

Yes, it's amazing that this possibly rocky planet is orbiting a star just 4 light-years away, possibly close enough to one day launch a mission to, but there is still so much we don't know about this brave new world.

Plus, Proxima b is far from being a twin of our planet.

Scientists aren't sure what kind of atmosphere it has or even if it's able to support a magnetic field, two things that it would need to sustain habitability in orbit around its active, flaring star.

We simply don't know if it can support water, life or much of anything on its surface at all.

Beyond the inaccuracy in this particular case, calling a planet "Earth-like" without knowing if it actually is, threatens to give members of the public a false sense of just how unique (or average) our Earth is.

[Hermit]

Did you not even bother reading the OP at the beginning of this thread:

Can you point to a statement wherein I disagree with Miriam Kramer's article?

[rainbow]

Did you not even bother reading the OP at the beginning of this thread:

Can you point to a statement wherein I disagree with Miriam Kramer's article?

You seem to be working with a definition of "earth-like" I had not hitherto encountered.

Had you read the article, you'd know exactly where such a definition is being used.

[Hermit]

Did you not even bother reading the OP at the beginning of this thread:

Can you point to a statement wherein I disagree with Miriam Kramer's article?

You seem to be working with a definition of "earth-like" I had not hitherto encountered.

Had you read the article, you'd know exactly where such a definition is being used.

Let's have a look at the context, shall we?

At this stage we have no data point of an earth-like planet that does not contain life forms.

Venus.

Seriously? You seem to be working with a definition of "earth-like" I had not hitherto encountered...

Furthermore, nice job evading my question. I guess you had to, since I never even pretended to disagree with the article you allege I have not read.

[Forty Two]

For the third time: The probability is not calculable on empirical grounds. Haven't we agreed on this some time ago?

I would prefer to say that the probability is not presently calculable on any grounds, empirical or otherwise.