64 votes
Accepted

Serious alternate form of the Drake Equation, or graffiti?

Given the font, it's xkcd 384, The Drake Equation. The two $X$'s are the other $f$ terms from the original Drake equation, while the $B_S$ is "amount of bullshit you're willing to buy from Frank ...
Rob's user avatar
  • 2,035
23 votes

Did the earth form outside the solar system?

The chance happenstance that Earth happened to be floating along and got captured is minuscule. How did Earth wind up floating through space? There's no established mechanism for terrestrial planets ...
zephyr's user avatar
  • 15k
16 votes

Did the earth form outside the solar system?

I think the Earth's orbit is by far the strongest argument you have that the Earth formed around the Sun. The orbit is nearly circular and almost in the Sun's equatorial plane, similar to the other ...
ProfRob's user avatar
  • 152k
11 votes

What if we are looking for the wrong signs of life on other planets?

What if we are looking for the wrong signs of life on other planets? Are there any fields of astronomy that look beyond the "near-Earth" life comparisons and look for life in other (...
userLTK's user avatar
  • 24k
5 votes
Accepted

What planets and moons have we seeded with life (if any)?

This would seem to be constrained to planets and moons earth has landed on or impacted at all, as we have no way of telling after the fact whether a lander was perfectly sterilized. That list is as ...
Pulchritude's user avatar
5 votes

What if we are looking for the wrong signs of life on other planets?

We only have a sample of 1 - the Earth - for analysis or proposition of potential life-compatible conditions on other planets. Only carbon-based life can exist in this universe. Boron and Silicon are ...
QEDlin Saltum's user avatar
5 votes
Accepted

Have there been any searches for extraterrestrial life which doesn't require water, oxygen and carbon?

Some of the projects carried out by The Search for Extraterrestrial Intelligence (SETI) would appear to make no carbon/water-based assumptions - for example Laser Seti, which looks for optical beacons ...
ProfRob's user avatar
  • 152k
4 votes
Accepted

Chances of life on other planets, how watertight is the idea that 'As soon as life could occur, it did occur’?

Yes, early life on Earth does not imply easy life. Full disclosure: I have a paper on this, Snyder-Beattie, A. E., Sandberg, A., Drexler, K. E., & Bonsall, M. B. (2021). The Timing of Evolutionary ...
Anders Sandberg's user avatar
4 votes

Did the earth form outside the solar system?

It would be really difficult for the Earth to end up in a nearly circular orbit if it came from outside the solar system. Effectively falling from infinity, it would have a hyperbolic orbit and make ...
zeta-band's user avatar
  • 135
3 votes

Did the earth form outside the solar system?

Occam's razor defeats the hypothesis. There are no astronomical anomalies about earth's obit or position that require the complication of earth's insertion from beyond the solar system. Unless some ...
bobD's user avatar
  • 31
3 votes
Accepted

Life forms on planets not requiring water and oxygen as basic building blocks

The very short answer is, we don't know. Our only experience of life is what we have discovered on Earth. All life on Earth is based around RNA and DNA. RNA has been discovered in meteors and ...
Fred's user avatar
  • 2,169
2 votes

Conditions on Earth when Mars was warmer, wetter & had a thicker atmosphere

Carr & Head 2010 summarize the evidence for past martian flowing water (see Figure below), and contrast it with the corresponding timescale on Earth (timescale on far left). As is shown in the ...
AtmosphericPrisonEscape's user avatar
2 votes

Why haven't detected life in the universe?

The experimental data only shows that there is no life and no intelligent life in the parameter space where we could detect it. The experimental data doesn't explain the cause. That we are alone in ...
peterh's user avatar
  • 3,161
1 vote

Why haven't detected life in the universe?

There are a number of questions here on the Fermi Paradox with answers ranging from an Infinite Universe, the parameters for the Drake Equation and others. Well worth having a read through them. But ...
Rory Alsop's user avatar
  • 5,063
1 vote

What planets and moons have we seeded with life (if any)?

My best guess (though I don't know about every mission) is that we have at least seeded our moon with life when we visited it. We have also likely seeded Venus, Mars, and Jupiter with the various ...
Jonathan's user avatar
  • 4,385
1 vote

If we found evidence of life on Mars, how would we know that it originated on Mars rather than Earth?

We'd analyze the DNA and RNA sequences (assuming they had any) and the coding of amino acids, and compare them with the sequencing and coding on Earth. As far as we are evolutionary from Archaea and ...
Syd Henderson's user avatar
1 vote

If we found evidence of life on Mars, how would we know that it originated on Mars rather than Earth?

In addition to already present good answers, I would say that if we found life on Mars on a century there is a noticeably probability of it being made from Earth microbes accidentally taken there by ...
Pere's user avatar
  • 1,760

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