64
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 Drake"
26
There is currently only one planet known to be capable of supporting human life, and you're on it.
Several planets have been found in the region in which we expect water to be liquid on much of the planet. Of these, only one fits the criteria of being Earth-sized and well placed in the habitable zone: Kepler 186-f
However we know nothing about it's ...
23
What will happen to life on earth or human beings on earth?
Assuming that human beings, or life, still exists on Earth at that time, they will have survived so much due to the ongoing death of the sun, that the gravitational pertubations due to the galactic collision will be nothing.
Keep in mind that in about 1-2 billion years, the sun will be so hot and ...
19
4 billion years is the same timeframe of the life remaining to our Sun.
So if we have not yet invented interstellar voyages, we're screwed, with or without Andromeda.
Besides, stars do not interact directly with each other in a galactic collision. What we will notice from the several stars we are on is that star orbits around the galactic centre will be ...
18
First, note that by the time Andromeda is close enough for collisions with wandering stars to become a concern, Earth's average temperature will have changed significantly, and the planet will be unrecognizable.
When Sol is 8.5 billion years old, it will still have hydrogen available for fusion, but as it fuses it contracts and expands differentially. The ...
17
The most likely candidate would be the Tardigrade. These little guys handle vacuum and radiation just fine. So long as water is provided, according to tests done in LEO the Tardigrade would survive on Mars. Even if they do dehydrate, they spring back to life once water is provided again.
15
We actually have a very good idea of this because the Mars Reconnaissance Orbiter has been orbiting Mars for over a decade. The MRO is, basically, a spy satellite around Mars and is continually taking high-resolution photos of the surface. It has revisted much of the surface, taking pictures multiple times over the years.
As a consequence, we have a very ...
12
Direct collisions between stars and planets is highly unlikely, due to the relatively low density of objects in the Milky Way and Andromeda. For instance, the stellar density in the solar neighborhood is only 0.004 stars per cubic light year.
The problem is that gravitational interactions between objects is not low. Stars that eventually pass too close to ...
12
Well, first things first. It's not likely to have a planet orbiting near a black hole and in significant time dilation because the tidal effects would likely tear anything that close apart. Certainly a planet orbiting a stellar mass black hole would need to be quite far away so as to not be torn apart, so any time dilation would be pretty small.
Around ...
11
I had put off answering this question because it seems too broad without specifying what sort of detection methods are proposed. But if you answer it directly from the perspective of - if we were to take the solar system and put it at some distance from us, would we able to detect signs of life on planet Earth - then the answer is probably not.
Using ...
11
You may be interested in the number of habitable zone planets. These are planetary-mass objects in a sort of "Goldilocks" region from their respective stars: This region is just right, given adequate atmospheric conditions, to possibly permit the existence of liquid water on the surface. That's not a surefire sign that the planet is capable of supporting ...
10
The impact of Phobos, even in one piece (less likely), would be different from Chicxulub. Phobos is probably a little larger than the Chicxulub impactor, but much slower, and comes in almost perfectly tangential. The impact energy would be less than a 10th of the Chicxulub impact, and the energy would be distributed over a large region around the Martian ...
10
Normally when two galaxies collide, it is the gas that interacts with each other. The odds of stars impacting each other are nearly zero due to the huge distances between the stars. The same goes for planets hitting each other.
The timescales on this happening are so large that it is difficult for our mind to understand these distances (and the timescales ...
10
If you check 2001 A Space Odyssey saga, Europa is actually a satellite with Life.
Coming back to real space, the "comfort zone" for life is approximately from Venus' orbit to Mars' orbit. There, only Moon, Phobos and Deimos are satellites, and all of them are too dry to have any kind of life.
Beyond the comfort zone you need some other way for water not to ...
10
You're correct; extraterrestrial phosphine is not actually a new discovery. As you said, we've known for decades (see e.g. Ridgway et al. 1976) that phosphine can and does exist in some gas giant atmospheres, including Jupiter's. However, detailed modeling has been done of the associated photochemistry beginning at around the same time, and as far as I'm ...
9
The Drake equation is little more than a randomly assembled guess of relevant factors for intelligent life, and any use of it requires a number of hard to justify guesses for the various probabilities.
It is otherwise an attempt to give a foundation for making Fermi estimations on the number of civilizations, and the associated Fermi paradox. A Fermi ...
9
Why would we assume that the early martian life originated on Mars,
rather than Earth?
There's still a whole lot we don't know. As Wayfaring stranger points out in the comments, Origin is a whole different question. It's possible that life originated outside our solar system and came to either Mars and/or Earth from outside the solar-system. I don't ...
9
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 (drastically different)
forms?
and
I'm always bothered by these reports because they are all predicated
on the premise that life on other planets will closely resemble ...
9
No, nothing on Europa could possibly be photosynthesizing as we know it. Jupiter doesn't emit light, and what it reflects from the sun is not enough, plus there's no significant amount of carbon dioxide there.
However, the first life on Earth was not plants, it was chemotrophs. These bacteria gained their energy from the heat of hydrothermal vents, and if ...
8
Direct observation of exoplanets (and then of traces of life on them) is still a big challenge.
Up to now, there are several indirect methods (effects on the parent star or on other stars), and direct detection is performed by using devices such as coronagraphs on faint stars, where very bright planets are imaged.
A way to image things such as as "...
8
Lets say you put a billion balloons on a dart board. Now lets say you throw a million darts at that dart board. If you were to pick a specific balloon and calculate the odds that THIS particular balloon would be hit by a dart, the odds would be astronomically low. However, if you were to say that at least SOME of the balloons would be popped, the odds are ...
8
On the surface of Mars probably none, since it's too dry or too cold, or both, to stay active.
Spores or other dormant forms probably could survive for centuries, until radiation will gradually destroy the organic molecules necessary to get back into an active state.
But there are "Mars Special Regions", where either Earth microbes or potential Martian ...
7
That's one of the big questions. ESA scientists, at least, think it's worth looking for underground life. See ExoMars mission.
More likely than earth worms are microbes, since some microbes on Earth live under similar conditions as presumed for underground Mars.
7
The probabilites are unknown at the moment (March 2014), since there is only one known planet (Earth) harboring life. This doesn't allow any meaningful probability estimates for the occurence of life, based on empirical data.
The overall formation of life is too complex to allow simulations based on current technology.
Although some intermediate steps can ...
7
I've read lichens have been shown to survive in a Mars-like atmosphere, tested by NASA.
This other article says they can survive vacuum and radiation
http://www.astrobio.net/extreme-life/lichen-on-mars/
7
Proxima Centauri can't explode as supernova as it is about 2 orders of magnitude too small and light.
But if a supernova were to happen from that distance? How bright would it be?
You can use the formula:
$$\text{Apparent magnitude} = \text{Absolute magnitude}+5log_{10}(distance)-5$$
where the distance is in parsecs.
Proxima centauri is 1.3 parsecs ...
7
I'll touch on a few of these because I disagree with some of those ideas.
There are approx. 2000 planetary systems discovered, and all of them,
except the Solar System, have angular momentum mostly in a star
There's a few problems with that argument because planets close to their star are easier to identify. We don't have a complete picture of the ...
6
Depends on what you mean by detecting life. As is explained in this what-if post by Randall Munroe, the algae on earth will tell the aliens about us before we can tell them about us.
If you consider the presence of liquid water or the presence of $O_2$ as detecting life, then such detection can be made by studying the spectrum of extra-solar planets, ...
6
When you lose your keys on a dark night you look where the probability of finding them is highest (which is a combination of being likely to see them with their probability of being there), which is not necessarily where they are most likely to be. In the case of the search for extra-terrestrial life we have a fairly good idea what the signature of carbon ...
6
Did you mean to ask
Would life on Earth be possible if Earth was the only planet in the Solar system?
The answer is perhaps , we can only speculate and know too little about the evolution of the planetary system to give any firm answer.
The Moon, for example, (not a planet I know) stabilises the Earth spin axis, preventing it from flipping, which would ...
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