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11h
comment Could the James Webb Space Telescope detect biosignals on exoplanets?
I think that the fundamental (no, the practical) question really is what life has to make up in order to make it self detectable to our instruments. We could try to reason about the probability for that. Ozone in a relatively nearby exoplanetary atmosphere seems to be the best for JWST to hope finding. But looking at ourselves which unfortunately is the only sample of life, and considering the complexity of microbiology, well we couldn't make this stuff up (Microbes just say: Don't call us, we'll make you).
11h
comment What is the axial tilt of a planet measured relative to?
That's informative, I didn't know that. So it is not relative to the ecliptic (except for Earth)? For example, Ceres' has an axial tilt of only 3°, but its orbit has an inclination of about 10°. So it still has "seasons" that make up for the difference (or the sum, I suppose)?
12h
comment Do NEA (Near Earth Asteroids) have minable water ice?
But the young sun was fainter, and while forming with maybe violent eruptions, the disc was protected by material. How could the Sun ever have sublimated most water in asteroids 5 AU away?
14h
revised What is the next planned mission that can discover life on another planet?
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14h
comment Do NEA (Near Earth Asteroids) have minable water ice?
Okay, "ice" does not include hydrated minerals, that explains some of my confusion reading about this. Is there really a debate about where the frost line is? 2.7 or 5 AU is a huge difference, and I would think that it is pretty straight forward physics with insolation at different distances. Can't Dawn figure out where it is relative to the frost line?
14h
revised What is the next planned mission that can discover life on another planet?
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14h
answered What is the next planned mission that can discover life on another planet?
1d
comment Do NEA (Near Earth Asteroids) have minable water ice?
But are NEA's believed to contain some substantial fraction of water (ISRU-wise) under their hard outgassed dark crusts? Recent encounters with 67P and Ceres has given me the impression that the surface and the interior could be very different. But those objects aren't NEA. Boltzman, I think, talks about molecules exposed to the Sun in naked space. Not so much about the interior of asteroids.
1d
revised Do NEA (Near Earth Asteroids) have minable water ice?
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1d
asked Do NEA (Near Earth Asteroids) have minable water ice?
1d
comment Can we spot a gray-goo exoplanet?
Jason T. Wright has looked for waste heat from galactic super civilizations, but nothing has turned up. And there's the idea around that just like we detect star transiting exoplanets, we might detect something like a Dyson Sphere. Nothing artificial has been found, though. We are starting to put an upper limit to alien life, as we know it(?) But whatever "it" is, if it is, it is different than we imagine. "Gray goo" might be undetectable even if it is here on Earth now.
1d
comment Can we spot a gray-goo exoplanet?
Exoplanet's size and mass and orbit and sometimes basic atmospheric composition are quite possible to detect today. But what causes that appearance is up to theory to explain. And if your fantastic scenario is included in the possibilities, it becomes very hard to reason about it. (Btw, we already have undeniable evidence for aliens having been here: They've eaten almost everything, that's why space is so empty. We live in the Local Fluff which they left over between lunch and dinner.)
Jul
2
comment Is any meteorite known to come from a comet?
I read somewhere that about 50,000 meteorites have been collected and identified as meteorites. But really not even one comes from a comet? So the comets breaking up doesn't change the (vaporising) speed of the fragments alot, I suppose. Tells us they are all fluffy.
Jul
1
asked Are mass extinction events more likely during meteor showers / passing through comet debris?
Jul
1
revised Is any meteorite known to come from a comet?
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Jun
21
asked Is any meteorite known to come from a comet?
Jun
20
comment How did we come to the conclusion that light moves as fast as it does?
@zibadawatimmy But the speed was the first time "come up with" thanks to an astronomical method. I just don't find it OT at all to ask an astrophysicist about how the speed of light is measured.
Jun
20
comment How did we come to the conclusion that light moves as fast as it does?
@zibadawatimmy But it was discovered by an astronomer thanks to observations of Jupiter's moons. 220,000 km/s he measured, not bad back in 1676! Space is basically an extreme physics lab and physics as such was discovered only thanks to astronomical observations. So I don't think question is off topic.
Jun
15
comment Why doesn't this paradox disprove (some) multiverse quantum gravitational theories?
If our "plain vanilla" universe is topologically flat then it is infinite. And if matter is large-scale homogeneously distributed, which seems to be the best and simplest model today, then it already contains infinitely much mass. So the key part of the question is maybe "short distance in another dimension".
Jun
10
comment Why do dark objects look white from a distance? (Moon, Ceres, but not Earth!)
So we are color blind at low illumination. That must be an important part of the explanation. The Moon is indeed quite faint in daylight. But stars range from blue via yellow to red to the naked eye, so some distant objects do look colored. And Mars is red while Venus is white. Both are CO2 rich atmospheric reflectors of sunlight. Jupiter has gray scale features in a simple telescope. But to a probe out there it seems to be a very colorful place, especially with Io. Maybe the subjective human perception of color doesn't go all the way together with today's physics.