That essential amino acids can form spontaneously under reducing conditions is not news–we’ve even seen spectral traces of some amino acids in molecular clouds in the interstellar medium–and while it is evidence that the precursors to our kind of carbonaceous-nitrogenous-based life are commonly found in the universe, it is not direct evidence of any second or more origin of life on Earth (or anywhere else, at this point). All life on Earth that we have observed has a distinctly common origin based upon similarities in the structure of the genome which could not conceivably be due to chance.
There is reason to expect that life like ours (at the basic level of a nucleic molecule coding fro self-replicating proteins) could arise given suitable conditions of energy, liquid medium, and the just-so combination of chemical catalysts, but we have yet to see any direct evidence of independent formation of life (although I’d lay even odds on finding some kind of life-like system on one or more of the Jovian or Saturnian moons with a liquid water or hydrocarbon sea).
Indulge me, and actually read the two papers I linked to. This isn’t a matter of dust “kicked up” by the construction or deployment of a telescope on the surface of the Moon; the Moon has a tenuous atmosphere of electrostatically-charged dust which sticks to everything. Your perception of the solar wind as some kind of force that blows the dust is completely wrong; solar wind is comprised of the very charged particles that convey electrical charge to the dust. On Earth, those particles are captured in the magnetosphere and upper atmosphere, giving rise to phenomena such as aurorae and lightning, but on the Moon and other worlds without an atmosphere or magnetic dynamo it impacts directly on the surface.
Hubble can be pointed in any direction away from the Sun, with its solar shade keeping the optics free from any glare. A telescope on a fixed point on a rotating body will spend a significant amount of time unavoidably pointing in the general direction of the Sun, and with ambient light reflecting off of the adjacent terrain. Of course, you could build a satellite on the highest point in the area or deploy a very long shade to prevent direct and reflected light, but it still means that you can’t point the telescope in any arbitrary direction or keep it focused on a specific point away from the poles for more than a few days at a time. There is simply no reason to emplace a telescope on the Moon when it could just as readily be deployed in solar-orbiting space.
Setting aside that global [climate change] warming is not caused by adding heat but instead altering the atmosphere so it cannot radiate away as much heat-energy as it takes in, and that the amount of rockets we could conceivably launch in even the most optimistic projections would not be enough to make a dent in heat contribution, you would not use a nuclear thermal rocket for ground-to-orbit propulsion because the thrust-to-weight ratio is too low to be of use in that application. Nuclear thermal rocket (NTR) propulsion is useful as a low but long duration thrust for interplanetary trajectories in order to gain much higher total impulse than would be possible using chemical propellants whose exhaust velocities and energies are limited by the temperature of combustion. Of course, the higher temperature of NTR propulsion systems also brings with it the need to be able to get rid of greater amounts of waste heat, which requires large radiation surfaces, so it isn’t a trivial solution even if you assume such systems to be feasible for use in the near future.
Ignoring the energy costs to produce liquid oxygen from air and then distill the 0.2% of xenon/krypton out of it.
Xenon, the most appropriate fuel is also the most expensive gas primarily due to the energy requirements.
5.8971 kg/m³ and world production is 7,000 m³ so current world wide production is about 41,000 kg and you are going to need a lot more than that to get to high velocities.
I guess you could use solar etc… but it would have some impact.
You do understand we wouldn’t launch using nuclear rockets right?
Even if we did, rockets don’t heat the atmosphere to any appreciable degree. The problem of Climate Change is that increased CO[sub]2[/sub] levels minimize the amount of incident solar energy being sent back into space.
Similar energy problem, but I was responding to the inert claim. Hydrogen’s low molar weight does become problematic but at least there is more than 2 billion tons of it where we can reach it unlike xenon.
General reply:
Here is a slide deck from NASA talking about some of the challenges but note:
“Nuclear fission doesn’t have the energy density required”
NDRs are probably practical for around the Oort cloud unless we humans are willing to be very very patient getting even to the nearest stars. NTR will probably be able to double efficiencies over chemical rockets but we really need several orders of magnitude improvements. NTR + fusion would be great for multi decade trips to ~200 AU.
NTR does look very useful for interplanetary trips though.
Detecting free oxygen in the atmosphere would be a big deal, and should soon be possible, maybe with the Webb telescope. Do we know of any process besides life which can create an oxygenated atmosphere?
A space interferometer can only get you so far, because at some point you simply run out of photons. Just how many photons do you think we receive from some small object on a planet around another star?
If the object were always facing the same way and we could track it, you might be able to fix this by extremely long exposures like the Hubble deep field. Unfortunately, planets orbit and rotate, so this isn’t going to work.
In the near future (say, the next 20 years), it’s likely that we will know the atmospheric content in some detail for the closest exo lanets to us. We will have directly imaged many of them, but only to a resolution of a few pixels at most.
There is a new generation of telescopes coming online during that period that are going to revolutionize astronomy and exoplanet research. In space we’ll have the James Webb, GAIA (already at work, and doing incredibly important precise astrometry). In a few years the Large Synoptic Survey Telescope will come online, and after that a new generation of scopes with mirrors up to 30m in diameter. Combined with adaptive optics, these scopes will give us an order of magnitude better resolution than Hubble. We will be using them to, among other things, directly image some exoplanets and attempt to measure the composition of their atmospheres.
In that same timeframe, or shortly thereafter, we will hopefully get a new generation of space telescopes and a starshield that can be used to block starlight more effectively and allow us to get even better images and data from orbiting exoplanets.
The wild card is the solar lensing idea, which at least gives us the possibility of being able to magnify some distant planets to the point where we might actually make out large surface details, but that’s still highly speculative.
Photodissociation of water molecules. If the surface of the planet is virtually all water or ice, the dissociated oxygen will have no sink, except to recombine with the hydrogen. But some of the hydrogen will escape to space, so excess oxygen will build up in the atmosphere.
Oxygen is such a reactive element (from whence we get the term, “oxidizer” for the electron-receptors in redox reactions) that only fluorine is more electronegative. (Technically helium and neon are even more electronegative but they almost never form bonds under any normal condition, just stripping away electrons from some donor never to return.) Seeing an atmosphere with more than a couple percent of diatomic oxygen would definitely indicate some non-equilibrium thermodynamics going on that would be indicative of some self-organizing system if not actually life. As a practical matter, any ‘rocky’ world is going to have some amount of carbon compounds and silicates as well as iron and nitrogen given that these are respectively the 4th, 8th, 6th, and 7th most abundant elements in the universe.
Yes, but if all the rock (carbon, silicates, etc.) is buried under ice or deep water, it’s being sequestered from any oxygen in the atmosphere. So the oxy from photodissociation will not be able to react with it. Thus a build up of oxygen in the atmosphere.
This, of course, assumes there’s no gases like methane that will react with the oxy. Once any carbohydrates or ammonia in the original atmosphere oxidize, there will only be nitrogen, carbon dioxide, water vapor, and inert gases left. None of those will significantly oxidize.
Now vulcanism could change that by exposing fresh rock to the air. So the amount of oxygen could yo-yo up and down depending on how much vulcanism there is at any one time.
While it is certainly possible to have a world covered in ice or water, one without any impurities at all seems pretty unlikely, and of course oxygen will dissolve in water and percolate through ice even at relatively low atmospheric pressure. Even without vulcanism, a planet subject to enough heating to cause photodissociation will have upwelling or movement in an icy crust, and of course carbonaceous, ferrous, and silicate material that comes from meteorites will oxidize. Photodissociation can produce a few percentage of diatomic oxygen but once the level of free oxygen is high enough, it’s just going to recombined with whatever it separated from, whether it is hydrogen from water or other elements it can find in the environment.
If we found a planet with an oxygen content of 10% or more, it wouldn’t be conclusive proof that life existed on it, but it would be very difficult to explain through some other natural phenomena because maintaining that level would require constant replenishment. However, finding a world without oxygen doesn’t mean life can’t exist there; just that it does not use an aerobic metabolism like ours.
You have said this before, but it is not correct. dtilque has the right idea; photodissociation on an ocean world, where the rock that could act as an oxygen sink is not only covered by a hundred kilometres of water, but also several hundred kilometres of dense, high-pressure water ice, would probably create more than enough long-term oxygen to cause a false positive.
For a more academic source, try
We may be faced with many kinds of false positive if all we have to go on is remote observation. I think we will start seeing some of these false positives fairly soon - in fact, the internet noise around Tabby’s star is an example of a possible false positive with respect to the detection of civilisation.
