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Comment Re:Radiation? (Score 1) 271

As AC said, not necessarily for things evolved to survive in it. Tardigrades for example can handle fairly large doses just fine.

The planets are also likely tidally locked, and solar radiation would be a complete non-issue for anything on the dark side of the planet. Life has no need for light after all, it had been thriving on Earth for millions of years before the first bacteria evolved a light-sensitive protein that let them detect daylight and flee to deeper, safer water. And many millions of years more before one evolved the ability to harness light for energy.

Comment Re:What makes this special? (Score 1) 271

We're talking about space science - "someday" is usually presumed to be many decades or centuries in the future.

And is that all? Really? That's not too bad. Child's play once we get serious about astronomy and start building gravitational telescopes using our sun as the lens. What could you resolve with a 550-700AU focal length?

Comment Re:Sterile and shattered. Or Not (Score 1) 271

No, rotation isn't required for tidal forces, just for those forces to substantially "massage" a planet. Just squeezing the planet doesn't add heat, the squeeze needs to be changing to generate substantial heat.

It's true you'll still get some tidal effects due to eccentricity, but they'll be far smaller than if the planet was rotating - if you imagine the tides squeezing a stress-ball into more of a football shape, rotation means the bulges are traveling around the planet once per day. Without rotation you'll get just a slight change in how tight you're squeezing as the planet move closer and further from its primary, as well as some very slight oscillation of the bulge across the surface due to the associated libration.

I suppose though if we're talking about tight orbits around a huge primary, even a tiny fraction of the original tidal effects could still be quite large.

Hmm, and there will be another effect as well - that of the pulsating "tides" from the other planets - after all the distance between their orbits ranges between only about 2x and 4x that between the Earth and Moon, except for the outermost at ~6x the distance. That would be a factor with Jupiter's moons as well. I wonder how the magnitude of the effect would compare?

Comment Re:Sterile and shattered. (Score 4, Informative) 271

Where are you getting "a few percent" from?

There's only 400ppm total CO2 in the atmosphere, that 100ppm represents fully 25% of the total.
Perhaps you're thinking of the fact that CO2 is only a few percent of the total atmosphere? But that's largely irrelevant because almost all atmospheric gasses are completely transparent to thermal infrared radiation, and so don't provide any insulation at all. If they were the only things in the atmosphere the Earth would be as cold as the moon (colder actually, the moon is actually coal black and thus a good thermal absorber)

Water vapor, CO2, and methane are responsible for the overwhelming majority of Earth's atmospheric insulation. Water makes up about 0.4% of the atmosphere (mostly at low altitude), CO2 is about 0.04% of the atmosphere,and methane 0.0002%.

Water is obviously the biggest contributor, but it can't build up in the atmosphere since it rains out as the concentration builds, so it remains fairly constant at a given temperature. It's worth nothing though that it acts as a positive feedback system - the warmer the planet, the more water vapor builds up in the atmosphere, and the more heat will be trapped. So it will tend to make any global temperature changes more extreme.

Methane is actually a considerably more powerful greenhouse gas than CO2 per pound, but there's so little of it that it still only traps a fraction as much heat as CO2. It's also worth mentioning though that humans are estimated to be responsible for somewhere around 2/3 of global methane emissions - we're working hard on that front as well.

Which leaves CO2 as a sort of "thermostat" - more CO2 leads to a warmer planet and faster plant growth, which pulls CO2 out of the atmosphere leading to a cooler planet and slower plant growth, which lets CO2 build up in the atmosphere again... it's a self-stabilizing system that oscillates around some "average" point until something disrupts it - such as dumping carbon into the atmosphere that's been locked underground for millions of years.

As for what difference a few percent can make? Lets do some rough math. Say CO2 is responsible for about 10% of the total greenhouse gas "insulation" (I have no idea, but it makes up about 10% of the total greenhouse gases in the atmosphere so that seems like a good guess). The 100ppm increase would therefore be responsible for about 2.5%. That means the Earth will have to warm up enough to radiate 2.5% more heat in order to shed the same amount of energy through the insulation to restore the energy balance and stop heating up. The amount of heat radiated is proportional to the fourth power of temperature, so a 2.5% increase in radiant heat translates to ...1.025^(1/4) = 1.006... a 0.6% increase in temperature. Earth currently averages about 61F, or 289K in absolute terms, and a 0.6% increase of that translates to 1.8K, or about 3.2F.

A three degree increase doesn't sound terribly catastrophic all on it's own, but that's assuming nothing else changes, which isn't the case.
First off as things warm up we'll have more water vapor in the air, further increasing the amount of insulation.
More dramatically, the warming isn't uniform - the poles are heating much faster than the rest of the planet, which means those shiny white ice "mirrors" that currently reflect sunlight back into space before its absorbed are being replaced with dark sunlight-absorbing water. That means the planet is absorbing more energy from the sun, and it's going to heat up even further until it's radiating all that extra energy back into space as well.

And of course there's the rising oceans to contend with: water has a coefficient of expansion of 0.00012/*F, and the oceans have an average depth of about 12,100 feet. 12,100feet x 3.2*F x 0.00012/*F = 4.65 feet. So even without any icecaps melting, the ocean would rise that much. Which maybe doesn't sound too terrible, but something like 90% of the worlds population live within 10 feet of sea level. That's going to be a heck of a lot of infrastructure to rebuild a lot further inland. Dikes and other storm-surge control systems are an alternative, but they're not exactly a whole lot cheaper to build.

And that's before we even consider second-order effects, such as we're seeing with the warming poles robbing the jet streams of their force, allowing it to meander in winding paths that can trap storms in one place rather than sweeping them across the continent, resulting in flooding in some places and drought in others, which wreaks havoc on livestock and agriculture.

Comment Re:Let's set up a telescope array on the moon now (Score 1) 271

That only applies to looking at things in the plane of the solar system. If you look at right angles to that, then nothing local but the occasional asteroid will ever pass in front of you. And you can look pretty close to the plane as well, even the sun is only 0.5 degrees across as seen from Earth, meaning most of the sky is completely unobstructed.

Of course for something like the Hubble in a low-Earth orbit, the Earth is a somewhat bigger problem. But they conveniently placed it in a non-ecliptic orbit, so it has a pretty huge amount of unobstructed sky, the particular part of which change gradually over the course of a year. So, even if they want a long exposure of something in the ecliptic plane they can do so, they just have to wait for the time of year that they'll have a clear view. As it is, the Hubble Ultra Deep Field image is the longest exposure ever taken, at 50 days, and that represents a phenomenal opportunity cost in terms of other things that could have been looked at instead.

And of course, the higher the orbit, the less of an obstruction the Earth presents. By the time you reach geosynchronous orbit, the Earth is only about 26 degrees across.

Comment Re:What makes this special? (Score 1) 271

Umm, no.

The James Webb telescope will have a resolution of 0.1 arc-seconds, meanwhile even the closest star, Proxima Centauri, has an angular diameter of only 0.001 arc-seconds. There are larger stars, but even Betelgeuse, one of the largest as seen from Earth, is only ~0.05 arc-seconds across. So the Webb telescope won't even remotely be able to resolve an image of a star's surface, much less an exoplanet. They'll still be nothing more than single points of light.

From what I can find, it appears that the Webb will actually have roughly the same resolution as the Hubble - it's benefits will primarily be in being able to see dimmer objects, and across a wider band of the light spectrum (particularly further into the infrared). Which will allow it to better analyze the absorption spectra of the atmospheres of exoplanets, but not actually see them.

Comment Re:Sterile and shattered. (Score 1) 271

Though there is a point to be made that any early generational ship is unlikely to be able to turn around without first stopping at the target star to refuel. After all, turning around takes far more that 2x as much fuel as stopping, even before you include the additional fuel you'd need to stop once you got back to Earth (and the additional fuel needed to carry that fuel, and the additional ...). You could conceivably carry that much extra fuel, but you'd probably be better off dedicating all that payload to stuff that would be useful at your destination.

Basically any generation ship built in the forseeable future will be a one-way trip for those embarking. The generation that reaches the destination has the option of refueling and heading back, but they're unlikely to survive to see Earth, and meanwhile will be committing additional generations to be born on ship.

But then nobody asked me if I wanted to be born into a world being actively destroyed on a barely imaginable scale, or in a country that has apparently been convinced that waste and stupidity are aspirations to strive for. But, just like a hypothetical ship-born child, I always have to option to opt-out if I truly believe I would be better off not existing.

Comment Re:Sterile and shattered. (Score 1) 271

Actually the amount of CO2 we release is easily calculated from the amount of fuel we burn. And measurements consistently show the amount of CO2 in the atmosphere increasing more slowly than we're adding it - it doesn't take a genius to realize that if a swimming pool is filling more slowly than you're adding water, then it wouldn't be filling at all without your help.

Meanwhile the atmosphere now contains about 30% more CO2 now than it did a century ago, mostly because of fossil fuel emissions. 30% may not sound like much, but it tips of the scales in an energy flow that completely dwarfs all human activity - translating to more excess solar heat being retained every day than humanity uses electricity in a century.

As for plants being CO2 limited - so what? Obviously they're not taking up the slack, or CO2 levels wouldn't be increasing. And as a matter of fact it appears that global biomass is actually decreasing, rather than increasing to keep pace with the increasing CO2. Though admittedly that part probably has more to do with more direct pollution and environmental destruction for now. Perhaps if we were otherwise responsible stewards of the planet, it could neutralize our fossil CO2 emissions, but we're pretty much attacking it on all fronts instead.

Comment Re:Sterile and shattered. (Score 1) 271

Let's dial that back a little: *relativistic* space travel might be *difficult* near stars. That sucks for anyone dreaming of vacationing among the stars, but isn't really an issue for anyone patient enough to embark on a multi-generational voyage, or just slow down enough for sacrificial scout-ships to clear the way through the Oort cloud.

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