"After its discovery, it was generally believed that any atmosphere thick enough to keep the planet warm would become cold enough on the night side to freeze out entirely, ruining any prospects for a habitable climate.... To test whether this intuition was correct, Wordsworth and colleagues developed a new kind of computer model capable of accurately simulating possible exoplanet climates.... To their surprise, they found that with a dense carbon dioxide atmosphere -- a likely scenario on such a large planet -- the climate of Gliese 581d is not only stable against collapse, but warm enough to have oceans, clouds and rainfall."
Question. How the bloody hell do you validate a computer model of how an atmosphere unlike anything we can observe in our solar system works? Did someone fly out there and verify it before publishing? And I'm supposed to believe your computer model iterates correctly over geologic time? Really? Really?
(Obligatory-but-totally-serious that this is still cool work not counting the computer model part, and to be honest I don't really care either way what the computer model says; I would be equally skeptical if they produced a model that claimed any outcome at all.)
For instance, the use of RTMs for retrieving estimates of gas concentrations on Earth is routine. This idea is what the global CO2 maps produced by AIRS
are based on. You can sense back-scattered radiation, which tells you about the CO2 concentration in the air below the satellite. A good RTM is what allows the inversion of radiation into gas concentration.
Another related data point is that lots of investigators have been working for years on climate of Jupiter and Saturn using some of the same ideas. There are conference sessions about this topic, e.g.
Sensitivity analysis. Elements of the simulation are based wholly on proven, low-level physics (for example, calculating the amount of heat absorbed by a given amount of CO2 from a given amount of sunlight) whenever possible, and when that's infeasible the modelers test a range of possible values to see what happens. For example, you can't exactly calculate the density of condensation nuclei in the atmosphere (used for calculating cloud formation behavior), so they just ran the simulation with a bunch of believable values. Another example is pretty clearly laid out in the first sentence of the "results" section:
We performed simulations with 5, 10, 20 and 30 bar
atmospheric pressure and 1:1, 1:2 and 1:10 orbit-rotation
resonances for both rocky and ocean planets (see Table 1).
There is not enough data in a vague orbit and vague size (in a dataset that until recently contained a spurious planet) to feed a simulation like this, which means that the simulation was, mathematically necessarily (and I do not use this term lightly), made up from nearly whole cloth. And then we have no way to verify anything that it did say, assuming it even started from the correct place, especially with regards to stability on geologic time. Even an 99.9999999%-per-hour perfect simulation will still diverge on geologic time scales. For all we know, an atmosphere with a mountain range here will freeze out in a century, whereas a mountain range there could in fact result in a stable atmosphere over geologic time. This is all information-theoretic necessity. This is entertainment, not science.
That may be all the scientists claimed. It's still a fun result, even if I wouldn't put my grandchildren on a flight to Gliese on the strength of it. I'm reacting against the certainty expressed in the article.
Ok, I think I see what you mean now, and I agree with you. They've shown that the distribution assuming some set of priors includes some particular, interesting outcome. This is the first planet we've ever seen where we can say that given how much information we have about it, though, which means that it's still cool.
Yeah, we can still look at some extremely broad possibilities how how such a planet atmosphere could behave based on the little we know about the planet. Then the simulation gives some guide onto how each of these would play out.
Sure it's very speculative, but one step up from no data at all, which is the best we have now. At least have an idea of the size, the orbit and the sunlight intensity that would be hitting the planet.
By making predictions that can be checked with the next generation of telescopes. That's how science works: look at what you have, figure out what you still want to know and design an experiment that can discriminate between different alternatives.
Especially since researchers aren't able to accurately simulate Earth's climate over a smaller timescale, despite having much much better data about the current climate. Heck, for that planet they don't even know the composition of the atmosphere.
Welcome to science today. To their credit, at least when we find out the model was missing some key information they will update it and update their theories.
Why aren't we sending probes out right now? Yeah, we're not going to hear anything back for (probably) 100 years, but why not start now? If we had sent a probe out back in the 60s, this would be something that I'd see results from within my lifetime.
Of course, this is assuming that we can build fast interstellar transit systems...which is a huge if.
Because anything we might start now would be overtaken before it is one tenth there by anything we might start five hundred years from now. And if we won't be able to start anything faster by then, there would be no technological civilization left to receive the results. So it would be pointless, space is just too big. Once we can reliably reach 1/10 c we might think about sending a probe to Alpha Centauri, although even that would have more symbolic value as a technological demonstration than scientific value. You would have to wait more than half a century for a science mission of at most a few hours, because decellerating would require so much time and fuel to make the whole mission infeasible. A mission to Gliese 581 is a distant fourth or fifth project after that, and sending a planetary probe like the one we send to mars is even more distant.
(For reference, it took several years of swing by maneuvers to get a probe out of the orbital plane of the planets into an orbit that allows to examine the poles of the sun, and that takes far less energy than even reaching 1/100 c.)
It takes light 40 years to get there and back at 1,079,252,849 km/h, and the fastest spacecraft we have currently are the Helios Solar Probes at 252,792 km/h - it would take over 170,000 years before the probe returned.
Getting data back via radio seems physically realistic using the gravitational lensing of EM by our sun. It would require us to put a receiving and relay station very var out beyond the planets, at least 550AU, I think. But by the time we are sending a probe several light years, then 550AU should practically be child's play.
A good paper about using such lensing: "Interstellar radio links enhanced by exploiting the Sun as a Gravitational Lens" by Claudio Maccone.
Same reason we aren't doing a lot of other things - nobody wants to pay and sending an interstellar probe would be extremely expensive and full of engineering difficulties. It probably makes terraforming of Mars look quite feasible.
In the year 2200, if a 10 year old child were to travel to the planet at a speed of 0.9999c, then were to immediately turn around and travel back to Earth, they would be approximately 50 years old. However, what year would they arrive back on Earth?
Assumptions:
- no acceleration or deceleration time.
- the planet is exactly 20 light years away.
- the velocity of the ship remains exactly 0.9999c while in transport.
(The answer is not 2240. It's much greater. My question is, how much greater?)
If the child were moving at 0.9999c (which is less than 1.0000c) and the planet is 20 light-years away, then how could it take less than 20 years for the child to reach it? Let alone ~0.5 years?
EDIT: Here's an explanation from a friend:
light always travels at c even if you're already moving close to c
but it's impossible for anything to travel faster than c
so if you're traveling at .9999c
the passage of time must be scaled for the traveler
to make light on the ship appear to move at c
even though it's only moving at 1-.9999c
Amazing. I hope to some day wake up and have a deep conceptual understanding of the relationship between velocity and time in relation to the various bodies at play.
I also hope to have an understanding of what it means for a photon to be everywhere at once, from its own point of view.
In the end, I guess I just want to understand the universe just a bit more than I do.
Special relativity is actually quite accessible and really interesting - find a good book or set of lectures on iTunes U or something.
(General relativity, the generalised version including acceleration and gravity, is what makes people think relativity is hard).
Time dilation (special relativity) has nothing to do with wave-particle duality (quantum physics). The infinite time dilation of photons is due to their velocity, not their wave-like nature.
Furthermore, all particles (electrons, protons, quarks, etc.) have wave-particle duality just as much as photons do.
According to the traveler you're traveling as fast as you think the traveler is traveling. The only way to make that work out is that to the traveler the destination is much closer than it is for you. This is called length contraction.
And rounding it out, different observers disagree on which events are simultaneous. In particular until the traveler turns around, the traveler thinks that the Earth was left recently. After the traveler turns around, in the new reference frame the traveler left the Earth close to 40 years prior.
Relativistic travel would be one-way essentially. It would allow one to travel the visible universe within a current human lifespan (of course, with ridiculous power requirements). Anything left behind would have experienced thousands of millions of years of time.
Sci-fi dealing with this topic: Forever War, Ender's series, a few stories from Niven's Known Space universe.
See also the anime Gunbuster, which has teenagers piloting giant robots (so far no surprise) into deep space at measurable percentages of c. Getting back after saving the world they find their school friends have grown up and had kids.
Right. Time/space dilation effectively makes the trip shorter for the person traveling near c.
Here's a really mind-blowing thing: If you were able to accelerate at a fairly reasonable rate indefinitely - say - using an interstellar ramjet, you could conceivably circumnavigate the entire universe within a human lifetime (in your own frame of reference, of course)
Of course, interstellar ramjets might not actually work in practice... but still, the concept of time/space dilation holds.
Last I heard from the hard science fiction people, such ramjets have an upper speed limit imposed by some sort of drag. Can't remember for certain... maybe Atomic Rockets has something on them... yeah, http://www.projectrho.com/rocket/slowerlight.php#Bussard_Ram... . They say 0.12c is the best speed for ramjets.
40 years at 0.90000c = 91.76 years
40 years at 0.99000c = 283.55 years
40 years at 0.99900c = 894.65 years
40 years at 0.99990c = 2828.00 years
40 years at 0.99999c = 8944.00 years
Question. How the bloody hell do you validate a computer model of how an atmosphere unlike anything we can observe in our solar system works? Did someone fly out there and verify it before publishing? And I'm supposed to believe your computer model iterates correctly over geologic time? Really? Really?
(Obligatory-but-totally-serious that this is still cool work not counting the computer model part, and to be honest I don't really care either way what the computer model says; I would be equally skeptical if they produced a model that claimed any outcome at all.)