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Earth and Moon From an Alien's Perspective
Posted by
kdawson
on Fri Jul 18, 2008 11:07 AM
from the long-look-back dept.
from the long-look-back dept.
krygny writes "NASA's Deep Impact spacecraft (whose extended mission is called EPOXI) has created a video of the moon transiting Earth as seen from 31 million miles away. Scientists are using the video to develop techniques to study alien worlds. 'Our video shows some specific features that are important for observations of Earth-like planets orbiting other stars,' said Drake Deming of NASA's Goddard Space Flight Center... 'A "sun glint'" can be seen in the movie, caused by light reflected from Earth's oceans, and similar glints to be observed from extrasolar planets could indicate alien oceans. Also, we used infrared light instead of the normal red light to make the color composite images, and that makes the land masses much more visible.'" Here are links to the two videos, one red-green-blue and the other infrared-green-blue.
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Missing something (Score:5, Insightful)
Perhaps I am, but 31,000,000 miles doesn't seem that far away from an astronomical perspective - in fact it seems pretty darn close. A single light-year is about 5,878,625,373,183.61 miles (from Wiki), so 31M miles is roughly 1/190,000 of a light year.
The nearest star is ~4.2 light years away, so our potential alien visitor would have to travel a very long way towards us (and in that case why not come the last 0.0001% of the journey!) before this was a useful property.
Now I realise you can only take a video from as far away as your spacecraft really is, but I'd expect to see extrapolations to realistic distances before you start to claim things like "Making a video of Earth from so far away helps the search for other life-bearing planets in the Universe". - that's a bold claim, after all. I'm sure there's a standard line somewhere about extraordinary claims requiring extraordinary evidence to back them up...
I dunno, perhaps I'm just a grumpy old physicist, but there's all sorts of effects that only come into play at astonomical-scale distances (and the relativistic-scale speeds that commonly occurs between bodies that far apart), I guess I'd like to have seen more data and less hand-waving.
Simon.
Re:Missing something (Score:5, Interesting)
Space is largely empty so you can turn off most things and just leave your spaceship alone for the majority of the journey. A few microcalibrations along the way will see you right. Taking off is a lot harder but it's the sort of thing you can practise a lot too so you should be ok with that as well.
Doing something in the alien environment at the other end though, such as a solar system or a planet ... that's really hard. You have to design your craft to be able to deal with thousands of unknown, or known-at-an-extreme-distance, factors. That could well put a travelling alien off coming the last 0.0001% of the journey.
Parent
Re:Missing something (Score:5, Interesting)
I'm sorry, I think you're underestimating the survival problems imposed by such vast distances...
A gedanken experiment: Assuming you're right, and the distance isn't that much of a problem, *we* have launched spacecraft which have travelled to and landed on different (far closer) planet(oid)s, I have difficulty believing an alien civilisation that can navigate the truly immense gulf between planetary systems having any difficulty at all with a landing or navigation of a solar system (which is also pretty empty, btw)
You do get to make a billion or so observations of the destination as you're travelling towards it, after all. It's not going to be a complete unknown or anything...
Simon
Parent
Re: (Score:2)
But your craft was designed and launched without the benefit of those billion (relatively close-up) observations. So any adjustments based on them need to be possible based what you already packed for your trip.
Let's say I want to go on a pic-a-nic and do not pack a gun because it is too heavy. Then, as I get closer to my most favorite pic-
Re: (Score:3, Interesting)
If you get close enough to lightspeed your time slows down so it becomes feasible to live through the journey. The hard part is the acceleration and deceleration (even if you can produce the necessary thrust you have to consider the maximum force the crew can survive vs the time needed to accelerate at that force). I think once SciFi implementation of regular travel with time dilation has been used in Soukou no Strain (anime), a central theme was the time that passed while the spaceships were travelling at
Re: (Score:3, Interesting)
Using simple, non-relativistic math, you would surpass the speed of light by accelerating at a constant 9.8m/sec in just under a year. That means you get to live on your spaceship with simulated earth gravity due to your constant acceleration. That means we don't need to turn the inside of our spaceships into pink goo to accelerate to relativistic speeds within a reasonable amount of time.
The only problem is fuel. How do you power a ship at 9.8m/s^2, or any other 'sizable' acceleration? for that long? And d
Re: (Score:3, Interesting)
You would be right except relativity is an important factor and cannot be simply excluded. Your example makes the assumption that there are no relativistic effects, which is not correct, hence your conclusion is way off too. D-
Relativity is pretty weak up to very close to c. Even at 98% of light speed, the Lorentz factor (mass increase, time dilation, etc.) is only somewhere around 5. So, allowing for a decent fudge factor, classical physics isn't a half bad assumption.
So, making it to such speeds is not extremely unfeasible (fuel required would be around the same order of magnitude and such). The trade off is really the amount of fuel required to attain a certain speed, and the benefits in terms of time dilation you get.
Missing something, no sound or music ! (Score:2)
Here you go, grumpy old man ; )
http://www.youtube.com/v/AFks9A9TCF0&hl=en&fs=1 [youtube.com]
Re: (Score:2)
Yeah, it does seem to be a little useless.
I mean, we're talking less than the distance from here to the sun (93 million miles).
Maybe this will be useful for determining if Mars has giant oceans on it.
Re:Missing something (Score:5, Insightful)
Nonetheless, this distance is a new data point - that much is for certain. Even A single data point can really illuminate a function.
2, 4, 8, 16 means something completely different than 2, 4, 8, 32, after all.
Still, I do agree that the claim does sound a bit inflated.
Parent
Re: (Score:2)
4, 8, 15, 16, 23 and 42 are better numbers IMO.
Re:Missing something (Score:5, Interesting)
You can't resolve objects at the separation of the moon and earth from 30 trillion miles away, not even with the Hubble or Keck telescopes, and especially not with spectroscopes that can give you clues to what chemicals are present on those bodies. By studying star wobbles an astronomer might infer the presence and mass of a "planet," but that won't tell him if it's really a single planet or a planet-moon system. Look at the video and notice that as the moon crosses the earth, the total reflected light from the earth and moon would be decreased by the ratio of the area covered (about 7%) because the moon is blocking part of it. From that, the astronomer can infer not just the presence of the moon, but the relative sizes of the planet and moon.
Assuming the Space Interferometry Mission goes forward as planned, the astronomer might eventually be able to get a spectrum from the planet without being washed out by the parent star. By watching how the spectrum changes during such transits, they can figure out what elements and compounds (like water) are likely present on the planet, and what ones are present on the moon.
It may sound far out, but it's already being done with exoplanets and their stars, and transits of Pluto and it's moon are how we got a lot of our information so far about those two bodies.
Parent
Re: (Score:3, Informative)
Hmm. PhD in Physics. Not *too* far over my head, I think. I can always be wrong (astrophysics wasn't my specialty), but I actually think it *is* a bold claim. When you extrapolate (note, not interpolate) *anything* by several orders of magnitude, you better be sure of your deductions.
Radiant energy intensity falls off with the square of the distance. Variation within that intensity therefore falls off at the same rate, and is consequently harder to detect above the noise threshold - with the relative distan
Beautiful (Score:5, Interesting)
I wish Sagan could be here to see this.
Re:Beautiful (Score:5, Insightful)
Actually, no, I don't. I think if Sagan was miraculously reconstituted today, he would take one look at the shape of our Education System and of the Sciences and Space Program in the States and he would die of shock and sadness.
Parent
Re:Beautiful (Score:4, Interesting)
I think if Sagan was miraculously reconstituted today, he would take one look at the shape of our Education System and of the Sciences and Space Program in the States and he would die of shock and sadness.
He only died in 1996. You think things have changed much in 12 years?
As far as Space goes, there are actually some encouraging signs, much more than 12 years ago. The shuttle is finally being put in the shitcan like the unbelievably wasteful pile junk it is, we have several landers on other planets, and private industry (finally) looks like it might produce some interesting private space trips.
Unless your sole metric for success is government largess, space is much healthier than it was 12 years ago.
Parent
Re: (Score:2)
Maybe. So far everything is being done in the interests of space tourism. I'd like to see private industry strive to do something useful.
Useful? If you don't like tourism, private industry already puts satellites in orbit.
But I would say Tourism is by far the most useful thing we could be doing right now. That puts direct downward cost pressure on putting people in space for as little money as possible. The biggest holdup in whatever your definition of "useful" is, is the cost to put payload in space. If
Re:Beautiful (Score:4, Informative)
>>You think things have changed much in 12 years?
>Yes. They've gotten much worse.
Maybe the big picture is worse, but I note that incoming freshmen at the university where I work, are
coming in quite strong with physics, chemistry, calculus, writing, and most even have good placement in
a second language. My local, small, unscientific sample indicates a strong high school system, turning
out students who are as well-prepared for university as we could ask for.
Are you seeing different results among graduating seniors?
Parent
Re: (Score:2)
but I note that incoming freshmen at the university where I work, are coming in quite strong with physics, chemistry, calculus, writing, and most even have good placement in a second language
Are you sure that they are not coming from outside the United States (Europe, Russia, India, China etc)? They sound like an exact description of the well prepared and intelligent students that are frequently attracted to American universities from abroad.
Re:Beautiful (Score:4, Insightful)
Facts have no bearing on these kinds of opinions. There are people for whom things are always worse, as current situations are constantly compared to an idealized past that never actually existed.
Such people get joy out of believing that they are the last of some special breed of amazing people, never to be seen again. It's just part of the human condition.
It deserves pity, but not recognition or respect.
Parent
Re: (Score:2)
As do I... I feel so melancholy thinking of the absence of Douglas Adams, Asimov, Clarke and the like as these amazing things come to be.
After a deep sigh I try to pep-up by imagining that they would be happy that at least we are here to see it.
I think to myself that although I probably won't be here to see interstellar travel, but if humanity does make it to the stars then I know I would have been happy that we did.
Wow (Score:5, Insightful)
Watch Sunshine! (Score:2)
Go watch Sunshine [imdb.com], that movie definitely evoked those same kind of feelings in me.
There's an amazing scene where they watch Mercury transit across the Sun, and while we admittedly have the same view from here on Earth, imagining those folks were really on their way to the heart of the solar system, with one last, tiny gatekeeper between them and the monster that is the Sun is just AWESOME.
Goose-bump city.
Re: (Score:3, Interesting)
Re: (Score:2)
What really kicks up the awe is just how loud sunlight is when you get close...
That was the stupidest movie since Red Planet [imdb.com].
Re: (Score:3, Informative)
Sound is a pressure wave...so yeah, it is loud near the Sun. This was discussed on The Universe (History Channel).
Re: (Score:3, Interesting)
That was the stupidest movie since Red Planet [imdb.com].
http://www.sci-fi-online.50megs.com/2006_Interviews/07-08-27_brian-cox.htm [50megs.com]
http://en.wikipedia.org/wiki/Brian_Cox_(physicist) [wikipedia.org]
"I've discovered this whole new set of people - science fan boys - that I didn't know existed, really. They're interesting. Their almost fundamentalists, in a way. They are much more pedantic than professional scientists. I just interact with professional scientists most of the time and I must say, I've said this a couple of times now, but I've found the scientists that I like to work
Re: (Score:3, Insightful)
Holy cow, it's Uwe Boll imitating Buckaroo Banzai. That explains everything.
The problem with the film isn't the ridiculous number of creative liberties taken with physics. It's the fact that of all the highly qualified, professional people who would undoubtedly volunteer in droves to save the world, the crew is made up of a bunch of unstable, narcissistic emo whiners, and the ship is designed in such a way to give them endless opportunities to fail. It's a slow horror movie, and like all bad horror movies,
Relative albedo of earth and moon (Score:3, Interesting)
When we look up at the moon, it moon looks like a pretty bright, reflective object. But in images containing both the earth and moon, you can see that the moon looks positively dim and dingy compared to the cloud-covered portions of Earth.
Re: (Score:2)
Yes, I first realized this when I saw a sample of moon rock at the Smithsonian. It's almost black.
Re: (Score:2)
I actually WTFV, too. The moon swung around in an orbit nearly on a plane with the observer and continued merrily on its way. Given that the sun also appeared to be even with the observer, shouldn't that have caused a shadow (lunar eclipse) on the Earth?
(Insert obligatory Patsy quote: "It's only a model.")
Cool, but then again.... (Score:5, Funny)
That's cool but then again, I'm a sucker for any movie I'm actually in.
Hey.. (Score:5, Funny)
Habitable planets must have large moons? (Score:4, Interesting)
Huh? Did he just say that habitable planets must have large moons? (I've heard a similar argument before - something about two widely spaced bodies keeping the big one from wobbling too much.)
Re: (Score:2)
Re: (Score:2)
Well as far as I understand, the theory is that a single large moon keep the earth's tilt relatively constant. In simulations, if the large moon is not present, it varies wildly anywhere from 0 to 90 degrees.
The expected result of this would be no "perminant" ice caps on the poles since they would be exposed more directly to the sun just as much as any other part of the planet. Net result... Higher oceans constantly, and much more erratic weather patterns.
Some believe that life would have evolved anyway, bu
Mostly... (Score:4, Funny)
...harmless
That's no moon... (Score:5, Funny)
Because real reality isn't real enough... (Score:5, Funny)
Also, we used infrared light instead of the normal red light to make the color composite images, and that makes the land masses much more visible.
Sigh...everything's gotta be special effects these days...
FMV version? (Score:2)
Anyone got FMV versions of these videos? I don't have Quicktime installed on my work (Windows) laptop, and would rather not jump through all those hoops just to view what sounds like an interesting vid.
(Alternatively, I can wait until I get home from work and use Gplayer.)
Earth/Moon Model Screensaver? (Score:2)
Is there a GNOME (Ubuntu) screensaver that shows a realistic model (in scale, accurate surfaces) of the Earth and Moon orbiting each other?
I'd like to see our system from an alien's perspective whenever I've stopped working for a few minutes. Really give me the feeling of being "away from my desk".
A word from the EPOXI team (Score:5, Informative)
Re: (Score:3, Informative)
The importance isn't the image itself. It's how the image changes with time, including the rotation of the earth changes the reflected light and the position of the moon.
There are certain things we can guess, but in trying to build a model of how to observe other Earth-like planets from a distance, an actual observation, even from a much shorter distance, can improve the technology many times over.
In the end, when we look for extra-solar planets, we aren't looking for pretty images, we're looking for funny
Re:*.MOV - WTF? (Score:4, Informative)
.mov is QuickTime, which is old and not proprietary; I have a book here describing the format. However, that's just the container format; it's the codecs commonly used within QT these days that are proprietary.
And according to mplayer, the codecs used here are mp4v for video, and aac for audio. In other words, (tada!) MPEG.
Parent
Re: (Score:2)
MPEG non-proprietary?
MPEG2 maybe, but only because the patents have died.
Think before you post.
Re: (Score:2, Interesting)
Also, as soon as you're a part of some system, the system is never the same as it would be without you. And you can't even observe a system without being a part of it and having an impact on it.
The buble must burst. (Score:2, Insightful)
Yup, but to me (and damn near 100% of everyone else), you're really close to nothing. Outside of this planet, you're even closer to nothing.
Hence, insignificance.
Re:Viewable videos (Score:4, Informative)
VLC will play them.
Parent
Re: (Score:3, Informative)
Re: (Score:3, Informative)