Earth and Moon From an Alien's Perspective

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.

Comments

Beautiful

[PakProtector]

I wish Sagan could be here to see this.

Re:Beautiful

[Reality Master 101]

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.

Re:Missing something

[onion2k]

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!)

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.

Habitable planets must have large moons?

[xxxJonBoyxxx]

"Making a video of Earth from so far away helps the search for other life-bearing planets in the Universe by giving insights into how a distant, Earth-like alien world would appear to us," said University of Maryland astronomer Michael Aâ(TM)Hearn

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:Missing something

[Space cowboy]

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

Re:Missing something

[iamlucky13]

You're correct that the distances are wildly different, but for some observation techniques that really doesn't matter much. The distance between the earth and the moon compared to the distance to the spacecraft is small enough to be just as negligible. There's no reason why something that works 30 million miles away shouldn't work 30 trillion miles away. The only real differences are the brightness and resolution (well...perhaps some of the spectrum may be reduced by the interstellar medium, but that's a pretty specific factor).

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.

Re:Missing something

[KDR_11k]

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 near lightspeed though the implementation of physics wasn't that consistent IIRC.