An Alien View of the Moon Transiting Earth


Ever wonder what an approaching alien spacecraft would see as it comes within tracking range of our Earth/Moon system? NASA’s EXPOXI mission, which uses the old Deep Impact spacecraft, has created a video of the moon transiting (passing in front of) Earth as seen from the spacecraft’s point of view 50 million kilometers (31 million miles) away. Scientists are using the video to develop techniques to study alien worlds. “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 astronomer Michael A’Hearn, principal investigator for the Deep Impact extended mission, called EPOXI. The video is pretty amazing and there’s actually two versions of the video; the first one uses a red-green-blue filter, showing how it looks with our human eyes, and the second uses an infrared-green-blue, which makes the vegetation on the land masses show up in red.

And the infrared version:

EPOXI is a combination of the names for the two extended mission components: a search for alien (extrasolar) planets during the cruise to Hartley 2, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact eXtended Investigation (DIXI).

“To image Earth in a similar fashion, an alien civilization would need technology far beyond what Earthlings can even dream of building,” said Sara Seager, a planetary theorist at the Massachusetts Institute of Technology, Cambridge, Mass., and a co-investigator on EPOXI. “Nevertheless, planet-characterizing space telescopes under study by NASA would be able to observe an Earth twin as a single point of light — a point whose total brightness changes with time as different land masses and oceans rotate in and out of view. The video will help us connect a varying point of planetary light with underlying oceans, continents, and clouds — and finding oceans on extrasolar planets means identifying potentially habitable worlds.” said Seager.

Pretty exciting stuff!

Original News Source: NASA Press Release, with a little help from Bad Astronomy for the videos

7 Replies to “An Alien View of the Moon Transiting Earth”

  1. Cynthia, wouldn’t the earth just be a black circle? There’d be no light on our side, so we’d just see a black dot moving in front of the sun.

  2. Beautiful celestial mechanics.

    How about showing a transit of the Earth and Moon of the Sun? If we’ve got people on Mars, I think they’ll see a transit like that in November, 2084.

  3. Beautiful!

    Notice how dark the Moon Looks as it transits the Earth? Even it’s sunlit side is only about as bright as the ocean and much dimmer than the land areas. I remember reading (or hearing on Astronomy Cast?) that even though the Moon looks pretty bright at night to us Its surface is really VERY dark and reflects only a small part of the light it receives. I seem to remember that the lunar dust that the Apollo astronauts tracked into the LEM was described as being the color of charcoal. This video really shows how little it reflects as compared to the Earth.

  4. “To image Earth in a similar fashion, an alien civilization would need technology far beyond what Earthlings can even dream of building,”

    I don’t know; I can dream an awful lot. I think this mindset does not befit a scientist. I’m sure Sara Seager is a wonderful planetary theorist, and we can forgive the statement as a use of cliche.

  5. I never really thought about it before, but the moon seems fairly large relative to Earth, and also compared to some of the other moons in the solar system. No wonder its gravity affects
    and stabilizes Earth so much. Seems to lend some credence towards the idea of the moon being a dislodged chunk of earth, yes?

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