Earthshine may help yield clues to life on other planets
A setting crescent moon amid the thin line of Earth's atmosphere.
February 29th, 2012
01:00 PM ET

Earthshine may help yield clues to life on other planets

Did you ever look up at the sky on a clear night during a crescent moon and see the faint outline of the "dark" side of the moon?

What you are actually seeing is the reflection of the Earth’s light on the surface of the moon. The part of the moon you are observing really isn’t the dark side, or you wouldn’t be able to see it. Scientists call this reflection “earthshine.” They are studying the characteristics of this faint light to see if it could someday be used to determine the atmospheric and surface compositions of Earthlike planets outside the solar system (exoplanets), and whether these distant planets could host life.

A group of scientists led by Michael Sterzik at the European Southern Observatory are using the Focal Reducer/Low-dispersion Spectrograph (FORS) mounted on the Very Large Telescope in Chile to study the characteristics of earthshine. These characteristics are being used to create theoretical models that could identify Earthlike exoplanets harboring life.

Previous techniques have used the light bouncing back from exoplanets to determine the makeup of their atmospheres. However, these observations need to be fine-tuned in order to determine whether life exists on these planets.

The new technique used by Sterzik uses a property of light called polarization. Polarization tells scientists not only how bright an object appears, but also measures the shifting rotation of electromagnetic waves. Light reflected by surfaces such as water, land, or vegetation is polarized. This polarized light can be used to determine the characteristics of a reflecting surface. In the case of the reflected light called earthshine, it tells us the properties of Earth’s atmosphere and surface, Sterzik explains.

So how will these observations be used to determine if life exists on exoplanets? That’s where biosignatures come in. A biosignature is any substance such as an element, isotope, molecule or phenomenon that provides scientific evidence of past or present life.

When scientists look through their telescopes, they do not expect to see intelligent forms of life. However, they can detect gases such as oxygen, ozone, methane and carbon dioxide. These gases can occur without the presence of life. However, an abundance of these gases existing individually alongside each other could indicate the existence of life. If life isn’t present, these gases would react and combine with one another.

Current techniques only provide a rough characterization of giant exoplanets using today’s instrumentation and telescopes. Detecting water and oxygen in exoplanets is currently out of reach, and new telescopes and sensors will be needed to directly observe the characteristics of an exoplanet’s atmosphere.

In the meantime, scientists will continue explore earthshine in order to fine-tune theoretical models that could one day be used to determine if life is present on other planets.

Post by:
Filed under: In Space
soundoff (88 Responses)
  1. Aras

    Ifound that the earth travel raound the sun once avery year and it spins raound once every 24 hours.The Earth also spins on its own axis. The axis is an imaginary line through the centre of the Earth from the North Pole to the South Pole.The Earth is just one of the nine planets that travel raound the Sun. The other planets are called Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune.Earth is a small, rocky planet which supports a variety of life. As far as we know, Earth is unique from all other planets in this respect.The Moon travels raound the Earth , It goes round once every 28 days.We only see the part of the Moon that is lit by the Sun.The Moon takes about 27 days (27 days, 7 hours, 43 minutes, 11.6 seconds) to go all the way raound the Earth and return to its starting position.Most rocks on the surface of the Moon seem to be between 4.6 and 3 billion years old.The Moon travels raound Earth at a speed of 2,288 miles per hour (3,683 kilometers per hour).The Moon has no air because its gravity is too weak to hold an atmosphere. The Sun is a star and gives out heat and light.It is roughly spherical in shape and is much, much bigger than the Earth.The surface of the Sun is much cooler than its atmosphere.The Sun is by far the largest object in the Solar System.Because the Sun is so large compared to everything else, it is easily able to hold on to the rest of the matter, causing everything else to orbit raound it.The Sun is a star it is not a planet. Our Sun is just like the stars we see in the night sky. The Sun is also the only star we see during the daytime.

    April 6, 2012 at 3:50 pm |
  2. Mike in NoVA

    Truth be told, there is no "dark" side of the moon... just like there is no "dark" side of the earth. When the tidally locked earth-facing side of the moon is dark (aka NEW) the back side is lit.

    This poorly written article just perpetuates the ignorance...

    March 1, 2012 at 1:22 pm |
  3. SB

    Who do we lobby to get a permanent Science headline section on the front page? It irks me that articles like this are lumped into odd categories, to be replaced and wiped off the front page by totally unrelated news items.

    March 1, 2012 at 12:19 pm |
    • Lokari

      Hey, c'mon, the latest Snooki rumors are IMPORTANT!!!111!

      March 1, 2012 at 12:42 pm |
  4. That's What's Up

    Not sure why anyone would want to live on another planet. It would take years just to get the Cable TV up and running

    March 1, 2012 at 11:57 am |
    • Lokari

      Wouldn't matter – there still wouldn't be anything worth watching.

      March 1, 2012 at 12:42 pm |
  5. :D

    Karate kid :p

    March 1, 2012 at 11:46 am |
  6. :D


    March 1, 2012 at 11:45 am |
  7. abdulthebutcher

    We need this research so we can find a plante for all the Asian, black and white people. That would remove all racism.

    March 1, 2012 at 11:43 am |
    • Kayla

      Or we could find a planet for people like you. That would remove all the racism.

      March 1, 2012 at 1:29 pm |
    • butchwack

      You got that right Chief rain in the pus

      March 1, 2012 at 1:43 pm |
  8. KawiMan

    "There is no Darkside of the Moon. In fact, it's all dark."

    Roger Waters – Pink Floyd – Dark Side of the Moon

    March 1, 2012 at 11:08 am |
  9. Libby

    We only see one side of the moon,at full moon we see the full face,at new moon we see nothing at first and last quarter we see one half of the moon the only exeption is when the the moon passes through our shadow and we call that a lunar eclipse which always happens on full moon.
    The only people that ever saw the backside or the far side of the moon are our astronauts who orbited the moon.

    March 1, 2012 at 9:34 am |
    • Big Generator

      What the astronauts saw on the backside of the moon,
      is the reason we havent gone back.
      A lunar station, "we" did not put there.

      March 1, 2012 at 10:31 am |
      • Anonymous


        March 1, 2012 at 10:53 am |
      • peter

        isnt the internet great? every crack-pot has the ability to post their paranoid drivel.

        March 1, 2012 at 10:56 am |
      • LeRoy_Was_Here

        It's the Nazis! They built a secret base there back in the 1940s! Adolf Hitler is still there! He's still plotting to take over the wolrd!

        SOMEBODY gotta stop him!!!!!

        March 1, 2012 at 11:02 am |
      • Chase

        @Leroy, believe it or not that is actually a movie coming out soon. Not even kidding.

        March 1, 2012 at 11:13 am |
      • Epidi

        @LeRoy_Was_Here Actually it was the Russians. Check out Apollo 18. Good flick.

        March 1, 2012 at 11:16 am |
      • LeRoy_Was_Here

        Nah, it's not the Russians!! The Russians said they were planning a manned expedition to the Sun. Someone said, "But you'll burn up!"

        The Russians said, "Nyet! Nyet! We have all figured out! We plan to go at night!"

        March 1, 2012 at 11:22 am |
      • :D

        Your scaring people... LOL

        March 1, 2012 at 11:51 am |
      • raawww

        Haha sad they didn't tell us but true there's Nazi bade on moon they had technology to do it but why would say they made it to the moon governments been covering up for eternity the truth USA no different dam them Nazis need proof YouTube lunar base and enjoy

        March 2, 2012 at 10:24 am |
    • Iconoclast

      So the astronauts saw the backside of the moon eh? That makes it a Lunar Mooning!

      March 1, 2012 at 1:03 pm |

    Great article, but aren't we being a little bit biased here? Why do we always presume that in order for their to be life, that another planet must have conditions like our own? If there is one thing that we have found out, life finds a way, even in the most harsh conditions. Thousands of miles below the surface, in non oxygenated areas, in fact, usually full of methane or sulfur. Life may not need Oxygen, H20, or even Carbon Dioxide.

    March 1, 2012 at 9:32 am |
    • Dan

      We aren't assuming that all life, or even most life, is like us, only that if we do find these markers, it probably, or at least possibly, indicates that that is where we we may find life that IS like us. And it's more likely that we can find a way to communicate with life forms more like us than with life forms that are very different from us. No, we won't be able to carry on any reasonable two-way conversation, but if we find an exoplanet that seems to fit the bill, we can direct a signal there-to, and perhaps one of their future generation of scientists will discover that they are not alone (if they don't already know it). And we can hope that some other life form like us is doing the same thing somewheere, and perhaps directing a signal toward us.

      March 1, 2012 at 10:20 am |
      • John

        I would say they mean similiar to life on earth. This includes cows. A herd of alien elephants while initially exciting, wouldn't really do much for us. Or to us. It would be like discovering a new species of ant here on Earth. Nice to know, but nothing earth shattering.

        March 1, 2012 at 12:43 pm |
      • Mario

        Wait a minute! How big are these alien elephants? And how tasty are them?

        March 1, 2012 at 1:29 pm |
    • SB

      Mike, no one is presuming that all life in the universe must be like life on Earth. However - and this is a strongly emphasized however - all the 2.5 million species of life that we currently know about do in fact live here on Earth. Earth-like life doesn't mean "only human beings". It also means everything that walks, flys, slithers, swims, oozes, grows, and otherwise lives here on Earth.

      We know that a planet with Earth-like conditions can support all manner of life. That's why you look there first.

      March 1, 2012 at 12:17 pm |
  11. bill

    There are visitors from other planets who have come to earth during their search for intelligent life. Finding none, they never land but pass us by and keep on traveling.

    March 1, 2012 at 8:45 am |
  12. Dorie

    "The surest sign that intelligent life exists elsewhere in the universe is that it has never tried to contact us." –Bill Watterson, Calvin & Hobbes.

    March 1, 2012 at 8:18 am |
    • guitarharry

      Funny and true!

      March 1, 2012 at 8:50 am |
    • intothemoonbeam

      Other intelligent life may not look at us as being intelligent, they may have tried to communicate with us but their way of communication may be so foreign that it goes completely unnoticed by Earth.

      March 1, 2012 at 9:33 am |
  13. palintwit

    Astronomers at the famous Sarah Palin Galactic Observatory / Bait Shop have been studying the earthshine phenomenon for quite some time now. They have determined that reflection is caused by thousands of bald headed teabaggers attending a nascar event.

    March 1, 2012 at 8:11 am |
    • PU-239

      Actually, Palin has been taking part and studying the effects of moonshine.

      March 1, 2012 at 8:14 am |
      • palintwit

        That would explain her inability to form a complete sentence.

        March 1, 2012 at 8:20 am |
      • Big Generator


        March 1, 2012 at 10:33 am |
  14. cwa11


    March 1, 2012 at 7:46 am |
    • stvnkrs10

      too bad you were looking up at the sky when they taught about caps lock

      March 1, 2012 at 7:53 am |
    • Big Generator

      This is what happens when you continue to stick your face in the bug zapper.

      March 1, 2012 at 10:35 am |
    • Peter

      The Sun is the most prominent erutafe in our solar system.It is the largest object and contains approximately 98% of the total solar system mass.One hundred and nine Earth's would be required to fit across the Suns disk, and its interior could hold over 1.3 million Earth's.The Suns outer visible layer is called the photosphere and has a tempreture of 6,000 Celsius (11,000 F). This layer has a mottle appearance due to the turbulent eruptions of energy at the surface.

      April 9, 2012 at 12:17 am |
  15. JL

    The Earthshine technique is not was first demonstrated over a decade ago as a way of visualizing what an Earth-like planet around another star would look like by Neville Woolf and colleagues at the University of Arizona in Tucson,

    March 1, 2012 at 7:45 am |
  16. LOW LYF


    March 1, 2012 at 6:24 am |
    • stvnkrs10

      i bet Uranus could support quite a load

      March 1, 2012 at 7:55 am |
      • Scotty

        I'm givin' her all she's got, Captain! If I push it any harder the whole thing will blow!

        March 1, 2012 at 8:18 am |
    • Mario

      Does Uranus have a backside? Or is that redundant?

      March 1, 2012 at 1:38 pm |
  17. gliese42

    A telescope will only aid us but we need to revive NASA and lets get going where no man has gone before.

    March 1, 2012 at 5:07 am |
    • Dave

      We need to stop letting them spend money looking for planets we will never be able to reach..

      March 1, 2012 at 5:21 am |
      • guitarharry

        That's really the big question here. I think anyone can see we will discover other planets with 'people' who can make telescopes and transmit em waves. But figuring out how to travel 100 light years in a short period is the trick. SciFi proposes this is easily done, but in fact there is no way to travel or warp" faster than light. In the end, humans will lose interest in extra-terrestrial life; we will find out that 'talking' to people who live light years away is very time-consuming and boring.

        March 1, 2012 at 9:04 am |
      • intothemoonbeam

        You're wrong, we need to start somewhere. We need to take the first step for the next generations. It's a fact that the Earth won't be around forever, whether it's 100 years or 1 Billion years. It's important we take the first steps to find other habitable planets so future generations can take the next step.

        March 1, 2012 at 9:38 am |
      • BimmerDr

        Nothing is impossible, but something maybe really really hard. We need to have "faith" in ourselves and our abilities.

        March 1, 2012 at 11:10 am |
    • SPW

      The only part of NASA that 'died' was the Shuttle portion, which right now serves us no purpose as we have drones. The only reason to send humans into space is to experiment the effects that it has on humans.

      I'd love to have space flight become a common thing for humans as much as any other scifi fan, but we were born a few generations ahead, right now all we can do is research the best possible ways to achieve this success, there is no reason to waste money outside of the usual NASA think-tank.

      March 1, 2012 at 6:07 am |
  18. Lisa

    I like how we as humans constantly strive for answers in such unique and distinct ways. As far as science and religion are concerned, I think Albert E. said it best "Science without religion is lame. Religion without science is blind."

    March 1, 2012 at 3:16 am |
    • PU-239

      And a planet without religion is at peace with itself.

      March 1, 2012 at 8:20 am |
    • Primewonk

      I like this quote from Einstein even better –

      “It was, of course, a lie what you read about my religious convictions, a lie which is being systematically repeated. I do not believe in a personal God and I have never denied this but have expressed it clearly. If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it.”

      March 1, 2012 at 8:36 am |
      • guitarharry

        Einstein softens his atheism a little with the "personal God" caveat. Like many other brilliant historical scientific men&women, Einstein was not religious; it just shows that fundamentalist religious beliefs are a holdover from less-enlightened times.

        March 1, 2012 at 9:18 am |
    • SB

      It seems to me that the idea of a personal God is an anthropological concept which I cannot take seriously. I also cannot imagine some will or goal outside the human sphere. Science has been charged with undermining morality, but the charge is unjust. A man’s ethical behavior should be based effectually on sympathy, education, and social ties and needs; no religious basis is necessary. Man would indeed be in a poor way if he had to be restrained by fear of punishment and hope of reward after death.

      Albert Einstein

      March 1, 2012 at 10:45 am |
  19. Chris

    I think we should call any part of the moon that happens to be dark at the moment, the "dark side". The part we never see should be the moons "backside"

    February 29, 2012 at 9:15 pm |
  20. sharoom

    What saddens me is apparently this article has been online since the early afternoon, but now in the evening there's only been 7 comments so far.

    February 29, 2012 at 9:12 pm |
    • Chip

      Cheer up. There is an article on CNN's home page regarding Snooki and if she is pregnant or not. You don't seriously expect this article to top that one.

      February 29, 2012 at 9:32 pm |
      • Steve

        Nice one. I was thinking the same thing. It amazes me that "events" like Snooki top actual news where one might learn something. People need to turn the TV off and read a book every now and then.

        February 29, 2012 at 11:07 pm |
      • Guest

        To be fair,not as many men have been on the moon

        March 1, 2012 at 2:20 am |
      • guitarharry

        Who's Snooki? 🙂

        March 1, 2012 at 9:39 am |
    • Big Generator

      Give it time, when they are done Bashing Obama,
      they will get here.

      March 1, 2012 at 10:38 am |
      • TWM

        Bashing Obama is just too easy. This at least takes some reflective thought.

        March 1, 2012 at 10:47 am |
    • raawww

      At least the comments in hear are funny educational and not filled with ignorance hop over to the religious blogs man wow

      March 2, 2012 at 10:31 am |
  21. bobcat2u

    But remember, when god made heads, he only made a few perfect ones. The rest he put hair on.

    February 29, 2012 at 8:29 pm |
  22. jason

    it's the graybeans ,there here to anal probe everyone on earth...

    February 29, 2012 at 7:45 pm |
  23. Phil

    "What you are actually seeing is the reflection of the Earth’s light on the surface of the moon. The part of the moon you are observing really isn’t the dark side, or you wouldn’t be able to see it. Scientists call this reflection “earthshine.”"

    Doesn't everyone know these things? Maybe it's because I've been involved with astronomy for over 30 years - but this all seems like common knowledge.

    February 29, 2012 at 6:27 pm |
    • Rim

      It should be common knowledge but unfortunately we have a large section of this country that adheres to bible BS instead of gathered facts and evidence.

      February 29, 2012 at 7:13 pm |
      • ktisis

        Amazing Rim...two important things revealed in your short diatribe (1) inexplicable intolerance of Christianity, and (2) False stereotypical assessment of Biblical information. The scriptures record an assessment of the origin of the Universe that was only recently verified by Big Bang cosmology (instantaneous emergence of the tri-universe from nothing (space-time-matter/energy). The spherical nature of the Earth (revealed in Isaiah about 700 BC), that the Earth hangs in space upon nothing (book of Job approx. 2000 BC), the Hydrologic cycle, Ocean currents, Entropy, etc.
        When you add fulfilled, highly specific prophecy, explanations concerning the transcendent qualities of sentient life (self-awareness, personality, intelligence), along with the fundamental scientific revelation–not bad for a compilation put together (let me guess) by-umm--ignorant goat herders??? Please research before making blanket statements of intolerance.

        February 29, 2012 at 10:34 pm |
      • Commojoe

        An anti-Christian comment like that oculd only come from a self-righteous, God-denier. I'm sorry you don't appreciate His creation and everything about the way He made it.

        March 1, 2012 at 12:34 am |
      • Hobs

        I was actually thinking how wrong they got this. While it is referred to as 'earthshine', there is no such thing as 'earth's light'. It is the sun's light, reflected off of the earth onto the moon. There IS a dark side and the only time we CAN'T see it is during a full moon. The part of the moon that we can never see from earth is more accurately termed the FARside, as opposed to the nearside.

        As to the Bible accurately describing cosmology, uh, no. 1) The Big Bang Theory does not claim the universe was instantaneous formed from nothing. 2) I assume you are referring to Isaiah 40:22. Anyone how managed to pass introductory geometry should be able to realize that there is a difference between a circle and a sphere. 3) While Job 26:7 makes and interesting reference to hanging the earth on nothing, Job 9:6 and Samuel 2:8 refer to it sitting on pillars. There is in fact no specific information that couldn't be figured out by a reasonably intelligent person from any era, particular at a time in history when you had to be much more aware of your environment just to survive, unlike today.

        March 1, 2012 at 6:31 am |
      • Big Generator

        Too Mordor we will take you.

        March 1, 2012 at 10:41 am |
      • John

        Do you explain things to children the same way explain them to educated adults? No?? Imagine trying to explain God's work to someone who has never even heard of physics. Scientists are discovering how God did all of his work. It does not mean God did not do the work. Just like how when you were a child you thought your parents knew everything and could do it all. Now that you are an adult, you know better. Does that mean your parents did not exist after you "grew up"? Does it mean as soon as you learned something your parents knew, they just ceased to exist?

        March 1, 2012 at 12:36 pm |
      • Hobs

        Yes, I explain things to a child in simpler terms than I do to an adult. Well, at least some adults. However, that simpler explanation is not one that is demonstrably wrong. Yes, maybe a god did everything you claim, but before you can attribute things to him you need to actually demonstrate that he exists. Otherwise you are just making an bald assertion. Believers have been trying to prove that gods exist since there have been humans, maybe longer. The fact that many millenia later, we are still having the discussion would seem to indicate where the true answer lies. While in general I agree with Carl Sagan, sometimes absence of evidence is indeed evidence of absence.

        March 2, 2012 at 6:27 am |
    • Caddolakeguy

      It was probably common knowledge at one time. But never underestimate the ignorance of the current
      crop of public school graduates

      February 29, 2012 at 8:43 pm |
      • Dave

        Who said God was a He?

        March 1, 2012 at 12:47 am |
    • Chris

      If you listen carefully at the very end of Pink Floyd's "Dark Side of the Moon", a faint voice says, "There is no dark side of the moon, really. As a matter of fact, it's all dark." It sounds like a typical thing to hear on a Pink Floyd album, but those statements are literally true. No side of the moon is permanently dark - the moon has daytimes and nighttimes of about 15 days each. However, the surface of the moon is made of fairly dark matterial - it only looks bright because it's reflecting sunlight in our night sky.

      February 29, 2012 at 10:26 pm |
    • Bob Knippel

      No kidding. I'm surprised they didn't mention the fact that it is now quite well known that the moon is not actually made of green cheese, either.

      February 29, 2012 at 11:12 pm |
      • SixDegrees

        I like cheese.

        March 1, 2012 at 3:43 am |
    • guitarharry

      Former high school teacher here, Phil. You'd be surprised...I taught reading/English, and I was continually shocked by how little students seemed to know about stuff I thought was 'common knowledge' science, history, etc. Example; most of them knew absolutely NOTHING about basic chemistry: "How many electrons in a hydrogen atom?" or "What elements combine to make water?" Blank stare....No wonder the Chinese are running the world.

      March 1, 2012 at 9:33 am |
  24. Rufus Crank

    The only thing about my planet that isn't cool is the species that thinks it's intelligent. Of all the places to live in the universe,Earth is really very cool,and I'm happy she is letting me spend some time with her.

    February 29, 2012 at 5:35 pm |
    • Flipper

      I hear ya. Those dolphins are pompous arrogant jerks, aren't they?

      March 1, 2012 at 12:04 am |
      • Big Generator

        Hey, when we get done screwing this place up,
        The Dolphins are next in line to fix it.

        March 1, 2012 at 10:43 am |
  25. superplus

    Earthshine? That's mostly the light from street lights reflected off the tops of bald-headed men.

    February 29, 2012 at 4:55 pm |
    • PU-239

      Wax on....Wax off. 😀

      March 1, 2012 at 8:15 am |


  • Elizabeth Landau
  • Sophia Dengo
    Senior Designer