Mirror Earth: Science Closes in On Our Planetary Twin

The hunt for a habitable world like ours heats up—and bears results

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The number of confirmed exoplanets, or worlds orbiting distant suns, shot past 1,000 last week, according to the semi-official Extrasolar Planets Encyclopedia. That’s pretty heady stuff considering that just over 20 years ago we didn’t know of any at all.  But the ultimate goal of finding a true Earthlike world has continued to elude astronomers.

That landmark discovery, however, appears to be closer than ever, particularly after the release of a pair of papers in the journal Nature this week, concerning a planet known as Kepler 78b. The new world is not only close to Earth in size (it’s just 20% bigger), but it has almost exactly the same density. The implication, says University of Hawaii astronomer Andrew Howard, lead author of one of the papers: “We think it’s made of the same stuff as Earth—primarily rock and iron.”

What makes this find truly compelling, however, is the very fact that there is not just one paper, but two. And that second one, based on independent observations from a European team, reaches exactly the same conclusion. “When results agree like this,” says Howard, “that’s really the gold standard.”

(MORE: Cloudy With a Chance of Aliens)

The planet was found earlier this year in data beamed down by the now-defunct Kepler satellite, but Kepler can tell scientist only how physically large an exoplanet is, based on what percentage of light it blocks as is it moves in front of its parent star. Before they began finding exoplanets in droves, theorists mostly assumed size and composition went hand in hand—that a planet in the size range of Jupiter, for example, must be like Jupiter in all respects.

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Turns out they were wrong. Among the very first worlds discovered by Kepler, for example, one, Kepler 7b, is 50% bigger than Jupiter, but with the density of Styrofoam. Another, Kepler 10b is about the size of Earth but is nearly as dense as pure iron. Yet another, GJ 1214b (this one wasn’t found by Kepler), is less than three times the size of Earth, and has a density that suggests it’s probably half-rock and half-water. “There have been a lot of surprises,” Howard admits.

But it would have been downright astonishing if there were no true twins of Earth out there in the Milky Way, and both Howard’s team and the competing team, led by the University of Geneva’s Francesco Pepe, nailed down the composition of Kepler 78b with the same technique: the planet’s tug on its star as it orbits, pulling it almost imperceptibly in one direction and then the other. By measuring subtle changes in the star’s color induced by those wobbles, the astronomers can judge how fast the star moves as it approaches and retreats—and that speed depends on the planet’s mass.

(MORE: The Kepler Space Telescope May Be Dead, But its Planet-Hunting Mission Continues)

It also depends on how tight the planet’s orbit is: the closer it is to the star, the more leverage it exerts. And Kepler 78b is crazy close—so close that its “year” last just 8.5 hours. “I mentioned this to a kid in my neighborhood,” says Howard, “and he said ‘wow, that would be great! I would have 10,000 birthdays already. That’s a lot of presents!’”

The simultaneous publication in Nature is not a coincidence. When the planet’s discovery was announced last spring, says Howard, his team asked the astronomers in Geneva to join them in a supporting role in measuring its mass. The Swiss liked the idea of a partnership—provided they were the ones taking the lead spot. “Neither of us wanted to play second fiddle to the other,” Howard says, “so we agreed to observe independently and submit our results to the same journal on the same day.”

(MORE: ‘No Chinese Allowed.’ NASA’s Short-Lived Rule)

Finding an Earth-size planet with an Earthlike composition is a major milestone in exoplanetology, but as a University of Maryland astronomer observes in a commentary, also published in Nature, the extra leverage—and close proximity to the parent star—that made the planet relatively easy to weigh “comes at the price of a hellish environment.” With a surface temperature of up to 8,500°F (4,700°C), says Howard, it’s “one of the hottest that’s ever been discovered.”

Kepler 78b is clearly not a place you’d expect to find life, in other words, and it may be that no current technology can discover such a planet. But a new space telescope called the Transiting Exoplanet Survey Satellite (TESS), coupled with powerful new wobble-measuring spectrographs on huge ground-based telescopes, could find a truly habitable Earthlike world. TESS won’t fly until 2017 at the earliest, but that’s nothing in cosmic time. If there’s a second Earth out there to be found, it’ll still be waiting when the new satellite opens its eyes.

(MORE: The Most Adorable Planet Yet)

36 comments
sseattleboy
sseattleboy

.....given the hundreds of billions of galaxies, clearly there is other life out there.

But it is so many light years away, it is irrelevant.

Furthermore, any intelligence with the technology to overcome those distances would be so far advanced from us, why would they bother ?  Scarce resources ? Again, their massively advanced tech would make the issue of gold or some other earth resource moot because they could locate and extract it like we pour water from the abundance of the universe.

chillmeoutbrother
chillmeoutbrother

I thought the creationist arguments would have begun by now....

come on guys!

WendieLemieux
WendieLemieux

I have always said we were brought here. Not created, not evolved, but brought here.

JackStevenson
JackStevenson

We have finally mastered survival on the Earth after millions of years of evolution. But we have not mastered survival on other planets to ensure the survival of our species.  It would be a shame to let our intelligent species be wiped out on Earth by a cosmic event. This is why we need to find practical ways to survive on Mars, Europa, and other possible planets in our solar system as a back up plan in case of another asteroid like the one that wiped out the dinosaurs.........

JasonKing
JasonKing

I believe we'll find plenty of earth like planets that we can habitate and survive on.  Maybe even find a planet better than Earth. 

We'll never find another planet that we could wake up on and not immediately know it's not earth. 

A planet we can survive on is one thing. A mirror earth will never be found. The new planet will be bigger or smaller. Gravity will be different (we might weigh more/less). Oxygen will be richer/thinner. The sky will be purple instead of blue. 

There's so many things involved with making earth as we know it 'earth' that aren't necessary to be exactly the same as earth in order to be livable. 


rwscott2001
rwscott2001

There will never be an Earth "twin".  These stories are misleading.  These planets do not have the same atmosphere, gravity, magnetic field, or chemical makeup that our bodies adapted to here on Earth.  To live on these other planets will require genetic manipulation of the human genome, so that the human body becomes more "alien" and can adapt to that planet's atmosphere.  The higher gravity alone would put stress on our hearts and bones.  These planets are more like Venus and Mars, which we can not live on without a spacesuit or unless we terraform them.

porichkid
porichkid

whoaaaaaathis this is about outer space and planets,not the empty space between politicians ears 

BenJamN
BenJamN

Again CNN & Time fail to mention the most important part of this sort of story and subject: the primary means of detecting exoplanets/'extrasolar planets' is using techniques that have a statistically higher likelihood of finding planets that are either high mass, close to their host star, and/or orbiting very fast around their host star.  Even the optical blanking technique now used for detecting some of them tends to skew in favor of larger planets and/or those closer to their host star.  That is THE most important part in all of this, not the actual planets that have been found thus far.  That ANY planets are being found with techniques such as this is amazing and more telling than the type of planets that are being found.  That the type of planets that have been found thus far have fit with the expected statistical distribution lent by the means of detection actually gives high confidence that planets of ALL TYPES (INCLUDING EARTH-LIKE) are likely common in the universe.

tonyh9853
tonyh9853

Talk about intelligence! The parrots post about Politics and Obamacare.  Way to push your boundaries.

DanBruce
DanBruce

Maybe they can find a planet without Republicans. Too bad this one isn't it.

PhillipBunn
PhillipBunn

Maybe they have a international health care plan that works.

bojimbo26
bojimbo26

If it is inhabited , I hope they are more intelligent than us .

oddegg69
oddegg69

Amazing, we can find all this stuff in the Universe, but can't find any intelligence in Washinton.

BenJamN
BenJamN

@sseattleboy Who said anything about minerals being the ultimate and final scarce resource for advanced civilizations?

DeweySayenoff
DeweySayenoff

@JackStevenson Meaning this in as non-hostile of a manner as is possible, given the behaviors of our fellow man, I have to question your assertion that our species is intelligent as a whole.

Sean_Bruno
Sean_Bruno

@JasonKing Hey Jason!  I agree with you; but I also like to think about the possibility of parallel universes that mirror our own - so an exact replica of Earth, Sun, Comet ISON, etc...  Far out, for sure...  But impossible?  Not necessarily.  If the Universe is indeed infinite, and thus spatial probabilities infinite as well, the odds are immeasurable, but somewhere out there, the random arrangement of atoms that make us and the Earth, etc., are bound to repeat.  Alas, it is extremely far-fetched and hurts my head to even think about it.  lol.  Happy Thursday!

sseattleboy
sseattleboy

@rwscott2001 

....yes, our presence is the result of so many random happy, and tragic, accidents, it could never be duplicated.

While other life is indisputable, we may not even be able to recognize it.


BenJamN
BenJamN

@rwscott2001 Your first sentence is unjustified.  Your second sentence is probably correct, but not because of the reasons you think.  Your third sentence is more rational. 

Sean_Bruno
Sean_Bruno

@BenjaminGoulart Great points - I'd highly recommend planethunters.org for anyone who wants to know more about the detection techniques related to the data collected from Kepler.  It presents the methods in a very simple fashion and even solicits assistance from visitors to detect anomalies in the data.  COOL!  

JenniferBonin
JenniferBonin

@BenjaminGoulart Thank you.  I was just about to have to post something like that.  And if people understood the techniques used by the astronomers, even a little, they'd easily see why what you said must be true.  It's not that complicated -- a high schooler can understand it -- but "science" reporters don't ever like to actually explain SCIENCE in articles, alas.  :(

GeorgeRussert
GeorgeRussert

@bojimbo26  The first sign of extraterrestrial intelligence would be to not let this planets inhabitants know about it. Why would an advanced civilization have even the remotes interest in us?

I'm sure there are many already imagining how these new worlds can be exploited for profits in time to escape the demise we've caused to this planet's environment. We are the universal mass extinction event! LOL


sseattleboy
sseattleboy

@BenjaminGoulart @sseattleboy

".....gold or some other earth resource...."


You're right--probably other major resources available in the universe--we can't even describe "dark matter" yet.

guymon2468
guymon2468

@BenjaminGoulart @rwscott2001 

You'd be a fool to live on any other planet without a spacesuit. Unknown viruses, allergens, parasites, radiation... come on, doesn't anybody watch Sci Fi movies anymore!

BenJamN
BenJamN

@GeorgeRussert @bojimbo26  

1) You sort of answered your own question ("Why would an advanced civilization have even the remotes (SIC) interest in us?") with your surrounding statements.  Re-read what you wrote and think about it for a few moments.

2) For a society hell-bent on genetically-improving itself and ensuring robust perpetual diversity within a stagnant technocracy, in-silico simulation of prospective improvements would not be fruitful due to one of the basic principles of not only organic chemistry, but chemistry in general: you cannot perfectly predict the properties of new molecules and compounds; you must experiment.  And in genetics that means with living organisms.  Hence, such a society would have to literally seek out new life (with intelligent life being the most relevant) in order to find new genes to exploit outside of their otherwise closed system.  That would likely be after societal genetic improvement and its associated caste-like system had arisen and persisted as a high-priority for a very long time.

Just... you know... for the sake of argument.  Feel free to ask about things like artificial wombs and certain core long-game-R&D physics technologies such a society would have to possess to get here and how we ‘just so happen’ to have those particular gaps in our own understanding of the universe.  Then we can have a rib-roaring time while you try to figure out how layman and even completely science-illiterate people all over the world could have possibility fabricated these types of stories with such startling compliance with the aforementioned necessary traits such an ET society would likely possess… and that includes said ET society’s desire for secrecy. 

Hint: most of the overt stuff you hear about is probably swamp gas, DSP artifacts of video cameras, or the result of hoaxers.

OccamsRazor1349
OccamsRazor1349

@oddegg69 How long have you been holding that in your back pocket. :-)

guymon2468
guymon2468

@jcwilson @guymon2468 

Ahhh.  OK.  You go out first.  I need to a do a few things here in the ship before I head out.

Ship to JC...... Ship to JC..... Hello?

jcwilson
jcwilson

@guymon2468 While things like alien viruses and bacteria may make for good stories the simple fact is that even if we found a planet that was nearly identical to Earth in every way there would still be a large chance that any life already there would have a completely different biochemistry.  Meaning that those germs would be physically incapable of surviving in our bodies.

Then even minor difference in the makeup of the planet would make for even greater differences in biochemistry so those things become even less likely.

As for radiation, exoplanets could have higher radiation levels in the atmosphere, they could have lower.  Radiation would actually be the least of my worries since that is the easiest thing to detect.

In the end what makes a lot of it moot though is that regardless of whether we find such planets everything we know now and that even appears theoretically possible points to the faster than light travel being impossible.  If that continues to hold true, then any sort of colonization would take thousands of years at a minimum and would most likely have little to no economic value, i.e., no incentive to undertake in the first place.

Frankly, as difficult as it would be, I think that we'll be able to terraform and make habitable other planets and moons in our own solar system long before we can even consider interstellar travel.

Regarding earlier poster's assertions about atmosphere, gravity and so making it impossible to to consider other "near Earths" - I think you're speaking from the hip.  While zero or extremely low/high gravity is definitely a problem for humans even in for short timeframes there is every reason to believe that relatively small differences in gravity could be easily tolerated even by Earth-born humans and even better so by the first few generations of those colonists descendants.  There have been a number of theories suggested that actually low gravity above a certain minimum would actually greatly expand human life, for instance that living on the moon could result in lifespans in excess of 200 years.  I guess my overall point is that it's certainly feasible for humans to tolerate relatively small variations in gravity over long terms, say somewhere from the 1/6th of the moon up to 150% on slightly larger planets.  With larger planets too it is important to keep in mind that a planet that is a certain amount larger than Earth doesn't immediately mean that the surface gravity is exactly proportional the size difference.  Surface gravity depends on things like the total mass (so a  much larger planet with a lower overall density could only be a little higher in surface gravity).