The smallest exoplanets yet
Posted 12.20.2011 at 2:00 pm
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Kepler-20e
Kepler-20e orbits its star every 6.1 days. At just 4.7 million miles from its star, its surface temperature reaches a searing 1,400 degrees F.
NASA/JPL-Caltech/T. Pyle
Two small, scorched Earth-sized worlds orbiting a reddish sun-like star in the Cygnus constellation mark yet another milestone for the storied Kepler Space Telescope mission. They're the smallest exoplanets found to date — one of them is just 1.03 times the size of Earth, a veritable body double. The planets aren't in their star's habitable zone, but they are the right size — and as such, they fill in even more of the interstellar planetary puzzle.
The planets exist in a strange configuration that sandwiches them among three gas giants, and they're all well within the orbit of Mercury. They were buried in nearly two years of data, and astronomers had to use some ultra-refined computational techniques to be sure they're really planets.
One of the planets, Kepler-20f, could potentially harbor a water-vapor atmosphere, although astronomers don't know for sure. What they do know is that it's just barely bigger than our own planet (and only slightly more massive).
"It is the closest object to the Earth that we have seen in the universe," said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics, lead author of a paper on the new worlds.
Kepler-20f: This world is 1.03 times the size of Earth, the closest to our own planet's size of any exoplanet yet discovered. It has somewhere less than three times Earth's mass. It's just 10.3 million miles from its star (we're 93 million from ours) and as such makes an orbit in just 19.6 days. Its surface temperature is about 800 degrees F, but astronomers believe it may have held on to a water-vapor atmosphere. NASA/JPL-Caltech/T. Pyle
Both planets orbit around a star called Kepler-20, a G-type star slightly cooler than the Sun, located 950 light-years away. (It would take the space shuttle 36 million years to travel to Kepler-20, as the CfA helpfully points out.)
Based on their size and location around their star, the planets might have a very Earth-like composition, Fressin said in an interview. Their proximity to Kepler-20 exposes them to prodigious doses of radiation, and they’re too small to have held on to lighter elements like hydrogen and helium in the face of those stellar winds — so the evidence would suggest that they’re rocky. It’s just a matter of the ingredients, whether they have significant amounts of iron or silicate.
The planets could not have formed where they’re currently located, and must have migrated inward, he said. It’s possible that earlier in its life, Kepler-20f had an atmosphere with significant water vapor, which would make it habitable, at least according to most planetary habitability indices.
“If it indeed migrated from the outer solar system, it could have been habitable in its earlier history,” Fressin said.
Kepler-20 Planetary Comparison: NASA/JPL-Caltech/T. Pyle
The discovery comes on the heels of a major data dump by the Kepler team earlier this month, which also included the news of the first Earth-like world orbiting in an Earth-like place around its star. That planet, Kepler-22b, is much bigger than Earth, but exists in a temperate zone just right for liquid water to exist. It may not have a rocky surface, however. These new planets are too hot for water, but they’re much more Earth-like in rocky form and smaller size.
“I think of Kepler-22b on one side, and Kepler-20e and 20f on the other, as two pieces of the puzzle,” Fressin said. “We need to combine the finding of an Earth-sized planet in a habitable zone.”
Kepler was designed to look for blips in brightness across the faces of 144,000 stars in the constellations Cygnus and Lyra, aiming to find sun-like systems harboring Earth-like planets. In its two years of operation, the cosmic census has mushroomed to more than 2,000 worlds, including super-Jupiters, super-Earths, inky black light- and heat-absorbing worlds, and many more. But the hunt for an Earth twin has proven difficult. Part of the problem is criteria — an Earth analogue would need a similar size, location, composition, rotation and many other factors to be truly Earth-like, Fressin said. Take Kepler-22b: It’s the right temperature, but it’s 2.4 times the radius of Earth, so it has much more volume.
“I don’t foresee us finding a true, clear Earth twin very soon — there are so many different levels,” Fressin said. “Maybe we don’t only need a planet in a habitable zone and at the right size, but the star similarity. If we don’t know what is in the atmosphere, or we don’t have any constraints on the atmosphere, how can we say it has the right signature to be an Earth twin?”
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Science, Rebecca Boyle, distant solar systems, earth-like, exoplanets, Kepler, kepler space telescope, neptune, solar system, super-earthsThese planets are arrayed in a very strange system, alternating between rocky and gassy, which is unlike anything astronomers have ever seen, said co-author David Charbonneau of the CfA. He challenged his fellow astronomers to help him explain it.
"The freshmen in my class are going to be quick to point out that the model of our solar system formation is deeply challenged by the discovery that is being presented today," he said.
Their small companions were difficult to see because of their size, and previous attempts to spot them were unsuccessful, Fressin explained. Astronomers had seen some blips they thought might be transiting planets moving across the face of Kepler-20, but an analysis a year ago couldn’t rule out other possible sources. Additional data from the space telescope and additional calculations by Fressin and colleagues led to the final eureka moment.
When a planet moves across the face of its star, the star dims a tad, and this is what Kepler is designed to notice. Scientists have to rule out other possible causes like a background star, a brown dwarf, an eclipsing binary, and so on. To confirm planets’ existence, astronomers check for a tiny wobble caused by the planets’ gravitational pull. This can be verified from the ground, using the huge Keck telescopes in Hawaii. But in this case, the new planets were too small for these ground-based verifications.
Fressin used software called Blender, which he developed with CfA astronomer Willie Torres (and which has also been used to verify other planet findings, including Kepler-22b). Fressin and nearly 30 collaborators used Blender to run millions of simulations, and were able to rule out any other source of dimming other than the putative planets.
This is neat, because as astronomers enter this new mass range of planets — little worlds the size of Earth or smaller — they’ll need sophisticated analysis to verify what they’re seeing. This paper combines a new computational technique with the old, pre-Kepler technique of checking for stellar wobble.
The study appears online today in the advance online edition of the journal Nature.
Kepler-20 System: The planets of the Kepler-20 star system are arranged in a bizarre pattern, with small, Earth-sized and probably rocky worlds sandwiched between gas mini-giants. This system of flip-flopping planets is very different from other solar systems discovered thus far. The planets could not have formed in their current locations, but must have migrated inward, probably through gravitational interactions with the dusty gas disk from which they were born. They orbit their star very tightly, closer than Mercury is to our sun. Harvard-Smithsonian Center for Astrophysics
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The most likely way of finding an Earth-like planet in the habitable zone, is to look for Jupiter sized planets in equivalent orbits to Jupiter around stars similar to our Sun and then focus on the habitable zone.
i think nasa should concentrate on colonizing the moon and than mars before even thinking of Intergalactic travel. baby steps is the best way to learn walk than run than swim and lastly fly.
"religion is like a prison for the seekers of wisdom"
-Killah Priest
JediMindset,
2 questions please. Why you change you icon and why you change you closing statement? Thanks, you know who.;)
@NOM
I highly doubt there is a rule to finding a carbon copy of Earth in the cosmos. Seems to me like planetary composition, size, mass and orbital periods are random in construct. Of course, life has already been proven not to be so fragile as to need perfect conditions to exist. Planets may need to be the right distance from a star with the right chemical make up, but they do not need the right number of neighboring planets, organic satellites, or star type to harbor life.
@JediMindset
Everything is approached as a step by step process. If we don't do the research now, we will not have a repository of possible destinations in the future to explore the moment we create the capability to reach as far. You don't find a train to get on without having a place to go. By the time we have the capability to get out there, we will have a growing repository of thousands of worlds to visit just in our neck of the woods. We'll develop that capability in the first place, first by mining resources from the entire solar system. That's the only way it's really possible, we'll never build a starship with just resources from this planet. It's impossibly uneconomical (though not impossible). NASA's on the right track, it just needs a little love, even if the objective is to support private endeavors, because they'll help us get out there too.
They probably shouldn't name a software the same name as a popular 3D tool. Just sayin'.
@Space
its the first time i have changed it......i think its weird that you realize this being a new member. you joined like 7 hours ago. you have great observation skills nonetheless...
@ pheonix1012
you are correct that. "its better to be safe than sorry" applies to what you say. but i still think we should colonize the moon and mars before leaving this solar system
"religion is like a prison for the seekers of wisdom"
-Killah Priest
I think by the time we have technology that would enable us to travel to other stars, we won't need to colonize planets. Even by the time we learn how to live away from the Earth, it would likely be simpler, and more economical to simply live in giant space stations.
For thousands of years, people have been trying to gain more and more control over one thing: their environment. We continue to build better and better structures to isolate us from our surroundings. We control temperature, humidity. We keep our space separate from other creatures in our world (animals, rodents, insects etc.) We choose what grows in our yard.. Basically a giant isolated habitat floating in space is ideal to what we have been striving for for so long.
It is also more efficient to mine materials and build in a weightless environment. It is likely, the way computing and robotics are going (not to mention 3d printing), that our future homes may be built automatically by machines with minimal human supervision.
So why are we looking at other solar systems? To learn. To learn more about how they form, more about what else is out there... who else is out there?
JediMindset,
While I am new, this does not mean I am new. I am a great admirer of the people who comment on POPSCI; you being one of them. I was looking forward to your response. You neglected to answer my questions, oh hum.
I find this article wonderfully amazing and inspire me so much each time I hear about a goldilocks planet. I wish so much I were traveling the cosmos faster than light; going to all these places. Heavy Sigh.....
..........................................
See life in all its beautiful colors, and
from different perspectives too!
@pheonix1012
Agreed.
But to up the odds, my suggestion is based on a few assumptions.
About the Star:
. a stable star is needed
. there should be high amounts of heavier elements
About Jupiter type planets:
. they act as a stabiliser for the whole solar system
. they stir up the elements so planets closer to the star have more water
. they eventually reduce the number of dinosaur-killer type asteroids
I think that the closer the overall conditions are to our solar system, the more likelyhood of finding a planet with all the right conditions to support life.
I can see space stations for short term but I don't think we could survive long term. People want space, fresh air sunlight, etc. A confined structure I don't think could provide that. On a side note, I can't seem to remember if Kepler looks for planets on the same orbital plane as earth or for planets on different planes.
@ nom, I completely agree about needing gas giants. They are important in stabilizing the system and keeping things in order.
Science always asks "can we," but doesn't seem to ask "should we."
Its not about intergalactic travel or finding a way to get to those planets. Its all about knowing that they are out there! Just being able to prove they are there, or that a habitable planet exists outside our own solar system is the key to understanding out universe. More-so, to understand and better ourselves on our current planet or to have a sense of urgency to get off this rock and start spreading out in our current solar system and get a grip on our future.
People dream about intergalactic travel I know for a fact. I'm one of them! But the more realistic thing to think about when you read about an article like this is to understand that just being able to look out there and see other planets is completely new. This is all new news! Not many years ago we were arguing about how we were the center of the universe and how planets had epicycles.
@NOM...i believe the researchers observe a section of the sky and then sift through all the data to find planets, there is no way to realize what type of planetary system they are discovering until after discovering it, hence, there is no way to concentrate on just systems similair to ours, did that make sense? cheers
@drchuck1 Perfect sense. The blanket approach works well for discovering the Jupiter-size planets. Unfortunately, it isn't so good for finding the Earth-sized planets in Earthlike orbits.
Once we have identified the stronger candidates, it would take more detailed observation of just the stars we are interested in using far more powerful telescopes. Then we could hopefully find the smaller planets.
Avatar may actually happen in the future.....