Kepler 20e, 20f - First Found Earth-Sized Exoplanets

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NASA / NASA JPL:
NASA Discovers First Earth-Size Planets Beyond Our Solar System

December 20, 2011

PASADENA, Calif. -- NASA's Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system. The planets, called Kepler-20e and Kepler-20f, are too close to their star to be in the so-called habitable zone where liquid water could exist on a planet's surface, but they are the smallest exoplanets ever confirmed around a star like our sun.

The discovery marks the next important milestone in the ultimate search for planets like Earth. The new planets are thought to be rocky. Kepler-20e is slightly smaller than Venus, measuring 0.87 times the radius of Earth. Kepler-20f is slightly larger than Earth, measuring 1.03 times its radius. Both planets reside in a five-planet system called Kepler-20, approximately 1,000 light-years away in the constellation Lyra.

{colsp=3}
Click on images for details​
This chart compares artist's concept images of the first Earth-size planets found around a sun-like star to planets in our own solar system, Earth and Venus.
Image credit: NASA/Ames/JPL-Caltech​


Kepler-20e orbits its parent star every 6.1 days and Kepler-20f every 19.6 days. These short orbital periods mean very hot, inhospitable worlds. Kepler-20f, at 800 degrees Fahrenheit (427 degrees Celsius), is similar to an average day on the planet Mercury. The surface temperature of Kepler-20e, at more than 1,400 degrees Fahrenheit (760 degrees Celsius), would melt glass.

"The primary goal of the Kepler mission is to find Earth-sized planets in the habitable zone," said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., lead author of a new study published in the journal Nature. "This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them."

The Kepler-20 system includes three other planets that are larger than Earth but smaller than Neptune. Kepler-20b, the closest planet, Kepler-20c, the third planet, and Kepler-20d, the fifth planet, orbit their star every 3.7, 10.9 and 77.6 days, respectively. All five planets have orbits lying roughly within Mercury's orbit in our solar system. The host star belongs to the same G-type class as our sun, although it is slightly smaller and cooler.

The system has an unexpected arrangement. In our solar system, small, rocky worlds orbit close to the sun and large, gaseous worlds orbit farther out. In comparison, the planets of Kepler-20 are organized in alternating size: large, small, large, small and large.

{colsp=2}
Click on images for details​
| This artist's conception illustrates Kepler-20e.
Image credit: NASA/Ames/JPL-Caltech​
| This artist's conception illustrates Kepler-20f.
Image credit: NASA/Ames/JPL-Caltech​


"The Kepler data are showing us some planetary systems have arrangements of planets very different from that seen in our solar system," said Jack Lissauer, planetary scientist and Kepler science team member at NASA's Ames Research Center in Moffett Field, Calif. "The analysis of Kepler data continues to reveal new insights about the diversity of planets and planetary systems within our galaxy."

Scientists are not certain how the system evolved, but they do not think the planets formed in their existing locations. They theorize the planets formed farther from their star and then migrated inward, likely through interactions with the disk of material from which they originated. This allowed the worlds to maintain their regular spacing despite alternating sizes.

The Kepler space telescope detects planets and planet candidates by measuring dips in the brightness of more than 150,000 stars to search for planets crossing in front of, or transiting, their stars. The Kepler science team requires at least three transits to verify a signal as a planet.

The Kepler science team uses ground-based telescopes and the Spitzer Space Telescope to review observations on planet candidates the Kepler spacecraft finds. The star field Kepler observes in the constellations Cygnus and Lyra can be seen only from ground-based observatories in spring through early fall. The data from these other observations help determine which candidates can be validated as planets.

To validate Kepler-20e and Kepler-20f, astronomers used a computer program called Blender, which runs simulations to help rule out other astrophysical phenomena masquerading as a planet.

On Dec. 5, the team announced the discovery of Kepler-22b in the habitable zone of its parent star. It is likely to be too large to have a rocky surface. While Kepler-20e and Kepler-20f are Earth-size, they are too close to their parent star to have liquid water on the surface.

"In the cosmic game of hide and seek, finding planets with just the right size and just the right temperature seems only a matter of time," said Natalie Batalha, Kepler deputy science team lead and professor of astronomy and physics at San Jose State University. "We are on the edge of our seats knowing that Kepler's most anticipated discoveries are still to come."

{...}






NASA Press Release: RELEASE : 11-421 - NASA Discovers First Earth-Size Planets Beyond Our Solar System


SPACE.com:

NewScientist: Smallest planet is tinier than Earth


Universe Today: First Earth-Sized Exoplanets Found by Kepler


Discovery News: First Earth-Sized Planets Orbit Distant Star


Parabolic Arc: NASA Discovers First Earth-Size Planets Beyond Our Solar System


CBS News Space: First confirmed Earth-size worlds found orbiting another star


Aviation Week: Earth-Sized Planets Discovered



 

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The Planetary Society Blog: Separating fact from speculation about Kepler-20's Earth-sized planets

Universe Today: Discovery of Earth-Sized Worlds – Google+ Hangout


Nature: Two Earth-sized planets orbiting Kepler-20


NASA Ames - Kepler Discoveries:

Stellar properties:
Effective temperature, T eff |5466 ± 93 K

Surface gravity log g (cgs)|4.443 ± 0.075

Metallicity [Fe/H]|0.02 ± 0.04

Projected rotational velocity, v sin i|0.4 ± 0.5 km s -1

Stellar mass, M s |0.912 ± 0.035 M Sun

Stellar radius, R s |0.944 +0.060 -0.095 R Sun

Stellar density, ρ s |1.51 ± 0.39 g cm -3

Luminosity, L s |0.853 ± 0.093 L sun

Distance, D|290 ± 30 pc


Transit parameters and physical properties:
 | Kepler-20e (KOI-070.04) | Kepler-20f (KOI-070.05)

Orbital period, P|6.098493 ± 0.000065 days|19.57706 ± 0.00052 days

Times of centre of transit, Tc|2454968.9336 ± 0.0039 BJD16|2454968.219 ± 0.011 BJD

Eccentricity|< 0.28|< 0.32

Planet/star radius ratio, R p /R s |0.00841 +0.00035 -0.00054 |0.01002 +0.00063 -0.00077

Scaled semi-major axis, a/R s |11.56 +0.21 -0.29 |25.15 +0.47 -0.63

Impact parameter, b|0.630 +0.070 -0.053 |0.727 +0.054 -0.053

Orbital inclination, i|87.50 +0.33 -0.34 degrees |88.68 +0.14 -0.17 degrees

Planet radius, R p |0.868 +0.074 R -0.096 |1.034 +0.100 -0.127 R e

Planet mass, M p |< 3.08 M e (spectroscopic limit)
0.39 Me < Mp <1.67 Me (theoretical considerations)​
|< 14.3 M e (spectroscopic limit)
0.66 Me < Mp < 3.04 Me (theoretical considerations)​

Planet equilibrium temperature, T eq |1040 ± 22 K|705 ± 16 K


Light Curve for Kepler-20e:


Light Curve for Kepler-20f:
 

JEL

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NASA Discovers First Earth-Size Planets Beyond Our Solar System

If going by the completely unfounded assumption they have life like ours (and the article says they don't, but for the fun of speculation), then we are seeing them as they were at year 1011, while they are in fact at year 2011 seeing us a we were in year 1011.
Am I correct in that? Or could the relative timings between us be different? (if their system moves faster or slower than ours, for example)
 

Jarvitä

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If going by the completely unfounded assumption they have life like ours (and the article says they don't, but for the fun of speculation), then we are seeing them as they were at year 1011, while they are in fact at year 2011 seeing us a we were in year 1011.
Am I correct in that? Or could the relative timings between us be different? (if their system moves faster or slower than ours, for example)

You're correct. Also, the relative velocity isn't large enough to contribute significantly via special relativity.
 

fsci123

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Imagine how beautiful it really is.
 

Hielor

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Given how close they are to the star, shouldn't their orbits potentially interfere? Or is there some kind of resonance keeping them stable?
 

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SPACE.com: Do Newfound Alien Planets Need Better Names?:
{...}

"We need SPACE.com to hold a naming contest!" Marcy wrote in an email to SPACE.com.

We were thinking along similar lines. After the announcement of Kepler-20e and Kepler-20f, SPACE.com asked readers on Facebook to vote for their favorite names for the Earth-size planets. The winning monikers? Romulus and Remus, which "Star Trek" fans will recognize as the names of the twin homeworlds for the fictional Romulan alien race.

{...}
 

T.Neo

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I suggest Colbert.
 

GigaG

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Considering how hot they are, maybe Hades and Cerberus?
 

RisingFury

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Imagine how beautiful it really is.

Both of these planets are probably just hot rocks, similar to Mercury. Due to being so close to the host star, their atmosphere has probably been blown away already, with the only atmosphere left are the liberated particles that get blasted up by the solar wind.


Given how close they are to the star, shouldn't their orbits potentially interfere? Or is there some kind of resonance keeping them stable?

The inner two planets (b and e) are in a 5:3 resonance. IIRC, that one is stabilizing due to the symmetry. The eccentricity of both planets will wobble around, but it won't shoot one or both planets into a highly eccentric orbits.

There are two other possible ones:
c and b have orbital periods with a ratio of 2.95. That's close to a 3:1 resonance. The data I have isn't accurate to second decimal, so this may actually be 3. If it is not, I can understand that too - 3:1 resonance is unstable and will tend to break itself. Objects tend to drift out of resonance, so 2.95 would indicate this resonance has been broken.

Similarly goes with c and b, with orbital periods with a ratio of 1.79, close to 7:4, though 7:4 is on the limits of what I'd call orbital resonance...
 
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