Author Topic: NASA - Kepler updates  (Read 162625 times)

Offline Mongo62

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Re: NASA - Kepler updates
« Reply #420 on: 07/24/2015 01:26 AM »
If this planet's radius is 1.6 times that of Earth, it isn't an Earth-like planet. The papers I have read conclude that the transition from Earth-like (which includes planets like Venus) to Neptune-like is not at a single radius, but occupies a range of radii from ~1.2 Earth radii to ~1.6 Earth radii. So if this discovery had been of a planet with 1.2 Earth radii, then it would probably have been an Earth-like planet. But at 1.6 Earth radii, it's almost certainly a Neptune-like planet.

Offline Star One

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Re: NASA - Kepler updates
« Reply #421 on: 07/24/2015 06:47 AM »

If this planet's radius is 1.6 times that of Earth, it isn't an Earth-like planet. The papers I have read conclude that the transition from Earth-like (which includes planets like Venus) to Neptune-like is not at a single radius, but occupies a range of radii from ~1.2 Earth radii to ~1.6 Earth radii. So if this discovery had been of a planet with 1.2 Earth radii, then it would probably have been an Earth-like planet. But at 1.6 Earth radii, it's almost certainly a Neptune-like planet.

From what I've read two Earth radii is the more likely upper limit on rocky planets so this falls well within that limit.

http://arxiv.org/pdf/1311.0329v1.pdf

This paper puts the transiting line at 1.7R so this planet is still within that limit.

Offline Star One

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Re: NASA - Kepler updates
« Reply #422 on: 07/24/2015 01:00 PM »

If this planet's radius is 1.6 times that of Earth, it isn't an Earth-like planet. The papers I have read conclude that the transition from Earth-like (which includes planets like Venus) to Neptune-like is not at a single radius, but occupies a range of radii from ~1.2 Earth radii to ~1.6 Earth radii. So if this discovery had been of a planet with 1.2 Earth radii, then it would probably have been an Earth-like planet. But at 1.6 Earth radii, it's almost certainly a Neptune-like planet.

Why?  They can calculate the planet's diameter and also its mass and refine that calculation with each year the planet passes in front of its star.  A Neptune-like planet could be as small as 1.6 Earth radii, but it would also have a low mass compared to a rocky world the same diameter.  The scientists said it had "a better than 50/50 chance of being rocky."  That's a very different statement than "almost certainly a Neptune-like planet."

The paper I linked to above is actually taken from Kepler data.

Offline JasonAW3

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Re: NASA - Kepler updates
« Reply #423 on: 07/24/2015 04:41 PM »

If this planet's radius is 1.6 times that of Earth, it isn't an Earth-like planet. The papers I have read conclude that the transition from Earth-like (which includes planets like Venus) to Neptune-like is not at a single radius, but occupies a range of radii from ~1.2 Earth radii to ~1.6 Earth radii. So if this discovery had been of a planet with 1.2 Earth radii, then it would probably have been an Earth-like planet. But at 1.6 Earth radii, it's almost certainly a Neptune-like planet.

From what I've read two Earth radii is the more likely upper limit on rocky planets so this falls well within that limit.

http://arxiv.org/pdf/1311.0329v1.pdf

This paper puts the transiting line at 1.7R so this planet is still within that limit.

     Bear in mind, this also assumes that the planet is distant from the star when it ignites.  As we are finding in proto systems, the orbital characteristics of all planetismals (or protoplanets if you will) are fairly unstable and can swing out very distand and in again close enough that were the central sphere a star, it would be scourched.

     It may be possible for a high mass planet, Neptunian in configuration, to be close enough that, when the star ignites, the vast majority of it's atmosphere, if not all of it, is stripped away.  I would not be too suprised if this is a more common occurance than we currently suspect.

     However; I have an interesting question to pose;

     Is it possible that low gas / high dust ratio clouds of matter may follow similar planetary / star system formation, forming planets, but with a Hyper Jupiter type object as the system primary, rather than a star?  This would seem to be much like a Super Jupiter but with a MASSIVELY larger brown dwarf at the center than would otherwise be normal?
My God!  It's full of universes!

Offline MattMason

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Re: NASA - Kepler updates
« Reply #424 on: 07/24/2015 05:16 PM »
At 1,400 light years away I don't think any planed future telescopes will be able to do spectroscopy on the planet. That is too bad because the atmosphere of a planet like this has got to be interesting. At the press conference they mentioned that it should still be very volcanically active. I'd bet that it has a magnetic field, perhaps even stronger than Earth's. Those things and the increased gravity compared to Earth makes me think this planet must have a pretty thick atmosphere.

Whether we have instruments that can detect a significant magnetic field around an exoplanet is for more illuminating than the body's size. We have plenty of examples of planets and moons with significant atmosphere. Only one has a powerful magnetosphere that doesn't cause the planet to allow its atmosphere to be blown and/or frozen off, go into a greenhouse mode and/or irradiate its surface.

That, as far as we know, isn't a matter of a planet's size. Seems the data is more in discussing size and distance than the planet's consistency. It's like a strange cosmological jingle to a commercial.

"When the moment is right for your solar system, a Little Blue Planet with its patented Core may bring life to your experience. (Side effects include occasional switching of poles and light flashes around the poles. Don't use the Little Blue Planet if you cannot place it within a specific location that doesn't cause freezing or melting of its populace.)"
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Offline llanitedave

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Re: NASA - Kepler updates
« Reply #425 on: 07/24/2015 09:27 PM »
We have plenty of CO2, fortunately we also have plenty of water to lock that CO2 into carbonate minerals.
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Offline AnalogMan

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Re: NASA - Kepler updates
« Reply #426 on: 07/24/2015 10:31 PM »
This paper was listed amongst the Kepler media briefing materials, but I didn't see a link posted to it in this thread.
It was published July 23, 2015

Discovery and Validation of Kepler-425b - A 1.6-R+ Super Earth Exoplanet in the Habitable Zone of a G2 Star
https://www.nasa.gov/sites/default/files/atoms/files/ms-r1b.pdf

(copy also attached)

Offline yg1968

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Re: NASA - Kepler updates
« Reply #427 on: 07/25/2015 04:54 AM »
Here is the audio of the Kepler 452b teleconference of July 23rd on YouTube.



The slides for the teleconference can be found here:
http://www.nasa.gov/keplerbriefing0723
« Last Edit: 07/25/2015 05:05 AM by yg1968 »

Offline DRussell

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Re: NASA - Kepler updates
« Reply #428 on: 07/25/2015 12:58 PM »
Even going back to the mass-radius relationships studied by Seager et al. (2007) a terrestrial planet with a radius of 1.6 RE should have a mass of 5-6 ME

http://adsabs.harvard.edu/abs/2007ApJ...669.1279S

As a recent example of a terrestrial exoplanet there is Kepler 93b with a radius of 1.478 +/- 0.019 RE and a mass of 4.02 +/- 0.68 ME.

http://adsabs.harvard.edu/abs/2015ApJ...800..135D

So this new planet must be ~5-6x the Earth's mass if it is terrestrial in nature.

Dave

Offline Mongo62

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Re: NASA - Kepler updates
« Reply #429 on: 07/25/2015 01:21 PM »

If this planet's radius is 1.6 times that of Earth, it isn't an Earth-like planet. The papers I have read conclude that the transition from Earth-like (which includes planets like Venus) to Neptune-like is not at a single radius, but occupies a range of radii from ~1.2 Earth radii to ~1.6 Earth radii. So if this discovery had been of a planet with 1.2 Earth radii, then it would probably have been an Earth-like planet. But at 1.6 Earth radii, it's almost certainly a Neptune-like planet.

From what I've read two Earth radii is the more likely upper limit on rocky planets so this falls well within that limit.

http://arxiv.org/pdf/1311.0329v1.pdf

This paper puts the transiting line at 1.7R so this planet is still within that limit.

Here are some more recent papers than the out-of-date paper referenced above, in reverse chronological order.

How Rocky Are They? The Composition Distribution of Kepler's Sub-Neptune Planet Candidates within 0.15 AU

Quote
5.3. The Rock-Gas Transition

Figure 6 also has implications for the expected transition between rocky and gaseous planets, assuming these planets do not have an appreciable mass fraction of water. In particular, we see that planets with 1.2 < Rpl < 1.8 R⊕ can be either rocky or gaseous, with f-env posteriors that span both compositions. This is consistent with the finding of Rogers (2014), which places the transition between rocky and gaseous planets at 1.5 R⊕ based on 50 Kepler confirmed planets with radial velocity mass measurements, primarily from Marcy et al. (2014).

Most 1.6 Earth-Radius Planets are not Rocky

Quote
5.4. The Nature of sub-Neptune-size Kepler Planet Candidates

Our hierarchical bayesian analysis gives insights into the nature of the thousands of transiting Kepler planet candidates that do not have measured masses. Based on the sample of Kepler planets with RV follow-up, we found that most planets larger than 1.6 REarth are so low-density that a volatile envelope must contribute significantly to their transit radius. The Kepler Mission developed a working nomenclature for planets, based solely on their radii; describing planets < 1.25 REarth as Earth-size, 1.25 to 2.0 REarth as Super Earth-size, and 2 to 6 REarth as Neptune-size (e.g., Borucki et al. 2011). Our results (Figure 5) provide quantitative estimates of the fraction of planets in each of these ranges that are suficiently dense to be rocky. One of the primary science goals of the Kepler mission is to calculate the occurrence rate of Earth-like planets in the habitable zones of sun-like stars. We suggest that the operational definition of Earth-like" focus on planets with Rp < 1.6 REarth, to consider planets with a significant probability of having a rocky composition.

The limits on the fraction of planets of a given size that are dense enough to be rocky derived in this work should be regarded as upper bounds; it is likely that a smaller fraction of planets of any size are rocky. We have specifically investigated the fraction of planets that are suficiently dense to be rocky (i.e. more dense than an iron-poor, pure silicate composition). Planets suficiently dense to be rocky may still harbor a thick envelope of volatiles that contributes to its transit radius, if the volatiles are offset by a more iron-rich make-up for the rocky-component of the planet.

Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets

Quote
Figure 51 shows planet density vs radius for the 30 transiting planets having an uncertainty in density less than 6.5 g cm^−3. Planet density decreases with increasing planet radius from 1.5 to 5 R⊕. The densities of planets smaller than 1.5 R⊕ are systematically greater than ~5 g cm^−3, similar to that of Earth (5.5 g cm^−3), indicating that these planets have mostly rocky interiors.

The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii

Quote
5. CONCLUSIONS

The weighted mean exoplanet density peaks at approximately 1.4 R⊕ and 7.6 g cm−3 which is consistent with an Earth-composition planet. Planet density increases with radius up to 1.5 R⊕, but above 1.5 R⊕, planet density decreases with planet radius. Planets smaller than 1.5R⊕ are consistent with a linear density-radius relation, and are also consistent with the Seager et al. (2007) Earth composition curve. Above 1.5R⊕, the decrease in planet density with increasing radius can only be due to the inclusion of volatiles, and so planets larger than 1.5 R⊕ are generally inconsistent with a purely rocky composition. Among planets larger than 1.5R⊕, the gentle rise in planet mass with increasing radius indicates a substantial change in radius for very little change in mass, suggesting that lightweight H/He gas is present in increasing quantities with increasing planetary radius.

« Last Edit: 07/25/2015 01:24 PM by Mongo62 »

Offline yg1968

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Re: NASA - Kepler updates
« Reply #430 on: 07/25/2015 04:35 PM »
Kepler 452b SETI Google Hangout:

« Last Edit: 07/25/2015 04:35 PM by yg1968 »

Offline DRussell

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Re: NASA - Kepler updates
« Reply #431 on: 07/25/2015 06:19 PM »
Quote from: Mongo62
Here are some more recent papers than the out-of-date paper referenced above,

The 2007 paper by Seager et al. is not dated.  According to ADS it has been cited 232 times including 24 times in 2015.  It is cited by every single one of the papers you referred to.  The Seager paper is a theoretical paper.  The papers you have cited are based upon observational data and they use the Seager et al. theoretical mass-radius relationships to help interpret the observations.  Here’s just one example from the paper by Weiss & Marcy you cited:

Quote from: Weiss&Marcy
  Many authors have explored the relationship between planet mass and radius as a means for understanding exoplanet compositions and as a predictive tool.  Seager et al. (2007) predict the mass-radius relationship for planets of various compositions. 

In their section on “Implications for planet compositions” section Weiss and Marcy note:

Quote from: Weiss&Marcy
Following Seager et al. (2007) prediction for the density of an Earth-composition (67.5% MgSiO3, 32.5% Fe) planet, we see a predicted increase in planet density with increasing planet radius.  …. Equation 1 and the density-radius relation from seager et al. (2007) are both consistent with the interpretation that planets smaller than 1.5 RE are rocky, but Equation 1 has advantages in that it (a) is empirical, and (b) passes closer to Earth, Venus, and Mars, which are known to be rich in silicon and magnesium (unlike Mercury, which is iron-rich).


And from the Weiss & Marcy conclusion:

Quote from: Weiss&Marcy
Planets smaller than 1.5 RE are consistent with a linear density-radius relation, and are also consistent with the Seager et al. (2007) Earth composition curve.

Your claim that the paper is out-of-date is simply not correct.

And the point I was making was that if ... if ... the planet is of Earth-like composition then it must be about 5-6 Earth masses based upon the not out-of-date  mass-radius relations investigated by Seager et. al (2007).  Of course it could be less massive, and lower density with a higher percentage of water or other volatiles.

Offline Mongo62

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Re: NASA - Kepler updates
« Reply #432 on: 07/25/2015 06:48 PM »
And the point I was making was that if ... if ... the planet is of Earth-like composition then it must be about 5-6 Earth masses based upon the not out-of-date  mass-radius relations investigated by Seager et. al (2007).  Of course it could be less massive, and lower density with a higher percentage of water or other volatiles.

I was not responding to you. Your point is true, but irrelevant to the point I was making. I was responding to Star One's assertion that the upper radius limit of Earth-like planets is 2 Earth radii, when the actual limit is probably 1.5 Earth radii.
« Last Edit: 07/25/2015 06:49 PM by Mongo62 »

Offline DRussell

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Re: NASA - Kepler updates
« Reply #433 on: 07/25/2015 09:36 PM »
And the point I was making was that if ... if ... the planet is of Earth-like composition then it must be about 5-6 Earth masses based upon the not out-of-date  mass-radius relations investigated by Seager et. al (2007).  Of course it could be less massive, and lower density with a higher percentage of water or other volatiles.

I was not responding to you. Your point is true, but irrelevant to the point I was making. I was responding to Star One's assertion that the upper radius limit of Earth-like planets is 2 Earth radii, when the actual limit is probably 1.5 Earth radii.

Sorry - my apologies.   I misunderstood who you were responding to.  You are correct - the latest research suggests that exoplanets with radii larger than ~1.6 Earth radii as a population will not be Earth-like - so less than 50% of the planets with radii from 1.6-2.0 Earth radii will be terrestrial. 

Offline Star One

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Re: NASA - Kepler updates
« Reply #434 on: 07/25/2015 11:40 PM »

And the point I was making was that if ... if ... the planet is of Earth-like composition then it must be about 5-6 Earth masses based upon the not out-of-date  mass-radius relations investigated by Seager et. al (2007).  Of course it could be less massive, and lower density with a higher percentage of water or other volatiles.

I was not responding to you. Your point is true, but irrelevant to the point I was making. I was responding to Star One's assertion that the upper radius limit of Earth-like planets is 2 Earth radii, when the actual limit is probably 1.5 Earth radii.

Sorry - my apologies.   I misunderstood who you were responding to.  You are correct - the latest research suggests that exoplanets with radii larger than ~1.6 Earth radii as a population will not be Earth-like - so less than 50% of the planets with radii from 1.6-2.0 Earth radii will be terrestrial.

If it's less than 50% that still means some of them will be terrestrial which invalidates the OP's point because it means there is a chance this is rocky. When their original post seemed to be implying there was no chance of this.

Offline Vultur

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Re: NASA - Kepler updates
« Reply #435 on: 07/28/2015 12:27 AM »
[quote author=Eer link=topic=16581.msg1408529#msg1408529 date=1437670019
And because of the fact that it is so far from the star (orbital period of 300+ days) I find it much better place to live (in my imagination) than those other ESI Top-10 planets, which have orbital period of about 30 days. No matter if the star they orbit is small, it still might have harmful flares etc. scorching the nearby planets... Also tidal locking is guaranteed with those planets.

Flares might strip away the atmosphere*, but I don't think tidal locking is necessarily a problem. From what I've read, oceans & atmosphere would redistribute heat rather well so the temperature range would be rather Earth-like: permanent Saharan summer noon at the subsolar point and permanent polar winter night at the opposite point, but with large pleasant areas in between.

*would a magnetic field protect sufficiently? If so, it would probably be fine. The heat output variations should be mitigated by oceans and atmosphere.

Offline mcgyver

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Re: NASA - Kepler updates
« Reply #436 on: 07/28/2015 09:12 AM »
Why is this announceworthy?
Many people ask for this.
I read a similar first-page-news ona PAPER newspaper... around 20 years ago!

But his time:
Planet is 1.6 times the Earth.
Its star has almost same temperature of our star.
Its star sends it 1.1 times the energy our star sends to us.
Its star is 1.1 AU from it.
The solar system is older than ours, and the planet always staid in the habitable zone, for 6 billions of years (2 billions more than Earth).
Its year is 1.1 times our year. I think this is the most unusual thing: till now I've always read of hours-lasting or days-lasting "years"; this could mean that now we have (or have analyzed) enough data to start finding earth-year-like systems at last! Even planets 1 YL apart rather than 1400. :-) And a planet like 452b but 1 YL far would be much intriguing!
 

Offline plutogno

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Re: NASA - Kepler updates
« Reply #437 on: 07/28/2015 11:21 AM »
Planet is 1.6 times the Earth.

since you didn't specify it: planet is 1.6 times the SIZE of the Earth. we don't know its mass. for all we know it could be a mini-Neptune instead of a giant Earth.
and even the authors of the discovery are skeptical (see http://arxiv.org/abs/1507.06723 ):

Quote
We note that it is unlikely that Kepler-452b has an Earth-like composition


Offline DRussell

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Re: NASA - Kepler updates
« Reply #438 on: 07/28/2015 11:41 AM »
Planet is 1.6 times the Earth.

since you didn't specify it: planet is 1.6 times the SIZE of the Earth. we don't know its mass. for all we know it could be a mini-Neptune instead of a giant Earth.
and even the authors of the discovery are skeptical (see http://arxiv.org/abs/1507.06723 ):

Quote
We note that it is unlikely that Kepler-452b has an Earth-like composition

Right - using mass-radius relationships a planet with 1.6x the Earth's radius would have ~5x the Earth's mass if it had an Earth-like composition.

Offline DRussell

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Re: NASA - Kepler updates
« Reply #439 on: 07/28/2015 12:01 PM »

And the point I was making was that if ... if ... the planet is of Earth-like composition then it must be about 5-6 Earth masses based upon the not out-of-date  mass-radius relations investigated by Seager et. al (2007).  Of course it could be less massive, and lower density with a higher percentage of water or other volatiles.

I was not responding to you. Your point is true, but irrelevant to the point I was making. I was responding to Star One's assertion that the upper radius limit of Earth-like planets is 2 Earth radii, when the actual limit is probably 1.5 Earth radii.

Sorry - my apologies.   I misunderstood who you were responding to.  You are correct - the latest research suggests that exoplanets with radii larger than ~1.6 Earth radii as a population will not be Earth-like - so less than 50% of the planets with radii from 1.6-2.0 Earth radii will be terrestrial.

If it's less than 50% that still means some of them will be terrestrial which invalidates the OP's point because it means there is a chance this is rocky. When their original post seemed to be implying there was no chance of this.

One of the uncertainties is about definitions: what do we mean by "Terrestrial" and by "Earth-like"?   Mercury, Venus, Earth, and Mars are clearly terrestrial.  But what if we add a 1% by mass H/He envelope around a terrestrial planet.  I would argue such a planet is still terrestrial, but is it still "Earth-like"?  A lot of these planets with radius > 1.6 Earth will have a H/He gas envelope ranging from 0.5% to 16% of the total planetary mass.   

A great example of this type of planet would be the planets of the Kepler 11 system:

http://adsabs.harvard.edu/abs/2013ApJ...770..131L

Lissauer et al. note that for several of the planets in the Kepler 11 system about 50% of the observed radius would be from the H/He envelope.    This is very different from the structure of the terrestrial planets and the gas giants.  Jupiter and Saturn are only ~8-22% by mass elements heavier than H/He. 

As we move up the radius scale above 1.6 Earth radii it becomes increasingly likely that we have these sort of gas envelopes surrounding the planets.

Dave

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