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.
Quote from: Mongo62 on 07/24/2015 01:26 amIf 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."
Quote from: Mongo62 on 07/24/2015 01:26 amIf 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.pdfThis paper puts the transiting line at 1.7R so this planet is still within that limit.
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.
5.3. The Rock-Gas TransitionFigure 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).
5.4. The Nature of sub-Neptune-size Kepler Planet CandidatesOur 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.
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.
5. CONCLUSIONSThe 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.
Here are some more recent papers than the out-of-date paper referenced above,
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.
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).
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.
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.
Quote from: DRussell on 07/25/2015 06:19 pmAnd 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.
Quote from: Mongo62 on 07/25/2015 06:48 pmQuote from: DRussell on 07/25/2015 06:19 pmAnd 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.
[quote author=Eer link=topic=16581.msg1408529#msg1408529 date=1437670019And 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.
Why is this announceworthy?
Planet is 1.6 times the Earth.
We note that it is unlikely that Kepler-452b has an Earth-like composition
Quote from: mcgyver on 07/28/2015 09:12 amPlanet 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 ):QuoteWe note that it is unlikely that Kepler-452b has an Earth-like composition
Quote from: DRussell on 07/25/2015 09:36 pmQuote from: Mongo62 on 07/25/2015 06:48 pmQuote from: DRussell on 07/25/2015 06:19 pmAnd 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.