KOI-2626.01 is finally confirmed!

[ProtoJeb21]

Finally! The exoplanet KOI-2626.01, which has been a rather well-known candidate for YEARS now, has been confirmed at Kepler-1652b. It's about 1.6 times the radius of Earth with a density of 9.9 g/cm^3, suggesting a mass of around 7.356 Me. This makes Kepler-1652b one of only three habitable zone "Mega Earths", the others being LHS 1140 b (6.6 Me) and K2-3d (11.1 Me). 

https://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=kepler-1652+b&type=CONFIRMED_PLANET

[PB666]

Geeze, must be radioactive as hell. d = 9.93 . . . . . . .

[Scotius]

Maybe it's just a LOT of lead....

[ProtoJeb21]

I'm honestly not sure how they even found density for KOI-2929.01 and the other planets in the study. It could easily be something else entirely.

[Hypercosmic]

No, it's probably not lead or radioactive materials (those are extremely rare in the nature). It's probably because it's just that massive. Gravity attracts, rocks get compressed and become denser. Simple gravitational compression.

And a lot of iron.

Edited November 18, 2017 by Hypercosmic

[PB666]

Its not possibly massive enough to compress to 9.93. 1.6 times the radius of earth is 7.4 earth masses, its not massive enough to produce exotic materials at its core.

[KerikBalm]

Earth is roughly 20x the mass of mercury, yet it has nearly the same density. Earth is the densest planet in our solar system. (gas giants have all that hydrogen and helium). 

While gravitational compression of a planet 7x the mass of Earth would not be insignificant, its not going to double the density.

Quote

Mercury's density is the second highest in the Solar System at 5.427 g/cm³, only slightly less than Earth's density of 5.515 g/cm³.^[3] If the effect of gravitational compression were to be factored out from both planets, the materials of which Mercury is made would be denser than those of Earth, with an uncompressed density of 5.3 g/cm³ versus Earth's 4.4 g/cm³

 

[Green Baron]

That's because Mercury has a higher metal part than a planet its size "normally" (according to the standard model for the forming of our solar system) would have. The working hypothesis is that it has been stripped from a part of its mantle by collisions back in the day.

It becomes clearer (i think) that there is no general rule to the densities of planets and the model for our solar system isn't easily transportable to other systems. It might well be that some planets are just naked iron cores (density 10 or even more g/cm³) while other might have a high part of volatiles, like, let's say a KBO in our system, density ~3g/cm³ and less.

[kerbiloid]

13 hours ago, ProtoJeb21 said:

density of 9.9 g/cm^3

Alien dump of depleted uranium.

[magnemoe]

7 hours ago, Green Baron said:

That's because Mercury has a higher metal part than a planet its size "normally" (according to the standard model for the forming of our solar system) would have. The working hypothesis is that it has been stripped from a part of its mantle by collisions back in the day.

It becomes clearer (i think) that there is no general rule to the densities of planets and the model for our solar system isn't easily transportable to other systems. It might well be that some planets are just naked iron cores (density 10 or even more g/cm³) while other might have a high part of volatiles, like, let's say a KBO in our system, density ~3g/cm³ and less.

Suspect some degenerated matter, its talk about some planets with density at 30 g/cm^3. They tend to be very hot and close to the star making it likely its cores of gas giants. 
It look like degenerated matter is meta stable at least in higher pressure like deep down in an planet so an gas giant who loose its gas would leave an very dense body. 

[Green Baron]

Yeah, i have read that as well. If needs degenerated matter for the densities at earths inner core then so be it.

Read the paper that @ProtoJeb21 linked in the Trappist thread : https://arxiv.org/pdf/1711.05691.pdf

Besides (dull slogan:) moar data ! we also need more methodology work because there are a lot of variable properties of the stars, that we just assume to have certain values and deduct then the properties of our assumed planets from them. A slight change, for example in the density of sun spots on the respective sun's surface, changes planet properties likewise for those who have been deducted with the transit photometry method.

Edited November 19, 2017 by Green Baron

[Spaceception]

How did they find the density? Did they look at it with some other method?

And from PHL, with has the same Teq as GJ 180b (268K) as seen in the site, it seems to have a stellar flux of 1.23. Not bad, but seeing as it's a mega Earth, it may be more similar to a mega Venus. Still though, research  on these massive planets can only be interesting. Especially if one was to support life.

[Green Baron]

1 hour ago, Spaceception said:

How did they find the density? Did they look at it with some other method?

 

Yeah, don't give too much for it. It is only a very coarse estimate from the size (in case of the transit method the duration of the drop) and the orbital period which leads to the mass (example: http://news.mit.edu/2013/new-technique-measures-mass-of-exoplanets-1219). With radial velocity (large planets only i think) determining mass is a little easier if we assume that our understanding of a sun's mass is correct. Sun's are naturally somewhat better understood as planets :-)

And always keep in mind that with very few exceptions all measures are indirect and may change as our methodology evolves and instruments get better.

More links with easy explanations:

http://lasp.colorado.edu/education/outerplanets/exoplanets.php

https://www.nasa.gov/ames/kepler/measuring-the-mass-of-a-mars-size-exoplanet

But maybe somebody else can shed more em emissions on it ? I am hasty ...

And always do read the papers that announce a discovery, methods are described if they are serious ;-)

Edited November 19, 2017 by Green Baron

[PB666]

If its the core of a gas giant that has blown away then its not earth like. The latent heat of formation is much higher than that of earth, and the amount of radioisotopes in the core is much greater. Its unlikely that water would be stable on such a world for the two reasons stated.

1. If there is sufficient enough latent heat and ensolance to blow of the gas, then there is enough to blow off all the water.
2. If there is a tremedous amount of latent heat, given its pressure then there is  enough to boil off all of the water via geothermal activity. (expect it to be a magnitude higher than earth)
3. Iron is the principle final product in current generation of stellar activity, it is the most stable product. The only way to get 9.93 is to have collected the dust from primarily supernova or from neutron star mergers.
The earths density is a composite between the densities of Iron and Nickle (around d=8.0) of the cores and the oxygen (44% of the mantle) SiliconOxide (d=2.196) and Magnesium Oxide (d=3.6). In order for the planet to be double that of earths the oxides basically need to be gone, which means no water. In addition that oxide would need to be replaced with substantially more heavy metal.

Final point, they reported density to 9.9 (two decimal places). This implies the result is accurate, therefore either it is accurate or their reporting method is wrong, in which case do not trust any of their data.

Edit. This is what they reported 9.900 +0.880 to -1.340 (this is one S.D.) two S.D. (95.4% confidence interval) would be 7.22 to 11.66.  Thus they might not have much radioactivity, but the planet would be largely, almost solely Iron and nickle with very little oxygen. Of course the density could be higher also, which means potentially very radioactive planet.

Edited November 19, 2017 by PB666

[Green Baron]

Well, as the supposed high density seems to be of such concern, that is really not a problem. We all know that there is no excuse for density to not become infinite if under the persuasive influence of enough gravitation :-) (was that grammatically correct ?)

Density of earth's assumed iron center is estimated to around 13.0 to 13.6 g/cm³.

Edited November 19, 2017 by Green Baron

[ProtoJeb21]

I looked at where KOI-2626b would fall on Sara Seager's exoplanet mass-radius relationship diagram:

It's somewhere around an Earth-like composition with a bit more iron by mass (maybe 20-25%). That high density is mainly due to compression. However, with planets like 55 Cancri e and Tartarus, it seems like there are quite a lot of exceptions to this.

[Spaceception]

15 minutes ago, ProtoJeb21 said:

I looked at where KOI-2626b would fall on Sara Seager's exoplanet mass-radius relationship diagram:

It's somewhere around an Earth-like composition with a bit more iron by mass (maybe 20-25%). That high density is mainly due to compression. However, with planets like 55 Cancri e and Tartarus, it seems like there are quite a lot of exceptions to this.

So, what's the gravity?

I'd check myself, but I'm busy at the moment

[PB666]

1 hour ago, Green Baron said:

Well, as the supposed high density seems to be of such concern, that is really not a problem. We all know that there is no excuse for density to not become infinite if under the persuasive influence of enough gravitation :-) (was that grammatically correct ?)

Density of earth's assumed iron center is estimated to around 13.0 to 13.6 g/cm³.

That is not entirely due to iron. The core is rich in heavy siderophiles because of gravimetric sifting during the gravitational heat formation of the early earth. The assumption is that the early earths core was hotter (due to a higher abundance of radioactivity) and was more molten these sifted to the center and formed concentric spheres as the core cooled.
 

Quote

specifically the siderophile elements then these would necessarily have differentiated to the very center of the core into concentric nested spheres by Planetary differentiation. The most dense (and stable, i.e. platinum, iridium, and osmium, (etc.) in order of density) of these forming the innermost spheroid(s).^[12] Wkipedia - Inner Core.

Platinum - d =  21.45 
Iridium (a common component formed from asteroid collisions) - d = 22.56
Osmium - d = 22.59

if d = 13.3 and density of iron compressed = 9 then relative volume of center is 2.25 Iron:1 siderophile

[Green Baron]

2 minutes ago, Spaceception said:

So, what's the gravity?

On the surface ?

If you're content with ole Newton then g= m/r² where m is the mass of the body and r is the radius. Result in multiples of earth's g.

[ProtoJeb21]

5 minutes ago, Spaceception said:

So, what's the gravity?

I'd check myself, but I'm busy at the moment

About 2.875 gees. Still less than that of LHS 1140 b at 3.25 gees. 

[PB666]

If we were to apply the ratio 9.9 /5.5 = 1.8. 1.8 time 13.3 = 23.94 then the core of this 'Earth-like' planet is entirely heavy metal siderophiles.

 

[Spaceception]

1 minute ago, ProtoJeb21 said:

About 2.875 gees. Still less than that of LHS 1140 b at 3.25 gees. 

That's still a lot. Any possible life would be stocky and hunkered towards the ground. Would intelligence be possible? I doubt space travel would be, except for aliens offworld who are already pros at it.

Kinda unfortunate for these potentially habitable mega Earths, even if they have aliens that develop a society, and primitive tech, they'll be stuck in their homeworld.

[PB666]

dV required to get to orbit. . . . . .18303.3 (v orbit at surface). Add another couple thousand for height related stuff . . . . .20,000 m/s it almost approach earths orbital speed about the sun.

mu = 4E15 (notice my decimal places)

And Koibels running around with 20k dV rockets . . . . lol.

 

 

 

5 minutes ago, Spaceception said:

That's still a lot. Any possible life would be stocky and hunkered towards the ground. Would intelligence be possible? I doubt space travel would be, except for aliens offworld who are already pros at it.

Kinda unfortunate for these potentially habitable mega Earths, even if they have aliens that develop a society, and primitive tech, they'll be stuck in their homeworld.

Giraff's would have shorter necks, rain would hurt, hail would be lethal,

[Hannu2]

As far as I know density in Earth's core agrees what is known about iron (theoretically and experimentally). It is just hydrostatic compression. More massive elements are very rare compared to iron (parts per million instead of percents) and it is not credible that there are large concentrations of such elements or some more exotic forms of matter in Earth's core or at other planets, too. If superearth has 7 earth masses at about 4 times higher volume, I would say it has just high iron concentration.

[Green Baron]

That is my information as well, @Hannu2. The composition of earth's core is mostly inferred from iron meteorites which are composed of Iron, Nickel and  ppm of other elements.

Edit:

Ok, so i went on a search since the density discussion may come up again. I knew experiments were carried out with diamond anvil cells but i didn't remember when and where. It is not ready knowledge as it is all a little impractical :-)

Here you go, iron experimentally compressed to 72GPa, density 9.64g/cm³, indeed needs to be mixed with lighter elements (like S/Si) at the earth's core in order to meet the geological constraints.

So, no problem with the high densities of planets. In contrary, even the high densities allow for a whole lot of "rocky" material. If you ask why then look at the assumed pressure of the earth's inner core ;-)

Edited November 22, 2017 by Green Baron
simplified ;-)