Potentially Habitable Exoplanets

[Spaceception]

Don't remember when, but I'm quite sure I said something about this in relation about a past article

https://www.universetoday.com/136837/another-nearby-red-dwarf-star-system-another-possible-exoplanet-discovered/amp/

[ProtoJeb21]

4 hours ago, Spaceception said:

Don't remember when, but I'm quite sure I said something about this in relation about a past article

https://www.universetoday.com/136837/another-nearby-red-dwarf-star-system-another-possible-exoplanet-discovered/amp/

Yeah, I remember that the possibility of a third planet of GJ 832 within the habitable zone was predicted last year. I hope they can find it - or maybe even more worlds!

[ProtoJeb21]

Lots of new discoveries! I'm not letting this thread die when there are so many new potentially habitable worlds and updates to them.

 

Just today, a paper was released describing the mass of the large habitable zone planet K2-18b. It's 2.28 times the size of Earth, and is now confirmed to be 8 M_E with a density of 3.7 g/cm³. This indicates that it is a giant oceanic planet, with about 50% of its mass being water. Cool! The team also found a second planet of 7.5 M_E orbiting three times closer in, but not transiting.

https://arxiv.org/pdf/1707.04292.pdf

 

The planets around TRAPPIST-1 are actually about 8% smaller in radius than originally calculated, due to different forms of stellar activity messing with the lightcurves gathered by Kepler. They are all denser as well, with the authors of the study also finding that the original mass values reported by Gillion et al. are the most accurate. This means that 5 of the planets are pure rock and iron worlds, while 1b (Theros) and 1f (Irene) are about 15-25% water by mass.

https://arxiv.org/pdf/1711.05691.pdf

 

Candidate planets KOI-2626.01 and KOI-4550.01 have now been confirmed, the former being a candidate for the last 4 years. They are now known as Kepler-1652b and Kepler-1653b. 1652b is 1.60 R_E with a temperature of 261^oK and a stellar flux 0.81 times that of Earth. It orbits a red dwarf 38% the radius of the Sun. Kepler-1653b, on the other hand, is 2.17 R_E, takes 140 days to orbits its star, has a temperature of 284^oK, and receives a stellar flux of 0.98. The paper where both of these were confirmed gives densities based off a method that I do not understand yet, but hope to apply to my candidate planets. Kepler-1652b appears to be a Mega-Earth, with a density of 9.9 g/cm³ and a mass around 7.36 M_E. Kepler-1653b is significantly less dense at 3.08 g/cm³, indicating a mass around 6.19 M_E and a water-rich composition, similar to K2-18b mentioned above.

https://arxiv.org/pdf/1711.01267.pdf

 

Finally, there's Ross 128b, the second-closest potentially habitable exoplanet to Earth. It's only about 1.35 times as massive as Earth and gets only 38% more sunlight. More info about the planet can be found in the following links:

http://www.drewexmachina.com/2017/11/16/habitable-planet-reality-check-the-nearby-ross-128/

https://en.wikipedia.org/wiki/Ross_128_b

https://www.eso.org/public/usa/news/eso1736/

https://arxiv.org/pdf/1711.06177.pdf

[Spaceception]

@ProtoJeb21 Could TRAPPIST-1b be a hot Oceania? I see a ton of those in Space Engine, life imitates art? The possibility of life is cool.

Thanks @ProtoJeb21 for the update, hadn't been able to get around it

But here's a pretty picture by the guys at PHL

That Kepler data tho.

[ProtoJeb21]

35 minutes ago, Spaceception said:

@ProtoJeb21 Could TRAPPIST-1b be a hot Oceania? I see a ton of those in Space Engine, life imitates art? The possibility of life is cool.

I'm pretty sure it is. Theros' equilibrium temperature is just a bit above the boiling point of water, and a large reflective cloud cover can help lower surface temperatures to more comfortable values. However, its mass is pretty uncertain, so it may still be a rocky planet. If an ocean world, I'd expect something like the hot springs at Yellowstone National Park (minus idiot humans falling into boiling water and a giant death volcano under the surface). 

 

What I'm hoping is that there are some salty and rocky land masses - maybe like tiny intertwining archipelagos. This could create those "warm little ponds" that may have led to the first cells on Earth. 

[DAL59]

Can you please add Trappist to the poll?

[ProtoJeb21]

It turns out TRAPPIST-1 is a bit larger than initially thought. A detailed study by Grootel et al was able to pin down the radius, mass, and luminosity of the star with an error of less than 7e-3 solar units. TRAPPIST-1 is actually 0.121 R_Sol and 0.089 M_Sol, with a luminosity of 0.000522 L_Sol and a temperature of 2516 K. The mass and radius values are a bit higher than before, meaning that the radii and semi-major axes of the 7 planets will be slightly higher as well. However, the new luminosity has not changed much from the original parameters from Gillion et al earlier this year. Doing a bit of calculations reveals that the equilibrium temperatures (and incident fluxes) of the planets are lower than expected. This is both good and bad. On one hand, it makes Theros/1b seem more likely to be an ocean world, and gives Thallo/1d a stellar flux of 1, which would give it an ESI of at least 0.91. However, the outer three planets, including Irene/1f and Carphos/1g, are now less likely to be habitable, and instead may be icy "super-Marses". The new equilibrium temperatures for the 7 planets are 359, 307, 258, 225, 197, 178, and 155 Kelvin. Research paper is linked below:

https://arxiv.org/pdf/1712.01911.pdf

As great as all these new updates to the TRAPPIST-1 system are, it's VERY annoying for me, because it gives me more and more and more things I need to change about my renditions of the TRAPPIST-1 system in Interstellar Adventure Revived. To make matters worse, new radius and mass values are not given by Grootel et al. While radius will be easy to re-calculate, I cannot find the new mass values of the 7 planets. That would have to be done by someone who actually knows how to work with Transit Timing Variations.

 

BONUS PROBLEM: It turns out the eccentricity of the orbit of Tau Ceti e, as given by the 2017 paper, is rather high at e = 0.18. The planet's equilibrium temperature varies from as high as almost 330 K to as "low" as 272 K. This would most likely make Tau Ceti e a hellish Venus-like planet with extreme seasons. On the bright side, the much colder Tau Ceti f also has an eccentric orbit (e = 0.16) and can reach an equilibrium temperature as high as 204 K, but can drop down to 174 K. With a thick atmosphere, there could be some areas on Tau Ceti f that are warm enough for liquid water. Let's hope the system isn't face-on, or else both e and f are likely Mini-Neptunes.

Edited December 8, 2017 by ProtoJeb21

[Spaceception]

Wow... So much is happening with this system, I wonder if once James Webb, and the VLT come online, it will become the most comprehensively studied solar system second to our own. Or among the few prime targets good enough for that.

How much more Earthlike is TRAPPIST-1 e now? Higher chance of water?

And yeah. We could very well be looking at a hot Oceania, that'll be cool.

5 hours ago, DAL59 said:

Can you please add Trappist to the poll?

Sorry, no, limited number of options I can add.

[Mayer]

Being in a habitable zone doesn't mean habitable. Trappist-1 star may be too big and bombard its planets with intense radiation.

[Green Baron]

"Habitable" in this context means "equilibrium temp. is can be between 0 and 100 degrees Celsius somewhere on the surface, without any atmospheric influence and according to our models for stars and their energy production". That leaves a lot of room for speculation and does in it self not take into account for any of the factor necessary for life(tm).

But i think everybody is aware

Edit: i just realized that the proposals for our suns "habitable" zone now range from 1 to 10 AU (!) and atmospheres are included; according to the heap of hot waste called Wikipedia. When i last looked Mars was just outside of it ... the whole concept "lives" with hopes and expectations :-)

Edited December 8, 2017 by Green Baron

[ProtoJeb21]

Dammit, K2-18b isn't potentially habitable anymore  

https://arxiv.org/pdf/1712.06774.pdf

The star has been re-sized to half the radius of the Sun, which means that K2-18b is over 2.8 Earth radii with a temperature of 348 K. It's definitely more massive that original estimates showed, but I think it's more likely to be a mini-Neptune.

@UranianBlue looks like you were right.

At the very least, the upcoming near-infrared Radial Velocity spectrograph and its upcoming survey starting in 2018 promise to bring in some more potentially habitable worlds.

https://arxiv.org/abs/1712.06673

Edited December 20, 2017 by ProtoJeb21

[ProtoJeb21]

Okay and apparently Poltergeist and Phobetor, the two Super-Earths of the Lich pulsar system, are potentially habitable.

http://astronomy.com/news/2017/12/protecting-exoplanets-from-pulsars

[Spaceception]

8 minutes ago, ProtoJeb21 said:

Okay and apparently Poltergeist and Phobetor, the two Super-Earths of the Lich pulsar system, are potentially habitable.

http://astronomy.com/news/2017/12/protecting-exoplanets-from-pulsars

Whaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaat

Do you think it'll be added to PHL?

Those are exotic for sure.

 

And, so basically, the first planets we ever discovered.... are technically potentially habitable, given extreme conditions?

Wow.

Edited December 21, 2017 by Spaceception

[ProtoJeb21]

2 minutes ago, Spaceception said:

Whaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaat

Do you think it'll be added to PHL?

Those are exotic for sure.

I'm not too sure. The PHL deals with "classical" potentially habitable worlds - you know, likely rocky or water-rich planets orbiting within the habitable zone of their stars, which is defined by their stars' VISIBLE light. This new Lich habitable zone is defined by its X-RAY light. This makes it fundamentally different from every single potentially habitable system discovered before. In addition, Poltergeist and Phobetor will need to resemble Mini-Neptunes, once thought to be non habitable, in order to even be habitable. Oh, and don't forget that they're both likely carbon planets and bathed in an absolute onslaught of X-rays. Seriously, what the fu---

If you want something more "normal", I'd like to present Kepler-1308. Its a red dwarf about a third the size of the Sun with one Mars-sized planet of 0.50 R_E orbiting it every 2 days. I managed to find 3 potential new candidates from overlooked, weak signals. All of them are smaller than Earth at 0.20, 0.40, and 0.60 R_E and orbit every 4, 16, and 40 days in a 4-planet resonant chain. The last two are within the habitable zone with equilibrium temperatures of 298^oK and 221^oK, but Planet 3's small size suggest that it likely lost its atmosphere far in the past. Planet 4 may still retain a water-friendly atmosphere. In addition, I found a potential second planet to Kepler-1410, which is just about the same size as Earth and orbits every 113 days with an equilibrium temperature of 223^oK.

[Spaceception]

5 minutes ago, ProtoJeb21 said:

I'm not too sure. The PHL deals with "classical" potentially habitable worlds - you know, likely rocky or water-rich planets orbiting within the habitable zone of their stars, which is defined by their stars' VISIBLE light. This new Lich habitable zone is defined by its X-RAY light. This makes it fundamentally different from every single potentially habitable system discovered before. In addition, Poltergeist and Phobetor will need to resemble Mini-Neptunes, once thought to be non habitable, in order to even be habitable. Oh, and don't forget that they're both likely carbon planets and bathed in an absolute onslaught of X-rays. Seriously, what the fu---

If you want something more "normal", I'd like to present Kepler-1308. Its a red dwarf about a third the size of the Sun with one Mars-sized planet of 0.50 R_E orbiting it every 2 days. I managed to find 3 potential new candidates from overlooked, weak signals. All of them are smaller than Earth at 0.20, 0.40, and 0.60 R_E and orbit every 4, 16, and 40 days in a 4-planet resonant chain. The last two are within the habitable zone with equilibrium temperatures of 298^oK and 221^oK, but Planet 3's small size suggest that it likely lost its atmosphere far in the past. Planet 4 may still retain a water-friendly atmosphere. In addition, I found a potential second planet to Kepler-1410, which is just about the same size as Earth and orbits every 113 days with an equilibrium temperature of 223^oK.

So, a Mars-like planet that's probably warmer, and a Mars-like planet that could be more similar to Earth? Cool. Hopefully they get confirmed

[ProtoJeb21]

@Spaceception I did the math and yes, Poltergeist and Phobetor will need to be Mini-Neptunes in order to be habitable. The article I posted states that these two planets need atmospheres 1,000,000 times thicker than Earth’s to retain liquid water. For comparison, out atmosphere has a mass of 5.418e+18 kilograms, so something one million times thicker would be 0.907234 Earth masses (5.418e+24 kg). That would make Poltergeist and Phobetor about 21.1% and 23.3% atmosphere by mass. While this may sound unrealistically huge, this is about the same atmosphere-to-total mass percentage as Uranus and Neptune. Plus, atmospheres this thick could form from the hydrogen and helium ejected from the former host star after it went belly-up. In addition, this opens up the possibility of life on not only pulsar planets, but ice giants as well - as long as their atmospheres aren’t too thick and there’s a big enough core. 

[ProtoJeb21]

A few years old, but still very interesting for the implication of habitable exomoons.

http://beyondearthlyskies.blogspot.com/2015/05/large-water-rich-moons-around-super.html

[ProtoJeb21]

The three-planet EPIC 210897587 system, discovered by Vidar87, has now been confirmed. The final planet is much less promising then originally expected, but could still be a potentially habitable ocean world. 

https://arxiv.org/abs/1801.06249

https://www.zooniverse.org/projects/ianc2/exoplanet-explorers/talk/821/433893?comment=876235

With these news results, the now-renamed LP415-17 system is not nearly as promising as it was before, but it still holds potential. The final planet, LP415-17d, is about 1.90 R_Earth with a equilibrium temperature of 325 K (125 F) for an albedo of 0.3 and a stellar flux over 2.6 times that of Earth. While it may seem inhospitable, there's one glimmer of hope: composition. The planet likely has around 5 Earth masses, based off of Geoff Marcy's mass-radius relationship equation discussed in the paper linked above. This mass would give LP415-17d a composition of about 75% H₂O and 25% MgSiO₂, making it a giant ocean planet. Such a world is unlikely to become a Super-Venus, as there is too much water to evaporate. Plus the planet is still cool enough for ice crystals and water clouds to form in the atmosphere. Given this, along with another recent paper about the haze composition of Super-Earths and Mini-Neptunes (https://arxiv.org/pdf/1801.06512.pdf), it seems quite likely that LP415-17d has managed to acquire significant cloud cover, potentially enough to lower the planet's temperature and keep it habitable. An estimated albedo of 0.7 gives the planet an equilibrium temperature of 263 K (14 F), and an Earth-like greenhouse effect would raise that temperature to about 296 K (73 F). So all hope is not lost. The scientists who confirmed the system (and unfortunately didn't know of Vidar's original analyses) hoped to get precise radial-velocity measurements with the Very Large Telescope and possibly use the James Webb Telescope in the coming years to analyze the atmospheres of the LP415-17 planets.

A banner for the system I recently made:

Other things to note about the system:

• LP415-17b has a potential composition of about 55% H₂O and 45% MgSiO₂, or perhaps a mixed rock-iron composition with a thin H/He envelope above a water shell.
• LP415-17c could be very similar to Gliese 1214 b, albeit significantly cooler.
• Planets b and c are close to a 9:4 mean-motion resonance.
• Planets c and d are very close to a 3:1 mean-motion resonance.
• Despite the lack of stable first or second-order resonances, N-body simulations show that the system is very stable.
• The paper in the second arXiv link I provided gives evidence that LP415-17c likely has a haze rich in H₂O, CH₄, and CO₂, potentially giving it a deep blue/indigo haze and/or significant cloud cover.
• As of now, only LP415-17b shows signs of significant transit-timing variations. Not only is LP415-17d too far away from LP415-17c to have any significant gravitational effects on it, but both planets don't have enough data to reveal any significant TTVs. This will make mass estimates significantly more difficult.

Edited January 22, 2018 by ProtoJeb21

[ProtoJeb21]

Another research paper on EPIC 210897587/LP415-17. This time the star is given slightly lower parameters, which means that planet d is within the optimistic HZ and is probably an ocean world. 

https://arxiv.org/abs/1801.06957

[ProtoJeb21]

An infographic of the K2-72 system, based of my most recent and most accurate analysis. K2-72e and f are some of the most Earth-like planets found, with ESI values of 0.86 and 0.89. Approximate mass, density, and surface gravity values are given for each planet.

[PB666]

I don't know if nay of these are habitable but here's the appendage to the rest

https://www.scientificamerican.com/article/astronomers-haul-in-another-horde-of-kepler-planets/

[ProtoJeb21]

More precise masses for the three planets around K2-3, including its near-Habitable zone planet, have been released. Earlier studies have placed K2-3b at 8 M_Earth, 3c at 2.1 M_Earth, and 3d somewhere between 7.5 and 11.1 M_Earth. Each planet was thought to be a completely different type of planet: an ocean world, a gas dwarf, and an iron planet. However, these new masses, derived from 2.5 years of radial velocity data, have revealed that they’re almost identical triplets. 

https://arxiv.org/pdf/1802.08320.pdf

All three planets (which I had nicknamed after the sea deities Phorcys, Brigid, and Galene) have extremely similar densities between 3 and 3.2 g/cm^3, indicating almost identical compositions. The well-constrained Phorcys is about 2.3 times the size of Earth and 6.6 times the mass, compatible with a composition of almost 100% water. Brigid and Galene, however, have rather poorly constrained masses due to stellar activity. Both are similar in radius (1.77 and 1.65 R_Earth) and appear to be around 3.1 and 2.7 M_Earth, respectively. Depending on their exact masses they are either ocean planets or gas dwarfs. Their mean masses also indicate two possibilities: water-rich compositions of >50% water by mass, or rather dry interiors with hydrogen envelopes comprising about 0.3-0.4% of their masses. If Hubble or the JWST can take a look at the planets’ atmospheres and find a blank spectrum, it would mean that they are ocean planets. 

[cypher_00]

Apparently Proxima B is not longer considered habitable. 

Solar flares fried the atmosphere  a long time ago.

https://www.space.com/35649-proxima-b-alien-life-superflares.html

http://iopscience.iop.org/article/10.3847/2041-8213/836/1/L3

 

[dreadanaught]

What happened to the TRAPPIST-1 System? It has 7 planets with surface water, three of which are in the habitable zone.

[ProtoJeb21]

30 minutes ago, dreadanaught said:

What happened to the TRAPPIST-1 System? It has 7 planets with surface water, three of which are in the habitable zone.

It has its own thread. This one is for all potentially habitable exoplanet discoveries and updates. 

Also, TRAPPIST-1d, e, and f are the only planets in the system that likely have liquid water on their surfaces. TRAPPIST-1d is covered with 250 times more water than Earth, TRAPPIST-1e has a rocky composition that likely can support oceans, and TRAPPIST-1f, while cold, may have some melted ice on its front side.

2 hours ago, cypher_00 said:

Apparently Proxima B is not longer considered habitable. 

Solar flares fried the atmosphere  a long time ago.

https://www.space.com/35649-proxima-b-alien-life-superflares.html

http://iopscience.iop.org/article/10.3847/2041-8213/836/1/L3

 

*insert Pacman dying sound effect*