My Exoplanet Discoveries [Formerly "KIC 7848638 - My First Solar System"]

[ProtoJeb21]

14 hours ago, The Minmus Derp said:

ERMAGERD!!!! It’s because of you, @ProtoJeb21, that i will start on Plernert Hernters.

(misspell for the LOLz)

I actually recommend against Planet Hunters (unless your posting other results on the chat page). The reason why is because it’s very hard to find any new Kepler planets with just the eye alone. You can see the problems it’s caused in the past with systems like KIC 7848638, where I mistook stellar and data noise for planets when there actually were none. Exoplanet Explorers has already processed data to look at, so it will be far easier to find a candidate that’s likely a real object. 

[The Minmus Derp]

13 minutes ago, ProtoJeb21 said:

I actually recommend against Planet Hunters (unless your posting other results on the chat page). The reason why is because it’s very hard to find any new Kepler planets with just the eye alone. You can see the problems it’s caused in the past with systems like KIC 7848638, where I mistook stellar and data noise for planets when there actually were none. Exoplanet Explorers has already processed data to look at, so it will be far easier to find a candidate that’s likely a real object. 

Oh. I see.

[Wjolcz]

I kinda wish there was an app for searching exoplanets and exomoons like the thing that's in Eve Online.

[ProtoJeb21]

First off, I’m not dead. I’ve been finding planets but haven’t been posting them here. 

Secondly, this weekend I’m starting a more in-depth re-analysis of the K2-149 (EPIC 220522664) system. In case you don’t remember, this is a high end red dwarf with one confirmed planet and five other candidates found by me, Vidar87, and shutcheon on Exoplanet Explorers last October (wow, it’s been a full year already).  The exact physical parameters of the five other candidates have been dubious for a while, but I plan to refine them to the best of my ability. I will incorporate better light curve processing and transit folding techniques to remove as much data noise and glitches as possible, leaving the six cleaned-up signals behind to further analyze. Because of a VEX robotics competition and preparation yesterday into today, I only have access to mobile, meaning I haven’t been able to start my analysis. However, during my free time, I’ve been re-calculating the equilibrium temperatures and insolation of the planets, and found that my original estimates from January were completely messed up. The new results turned out to be more promising. 

- K2-149b: 402 K (264*F), 6.229 flux. 

- K2-149c: 356 K (181*F), 3.815 flux. 

- K2-149d: 326 K (127*F), 2.676 flux. 

- K2-149e: 300 K (80*F), 1.912 flux. 

- K2-149f: 278 K (41*F), 1.422 flux. 

- K2-149g: 230 K (-46*F), 0.669 flux. 

Refining my method of calculation revealed that all the planets are significantly cooler and less irradiated than my initial results showed. K2-149b, c, and d aren’t really worth talking about at the moment, but the final three are now looking very intriguing. K2-149e, as it turns out, has the exact same equilibrium temperature and stellar flux/insolation as Venus (also 300 K and 1.91 flux). This makes it likely to be a super Venus analogue, something that isn’t too common of a find. I don’t know of any other Super-Earth with the same temperature and insolation as Venus, which will make this planet one of a kind and worthy of further study. The other two, K2-149f and g, are looking more promising than before. K2-149f is still in the optimistic habitable zone, but at 1.42 flux, it is less likely to suffer a runaway greenhouse effect. It could easily resist such a scenario because of its high mass (probably 4-5 Earth masses) “holding down” all its water, and the fact that it’s likely to be tidally locked. Simulations have shown that synchronous rotating planets would develop star-facing storms, blocking out some incoming sunlight and allowing the planet to resist a runaway greenhouse at higher insolations of 1.3 to 1.5 flux, depending on the star. 

K2-149g is even more promising. Getting 66% as much sunlight as Earth, it is smack in the conservative habitable zone and very unlikely to have undergone a runaway greenhouse effect. Like K2-149f, it is expected to be an ocean planet (10-50% water by mass) due to its large radius. My upcoming radius re-analysis should determine its actual size and give an idea into its composition and water/volatile content. One thing that I immediately noticed with these two planets is how they’re almost identical to Kepler-296 Ae and Kepler-296 Af. Not only are the stars similar in size, but K2-149f and g’s orbital periods of 34.3125 and 60.3850 days are very close to the 34.1421 and 63.3363 days for the outermost Kepler-296 A planets. In addition, they’re stellar insolations are just about the same — 1.42 and 1.41 flux for K2-149d and Kepler-296 Ae; and 0.67 and 0.62 flux for K2-149g and Kepler-296 Af. Whether or not their sizes are also similar has yet to be seen, but the similarities so far are almost uncanny. 

I should have my analysis results posted either tomorrow or Monday. Stay tuned! Also, I’ll probably do a post on my Campaign 15 and 16 finds so far in the next couple of days. 

Edited November 10, 2018 by ProtoJeb21

[ProtoJeb21]

I’ve completed my re-analysis of K2-149, and the results are not what I expected. 

First I tried using the SFF data for the star, which isn’t as well-processed as the EVEREST data but does show multi-planet systems better. I deleted all the original signals and used the Box-Least Squared (BLS) algorithm to find better orbital periods for the planets after de-trending the light curve. Unfortunately, while K2-149b and K2-149c came out fine, the other four had problems. K2-149d and e turned out significantly larger than expected due to stellar noise messing up their transits. Meanwhile, I couldn’t find the signals for K2-149f and g at all. The closest I could get was a 47-day signal, which later turned out to be a false positive. Today I decided to take the signals from the SFF light curve and analyze them in the EVEREST light curve, which has significantly less stellar noise than the former. Not only were the parameters for K2-149d and e more believable, but I was able able to find slightly different orbital periods for K2-149f and g. 

- K2-149b: 1.69 Re, 746.8 ppm 11.336890 days, 0.08311 AU, 402 K, 6.225 flux.

- K2-149c: 1.68 Re, 734.75 ppm, 16.367583 days, 0.10616 AU, 356 K, 3.815 flux.

- K2-149d: 1.99 Re, 1029.1 ppm, 21.393409 days, 0.12691 AU, 326 K, 2.670 flux.

- K2-149e: 1.70 Re, 750.75 ppm, 28.750066 days, 0.15455 AU, 295 K, 1.800 flux.

- K2-149f: 1.62 Re, 685.6 ppm, 37.226523 days, 0.18360 AU, 271 K, 1.276 flux. 

- K2-149g: 1.55 Re, 626.4 ppm, 69.743461 days. 0.27903 AU, 220 K, 0.552 flux. 

With the exception of K2-149c, all of the planets have different orbital periods than initially calculated, either by a few minutes for the inner ones or by a few days for the outer ones. K2-149b and c are practically identical in terms of radius, temperature, and — presumably — composition. I expect both of them to be mainly rocky with a significant steam envelope, like larger versions of TRAPPIST-1b or LHS 1140c. K2-149d is the largest at almost twice the size of Earth and is probably a Mini-Neptune with a significant volatile (water, methane, hydrogen) envelope over a rocky center. Due to its temperature, much of its clouds are likely made of water vapor, with a haze of methane like Uranus and Neptune. 

K2-149e is where things get more interesting. At 1.7 Earth radii, it likely has a very similar composition to K2-149b and c. However, it’s signficantly cooler, getting just 80% more sunlight than Earth. This puts it outside most definitions of the habitable zone, but it could be just cool enough to not get too hot and have a liquid ocean underneath a steamy, sauna-like atmosphere. K2-149f is even cooler than calculated yesterday, due to its orbital period being about three days longer than my January analysis determined. At 1.62 Earth radii with an insoation about a quarter more than Earth’s, it is likely able to resist a runaway greenhouse effect and is a great candidate for a potentially habitable ocean planet. The dayside storm cooling method I mentioned yesterday will be quite effective here, helping to keep the planet’s climate temperate and stable even though it’s likely tidally locked. 

Finally, there’s the new K2-149g. More analysis needs to be done to make sure this actually is a planet. It only has two transit events, the final one of which is close to the last observed transit of K2-149b. So far it seems like a good candidate, enough to gain the designation K2-149g (unless it gets disproven). It is also by far the most promising of the entire system. It’s both the smallest and coolest planet of K2-149, at 55% larger than Earth while receiving 55% as much sunlight. This places it well within the conservative habitable zone by all definitions, and its small size means it is either entire rocky or has a very small layer of water, no more than 1-2% of its entire mass. An Earth-like Carbon-silicate cycle may be able to take place here, and volcanoes could create islands poking out of the watery surface — both of which would give K2-149g a significant edge over K2-149f in terms of potential habitability. Its low insolation also means a runaway greenhouse effect is nearly impossible; there isn’t enough radiation to evaporate enough water for this process to take place. Another potential advantage is how it may not be tidally locked. Its 69-day orbital period may place K2-149g far enough from its host to not become a synchronous rotator, and instad have a rotation period of several days to a few weeks. This could allow for a better distribution of heat across the entire surface, allowing more areas to support liquid water. 

More work needs to be done with K2-149. I would like to get an expert’s opinion on my results to see how well they hold up, so I may E-Mail one of the scientists I’ve been in contact with about this. If my results do hold up, it would make K2-149 a very rare and very promising system, and the first since Kepler-62 with two potentially habitable planets. 

[ProtoJeb21]

It turns out I messed up my calculations for the equilibrium temperatures and insolation of the K2-149 planets. I mistakenly used 0.043 L for the luminosity of the star, instead of the actual 0.049 L provided by Hirano et al 2018. My new results are below. 

- K2-149b: 416 K, 7.093 flux. 

- K2-149c: 368 K, 4.348 flux. 

- K2-149d: 336 K, 3.042 flux. 

- K2-149e: 305 K, 2.051 flux. 

- K2-149f: 280 K, 1.454 flux. 

- K2-149g: 227 K, 0.629 flux. 

Overall, there aren’t any huge changes to the planets. K2-149b, c, and d are just about the same as my initial calculations showed, and K2-149g still resides well within the conservative habitable zone. The fact that it’s slightly warmer actually improves its potential habitability. The two biggest changes are for K2-149e and f. The former is now slightly more irradiated than Venus, but because of its large mass and huge amounts of water, I’m still not too sure whether or not it has become a Super-Venus. K2-149f is also warmer and no longer near the inner edge of the conservative habitable zone. However, it still remains a pretty good potentially habitable ocean world candidate. 

[ProtoJeb21]

I spent several hours today updating the OP with multiple systems found by me, Vidar87, and shutcheon from Exoplanet Explorers, including K2-183, K2-155, and K2-229. The Planet Candidates section presents what we currently know about these worlds in an easy-to-read fashion that is far easier to understand than going back through all the posts in this thread and reading about the ones pertaining to a specific system. Seriously, don’t do that; some of the systems in the Planet Candidates section in the OP have barely been mentioned in the rest of the thread. 

[ProtoJeb21]

I will be updating the EPIC 220221272 with larger parameters calculated by fellow citizen scientist Mark Omohundro. While EPIC 220221272 f is no longer potentially habitable (although it could still be some weird steamy ocean planet), all the planets are significantly larger and now more dynamic and interesting. EPIC 220221272 b likely has retained an atmosphere, while EPIC 220221272 c, d, and e all likely have significant geological activity and thick terrestrial atmospheres. All the planets likely migrated inwards from near the Frost Line, so they all would’ve formed with about 5-20% water by mass. Depending on their size and final orbits, some would’ve lost this water, while for other planets it would’ve turned into a thick atmosphere. EPIC 220221272 b and c are probably too irradiated by stellar flares and too small to have retained their initial water layers, which would’ve made them 5-10% more massive than we see them today. EPIC 220221272 d and e may have formed with about 15% water by mass, but due to their low masses (around 2-4 Me) and exposure to stellar flares, most of this would’ve been lost as well. But keep in mind, I said most. EPIC 220221272 d is probably large enough to have held onto a thick water vapor atmosphere, and EPIC 220221272 e is far enough away to be the same. The latter probably formed with more water due to being further out in the system, and as a result its steam layer would be much larger and more Venus-like than EPIC 220221272 d. Finally, EPIC 220221272 f is now technically a Mini-Neptune, but could have a water fraction of 20-75%, depending on its exact size, with little to no hydrogen at all. 

Also, I’ll be adding the possible candidate EPIC 220221272 g as well, although it’s been a big maybe for over a year now. If it does exist, it’s a little smaller than Earth and gets about 38% more sunlight, making it like a smaller version of Ross 128 b. It also probably would’ve formed out near the Frost Line with more water, but due to its small size and mass, most of it would’ve been lost. A rather thin global ocean probably remains. But EPIC 220221272 g may not be a real planet, so don’t get too excited about it being potentially habitable just yet. 

[Adstri]

Really nice 

[ProtoJeb21]

I’ve been pretty inactive on the forums lately because TESS Sectors 1 and 2 data was released on Friday, and Planet Hunters was revived as well. Over the last week I’ve been searching for new planets, and me and a few other citizen scientists have found some pretty significant and bizarre finds. I’ll make a post on these planets this weekend. 

[ProtoJeb21]

For once, I'm doing a post here on schedule! I promised I would write about my TESS candidates this weekend, and here they are. For this post I'm only writing about the ones I am by far the most confident about and are unlikely to be eclipsing binaries. Believe it or not, EBs have been even more of an issue than before with the K2 mission, likely because TESS is looking at a greater amount of brighter and larger stars than Kepler was. That doesn't mean I don't have any cool red dwarf candidates, and the increased difficulty doesn't mean I don't have interesting finds to share.

 

TIC 30312676 b

• Radius: 11.11 R_⊕
• Orbital Period: 2.201266 days
• Semi-major Axis: 0.04306 AU
• Equilibrium Temperature: 2,783 K (4,550^oF)
• Insolation: 14,244.07x Earth
• Type: Ultra-Hot Jupiter

The first likely planet I found with TESS data is also one of the hottest and weirdest I've ever found. If that isn't a strong enough sign that I'm in for some bizarre planets with this mission, than I don't know what is. TIC 30312676 b is roughly the size of Jupiter and orbits every 2.2 days. At first glance, that doesn't seem very odd -- there are a few other Hot Jupiters with similar sizes and orbital periods -- but everything becomes horrifying once you realize that the host star is huge. At 2.24 solar radii with a temperature of 8,747 K and over 26 times the luminosity of the Sun, it is the largest and hottest star I've found to host a planet. This results in TIC 30312676 b to have an equilibrium temperature of nearly 2,800 K; for comparison, the star TRAPPIST-1 is about 2500 K. At these temperatures, the planet is probably extremely inflated and losing its gaseous envelope, with a day side of at least 3,100 K. But it may be worse. A different analysis on the same planet by an automated program designed by the TESS team found that this planet could have an orbital period of 1.1 days instead, which would give it an equilibrium temperature of 3,504 K (5,848^oF). If this is true, it would make TIC 30312676 b the second hottest gas giant planet known, just behind Kelt-9b.

 

TIC 388348917 b

• Radius: 1.73 R_⊕
• Orbital Period: 1.092019 days
• Semi-major Axis: 0.023268 AU
• Equilibrium Temperature: 2,408 K (3,875^oF)
• Insolation: 7,977.55x Earth
• Type: COSSN (Closely Orbiting Scorched Sub Neptune)

It's almost ridiculous that my FIRST TWO planets found with TESS are some of the hottest I've ever found. While not as horrific as the previous planet, TIC 388348917 b is still easily among my top 10 most hellish worlds, with an equilibrium temperature of around 2,400 K. For comparison, that's even hotter than the day side of K2-229b. It is my first COSSN candidate of the TESS mission, but not the first overall; the TESS team managed to find a ~2 R_⊕ around HD 213885 with an equilibrium temperature of almost 1,900 K. But back onto TIC 388348917 b, as amazing as it is, it's currently the least likely planet in this post to exist, as its transit depth is very small (~100 parts per million) and could be stellar noise. Thankfully, the host star is very bright (visual magnitude of 9.1), so if it does exist, radial velocity measurements should easily be able to detect it.

 

TIC 62762339 b

• Radius: 2.41 R_⊕
• Orbital Period: 4.805032 days
• Semi-major Axis: 0.04224 AU
• Equilibrium Temperature: 491 K (424^oF)
• Insolation: 13.844x Earth
• Type: Warm Mini-Neptune

TIC 62762339 b is my first TESS planet around a red dwarf, and is also one of the largest I've ever found around such a small star. At 2.4 times the size of Earth, it is a Mini-Neptune and likely has a thick layer of volatiles like hydrogen, helium, water, and/or methane. However, unlike most TESS targets, the host star is too dim for radial velocity studies with current equipment, so we'll have no idea what it's actual mass and composition is. Since there are no other planets in the system, TIC 62762339 b is probably rather massive, as it would've needed to accumulate nearly all the inner system's planet-forming material for no companions to exist, or be massive enough to toss any planetary siblings out of the way. It could be as massive at 12 M_⊕ with a 50-70% silicate and 30-50% water/methane composition.

 

TIC 141708335 b

• Radius: 1.95 R_⊕
• Orbital Period: 4.759894 days
• Semi-major Axis: 0.03817 AU
• Equilibrium Temperature: 438 K (329^oF)
• Insolation: 8.724x Earth
• Type: Warm Super-Earth

Yet another red dwarf planet candidate, TIC 141708335 b is currently my coolest TESS find, with a temperature around 440 K. While hot by human standards, it is also one of the coolest TESS candidates overall, and cool enough for it to retain a decent volatile envelope. This is reflected by its radius, just under twice that of Earth and above the 1.6-1.8 R_⊕ radius gap where rocky Super-Earths start to accumulate large water layers or hydrogen atmospheres. Thankfully, unlike the previous planet, TIC 141708335 b orbits a host star just bright enough in the J-magnitude to be targeted by the CARMENES spectrograph for radial velocity studies. For a water layer comprising about 20% of its total mass, TIC 141708335 b would be about 7 M_⊕ and have a RV semi-amplitude of about 5.6 m/s, which would be very easy to detect with CARMENES.

 

TIC 381855507 b

• Radius: 5.16 R_⊕
• Orbital Period: 0.808939 days (19.414 hours)
• Semi-major Axis: 0.01826 AU
• Inclination: 59.68^o
• Equilibrium Temperature: 2,954 K (4,856^oF)
• Insolation: 18,063x Earth
• Type: Neptune From Hell, COSSN

How many more of these ultra-hot gas planets are there?

TIC 381855507 b really tests the limits of what we know about planets and planetary formation. With a radius more than five times greater than Earth, it is the largest planet in the "Hot Neptune Desert", a range of planetary radii (2-6 R_⊕) and orbits (<0.1 AU) where there are very few known exoplanets. It is believed that most Hot Neptunes are unable to survive and have their hydrogen envelopes blown off, leaving behind Mini-Neptunes and Super-Earths. This makes it quite hard to believe that a Hot Neptune is somehow still alive with a temperature of nearly 3,000 K. In addition, the F-class host star is extremely metal-poor, and is possibly the most metal-poor exoplanet host star known, which makes it even more unlikely for TIC 381855507 b to even exist. It doesn't help that it would probably have to be around 80 M_⊕ with a huge core to not be destroyed in astronomically quick timescales, which may not be possible given the host's low metallicity. Thankfully, since the star is extremely bright with a visual magnitude of 8.81, it should be quite easy to learn more about this system and get a better understanding of why and how it exists.

 

HD 48611 b

• Radius: 1.78 R_⊕
• Mass: 6.70 M_⊕
• Density: 6.55 g/cm³
• Gravity: 2.114g
• Composition: >95% MgSiO2/Fe, <5% H2O
• Orbital Period: 18.552713 days
• Semi-major Axis: 0.1308 AU
• Eccentricity: 0.3
• Periapsis: 0.09156 AU
• Apoapsis: 0.17004 AU
• Equilibrium Temperature: 593 K (608^oF)
• Summer Temperature: 709 K (817^oF)
• Winter Temperature: 520 K (476^oF)
• Insolation: 29.33x Earth (average), 59.86 (max), 17.36 (min)
• Type: Hot Rocky Super-Earth

I saved the best for last. While not a find of my own, HD 48611 b -- formerly known as TOI-214.01 -- is now TESS's first rocky or mainly rocky Super-Earth, thanks to the efforts of citizen scientist EEfinder. He managed to uncover archived HARPS data of the host star gathered back from 2003 to 2006, but for some reason had never seen the light of day until now. The HARPS data, despite being limited in quantity (only about a dozen measurements), was enough to tease out the 1.8 m/s signal of this planet. That semi-amplitude corresponds to a planetary mass of 6.7 times that of Earth, which when combined with my radius estimate of 1.78 Earth radii, gives HD 48611 b a density of 6.55 g/cm³. When plotted on the exoplanet mass-radius diagram, HD 48611 b is right on the 100% MgSiO2 line. However, this doesn't mean it's purely rocky. It is probably almost entirely made of rock and iron with a thin volatile envelope or thick atmosphere that makes it seem less dense. Not only is the planet notable for having a nearly terrestrial composition, but it also has a rather eccentric orbit, swinging from 0.092 AU to 0.170 AU. This causes the planet to nearly double its temperature between winter and summer. However, such orbit swings likely impart significant tidal forces into HD 48611 b, which would lead to increased volcanic activity and a massive release of greenhouse gases like carbon dioxide, methane, and other kinds of volcanic material. Not only would a volcanic atmosphere caused by tidal heating create a Venus-like greenhouse effect, but it may also be the explanation behind the planet's thin volatile layer. The Super-Earth 55 Cancri e has shown us that atmospheres of heavy gases can make planets appear less dense, meaning that many worlds straddling the 100% MgSiO2 line don't need water envelopes to explain their densities. HD 48611 b could be one of them, and since its host star is bright, its own atmosphere may be able to be analyzed by either Hubble or the James Webb Space Telescope.

 

Those are all of my significant finds as of now. I do have a few more likely planet candidates, but they're all hot Neptunes and Mini-Neptunes that aren't very interesting or worth talking about. I hope to have some more cool finds for the end of the year, where I'll do a look back on my progress in 2018 and reflect on the year as a whole.

[4472TJ]

Amazing work, do tell me, is this Witch craft?

[ProtoJeb21]

Since the winter solstice has just arrived the other day, it's only fitting that I talk about some of the chillest planet candidates I've found. Over the next few posts, I will go over the results of my recent re-analyses on three potentially habitable red dwarf systems: EPIC 201663913, EPIC 201299484, and EPIC 210736056. I'll also present my findings from another re-analysis of K2-149, including a potential seventh candidate. Since there's so much to cover, I'll do EPIC 201663913 in one post, and the other three systems in a second, which should be out tomorrow. I may give K2-149 its own post if three system reports in one turns out to be too much.

EPIC 201663913

Out of the three systems of my re-analysis, EPIC 201663913 is either the most promising or the most disappointing. Each of the three candidates has the potential to host liquid water, but each have their own set of problems and uncertainties that could make them uninhabitable. Let's begin with the star itself. On ExoFOP-K2, EPIC 201663913 is given a radius of 0.403 solar radii, a mass of 0.461 solar masses, and a temperature of 3939 K. Originally, I calculated that the luminosity of the star would render the second planet an uninhabitable, Venus-like hell. It gets even worse when you take into account that ExoFOP-K2 parameters, especially for red dwarfs, aren't the most accurate. Many stars reported as small red dwarfs on ExoFOP-K2 by Huber et al turn out to be either larger red dwarfs or small orange dwarfs, and a few like EPIC 212525618 end up actually being yellow dwarfs! Thankfully, the newly launched ExoFOP-TESS contains much better estimates for the sizes and temperatures of the stars the telescope will observe, including nearly all stars in the Ecliptic Plane Input Catalog (EPIC). Unfortunately, no radius and mass estimates are given for this star, but a temperature estimate is: 3510 K. This is surprisingly compatible with Huber's estimates, so for this analysis I'm going to use a combination of K2 and TESS estimates.

The first candidate, EPIC 201663913 b, is by far the smallest, at just 0.65 R_⊕. Its orbital period of 17.648 days places it within the system's Venus Zone, with 2.1 times the stellar flux of Earth. However, this doesn't mean the planet is a Venus-like hell. Remember, it's just 65% the size of Earth, which may make it too small to even hold onto an enormous, crushing atmosphere, especially since the star appears to be moderately active. This stellar activity may also kill the possibility that this planet even exists. Its signal is not particularly strong and may end up just being a product of the star's typical variability. Until a more sophisticated analysis can be done, EPIC 201663913 b will hold onto its status as a planet candidate.

Next up is the Super-Earth EPIC 201663913 c, at 1.30 R_⊕ with a newly calculated stellar flux 1.21 times that of Earth. While outside typical definitions of the conservative habitable zone, it will be within the conservative habitable zone for synchronous rotators. I've mentioned this before, but extensive climate modelling has shown that tidally locked, temperate planets would probably develop day side cloud cover that would extend the inner limit of the HZ. With an orbital period of 26.707 days, EPIC 201663913 c is likely a synchronous rotator, which would prevent it from suffering a runaway greenhouse effect. Its signal is also much more prominent than that of its Mars-sized little sibling and extremely likely to exist. However, now that the promising aspects are out of the way, it's time for the problems. These have nothing to do with the planet itself; rather, they have to do with the host star. Even though the temperature from ExoFOP-TESS supports Huber's estimates, that does NOT mean EPIC 201663913 isn't larger than expected, possibly closer to half the radius and mass of the Sun. This could make 201663913 c both too irradiated and too large to prevent itself from experiencing a runaway greenhouse effect. In addition, EPIC 201663913 may have a nearby binary companion, which would make all three planets even larger if the companion and the host are being observed together. That might also kill the potential habitability of EPIC 201663913 c. So, while it seems quite promising as of now, don't be surprised if it turns out to not be so in the future.

Finally, there's the temperate Earth-sized candidate EPIC 201663913 d. If you recall from back in April, I found a circumbinary "Super-Pluto" orbiting around two dim red dwarfs that I nicknamed after the Star Wars Rebels ice planet Krownest. It now seems like EPIC 201663913 d would be a much better real-world analogue...maybe even an exact analogue. It's just a tad smaller than Earth at about 0.99 R_⊕ and orbits in the outer reaches of the habitable zone every 71.22 days while getting just a third of the starlight Earth receives from the Sun. Because this distance, the planet has one of the lowest equilibrium temperatures of any planet candidate I've found: just 193 Kelvin, or -112 degrees Fahrenheit. An Earth-like greenhouse effect could warm the planet to an average of around 220 K (-64 F) and warm some areas, especially around the equator, to temperatures suitable for liquid water. However, that's just assuming it even has an Earth-like atmosphere, and that it even exists. It's starting to look more likely that, instead of a ~71 day orbit, the third planet of EPIC 201663913 has an orbital period of around 48.13 days. If this is the case, it would be about the same size as before (0.96 R_⊕), but be rather warmer, with an insolation 55% that of Earth and an equilibrium temperature around 220 K. Unlike the possible changes to planets b and c, this would make EPIC 201663913 d both a better potentially habitable candidate and a better Krownest analogue. It's also quite likely to exist, with a clearer signal despite a longer orbital period. If there's any planet candidate around EPIC 201663913 to put your bet on for potentially being able to support life, I would definitely recommend planet d.

[ProtoJeb21]

EPIC 201299484

EPIC 201299484 and EPIC 210736056 are two very similar systems found by Vidar87 last year, with a Venus-like planet and a temperate ocean world orbiting a small (<0.3 Rs) red dwarf. However, with better TESS parameters, the two systems aren't as twin-like as they were before. EPIC 201299484 was found to be significantly larger and hotter, at 44.1% the radius and 46.6% the mass of the Sun with a temperature of 3601 K, giving it just under 3% the Sun's luminosity. This has resulted in the two planets to be larger and hotter as well, but that doesn't seem to be too much of a negative as one may expect.

EPIC 201299484 b is a large Super-Earth of 1.54 R_⊕, which would make it over four times more massive than Earth if rocky. It has a rather close orbit lasting 11.307 days and is certainly tidally locked. Because of the increase to its star's parameters, its stellar flux is now significantly higher than Venus's, at about 5 times greater than Earth's insolation, with an equilibrium temperature of 382 K (228 F). However, EPIC 201299484 b appears to be quite a massive rocky planet, which could help it retain a thick atmosphere and give it a Venus-like or greater greenhouse effect. Its sister planet, EPIC 201299484 c, is practically a polar opposite. They orbit on opposite sides of the habitable zone, and their radii are on the opposite sides of the ~1.75 R_⊕ radius gap. Despite having an equilibrium temperature of 240 K (-28 F) and 78% the insolation of Earth as a result of a 45.676-day orbit, placing it comfortably within the conservative habitable zone of its host, EPIC 201299484 c's radius of 2.03 R_⊕ makes it quite problematic. Planets of this size are poorly understood but almost always have some sort of volatile layer. This can be in the form of a thick gaseous atmosphere like the mini-Neptune GJ 9827 d, or a large water envelope like K2-229c. At this point, it is impossible to determine which scenario applies to EPIC 201299484 c, or if it defies expectations and happens to be a giant Super-Earth or Mega-Earth. To make matters worse, EPIC 201299484 is too dim for follow-up studies, so it's likely that we'll never know if its second planet can support life.

 

EPIC 210736056

The second of Vidar's twin systems, EPIC 210736056, has thankfully remained relatively unchanged with TESS data. The host star has been better measured at 0.272 solar radii and 0.257 solar masses with a temperature of 3271 K and just 0.763% the Sun's luminosity. Its two planets orbit every 9.948 and 29.0285 days in the Venus and Habitable Zones, respectively, and are likely to be tidally locked. The innermost, EPIC 210736056 b, has a radius of just 1.12 R_⊕, not much larger than our system's Venus. It also has a very similar equilibrium temperature of 314 K (106 F) and stellar flux (2.3 times Earth's). Combined with the planet's larger size than Venus and the greater amount of infrared radiation emitted by the host star, it appears to be that EPIC 210736056 b has an even worse runaway greenhouse effect, possibly raising surface temperatures to around 800 K (980 F) or more. The planet likely formed further out with a significant amount of water, as evident by its larger sibling, and had its oceans evaporate into an efficient heat-trapping steam atmosphere once it was shoved inwards.

EPIC 210736056 c, while not without its fair share of problems, is a better candidate for potential habitability than the larger EPIC 201299484 c. With a radius of 1.72 R_⊕, it is likely too large to be rocky, but probably only has a water layer comprising 5-15% of its total mass. There is a possibility that it is a gaseous mini-Neptune, but it doesn't seem as likely as with the previously mentioned planet. However, once I determined the planet's insolation, I realized something peculiar: it's the twin of LHS 1140 b. EPIC 210736056 c is not only practically identical in size to LHS 1140 b, but it also has just about the same orbital period (29.03 days vs 24.747 days) and stellar flux (0.55 vs 0.503). The similarities between the two planets are uncanny, and one may assume they also share a similar rocky composition. However, I doubt this is the case; their host stars have significantly different heavy element abundances and likely resulted in different formation processes. I think it's best to assume EPIC 210736056 c has a water envelope and isn't a huge rocky world like LHS 1140 b, but as of now it's impossible to know for certain.

 

I need to finish a few things today before I can get to the big reveal of K2-149's potential seventh planet. That post should be out either later tonight or early tomorrow.

[ProtoJeb21]

K2-149

It's time for the biggest reveal of the week, just in time for Christmas Eve: a possible seventh planet around K2-149, hereafter designated K2-149h until further notice. But before I go into this new discovery, I need to present a bit of context behind it.

Over the last three-ish weeks since TESS Sectors 1 and 2 data became public, I've developed an improved method for measuring the radius of transiting exoplanets in TESS and K2 data. First, I detrend the target light curve with LcViewer to a very specific level, where all stellar variability is no longer apparent and the data set is just about flat and punctured by transit events. However, it can't be too high to the point that it starts cropping out parts of the larger transit events. This level varies from star to star and LcViewer has detrending levels between 1 and 25, so for K2-149, I used 20 (for reference, the standard LcViewer detrending level is 16). Next, I had to change how I viewed and processed the folded transit. When LcViewer stacks all the transits of a planet into one average transit to analyze, you can change something called the Signal Region Timescale. Basically, it determines how much of the rest of the light curve will be in the same view as the folded/stacked transit. I usually change it to 5 Signal Durations (i.e., it includes a region 5 times greater that the length of the transit), but I realized that the large the SRT is, the more that noise and variability starts to impact the measurement of the folded transit. That's why for this analysis and many other recent ones, I set the SRT to be as low as possible before measuring the folded transit. 

Now that my methodology is out of the way, it's time to go into what I found. Out of the six original planets, K2-149c, e, and f remained relatively unchanged, with revised radii of 1.67 (±0.17), 1.69 (±0.17), and 1.61 (±0.15) R_⊕. The other three planets, K2-149b, d, and g, were either significantly larger or smaller than initially estimated. K2-149b is the only one with a larger radius, at 1.76 (±0.17) R_⊕, indicating a thicker volatile envelope. Stellar activity and rather high insolation, about 7 times greater than Earth's, may have prevented a stable hydrogen layer from staying around and instead leave K2-149b with a suffocating steam atmosphere, maybe turning it into another Super-Venus. Despite the size increase, K2-149b is still just smaller than K2-149d, which has been revised down to 1.81 (±0.18) R_⊕. This radius and its lower insolation still favor some amounts of hydrogen, but likely less than initially thought. A better explanation for its volatile layer is one made almost entirely out of water, with a methane-dominated atmosphere and possibly either a supercritical water ocean or a layer of crushed Ice-VII. Finally, the potentially habitable candidate K2-149g has also shrunk, with a radius now down to 1.47 (±0.15) R_⊕. This better favors a rocky, Earth-like composition of rock and iron with only small amounts of water and no significant volatile envelope, increasing its chances of being potentially habitable if it does exist. Thankfully, I'm a little more confident in its existence after this study. It's still a possibility that K2-149g is a result of data glitches and/or variability, but less so. However, it's possible all six planets here are smaller than I calculated. The 1.76 R_⊕ estimate I got for K2-149b is 7.4% higher than what Hirano et al 2017 found, which was 1.64 R_⊕. If all the other planets are this much smaller than I've calculated due to impacts from stellar noise and variability, they would be around 1.56, 1.69, 1.57, 1.50, and 1.37 R_⊕.

When finishing my analysis, I noticed something odd. The third transit of K2-149d appeared to be inside a much larger, ~6.4 hour transit-like event. I don't know how I never noticed it before, but it doesn't seem to be from a data glitch, and as far as I can tell, it's a decent new planet candidate. This K2-149h is difficult to study with just a single candidate transit transit, especially since it's being skewered by a transit of K2-149d. However, I was able to get a radius estimate of 1.73 R_⊕, which is probably slightly overestimated due to the previously mentioned K2-149d transit and impacts from stellar variability. Like the rest of the planets except K2-149g, K2-149h probably has a significant layer of water, but instead of in the form of a steam atmosphere or an ocean, it's probably entirely frozen over. The best estimate I can get for the candidate's orbital period is ~175 days, placing it well beyond the outer limit of the habitable zone and giving it an equilibrium temperature of around 167 K (-159 F). Even with an Earth-like or stronger greenhouse effect, K2-149h is too far from its dim star to have any regions warm enough for liquid water, making it one of my very few ice planet candidates. In fact, behind the circumbinary planet Krownest and a possible long-period Super-Earth from Campaign 14, K2-149h is my coldest planet candidate so far. That is, of course, if it even exists. It is easily the least likely of the K2-149 planets and still has a decent chance of being a data glitch. I haven't been able to find this transit-like event at the same time in any other Campaign 8 light curve so far, so as of now, it will be considered a potential planet. Just don't be too surprised if it turns out to be a false positive.

[Spaceception]

Looks like you expect it to be a Titan-esque world? Or think it could be? Really interesting find though!

[ProtoJeb21]

45 minutes ago, Spaceception said:

Looks like you expect it to be a Titan-esque world? Or think it could be? Really interesting find though!

K2-149h is probably too warm for liquid methane, but liquid ammonia can’t be ruled out, since it likely formed near or at its current location. The visual representation for it is actually a desert almost entirely covered in ice, which could be the case if the planet turns out to be smaller than I calculated. 

[ILoveStars]

is this all about TESS exoplanet discoveries?

[ProtoJeb21]

14 hours ago, ILoveStars said:

is this all about TESS exoplanet discoveries?

Only the TESS candidates I’ve found with LcViewer and Planet Hunters TESS. I primarily analyze K2 data, especially from the later campaigns (13, 14, 15, 16, and 18). 

[ILoveStars]

ok

 

[ProtoJeb21]

Something big is coming tomorrow...

https://aas.org/meetings/aas233/2nd-media-advisory#press_conf

[Spaceception]

Oh, that looks really cool. Does any of it potentially have anything to do with your finds, or is it mostly about the TESS finds in general in this context?

[ProtoJeb21]

10 minutes ago, Spaceception said:

Oh, that looks really cool. Does any of it potentially have anything to do with your finds, or is it mostly about the TESS finds in general in this context?

In the talk starting at 10:15 am PST, the third section will be about K2-138g. Jessie Christiansen, one of the founders of Exoplanet Explorers, mentioned over the summer that she and her team had used Spitzer to detect a third transit of that planet, and their results will be presented tomorrow. However, it’s the section after that I’m most excited about: “A Small Transiting Planet Discovered by Citizen Scientists”. Ever since Jessie said on Twitter how multiple citizen scientist exoplanet finds would be announced at AAS 233, several of us over on Planet Hunters have been hoping one of them would be EPIC 210693462 Ab/Natalie, the Super-Earth shutcheon, Vidar87, and I found in a binary red dwarf system almost two years ago. The title for this section hints that this could be the case. Not only does Natalie fit the title description, but it has also been studied so much and for so long that not announcing it tomorrow seems highly unlikely. It’s one of the most prominent EE finds, and one of the first that was targeted for follow-up observations. 

In preparation of Natalie’s possible discovery announcement, I deleted all my Imgur albums and the wiki page about the system. I don’t want the press and media to find and contact me or something over this discovery and getting into my Internet life. The last thing I need is my KSP stuff getting eaten up by content-hungry online reporters. Also, I don’t want them to find out about any other interesting but unconfirmed systems like EPIC 220221272, so I may need to delete a few other things tonight. 

Also, regarding the TESS talk, it is highly unlikely any of my very few discoveries will be mentioned, and I don’t know if it will even happen because of the whole shutdown issue. Something like 300 to 400 NASA scientists can’t go to AAS 233 because of it, and as a result multiple talks won’t have anyone to present them and will probably end up being cancelled last-minute. If the TESS talk does happen, I expect we could get some more new planets, or maybe even radial velocity measurements for the USP Super-Earth LHS 3844 b. 

[ILoveStars]

yeah. I'm looking forward to RV measurements for LHS 3844 b. I think it's around 2 to 3 earth masses.

 

 

and also, are you still working on IA-revived?

hope you are, it's a great mod.

Edited January 7, 2019 by ILoveStars

[ProtoJeb21]

3 hours ago, ILoveStars said:

yeah. I'm looking forward to RV measurements for LHS 3844 b. I think it's around 2 to 3 earth masses.

 

 

and also, are you still working on IA-revived?

hope you are, it's a great mod.

LHS 3844 b could be around the higher range of 2.5-3.5 Earth masses because of its close proximity to the host star’s Roche Limit. Similar to K2-229b, it’s probably a dense iron planet. 

Also, I am not working on IA-Revived anymore. I just haven’t been able to get back to it, and I can’t even keep up with my newest mods. 

 

I have some good news: it looks like the TESS press conference will be happening tonight! It’ll start at 7:00 pm PST (10:00 pm EST), so it will probably be a little too late for me to watch it, but I should be able to watch the K2-138g press conference. It starts in less than an hour at 10:15 am PST (1:15 pm EST), and I think you’ll be able to watch it here: 

https://aas.org/media-press/aas-press-conference-webcasts