Two Earth-mass planets in the Habitable Zone of Teegarden’s Star

[ProtoJeb21]

Ever since the seven Earth to sub-Earth sized planets of TRAPPIST-1 were announced all the way back in 2017, I was wondering if this system was unique, or if other tiny red dwarfs could host multiple small rock-dominated planets in temperate orbits. A new study of the M7 ultracool dwarf known as Teegarden’s Star using the CARMENES radial velocity instrument has revealed TRAPPIST-1 probably isn’t a fluke. Two planets, similar in mass to the largest TRAPPIST planets, have been found orbiting in the inner and outer boundaries of the system’s habitable zone, and the lead authors believe there might be more. 

https://relay.nationalgeographic.com/proxy/distribution/public/amp/science/2019/06/two-potentially-life-friendly-planets-found-12-light-years-away-teegardens-star

Teegarden b and c look very promising for both life and follow-up observations, but there are a couple of catches. The biggest: it doesn’t seem like either of these worlds transit. Even if they did, Teegarden’s Star is in the zodiac constellation Aries, and was not observed by NASA’s TESS mission. This will make accurate radius and composition measurements of the planets all but impossible, unless they do beat the odds and actually do transit, and a telescope like SPECULOOS or Spitzer is able to detect them. 

The other major catch is regarding where the planets are located in the habitable zone. Teegarden b, which is only 5% more massive than Earth, has an orbit of 4.9 days that gives it an insolation 1.14x Earth. This is well within the synchronous rotator inner limit of ~1.45 flux, which is caused by cloud cover forming on the day side of tidally locked exoplanets and helping them withstand higher insolations without going through a runaway greenhouse effect. However, the planet is rotating/orbiting so fast that dayside cloud cover won’t be able to form thanks to the Coriolis Effect. Teegarden b, therefore, finds itself in a similar predicament as TRAPPIST-1d, which can only be potentially habitable if its albedo is at least 0.3 (roughly the same as Earth, so it’s probably quite achievable due to 1d’s high water content). I assume this will be the same for Teegarden b. 

Teegarden c finds itself in the opposite  situation: it’s near the outer edge of the habitable zone. In fact, it’s almost an exact twin of TRAPPIST-1f in terms of insolation (37% that of Earth), mass (1.11x Earth), and orbital period (11.4 days). It is well within conservative outer limits for the HZ and outside the 10-day inner limit where the Coriolis Effect starts to destroy dayside cloud cover. The one problem Teegarden c has is how low its insolation is. Combined with the likely cloud cover on the star-facing side, it’s a concerning possibility that the planet has ended up too cold to be Earth-like. This doesn’t exclude a Europa-like scenario, but it makes the planet somewhat less exciting. 

However, not all hope is lost. Teegarden c still has a lot going for it, and there is still a chance for Teegarden b to be conductive for life; it also has the highest ESI of any confirmed exoplanet at an impressive 0.95. Also, as I mentioned before, some of the authors believe there might be additional planets hiding around Teegarden’s Star, and it’s possible at least one of them is an even better potentially habitable planet than the ones we already know about. I think exoplanets similar in mass to TRAPPIST-1d or h could’ve been too small for CARMENES to detect and could be waiting to be found. 

[KSK]

Cool! Thanks for the informative and interesting post.

I thought I’d better open with a serious note of thanks before registering a fond hope that Teegardens b and c will be named Coffee and Cocoa.

Or failing that, Lapsang and Souchong.

Edited June 19, 2019 by KSK

[Scotius]

I drew one conclusion: We need more planet-finders in space How many TESS-es we would need to cover 100% of the sky?

[ProtoJeb21]

4 hours ago, Scotius said:

I drew one conclusion: We need more planet-finders in space How many TESS-es we would need to cover 100% of the sky?

TESS is specifically avoiding the zodiac for its primary mission; however, maybe it could cover that area in its next mission extension. 

Also, here’s a new study about the potential habitability of the Teegarden planets: https://arxiv.org/abs/1906.07704

For Earth-like atmospheric properties, Teegarden b and c would have a wide but differing range of habitable locations. Teegarden b could have a mostly or entirely inhospitable day side with maximum temperatures reaching 550 K. However, the entire night side could be warm enough for liquid water, leaving any life without access to photosynthesis unless there are small lakes or rivers in the terminator boundary. Teegarden c could resemble a more typical Eyeball Planet, with only the immediate substellar point being too hot (400 K at the max) for liquid water. Between 30 and 75 degrees from the substellar point, temperatures are conducive for life, but afterwards it drops below 270 K and could result in a night side ice cap. 

[caballerodiez]

Astronomers have discovered a potentially habitable exoplanet around Teegarden's Star.

Teegarden is an old red dwarf star 12 light-years away in the Aries constellation.

The exoplanet found, called Teegarden b, has a minimum mass almost identical to Earth.

It orbits within the star's habitable zone. And it has a 60% chance of having a temperate surface environment.

Surface temperature should be closer to 28°C assuming a similar terrestrial atmosphere.

Teegarden b is the exoplanet with the highest Earth Similarity Index discovered so far: 95%.

This means that it has the closest mass and insolation to terrestrial values.

Source: https://www.youtube.com/watch?v=eNGXerXGnjo

[Gargamel]

Moved to S&S, and merged with a similar thread.

[cubinator]

This is very exciting! They are so close to home! Soon enough we will be able to explore these worlds...

[ILoveStars]

On 6/18/2019 at 11:11 PM, ProtoJeb21 said:

Ever since the seven Earth to sub-Earth sized planets of TRAPPIST-1 were announced all the way back in 2017, I was wondering if this system was unique, or if other tiny red dwarfs could host multiple small rock-dominated planets in temperate orbits. A new study of the M7 ultracool dwarf known as Teegarden’s Star using the CARMENES radial velocity instrument has revealed TRAPPIST-1 probably isn’t a fluke. Two planets, similar in mass to the largest TRAPPIST planets, have been found orbiting in the inner and outer boundaries of the system’s habitable zone, and the lead authors believe there might be more. 

https://relay.nationalgeographic.com/proxy/distribution/public/amp/science/2019/06/two-potentially-life-friendly-planets-found-12-light-years-away-teegardens-star

Teegarden b and c look very promising for both life and follow-up observations, but there are a couple of catches. The biggest: it doesn’t seem like either of these worlds transit. Even if they did, Teegarden’s Star is in the zodiac constellation Aries, and was not observed by NASA’s TESS mission. This will make accurate radius and composition measurements of the planets all but impossible, unless they do beat the odds and actually do transit, and a telescope like SPECULOOS or Spitzer is able to detect them. 

The other major catch is regarding where the planets are located in the habitable zone. Teegarden b, which is only 5% more massive than Earth, has an orbit of 4.9 days that gives it an insolation 1.14x Earth. This is well within the synchronous rotator inner limit of ~1.45 flux, which is caused by cloud cover forming on the day side of tidally locked exoplanets and helping them withstand higher insolations without going through a runaway greenhouse effect. However, the planet is rotating/orbiting so fast that dayside cloud cover won’t be able to form thanks to the Coriolis Effect. Teegarden b, therefore, finds itself in a similar predicament as TRAPPIST-1d, which can only be potentially habitable if its albedo is at least 0.3 (roughly the same as Earth, so it’s probably quite achievable due to 1d’s high water content). I assume this will be the same for Teegarden b. 

Teegarden c finds itself in the opposite  situation: it’s near the outer edge of the habitable zone. In fact, it’s almost an exact twin of TRAPPIST-1f in terms of insolation (37% that of Earth), mass (1.11x Earth), and orbital period (11.4 days). It is well within conservative outer limits for the HZ and outside the 10-day inner limit where the Coriolis Effect starts to destroy dayside cloud cover. The one problem Teegarden c has is how low its insolation is. Combined with the likely cloud cover on the star-facing side, it’s a concerning possibility that the planet has ended up too cold to be Earth-like. This doesn’t exclude a Europa-like scenario, but it makes the planet somewhat less exciting. 

However, not all hope is lost. Teegarden c still has a lot going for it, and there is still a chance for Teegarden b to be conductive for life; it also has the highest ESI of any confirmed exoplanet at an impressive 0.95. Also, as I mentioned before, some of the authors believe there might be additional planets hiding around Teegarden’s Star, and it’s possible at least one of them is an even better potentially habitable planet than the ones we already know about. I think exoplanets similar in mass to TRAPPIST-1d or h could’ve been too small for CARMENES to detect and could be waiting to be found. 

OH HELL YES!

[Mitchz95]

As cool as this is, I'm almost more intrigued by the fact that the star itself wasn't discovered until 2003 despite being twelve light-years away. Could that mean there may be other dwarf stars lurking in the vicinity, maybe even closer than Alpha Centauri, that we've overlooked?

[Hypercosmic]

Interesting find...

On 6/20/2019 at 11:09 PM, Mitchz95 said:

As cool as this is, I'm almost more intrigued by the fact that the star itself wasn't discovered until 2003 despite being twelve light-years away. Could that mean there may be other dwarf stars lurking in the vicinity, maybe even closer than Alpha Centauri, that we've overlooked?

If there is one, newer generation IR telescopes like WISE should've already detected it by now.

[StarStreak2109]

On 6/19/2019 at 7:26 PM, cubinator said:

This is very exciting! They are so close to home! Soon enough we will be able to explore these worlds...

I guess not in our lifetime though!

There isn't enough political will to explore the Moon or Mars, I guess the "jump" to another star system will meet even larger hurdles. I mean besides those small technical hurdles anyway...

[cubinator]

18 minutes ago, StarStreak2109 said:

I guess not in our lifetime though!

There isn't enough political will to explore the Moon or Mars, I guess the "jump" to another star system will meet even larger hurdles. I mean besides those small technical hurdles anyway...

Cosmologically very soon. And tiny laser-propelled robots seem promising.

[Mitchz95]

23 hours ago, Hypercosmic said:

If there is one, newer generation IR telescopes like WISE should've already detected it by now.

Darn. What about brown dwarves? Or even rogue planets?

Edited June 23, 2019 by Mitchz95

[UmbralRaptor]

On 6/23/2019 at 10:46 AM, Mitchz95 said:

Darn. What about brown dwarves? Or even rogue planets?

Closer than Proxima Centauri (1.3 pc)? Very unlikely for a brown dwarf and questionable for a jupiter, though there remains the possibility of medium or small planets in the oort cloud. That said, we still have some gaps in what's slightly farther out..