A terrestrial, temperate planet around Proxima Centauri

[|Glitch|]

I have another question regarding the possibility that Proxima b might sustain life. What are the chances Proxima is a 1st generation star? Is so, this would mean that Proxima b would not be able to sustain life (as we know it) since it would not have any carbon.

Red dwarf stars have a very long lifetime. Many (most?) of them will be 1st generation stars, that is, stars that do not include post primordial elements, aka "metals", created by super novae. It seems very likely that Proxima was created about the same time and from the same material that Alpha Centauri and Beta Centauri were created, but is this certain?

If yes, then since there is a reasonable likelihood that Alpha Centauri is a 2nd generation star, and therefore Proxima would be about the same age. Alpha's mass, 1.1 M☉, gives it a life time (slightly less) and a possible age similar to our sun, but I have not been able to find on the Internet anything specific about whether Alpha might be a 1st generation star. Presumably someone might know from Alpha's spectrum if this is so or not.

If on the other hand, is there is a significant chance that Proxima was created as a 1st generation star, and was later gravitationally captured by Alpha and Beta?

ADDED
Sorry I did not notice post #29 which gives an approximate age for Alpha and Beta.
@CygnusX-1: Does this imply these stars are 2nd generation?

We already know the age of Proxima Centauri: 4.85 billion years old. The same age as Alpha Centauri AB. Furthermore, we also know the metallicity of Proxima Centauri: 0.21 dex or 1.621 Z_⊙. The metallicity of Alpha Centauri A is 0.20 dex or 1.585 Z_⊙, and Alpha Centauri B has a metallicity of 0.23 dex or 1.698 Z_⊙. Which means that none of the stars in the Centauri system are first generation stars.

Source:
A Family Portrait of the Alpha Centauri System - European Southern Observatory Science Release, March 15, 2003
A physically-motivated photometric calibration of M dwarf metallicity - Astronomy and Astrophysics, Volume 519, September 2010
Asteroseismology and calibration of α Cen binary system - Astronomy and Astrophysics, Volume 392, Number 1, September 2002

 

[Buzz Bloom]

Which means that none of the stars in the Centauri system are first generation stars.

Hi Glitch:

Thank you for your post.

I would much appreciate your feedback on the other question I asked. Could Proxima be 1st generation, and much after it's birth and much independent movement by Proxima and the Alpha-Beta binary system (A-B) around the Milky Way, could Proxima become gravitationally captured by A-B?

ADDED
I missed your: We already know the age of Proxima Centauri: 4.85 billion years old.
Sorry about that.

Would you please explain the method for determining the age of a star. I am guessing it takes into account the mass and brightness, and the general rules regarding how brightness changes with age given a star's mass. Is this correct?

Regards,
Buzz

 

[Janus]

This study suggests that if Proxima b ever had an atmosphere, it was stripped away long ago.

https://www.space.com/37950-proxima...er6f150&utm_medium=social&utm_source=facebook

 

[stefan r]

Would you please explain the method for determining the age of a star. I am guessing it takes into account the mass and brightness, and the general rules regarding how brightness changes with age given a star's mass. Is this correct?

Regards,
Buzz

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

 

[stefan r]

This study suggests that if Proxima b ever had an atmosphere, it was stripped away long ago.

https://www.space.com/37950-proxima...er6f150&utm_medium=social&utm_source=facebook

It says

If Earth had formed where Proxima b orbits...

and

Proxima b could lose an Earth-equivalent atmosphere in only 100 million years, an eye-blink in the 4-billion-year lifetime of the planet

It is not earth. It is also not the solar system. A normal mix of gas and dust in the galaxy would include a lot of hydrogen carbon and oxygen. Earth (Mars Venus Mercury too) ended up with a lot of iron and silicon. Most of the hydrogen (water, ammonia, carbon dioxide etc) found a home in Jupiter and Saturn. So Proxima b could easily have had more than 40x the supply of gas molecules. It might be made of carbon dioxide and water (or few hundred kilometers). Stripping an Earth atmosphere mass off will just shift the total planetary mass.

The equivalent to the Oort cloud and Kupier belt type objects will not have a Jupiter to clear them out of the system. CO₂, ammonia, organics and water can stick to Oort could objects. The changes in Proxima b's atmospheric mass will be determined by the difference between gasses stripped and gasses added. I am not saying that there is evidence that Proxima b has a growing atmosphere. I would say that the current information is too limited to determine the net flow. High frequency comet showers would also be inhospitable to civilized human life but it is an either/or problem not really both.

 

[rootone]

It would be extraordinary good luck if the nearest stellar system to ours harbored a planet compatible with life that originated on Earth.
There is not even anything in our solar system that is like Earth, though Mars and Venus could have developed that way, but they didn't.

 

[|Glitch|]

Would you please explain the method for determining the age of a star. I am guessing it takes into account the mass and brightness, and the general rules regarding how brightness changes with age given a star's mass. Is this correct?

In the specific case of Proxima Centauri, the Very Large Telescope Interferometer (VLTI) was used to confirm the interferometric measurements of Proxima Centauri obtained with the two 8.2 meter VLT Antu and Melipal telescopes. These interferometers can produce higher resolution astronomical images than any other type of telescope. Once the interferometric observations have been made it is combined with other measurements, such as the star's mass, radius, effective surface temperature, inclination, and luminosity then comparisons are made with stellar evolutionary models, such as MESA. It is the most accurate means we have today for determining the age of main sequence stars.

Source:
New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit - Astronomy and Astrophysics, Volume 577, May 2015
Modules for Experiments in Stellar Astrophysics (MESA) - The Astrophysical Journal Supplement Series, Volume 192, Number 1, December 2010

 

[|Glitch|]

It would be extraordinary good luck if the nearest stellar system to ours harbored a planet compatible with life that originated on Earth.
There is not even anything in our solar system that is like Earth, though Mars and Venus could have developed that way, but they didn't.

I agree. The only advantage that Proxima Centauri b has is its mass. A more massive exoplanet would also imply a denser atmosphere, at least initially. Using our own solar system as a model, it is a fairly safe inference to assert that at least at one time in its history Proxima Centauri b should have had an atmosphere. Atmospheres on planets and moons seem to be fairly common once you reach a certain mass. Whether or not it still has its atmosphere seems highly unlikely after 4.85 billion years and its proximity to its star, but I would not rule it out entirely.

 

[|Glitch|]

A Day at the Beach on Proxima Centauri b

Intended to be taken with your tongue firmly planted in your cheek.

 

[litup]

We already know the age of Proxima Centauri: 4.85 billion years old. The same age as Alpha Centauri AB. Furthermore, we also know the metallicity of Proxima Centauri: 0.21 dex or 1.621 Z_⊙. The metallicity of Alpha Centauri A is 0.20 dex or 1.585 Z_⊙, and Alpha Centauri B has a metallicity of 0.23 dex or 1.698 Z_⊙. Which means that none of the stars in the Centauri system are first generation stars.

Source:
A Family Portrait of the Alpha Centauri System - European Southern Observatory Science Release, March 15, 2003
A physically-motivated photometric calibration of M dwarf metallicity - Astronomy and Astrophysics, Volume 519, September 2010
Asteroseismology and calibration of α Cen binary system - Astronomy and Astrophysics, Volume 392, Number 1, September 2002

Those Z numbers, are they ratios of metalicity compared to our sun?

 

[litup]

I agree. The only advantage that Proxima Centauri b has is its mass. A more massive exoplanet would also imply a denser atmosphere, at least initially. Using our own solar system as a model, it is a fairly safe inference to assert that at least at one time in its history Proxima Centauri b should have had an atmosphere. Atmospheres on planets and moons seem to be fairly common once you reach a certain mass. Whether or not it still has its atmosphere seems highly unlikely after 4.85 billion years and its proximity to its star, but I would not rule it out entirely.

Have all three stars been analyzed enough to say for sure whether there are planets around A and such?

 

[nikkkom]

Whether or not it still has its atmosphere seems highly unlikely after 4.85 billion years and its proximity to its star, but I would not rule it out entirely.

I am not so sure about this.
Look at this this way: if you shrink Earth to a 1 meter ball, oceans on it would be barely ~1mm deep in the deepest points! Our "vast" oceans are insignificant when you look at the whole planet. IOW: Earth actually has very little volatiles as a fraction of overall mass.

It's hard to imagine that having this little volatiles is some sort of typical thing. I expect that for planets around Earth mass, some will be much drier than Earth, and (importantly for this case) some will have much *more* water and other volatiles than Earth. With oceans, say, 4x deep as Earth, a planet can survive many billions of years of atmosphere loss and still not dry out.

We don't know where Proxima b is on the "water" scale. It may well be an "ocean world". We need more data. Spectroscopy would be great.

 

[nikkkom]

To demonstrate the point:

 

[Buzz Bloom]

To demonstrate the point:

Hi nik:

I am not sure I understand the point you are demonstrating. Is it that there is expected to be a wide variability with respect to H₂O/mass ratio for a planet or moon?

I would expect there to be an issue about how this variability depends on average body surface temperature. Europa is much colder than Earth, and it would therefore be expected that a greater fraction of a body's original H₂0 content would survive for billions of years on a colder body, even if it has less mass.

Perhaps some appropriately educated person might be able to create a plausible model showing how much H₂0 there was on Earth, Mars, and Europa say 4,500,000,000 years ago and how it came to be what is there today, based on mass, and temperature.

Regards,
Buzz

 

[Ophiolite]

No space imaging technology is based on the premise of sending a signal to a target and analyze it's bounce back.

Incorrect. For example:

Venus revealed in high-resolution radar images from Earth
Radar Images of Asteroid 2014 HQ124

Not to mention the radar imaging on early Russian probes to Venus, on the Magellan and Cassini probes, and on a dozen or more Earth orbiting satellites.
https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA18412

 

[|Glitch|]

Those Z numbers, are they ratios of metalicity compared to our sun?

Yes, Z = 10^dex

 

[|Glitch|]

Have all three stars been analyzed enough to say for sure whether there are planets around A and such?

Each of the three stars have been analyzed, but not the solar systems of these stars. There is a suspected planet orbiting Alpha Centauri B, but it has not yet been confirmed. One of the problems is that if there are planets orbiting any of these three stars they are not: A) Transiting their parent star; and/or B) Massive enough to create a noticeable wobble in their parent star. That certainly does not rule out the possibility of planets orbiting these stars, it just makes detecting them more difficult.

It should also be noted that Alpha Centauri A and B maintain an average distance of ~11 AU from each other, which puts a limit on the size of the solar system each star can have. The distance between Alpha Centauri AB and Proxima Centauri is 0.21 light years (13,280 AU) which gives Proxima Centauri much larger solar system possibilities.

Source:
An Earth-mass planet orbiting α Centauri B - Nature, Issue 491, November 8, 2012 (free preprint PDF)

 

[|Glitch|]

I am not so sure about this.
Look at this this way: if you shrink Earth to a 1 meter ball, oceans on it would be barely ~1mm deep in the deepest points! Our "vast" oceans are insignificant when you look at the whole planet. IOW: Earth actually has very little volatiles as a fraction of overall mass.

It's hard to imagine that having this little volatiles is some sort of typical thing. I expect that for planets around Earth mass, some will be much drier than Earth, and (importantly for this case) some will have much *more* water and other volatiles than Earth. With oceans, say, 4x deep as Earth, a planet can survive many billions of years of atmosphere loss and still not dry out.

We don't know where Proxima b is on the "water" scale. It may well be an "ocean world". We need more data. Spectroscopy would be great.

I was considering Proxima Centauri b's proximity (making it tidally locked) and the fact that its parent's star has the equivalent x-ray emissions as Sol, despite being 588 times less luminous. As of right now we just do not have enough information to make a determination either way. We can only infer possibilities based upon the information we have and that information is clearly incomplete. Hence, I would not rule anything out yet.

Source:
Stringent X-Ray Constraints on Mass Loss from Proxima Centauri - The Astrophysical Journal, Volume 578, Number 1, October 10, 2002. (free)
NASA Finds Planets of Red Dwarf Stars May Face Oxygen Loss in Habitable Zones - NASA Article, February 8, 2017

 

[stefan r]

Those Z numbers, are they ratios of metalicity compared to our sun?

Yes, Z = 10^dex

In that article I would read it as fractional mass of metals. The mass ratio of non metals to hydrogen in the Alpha Centauri at the time they formed is written (Z/X)_i. The ratio of metals to to hydrogen on the surface is written (Z/X)_s

As apposed to [Fe/H] which would be the logarithm of the ratio of the ratio of iron to hydrogen in alpha centauri to iron to hydrogen in the sun.
[Fe/H] = log₁₀((Z/X)/(Z_sun/X_sun))
or
[Fe/H] = log₁₀(Z/X) - log_{10(Zsun/Xsun)}

 

[Buzz Bloom]

We don't know where Proxima b is on the "water" scale. It may well be an "ocean world". We need more data. Spectroscopy would be great.

Hi nik:

I confess I have not been paying attention to exoplanet spectroscopy, so I did not know that the technology has advanced for this to begin to be an active aspect of current astronomy. Your remark prompted me to search for this topic and I found several interesting sources including:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140016974.pdf
http://spiff.rit.edu/classes/extrasol/lectures/spectra/spectra.html
http://hubblesite.org/hubble_discoveries/science_year_in_review/pdf/2008/probing_the_atmospheres_of_exoplanets.pdf .​

I am wondering is anyone knows about any efforts to use this technology for Proxima b.

Regards,
Buzz

 

[|Glitch|]

In that article I would read it as fractional mass of metals. The mass ratio of non metals to hydrogen in the Alpha Centauri at the time they formed is written (Z/X)_i. The ratio of metals to to hydrogen on the surface is written (Z/X)_s

As apposed to [Fe/H] which would be the logarithm of the ratio of the ratio of iron to hydrogen in alpha centauri to iron to hydrogen in the sun.
[Fe/H] = log₁₀((Z/X)/(Z_sun/X_sun))
or
[Fe/H] = log₁₀(Z/X) - log_{10(Zsun/Xsun)}

I agree. Metalicity is not the same as the iron to hydrogen ratio. Metalicity encompasses everything that is not hydrogen or helium. That includes iron, but also oxygen, carbon, silicon and everything else on the periodic table. Nevertheless, a star with a 0.21 dex is going to have 1.621 Z⊙. Which means that the star has a 62.1% higher ratio of non-hydrogen and non-helium elements than our sun. However, it should not be taken to mean that Proxima Centauri has a 62.1% higher Fe/H ratio.

 

[stefan r]

Hi nik:

I confess I have not been paying attention to exoplanet spectroscopy, so I did not know that the technology has advanced for this to begin to be an active aspect of current astronomy. Your remark prompted me to search for this topic and I found several interesting sources including:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140016974.pdf
http://spiff.rit.edu/classes/extrasol/lectures/spectra/spectra.html
http://hubblesite.org/hubble_discoveries/science_year_in_review/pdf/2008/probing_the_atmospheres_of_exoplanets.pdf .​

I am wondering is anyone knows about any efforts to use this technology for Proxima b.

Regards,
Buzz

Like this? linked to this paper.

I suspect people are already spending a lot of energy fighting about where to aim JWST. Choose between 1) beautiful awe inspiring pictures of nebula and other fireworks, 2) images of distant galaxies and details of the creation of the universe, 3) some debatable evidence that a rock which we thought was dead could really be dead.

 

[stefan r]

I agree. Metalicity is not the same as the iron to hydrogen ratio. Metalicity encompasses everything that is not hydrogen or helium. That includes iron, but also oxygen, carbon, silicon and everything else on the periodic table. Nevertheless, a star with a 0.21 dex is going to have 1.621 Z⊙. Which means that the star has a 62.1% higher ratio of non-hydrogen and non-helium elements than our sun. However, it should not be taken to mean that Proxima Centauri has a 62.1% higher Fe/H ratio.

Check this paper. Are they saying Alpha Centuari A currently has surface composition 71.5% Hydrogen, 25.8% Helium and 2.7%"metals"? They list (Z/X)_i as 0.0384 which can work if you adjust the rounding.

 

[|Glitch|]

Check this paper. Are they saying Alpha Centuari A currently has surface composition 71.5% Hydrogen, 25.8% Helium and 2.7%"metals"? They list (Z/X)_i as 0.0384 which can work if you adjust the rounding.

The paper gives Alpha Centauri AB the initial helium mass fraction (Y) of 30% ± 0.8% and an (Z/X)_i of 0.0459 ± 0.0019. Given that X + Y + Z = 1, that would make Alpha Centauri A's surface composition 66.93% hydrogen, 30% helium, and 3.07% other metals. Using the Skylab data from 1979, the sun is composed of 73.46% hydrogen, 24.85% helium, and 1.69% other metals. Which should have given Alpha Centauri A a Z⊙ = 1.817 or 0.259 dex instead of the 0.20 dex I posted above. Or they were using a different composition for our sun than the one I listed.

Source:
The Sun's Vital Statistics - Stanford Solar Center

 

[stefan r]

...the 0.20 dex I posted above. Or they were using a different composition for our sun than the one I listed.

The "i" is for initial. To me that would mean the gas cloud that formed both stars. Nothing we could see now.

On table 1 they list [Fe/H] as 0.20 under Alpha Centuari A.

 

[rootone]

Wikipedia has a good article on Proxima Centauri.

In my opinion Wikipedia is a good place to start with any new enquiry.
Some people criticize it for being not guaranteed accurate, but then what is?: