How many M-Class planets do you think there are?

[BK613]

@Asbo Zaprudder I'm seing different values than those (like the ones in the linked chart) but I concede i am no expert.

File:Stellar Classification Chart.png - Wikipedia

en.wikipedia.org

 

[Asbo Zaprudder]

@Asbo Zaprudder I'm seing different values than those (like the ones in the linked chart) but I concede i am no expert.

File:Stellar Classification Chart.png - Wikipedia

en.wikipedia.org

Yes, different sources give different estimates. There doesn't appear to be a consensus. There is perhaps 50% uncertainty in the population percentages and the total number of stars in the Milky Way might be as low as 50 billion or as great as 400 billion. It's hard to tell because the solar system is embedded inside it. Being within a factor of two of the actual values would be an achievement. That between 75 and 80% are class M red dwarfs isn't in doubt - even given their lower luminosity.

 

[BK613]

Yes, different sources give different estimates. There doesn't appear to be a consensus. There is perhaps 50% uncertainty in the population percentages and the total number of stars in the Milky Way might be as low as 50 billion or as great as 400 billion. It's hard to tell because the solar system is embedded inside it. Being within a factor of two of the actual values would be an achievement. That between 75 and 80% are class M red dwarfs isn't in doubt - even given their lower luminosity.

Oh I understand. Parsing the sources is also important. After all, you'll get different numbers if you consider all stars vs just main sequence stars.

 

[Asbo Zaprudder]

Oh I understand. Parsing the sources is also important. After all, you'll get different numbers if you consider all stars vs just main sequence stars.

Neither of us are quoting the latest peer-reviewed scientific literature. I haven't had access to that for decades. Wikipedia is not a primary source. I was using http://www.atlasoftheuniverse.com/startype.html, specifically this graphic:

90% of stars are on the main sequence so the numbers shouldn't be very different. I was surprised how much variation there is in various estimates I did find, given the size of the potential sample size. Your figures are similar to the ones that I remember from years ago.

If the power law of number with respect to mass continued into brown dwarfs and planetary bodies - either bound or unbound to parent stars - we should expect vastly more of those objects than even red dwarfs.

The salient term for stellar mass distribution is initial mass function. The estimates of this vary quite a bit below 0.5 solar masses - dim stars being harder to observe. A different power law might also apply,

There are large uncertainties concerning the substellar region. In particular, the classical assumption of a single IMF covering the whole substellar and stellar mass range is being questioned, in favor of a two-component IMF to account for possible different formation modes for substellar objects—one IMF covering brown dwarfs and very-low-mass stars, and another ranging from the higher-mass brown dwarfs to the most massive stars. This leads to an overlap region approximately between 0.05–0.2 M☉ where both formation modes may account for bodies in this mass range.

Source: By JohannesBuchner - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44779435

 

[BK613]

Neither of us are quoting the latest peer-reviewed scientific literature. I haven't had access to that for decades. Wikipedia is not a primary source.

At least Wikipedia does list their sources—and whenever possible, I do try to source those.
As near as I can tell, the data in the chart I linked to comes from The Real Starry Sky (Journal of the Royal Astronomical Society of Canada, Vol. 95, p.32)

90% of stars are on the main sequence so the numbers shouldn't be very different

Assuming 100 billion stars, 8 percent would be 8 billion.
90 percent of that assumed value gives an 8 percent value of 7.2 billion.
A difference of 800 million stars is not chump change IMO.

Anyway, whatever the percentages, the more main sequence stars you can include as viable, the better the chances for an Earth analog.

-----------
An aside: Thanks for the trip down Memory Lane. I haven't been to that site in years.

 

[Asbo Zaprudder]

You are assuming that the 90% fraction applies equally across all spectral classes. Still, as you say, it makes little difference. The Wikipedia data might well be the most current estimate. It ties in better with the numbers I had in my mind initially, but searching around threw up a few different values and I went with the lowest estimate. In any case, the human race is probably not going to visit any planets around any other star in our lifetimes and perhaps only using Von Neumann or Bracewell type probes within the next millennium, so it really is a bit of an academic exercise.