<blockquote>
<p>Have the many exoplanets we've discovered in the last several decades improved our estimates of , and ?</p>
</blockquote>
<p>Absolutely! The quantity <span class="math-container">$f_p n_e$</span> is a quantity of much interest in investigations of extrasolar planets, which effectively equates to the fraction of stars that have a habitable planet in their star's habitable zone. Plenty of studies have examined this specifically for Earth-sized extrasolar planets and place the value of <span class="math-container">$f_p n_e$</span> between ~<span class="math-container">$\frac{1}{6}$</span> (i.e. one in six stars have an earth-sized planet in a relatively close orbit to the host star) and ~<span class="math-container">$\frac{2}{5}$</span> <a href="https://www.nasa.gov/mission_pages/kepler/news/17-percent-of-stars-have-earth-size-planets.html" rel="nofollow noreferrer">[1]</a><a href="https://en.wikipedia.org/wiki/Drake_equation#Fraction_of_those_stars_that_have_planets,_fp" rel="nofollow noreferrer">[2]</a>. A 2013 comprehensive study by Petigura is a great paper to get familiar with the specifics and assumptions of how the Kepler surveys are conducted and the quantities of interest calculated <a href="https://arxiv.org/pdf/1311.6806.pdf" rel="nofollow noreferrer">[3]</a>.</p>
<blockquote>
<p>What is our current best estimate for ⋆ for the Milky Way?</p>
</blockquote>
<p>Unfortunately the answer is: it varies. Roughly, we think that the Milky Way puts out about 3 solar masses worth of new star every year <a href="http://www.ism.ucalgary.ca/Star_Formation/How_Often.html#:%7E:text=This%20quantity%20is%20called%20the,necessarily%20go%20into%201%20star." rel="nofollow noreferrer">[4]</a>. However, these don't have to be in one star. Since we think most stars are probably ~1 M<span class="math-container">$_\odot$</span>, this works out to ~3 stars/year. However, some estimates go less, and some estimates (based on chemical decay of elements like aluminum) go as high as 7 stars/year <a href="https://www.nasa.gov/centers/goddard/news/topstory/2006/milkyway_seven.html" rel="nofollow noreferrer">[5]</a>.</p>

CC BY-SA 4.0
2021-01-05T21:22:18.393Z
Most stars are more like 0.3 solar masses.
ProfRob
CC BY-SA 4.0
2021-01-05T21:28:26.443Z
@ProfRob The justification for my statement can be found in the source I linked: "However, stars like our Sun (1 solar mass) are quite common and so we can approximate the star formation rate to be about 3 stars (like our Sun) per year in our Galaxy."  However, I appreciate there are different estimates on this number, and I believe the qualifier in my answer: "However, some estimates go less, and some estimates (based on chemical decay of elements like aluminum) go as high as 7 stars/year" with appropriate citations addresses the issue.
Joseph Farah
CC BY-SA 4.0
2021-01-05T01:56:25.707Z
2021-01-05T01:56:25.707Z
Joseph Farah
<p><a href="https://en.wikipedia.org/wiki/Drake_equation" rel="nofollow noreferrer">Frank Drake's equation</a> is used to estimate <span class="math-container">$N$</span> the number of civilizations we might be able to communicate with in our galaxy:</p>
<p><span class="math-container">$$N = R_\star f_p n_e f_l f_i f_c L$$</span></p>
<p>where:</p>
<p><span class="math-container">$R_\star$</span> is the average rate of star formation in the galaxy</p>
<p><span class="math-container">$f_p$</span> is the fraction of stars with planets</p>
<p><span class="math-container">$n_e$</span> is the average number of <a href="https://www.nationalgeographic.com/astrobiology/goldilocks-worlds/" rel="nofollow noreferrer">goldilocks</a> planets per planetary system</p>
<p><span class="math-container">$f_l$</span> is the fraction of goldilocks planets that actually develop life</p>
<p><span class="math-container">$f_i$</span> is the fraction of life bearing planets that develop intelligent life</p>
<p><span class="math-container">$f_c$</span> is the fraction of civilizations that broadcast their existence into space</p>
<p>and <span class="math-container">$L$</span> is the length of time for which a civilization broadcasts their existence</p>
<h2>Question</h2>
<p>Have the many exoplanets we've discovered in the last several decades improved our estimates of <span class="math-container">$f_p$</span>, and <span class="math-container">$n_e$</span>?  Are these values different than what was guessed about prior to the discovery of the first exoplanets?  What is our current best estimate for <span class="math-container">$R_\star$</span> for the Milky Way?</p>

CC BY-SA 4.0
2021-01-03T19:43:07.867Z
Have you consulted wikipedia on this? It seems there is a long discussion section about current values.
AtmosphericPrisonEscape
CC BY-SA 4.0
2021-01-03T19:59:33.330Z
@AtmosphericPrisonEscape Yeah, I'd like to see a little more detail about $f_p$ and $n_c$, particularly.  Also it seems like the wikipedia entry may be a bit dated.  A lot of the stuff is from 2011.
Connor Garcia
CC BY-SA 4.0
2021-01-03T20:42:07.513Z
We collected a bunch of estimates in https://arxiv.org/abs/1806.02404 (see the supplementary files), showing their distributions, but for a deeper discussion see Vakoch, D. A., & Dowd, M. F. (Eds.). (2015). The Drake equation: estimating the prevalence of extraterrestrial life through the ages (Vol. 8). Cambridge University Press.
Anders Sandberg
<exoplanet><seti><drake-equation>
Current best-known Drake Equation values?
Connor Garcia
# Current best-known Drake Equation values?

(Asked by: username_0 on 2021-01-03)

[Frank Drake's equation](https://en.wikipedia.org/wiki/Drake_equation) is used to estimate $N$ the number of civilizations we might be able to communicate with in our galaxy:

$$N = R\_\star f\_p n\_e f\_l f\_i f\_c L$$

where:

$R\_\star$ is the average rate of star formation in the galaxy

$f\_p$ is the fraction of stars with planets

$n\_e$ is the average number of [goldilocks](https://www.nationalgeographic.com/astrobiology/goldilocks-worlds/) planets per planetary system

$f\_l$ is the fraction of goldilocks planets that actually develop life

$f\_i$ is the fraction of life bearing planets that develop intelligent life

$f\_c$ is the fraction of civilizations that broadcast their existence into space

and $L$ is the length of time for which a civilization broadcasts their existence

## Question

Have the many exoplanets we've discovered in the last several decades improved our estimates of $f\_p$, and $n\_e$? Are these values different than what was guessed about prior to the discovery of the first exoplanets? What is our current best estimate for $R\_\star$ for the Milky Way?

**Tags:** exoplanet, seti, drake-equation

> **Comments:**
> **username_1**: Have you consulted wikipedia on this? It seems there is a long discussion section about current values.  
> **username_0**: @username_1 Yeah, I'd like to see a little more detail about $f_p$ and $n_c$, particularly.  Also it seems like the wikipedia entry may be a bit dated.  A lot of the stuff is from 2011.  
> **username_2**: We collected a bunch of estimates in https://arxiv.org/abs/1806.02404 (see the supplementary files), showing their distributions, but for a deeper discussion see Vakoch, D. A., & Dowd, M. F. (Eds.). (2015). The Drake equation: estimating the prevalence of extraterrestrial life through the ages (Vol. 8). Cambridge University Press.  

---

## 1 answers

### Answer by username_3 on 2021-01-05. Score: 3

> Have the many exoplanets we've discovered in the last several decades improved our estimates of , and ?

Absolutely! The quantity $f\_p n\_e$ is a quantity of much interest in investigations of extrasolar planets, which effectively equates to the fraction of stars that have a habitable planet in their star's habitable zone. Plenty of studies have examined this specifically for Earth-sized extrasolar planets and place the value of $f\_p n\_e$ between ~$\frac{1}{6}$ (i.e. one in six stars have an earth-sized planet in a relatively close orbit to the host star) and ~$\frac{2}{5}$ [[1]](https://www.nasa.gov/mission_pages/kepler/news/17-percent-of-stars-have-earth-size-planets.html)[[2]](https://en.wikipedia.org/wiki/Drake_equation#Fraction_of_those_stars_that_have_planets,_fp). A 2013 comprehensive study by Petigura is a great paper to get familiar with the specifics and assumptions of how the Kepler surveys are conducted and the quantities of interest calculated [[3]](https://arxiv.org/pdf/1311.6806.pdf).

> What is our current best estimate for ⋆ for the Milky Way?

Unfortunately the answer is: it varies. Roughly, we think that the Milky Way puts out about 3 solar masses worth of new star every year [[4]](http://www.ism.ucalgary.ca/Star_Formation/How_Often.html#:%7E:text=This%20quantity%20is%20called%20the,necessarily%20go%20into%201%20star.). However, these don't have to be in one star. Since we think most stars are probably ~1 M$\_\odot$, this works out to ~3 stars/year. However, some estimates go less, and some estimates (based on chemical decay of elements like aluminum) go as high as 7 stars/year [[5]](https://www.nasa.gov/centers/goddard/news/topstory/2006/milkyway_seven.html).

> **Comments:**
> **username_4**: Most stars are more like 0.3 solar masses.  
> **username_3**: @username_4 The justification for my statement can be found in the source I linked: "However, stars like our Sun (1 solar mass) are quite common and so we can approximate the star formation rate to be about 3 stars (like our Sun) per year in our Galaxy."  However, I appreciate there are different estimates on this number, and I believe the qualifier in my answer: "However, some estimates go less, and some estimates (based on chemical decay of elements like aluminum) go as high as 7 stars/year" with appropriate citations addresses the issue.  

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