Is our solar system weird? The current odds (Introduction)

by David Turell , Sunday, July 10, 2016, 15:57 (3057 days ago) @ David Turell

It looks so far, based on planet discoveries, that our solar system is a rare bird:-http://nautil.us/blog/our-solar-system-would-be-weird-even-if-it-didnt-harbor-life-"Let's start with the sun. It turns out that our home star is a little bit unusual, but not a lot. This image shows a census of all the stars within 30 light-years of the sun:-"Our sun is a G star—normally white to yellow in color with a surface temperature around 5,000 to 6,000 Kelvin. There are 20 G stars within 30 light-years out of almost 400 total stars. The majority of stars are M stars, also known as “red dwarfs”. These small red stars have much longer lifetimes than G stars but shine much fainter. Among nearby stars, the sun is modestly weird. If you give our definition of a “sun-like” star some latitude, our star ends up being rare—10 percent of the nearby stars are like it, about the fraction of American adults who are vegetarian.-"Now let's turn our attention to Jupiter. First, take a look at our current census of extra-solar planets. Here is a plot of the almost 3,000 planets that have been discovered in the past two decades; the x-axis represents the planets' distance from their home stars, the y-axis their mass:-"Like the sun, Jupiters are just a little out of the ordinary. (As are our rocky planets: None of the known extra-solar planets line up with them, or with Saturn, Uranus, or Neptune. But we already knew this; it's why we are searching for sun-Jupiter systems and not complete solar systems.) Only 10-15 percent of sun-like stars have a gas giant planet like Jupiter, with a mass larger than 50 Earths. -"Another factor that makes our Jupiter more unusual is its orbit: It's nearly circular (an ellipse with an eccentricity of just 5 percent) and it's more than five times larger than Earth's orbit. Among the other known gas giants, on the other hand, only about 10 percent have orbits wider than Mars' (which is only 1.5 times larger than Earth's) that are nearly circular (with eccentricities less than 10 percent). Putting those together, only about 1 percent of stars like the sun has a Jupiter like ours—a little less likely than being dealt 3-of-a-kind in a 5-card poker hand.-"There is one more aspect of the solar system that is unusual. It's not something about the planets that we have; it's something that is missing. About half of all stars like the sun are orbited by at least one “hot super-Earth” planet. These planets are generally Earth-sized or larger, with orbits around the sun smaller than Mercury's. We don't know why the solar system is deficient in super-Earths, although one idea suggests that Jupiter may be the reason. -"Let's put the pieces together to calculate how unusual our solar system is: The fraction of stars that are like the sun (10 percent), multiplied by the fraction of sun-like stars with Jupiters (10 percent), multiplied by the fraction of Jupiter-like planets with Jupiter-like orbits (10 percent), multiplied by the fraction of sun-like stars with no hot super-Earths (50 percent), gets us 0.05 percent.-"This tells us that about one in every 2000 stars in our galactic neighborhood is a sun-Jupiter system. (my bold)-***-"But we don't know how many sun-Jupiter systems also have Venuses, Earths, Saturns or Marses. And we don't know how common Earths and Saturns are in systems without Jupiters or systems that orbit red dwarfs. We really want to know whether there is a reason for life-bearing planets to prefer sun-Jupiter systems, like ours. How exactly does the structure of a planetary system affect its ability to host life, if at all?"-Comment: I've not copied the illustrations. Take a look. We know the Earth has many special attributes that support conditions for life. We know Jupiter in its position sweeps up lots of asteroids and other objects that could strike the Earth if loose. So far the evidence is our solar system is rare but not an impossibly rare outliner. Turned around, it appears the presence of life does obviously require some very special conditions.-From the article: " astrobiologist Caleb Scharf in his 2014 book The Copernicus Complex. “But a big piece of the puzzle, a very big piece, seems to come from sheer, blind, unadulterated chance.'” -Or God is the engineer. Take your pick.