# Another Earth

Another Earth

The search for another planet that has the potential to support intelligent life has always interested me. With improvements in telescopes, we are beginning to locate potential candidates in our Galaxy. I prefer to just focus on the Milky Way since it is sufficiently large to limit our traveling capabilities for several centuries or longer.

The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.

The equation was written in 1961 by Frank Drake, not for purposes of quantifying the number of civilizations, but as a way to stimulate scientific dialogue at the first scientific meeting on the search for extraterrestrial intelligence (SETI). The equation summarizes the main concepts which scientists must contemplate when considering the question of other radio-communicative life. It is more properly thought of as an approximation than as a serious attempt to determine a precise number.

It goes like this:

The Drake equation is: N = R * fp * ne * fl * fi* fc * L {\displaystyle N=R_{*}\cdot f_{\mathrm {p} }\cdot n_{\mathrm {e} }\cdot f_{\mathrm {l} }\cdot f_{\mathrm {i} }\cdot f_{\mathrm {c} }\cdot L}

where:

N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone);

and

R = the average rate of star formation in our galaxy (recent estimate is 100 billion, there could be more)

fp = the fraction of those stars that have planets (based on stars observed so far there is at least one planet [on average] per star. Some have none, others have several)

ne = the average number of planets that can potentially support life per star that has planets (so far, the average is that 1 in 20 planets observed in in the “habital” zone.)

fl = the fraction of planets that could support life that actually develop life at some point

(I have arbitrarily assigned a factor of 1 in a 100)

fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations) (I have arbitrarily assigned a factor of 1 in a 100)

fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space (I have arbitrarily assigned a factor of 1 in a 100)

L = the length of time for which such civilizations release detectable signals into space. (not a clue on this?)

Based the above my math reveals: 100,000,000,000 x 1 x .05 x .01 x .01 x .01 = 5,000 potential planets with the possibility of containing advanced civilizations (not factoring in “L”. Others have applied estimates that indicate that there may be as many as 10,000.  While this sounds like a lot of plants with intelligent life, the Galaxy is a very large space. The average distance of any of these planets would be over 25,000 light years from the Earth. Some would be closer, some a lot further. If we received communication from any of them it is possible that their existence has been terminated by the time, we receive it.

One very interesting system that is relatively close to us (just under 40 light years) is:

https://www.theverge.com/2017/2/22/14674088/7-planet-solar-system-discovered-conditions-for-life-water-nature-nasa

TRAPPIST-1 is an ultra-cool dwarf star that is approximately 8% the mass of and 11% the radius of the Sun. Although it is slightly larger than Jupiter, it is about 84 times more massive. It is a red dwarf rather than a very young brown dwarf   The star has a rotational period of 3.3 days.

• thus proving that:
• Owing to its low luminosity, the star has the ability to live for up to 12 trillion years. It is metal-rich, with a metallicity  109% the solar amount. Its luminosity is 0.05% of that of the Sun

## ·         Planetary system all seven planets are all near Earth-sized.

• Relative sizes, densities, and illumination of the TRAPPIST-1 system compared to the inner planets of the Solar System.
• On 22 February 2017, astronomers announced that the planetary system of this star is composed of seven temperate terrestrial planets, of which five (bcef and g) are similar in size to Earth, and two (d and h) are intermediate in size between Mars and Earth. Three of the planets (ef and g) orbit within the habitable zone.
• The orbits of the TRAPPIST-1 planetary system are very flat and compact. All seven of TRAPPIST-1’s planets orbit much closer than Mercury orbits the Sun. Except for b, they orbit farther than the Galilean satellites do around Jupiter, closer than most of the other moons of Jupiter. The distance between the orbits of b and c is only 1.6 times the distance between the Earth and the Moon. The planets should appear prominently in each other’s skies, in some cases appearing several times larger than the Moon appears from Earth. A year on the closest planet passes in only 1.5 Earth days, while the seventh planet’s year passes in only 18.8 days
• The planets pass so close to one another that gravitational interactions are significant, and their orbital periods are nearly resonant. In the time the innermost planet completes eight orbits, the second, third, and fourth planets complete five, three, and two. The gravitational tugging also results in transit-timing variations (TTVs), ranging from under a minute to over 30 minutes, which allowed the investigators to calculate the masses of all but the outermost planet.
• On 31 August 2017, astronomers using the Hubble Space Telescope reported the first evidence of possible water content on the TRAPPIST-1 exoplanets.
• Planets c and e are almost entirely rocky, while bdfg, and h have a layer of volatiles in the form of either a water shell, an ice shell, or a thick atmosphere. Planets cde, and f lack hydrogen-helium atmospheres. Planet g was also observed, but there was not enough data to firmly rule out a hydrogen atmosphere. Planet d might have a liquid water ocean comprising about 5% of its mass—for comparison, Earth’s water content is < 0.1%—while if f and g have water layers, they are likely frozen. Planet e has a slightly higher density than Earth, indicating a terrestrial rock and iron composition. Atmospheric modeling suggests the atmosphere of b is likely to be over the runaway greenhouse limit with an estimated 101 to 104 bar of water vapor.