60 Billion Habitable Planets in the Milky Way Alone? Astronomers say Yes!
An artist’s conception of how common exoplanets are throughout the Milky Way Galaxy. Image Credit: Wikipedia
A new study suggests that the number of habitable exoplanets within the Milky Way alone may reach 60 billion.
Previous research
performed by a team at Harvard University suggested that there is one
Earth-sized planet in the habitable zone of each red dwarf star. But
researchers at the University of Chicago and Northwestern University
have now extended the habitable zone and doubled this estimate.
The research team, lead by Dr. Jun Yang considered one more variable in
their calculations: cloud cover. Most exoplanets are tidally locked to
their host stars – one hemisphere continually faces the star, while one
continuously faces away. These tidally locked planets have a permanent
dayside and a permanent nightside.
One would expect the temperature gradient between the two to be very
high, as the dayside is continuously receiving stellar flux, while the
nightside is always in darkness. Computer simulations that take into
account cloud cover show that this is not the case.
The dayside is covered by clouds, which lead to a “stabilizing cloud
feedback” on climate. It has a higher cloud albedo (more light is
reflected off the clouds) and a lower greenhouse effect. The presence of
clouds actually causes the dayside to be much cooler than expected.
“Tidally locked planets have low enough surface temperatures to be
habitable,” explains Jang in his recently published paper. Cloud cover
is so effective it even extends the habitable zone to twice the stellar
flux. Planets twice as close to their host star are still cool enough to
be habitable.
But these new statistics do not apply to just a few stars. Red dwarfs
“represent about ¾ of the stars in the galaxy, so it applies to a huge
number of planets,” Dr. Abbot, co-author on the paper, told Universe
Today. It doubles the number of planets previously thought habitable
throughout the entire galaxy.
Not only is the habitable zone around red dwarfs much larger, red
dwarfs also live for much longer periods of time. In fact, the Universe
is not old enough for any of these long-living stars to have died yet.
This gives life the amount of time necessary to form. After all, it took
human beings 4.5 billions years to appear on Earth.
Another study we reported on earlier also revised and extrapolated the habitable zone around red dwarf stars.
Future observations will verify this model by measuring the cloud
temperatures. On the dayside, we will only be able to see the high cool
clouds. A planet resembling this model will therefore look very cold on
the dayside. In fact, “a planet that does show the cloud feedback will
look hotter on the nightside than the dayside,” explains Abbot.
This effect will be testable with the James Webb Space Telescope. All in all, the Milky Way is likely to be teeming with life.
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