There is a great story on Nat Geo talking about habitable exoplanets. More specifically, some of the worlds we are detecting which may be -more-
habitable than the Earth.
(thanks to AliceBleachWhite for the tip)
People often think of the Earth as the epitome of habitability. For good reason, we're here and everywhere we look there is life. However there are
other planets out there which may be even more habitable than the Earth.
Here are a couple "Did you know?"s before an excerpt of the article on Nat Geo:
1. Did you know that Earth is a fairly dry planet? We think of it as a very wet world because water covers a good portion of surface area yet if you
took all of the water in the world and placed it in a ball this is the proportion of the Earth by volume that is water:
We know of worlds which have even more water by volume than the Earth. Perhaps they are even more habitable? All life as we know it needs water.
Specifically liquid water. A planet with more of it than Earth may have an even higher abundance of life.
2. Did you know that Earth doesn't exist in the middle of our solar system's habitable or "Goldilocks" zone? People tend to think the Earth sits smack
in the middle of our Solar System's habitable zone but in reality it is near the inner edge of it as shown in this graphic which compares our system
to the Tau Ceti system's habitable zone. (shown in green).
We know of planets which sit smack in the middle of this zone and there are other factors which make planets habitable as well, perhaps even more
habitable than our Earth.....
3. Did you know that there isn't just one definition of a habitable or "goldilocks" zone? The graphic below illustrates why this is:
So with that in mind...
Here's an excerpt of the article:
Continue reading at
Planet hunters have always been keen to find Earth's twin, but an astrobiology team now suggests that "superhabitable" planets may be even better
places to look for alien life.
Since 1995, astronomers have detected more than 1,000 worlds orbiting nearby stars, sparking a race to find the one that most resembles Earth, blessed
with oceans and an oxygen-rich atmosphere. That's because Earth is the only place in the universe where we know that life has evolved. (See: "More
Than 1,000 Potential New Planets Found.")
In the journal Astrobiology, however, researchers René Heller of Canada's McMaster University and John Armstrong of Weber State University in Ogden,
Utah, calls that idea too Earth-focused. "From a potpourri of habitable worlds that may exist, Earth might well turn out as one that is marginally
habitable, even bizarre from a biocentric standpoint," they write.
Instead, they suggest that astronomers should focus their planet hunting on worlds that might harbor conditions even more amenable to life. The
authors dub these hypothetical worlds "superhabitable." (See "Think Outside the Box to Find Extraterrestrial Life.")
Their report adds to a chorus of voices in the planet-hunting community that have called for rethinking the idea of "habitable zones" where worlds
that follow orbits friendly to oceans and life would exclusively exist.
What characteristics might make a world superhabitable? Like all potentially habitable worlds, they should have water, agree Heller and Armstrong. But
they list more than a dozen additional geological and atmospheric factors that could influence habitability.
For instance, older planets would presumably have had more opportunities for life to evolve. Larger worlds, ones up to three times as massive as
Earth, might be more likely to have an atmosphere due to more volcanic activity, which releases gases.
Earth itself is thought to be located on the fringes of the habitable zone, they note, so maybe planets that are located nearer to the center of the
habitable zone are more congenial to life.
Other scientists disagree about the usefulness of the concept of superhabitability. "A planet is either habitable or it's not," says atmospheric
scientist Jim Kasting, who first introduced the concept of the circumstellar habitable zone, which defines a planet as habitable if it orbits its star
at a distance where it's not too hot and not too cold for liquid water to form on the planet's surface.
Similarly, astrophysicist Steven Desch said that "calling a planet superhabitable is comparable to calling someone only a little bit pregnant ...
Having more of what is needed for life, in my mind, doesn't make it more likely to have life."
But Ravi Kopparapu, a physicist at Penn State University, agrees with the authors that the "binary" habitable zone concept (either friendly to life or
not) is too restrictive. Plenty of worlds within the habitable zone are unlikely to support life, while others—such as the icy moons of Saturn and
Jupiter, which may have vast underground oceans—could potentially support life but fall outside the habitable zone. As scientists continue to
discover a menagerie of exoplanets, considering more variables could help to prioritize which planets to target for follow-up.
This is interesting because it shows that with regards to habitability our ideas may be too influenced our Earth-bias.
Might we miss detecting life on other words far sooner than current plans call for by skipping worlds unlike the Earth but perhaps just as habitable
if not more habitable?
Here is a cautionary tale that is a true story....
In 1995 when the first exoplanet was announced by a Swiss team of astronomers orbiting the star 51 Pegasi and American team made up of Geoffrey Marcy
and Paul Butler was stunned.
The technique the Swiss team used was identical to theirs and the American team had taken data for some time but had not examined it to see if any
planet existed as the Swiss team did.
Why didn't they? Because they made an assumption based on our solar system that they wouldn't find anything for 10 years because the type of planet
they were looking for, a Jupiter sized planet was assumed to only orbit far out from its star. So they thought, "why bother looking, most planetary
formation models have big gas planets forming and orbiting far out, it will be years before we see anything in our data."
The Swiss team made no such assumption and made the first discovery of an exoplanet around a Sun-like star. It just so happened that massive planets
like Jupiter do sometimes orbit very close to their stars.
The discovery of that planet could have been made had Marcy and Butler looked at their data, they had even collected data on the same planet as the
The American team had to just be content with verifying the Swiss team's discovery.
Now the American team went on to make plenty of discoveries of their own and for quite some time has been the top planet hunters in terms of the
technique that was used to find 51 Pegasi b, 47 Ursa Majoris b, Tau Bootis b, etc.
But they missed out on making that first discovery due to an assumption about what is out there which was based on what was our only known planetary
system (our solar system) at the time (1995).
Lesson: If physics and chemistry do not prevent it, do not write it off. And always check your data even if you don't think anything is in it
edit on 18-1-2014 by JadeStar because: (no reason given)