In science however,
excitement must be tempered by sober examination of evidence, and there are some
good reasons why we should not get too excited by Kepler-22B just yet. In the first place, we don’t have a good estimate
of its mass yet, and probably won’t for a few more months. This is the most critical consideration as to
whether the new planet is a (relatively small) gas-giant world, like Neptune or
Uranus, only about half their diameters, or is truly an Earth-like planet, one
with a rocky core probably covered with deep oceans.
If the first scenario
is true is found to be the truth, this doesn’t automatically rule out life on
the new world. It might still possess
liquid water, here as cloud layers, and life could possibly begin in droplets
or drops of water seeded with ammonia, methane, hydrogen cyanide, and carbon
dioxide, a lá the Stanley Milgrim experiments of the 1950s. A distinct planetary surface is not actually
needed for life, or so current thinking runs.
However, its seems doubtful that such life would have evolved far beyond
the single cell, or prokaryotic, stage. Definitely
worth knowing however, if it turns out true.
The other,
mass-determined, probability is that of a “super Earth”, a planet like our own,
only considerably larger, and one probably covered by ocean-girdling waters and
a thick, greenhouse atmosphere. Again,
primitive life is a good candidate for the place, and here even complex,
multi-cellular organisms may have gotten a toe-hold. They could be swimmers and flyers, though
almost certainly little in the way of land dwellers, for there would be little
of any land to dwell on. Still, polar
icecaps might provide some of this. A
lot depends on the depth of the greenhouse effect, driven largely by water
vapor, carbon dioxide, and methane. All
three gasses should be copiously produced by volcanism, so we shall see.
Volcanism in turn is driven by a hot liquid core containing sufficient amounts of radioactive
atoms, atoms like uranium-235/-238, thorium-232, potassium-40 and strontium-87. Earth has significant amounts of them (creating
also our strong magnetic field which protects us from the solar wind) because
the creation of our solar system was probably initiated by a supernova type-II
explosion, seeding us with heavier elements, but it is not clear whether
Kepler-22 was born under similar circumstances (it is not all that unlikely
however, so we can reasonably speculate it).
If not however, Kepler-22B might be frozen over, with little internal
heat or heavy elements, leading to few prospects for life.
All this is speculation
right now, but it may be of the purely academic kind, for other conditions are
needed for life. The biggest problem is
the apparent lack of large gas giant worlds, situated further out than Kepler-22B. They may still exist, in slightly different
orbital places than 22B, such that we don’t see their occultations from Earth;
doppler “wobbles” in the star’s spectrum might yet root them out.
If they are not found,
however, this is troubling for life’s prospects on 22B. Jupiter and Saturn stand as staunch shields
against a large number of asteroid and comet impacts to our planet, impacts
that nevertheless occur to a disturbing degree and which could wipe out all
life here if large enough ones occurred with sufficient frequency. But we have a couple of heavy duty bar
bouncers that either suck up those impacts themselves, or hurl the offending
rock/ice worldlets out of the solar system, or park them in the asteroid belt.
If Kepler-22B doesn’t
have its own bouncers, then it is probably being regularly pounded by asteroids
and comets, so much so that life can’t get started there. Now perhaps its not that bad a problem out
there because the Kepler-22 system was not the result of a supernova explosion;
but then there might not be enough heavy elements to make a hot, molten core,
with its attending strong magnetic field and copious atmospheric components.
Then there’s the other
problem, which I’m not certain is truly severe or not. Earth has an axial tilt of 23° , which is
almost perfect for our seasons and the life adapted to it. The tilt does not vary greatly, and supposedly we have
our large moon to largely thank for that.
The reasonable length of our day is also due largely to the moon. Frankly, I don’t know how large of a problem
this really is; with the exception of Uranus (with a 98° axial tilt, rotating
virtually on its side), all the planets rotate on roughly vertical axes to the
solar system’s orbital plane, and only Mercury and Venus have unusual days, in
the first case one locked in a 2:3 resonance with its solar orbit, and in the
second, Venus’, case a slow retrograde axial orbit (opposite to its movement
about the sun).
If these parameters are
important (as suggested by the “Rare Earth” hypothesis) then 22B could be
in big trouble, though this is not certain.
But all of these considerations, taken together, should keep our
enthusiasm in check as we explore Kepler-22B further.
