Lately on this channel I’ve talked a lot about habitable exoplanets orbiting M-type
red dwarf stars.
For good reason, those stars are very long lived and at least in the Milky Way are very,
very common.
They are make up a significant portion of the closest stars to us with both Proxima
Centauri and Trappist -1 falling into that class.
But the discovery of exoplanets around both of those stars has opened up a debate as to
just how habitable the habitable zones of red dwarf stars really are, and the results
of the debate haven’t been good, at least so far.
The deck is seemingly stacked against the red dwarfs both for predicted instabilities
early in the history of those stars and also the fact that they are dim, and that means
that the habitability zone is very close to the star opening up planets within the zone
to high levels of radiation.
I tend not to place too much importance on the idea of a habitable zone though.
I have said on this channel many times that life is tenacious, whereever there is liquid
water and energy there is the possibility for it to arise.
Well, liquid water does not necessarily need to be within the habitable zone to exist,
look at Enceladus.
In fact, a planet or moon does not even need a star to have liquid water, all it needs
is geothermal energy from tidal flexing or radio active decay in the planet’s core.
So don’t count out the red dwarfs just yet.
But we do know that yellow dwarf stars can spawn civilizations, one spawned us.
So it makes sense to search for life around other sun-like stars.
Introduce Tau Ceti.
It’s a little under 12 light years away and in fact can be seen with the naked eye
in the night sky.
It’s a little smaller and dimmer than the sun, but of the same spectral type, and thought
to be a bit older than our sun based on its low metallicity composition.
Time is good when talking of evolving complex life.
And, for the last few years, there have been murmurs of planets around this star, including
two that are possibly within the habitable zone.
Evidence for these planets has been bolstered recently using the radial velocity method
of detection that suggests the presence of at least two, link to a paper by F. Feng and
colleagues on this subject in the description below.
And, past evidence suggested even more planets.
But Tau Ceti has an issue.
It’s a very dusty system that seems to have a lot of asteroids and comet material.
While that doesn’t mean life can’t arise and sustain in a system like that, it does
introduce the problem of complex life being subject to higher rates of extinction.
Every time something gets going, it could end up being reset.
But once it gets going, it’s hardly a problem for life in general, in another recent paper
by David Sloan and colleagues, they showed that microbes on earth are unlikely to go
extinct in any scenario that affects complex life, such as asteroid impacts.
Essentially to kill them off completely would require the sun to swell into a red giant
and cook the planet, which it will some day do.
The debris disk at Tau Ceti is thought to be similar to our own Oort cloud, which is
the likely origin of the object that killed the dinosaurs.
Tau Ceti’s analogue to that is thought to contain something around ten times as much
material, so planets in that system could be subject to a constant barrage.
But we don’t know that for sure, and the sun-like nature of Tau Ceti has made it a
popular target for SETI searches, though to date nothing has been found.
One has to take a look, but perhaps the presence of the debris disc itself says something too.
If any alien civilization that may be present there hasn’t bothered to clear out the comet
and asteroid threat, then what does that say?
Then again, we haven’t done that with our own system, so who knows.
And there is a count towards life in the universe in all of this; older stars like Tau Ceti
that don’t have high metallicity are thought to have less likelihood of forming systems
of planets and debris at all.
Yet, there Tau Ceti is.
But that’s a double-edged sword in a way.
There are some indications that debris discs like that of Tau Ceti are really common in
the universe.
In fact, our sun may be unusual for it’s lack of a substantial disc, despite there
being plenty of metals in this system.
Perhaps early in the solar system’s history much of the original debris disc was carried
away by a passing star and the Oort cloud is what’s left over.
And we may have captured something from that or another star, see my videos on this channel
about planets nine and ten.
But one take away from all of this is another option for SETI.
Perhaps stars that have a conspicuous lack of debris might be good candidates for searches.
A lack of debris might indicate that a star has a higher chance of hosting inhabited planets,
and could even suggest that someone cleared the system of materials.
While it was unlikely to be due to the activity aliens, something like this actually happened
once in near real time, there is a star known as TYC 8241 2652 that was observed in 1983
to have a substantial debris disk.
The star is young, and it’s not at all unusual to see that, it’s a normal part of planetary
formation early in a star’s history.
But in 2010 when astronomers looked again, the disk had disappeared and no indication
of it has been seen since.
All that material simply vanished without a trace sometime within the last 25 years.
Thanks for listening!
I am futurist and science fiction author John Michael Godier and if you’d like to help
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