Extraterrestrial Life on Tidally Locked Planets

Can small, red dwarf stars (M class) really support extraterrestrial habitability? Red dwarf stars are much cooler (~10% brightness) and smaller (10 to 50%) than our Sun. This pushes the habitable zone for planets much closer to the parent star of the system which, in turn, causes planets to become tidally locked (one hemisphere always facing the star like the Moon is to Earth). Also, being closer the planets are more exposed to infrared and flaring radiation. Yet, they have incredible lifespans in trillions of years (vs. the Sun’s 10B year lifespan) and comprise about 75% of all stars in the galaxy.

Gale & Wandell (2017) argue that perhaps tidally locked planets orbiting red dwarfs may develop life in zones of “continuous illumination with a considerable component of photosynthetic 400-700 nm radiation. This is analogous to the lush summer growth of vegetation on Earth, at very high latitude.” You can read the paper here: The Potential of Planets Orbiting Red Dwarf Stars to Support Oxygenic Photosynthesis and Complex Life

With the large number of red dwarfs, maybe we’ll discover biotic markers in future missions!

Does a Civilization have a Limit to Growth?

Growth of a planetary population, technology, productivity and energy consumption seems unstoppable - scaling to infinity over some finite time (millions of years??) When and if Earth becomes one large connected “city” the growth hits a wall, or, as Wong & Bartlett (2022) suggest - an asymptotic burnout - aka, civilization hits a limit of growth and either collapses or awakens. Is this the Fermi paradox and why we don’t see other extraterrestrial civilizations in the galaxy? Have most collapsed?

Read more here: Asymptotic burnout and homeostaticawakening: a possible solution to theFermi paradox?

Could Extraterrestrials be Spreading Biological Life?

It is a well-known hypothesis (but not fully agreed upon) by astrobiologists that extraterrestrial life could have hitched a ride on some interstellar cometary objects like 3I/Atlas (the unusual elongated comet that entered our Solar System recently) that have entered ours and other solar systems. This theory is known as panspermia - and both Carl Sagan and Avi Loeb have postulated that the biological seeds of intelligent life may have arrived via these comets spreading the material in stellar systems.

Loeb has even suggested that extraterrestrials may be spreading life across the galaxy as a fertilization mission. You can read more here: Did 3I/ATLAS Deliver Extrasolar Life to Our Backyard?

Could Different Arrangements of Matter Become Conscious?

Well, it is interesting when philosophers jump in on extraterrestrial life. Pober & Schwitzgebel (2026) published a recent and very speculative paper arguing on how extraterrestrial consciousness could arise in different arrangements of matter (think of what biological constructs are needed for human consciousness to arise). Their logic is simple:

  P1: The universe contains at least a thousand different behaviorally sophisticated species
  P2: These species have substantially different substrates

  P3: Some of these species with substantially different substrates are conscious

  Conclusion: Therefore, consciousness is possible in substantially different substrates

Adding some other thoughts - each galaxy has over a million planets - combine to that a relaxation of the constraint that it must be the same substrates as on Earth. Interesting to speculate on, but in terms of the levels of argument, it's a Level 4.

You can read the paper here: Substrate Flexibility and the Copernican Principle of Consciousness

Detected Habitable Planets?

Yesterday I mentioned Barnard's Star having four exoplanets but none of them are in the estimated habitable zone defined for a red M-dwarf parent star. So, where are we currently at for detection of potentially habitable planets? The current estimates are approximately 70 out of 5000+ detected exoplanets that are more likely to have a rocky composition and support surface liquid water. These would have varying parent stars that would typically be like our own Sun (G-dwarf) or cooler (K or M dwarfs)

One of the Closest Stars to Earth has 4 Exoplanets

Did you know that Barnard’s Star - one of the closest stars to Earth at approximately 6 light years away currently has 4 confirmed exoplanets. Also known as Proxima Ophiuchi (in the constellation of Ophiuchus), it is a small, red M-dwarf star of about 16% the mass of the Sun and 18% of the Sun’s radius. These 4 small exoplanets are only about 30% the size of Earth and orbit Barnard’s Star about every 2.5 to 7 days (moving outward to each planet). Unfortunately these exoplanets are not the in the star’s habitable zone - but being only 6 light years away, it is a prime candidate for continuing exoplanet research.

A Brief History of SETI

Universe Today has done a very good series this month on SETI (Search for Extraterrestrial Intelligence). It’s well written and worth the read.

Here is the first part: A Brief-ish History of SETI. Part 1: "Where is Everybody?"

Exoplanet Explosive Growth

Well, recent news has shown the explosive growth in exoplanet discoveries in the last year - up over 650 since last Sept. The TESS (Transiting Exoplanet Survey Satellite) output an all sky mosaic show both confirmed and potential exoplanet (5000+) systems. We’re now close to estimating that every star in the Milky Way has, on average, at least 2 planets - that’s 200+ billion planets in our own galaxy alone.

Certainly a Level 1 view of exoplanet science!