Very Elliptical Orbits and Possible Life

As Spock Would Say?

From time to time I read about how planets in very elliptical orbits, orbits which take the planet in and out of the star's habitable zone, will probably not harbor life. Just too extreme. Of course if such a planet can support life, it would be, as that saying by Mr. Spock goes "it's life, Jim, but not as we know it." (Yes, I know that the line was not spoken by Spock in the series, but only in The Firms' song "Star Trekkin.'") But wait a minute. In pondering the report mentioned in the Creatures Frozen for 32,000 Years Still Alive post below maybe we should revisit those assumptions.

Or Not

Bacteria have been found buried deep in solid rock - bacteria with very slow metabolic states and are probably thousands of years old. Penn State scientists discovered in Kalaallit Nunaat (Greenland) dormant ultra-small bacteria (Chryseobacterium greenlandensis) trapped 2 miles deep in 120,000 year old ice core samples. If Earth creatures can reanimate after being frozen for tens of thousands of years, if other Earth creatures can last for hundreds of thousands of years, or even millions, then 1) life can be possible in very elliptical orbits and 2) it still could be life as we know it. We have many example of extreme life on Earth, living under conditions scientists not long ago said were not able to support life: from deep in antarctic ice, to miles below the surface of the Earth, to boiling hot springs, to volcanic vents on the sunless depths of the ocean floor, to acidic mine drainage, to the stratosphere -- life is everywhere on this planet, and in many, many forms.

Kol-Ut-Shan, as Spock Would More Likely Say

So, is it truly implausible that life can evolve on planets that orbit in and out of the habitable zone? Evolution may possibly take longer, but the most common star, the red dwarf, develop very slowly, lasting up to hundreds of billions of years. Plenty of time for life to evolve and in its own fashion thrive. Most of the time we put a limit on where life can exist on the Earth, we later find we are wrong.

Maybe we should embrace the Star Trek Vulcan philosophy of IDIC: Infinite Diversity from Infinite Combinations (Kol-Ut-Shan according to an episode of ST: Voyager). Though if life has universal laws (like physics and chemistry, on which biology depends), I am not sure about the Infinite part. Natural laws do have some limits, boundaries, ranges. But  even so, the range of diversity that can arise is still vast. Maybe it should have been ADAC: Astronomical Diversity from Astronomical Combinations. Or IDAC: Incredible Diversity from Astronomical Combinations. Of course, it is a trivial difference to be concerned over.
 
What matters is that there is an incredible array of life on this planet. Especially if we not only consider all the varied environments life can be found now on Earth, but all the varieties of life that have existed in all the varied Earth environments (some radically different) in the past as well. An incredible, astronomical diversity. 


Reference:

Coghlan, Andy. "'Resurrection Bug' Revived after 120,000 Years." Life. New Scientist. 15 June 2009. Web. 30 July 2009. <http://www.newscientist.com/article/dn17305-resurrection-bug-revived-after-120000-years.html>

Helmuth, Laura. "Top Ten Places Where Life Shouldn't Exist... But Does." Science & Nature. Smithsonian Magazine. 13 October 2009. Web. 5 September 2012. <http://www.smithsonianmag.com/science-nature/Top-Ten-Places-Where-Life-Shouldnt-Exist-But-Does.html#ixzz25e81Ip2i> 

"IDIC" Memory Alpha, The Star Trek Wiki. n.d. Web. 5 September 2012. <http://en.memory-alpha.org/wiki/IDIC>

"Novel bacterial species found trapped in Greenland's ice." Penn State Live. Penn State University. 3 June 2008. Web. 30 July 2009. <http://live.psu.edu/story/31052>

Life in the Infrared

In1996 scientists were surprised to find a version of chlorophyll, chlorophyll d, in a cyanobacterium (blue-green algae or blue-green bacteria) that can photosynthesize light at 710nm, just in the infrared region. How it can get enough energy to photosynthesize is a mystery right now. It is possible that it acts more like chlorophyll a, passing on the captured energy to other chlorophyll molecules which then do the actual photosynthesis.

Recently, Dr Min Chen, from the University of Sydney, discovered in cyanobacterium living inside stromatolites another chlorophyll molecule which can absorb infrared light - this time deeper into the infrared range at 720 nm. This molecule, chlorophyll f, raises the same question as with chlorophyll d: how does it get enough energy from infrared light to photosynthesize oxygen? Or does it act as a helper, passing on the energy to other chlorophyll?

While this discovery has implications for biotechnology and bioenergy, it also has implications for life on other planets. As Dr. Chen remarks:

the fact that we have discovered a cyanobacterium that exploits a tiny modification in its chlorophyll molecule to photosynthesise in light that we cannot see, opens our mind to the seemingly limitless ways that organisms adapt to survive in their environment.

This helps expands the environmental range where we can look for life. For instance, it helps increase the possibility of life arising around class M stars (see Color of Life for more information). Yet more evidence that Dr. Ian Malcolm's (Jurassic Park) adage is correct: life will find a way.

Reference:

Chen, Min, et. al. "A Red-Shifted Chlorophyll." Science Magazine. 19 August 2010. Web. 21 August 2010. <http://www.sciencemag.org/cgi/content/abstract/science.1191127>

Panspermia, Long-Lived Bacteria, and Interstellar Distances

"Dark Matter" © DigitalBlasphemy.com

I was checking out astrobiology groups on Facebook and came across a discussion on astrogensis at the "Astrobiology - Life in the Universe" Facebook group. An entry by one poster made the statement "With regards to panspermia, distances are simply too vast for living organisms to be transferred from beyond the solar system." Let's take a closer look at this problem.

The Problem

The problem stated is one of vast distances - the time for even a fast traveling extraterrestrial asteroid from even the closest star system would take an exorbitant period of time. If the average speed of an asteroid in the main belt is around 47,000 mph, and the distance to Alpha Centauri is 4.4 light-years or 25,848,247,139.8 miles (Proxima Centauri is sometimes closer, but let's go with the main star), then it would take that asteroid about 101,304 years to reach Earth.

Hardiness of Bacteria

Recently, bacteria have been found buried deep in solid rock - bacteria with very slow metabolic states and are probably thousands of years old. Penn State scientists discovered in Kalaallit Nunaat (Greenland) dormant ultra-small bacteria (Chryseobacterium greenlandensis) trapped 2 miles deep in 120,000 year old ice core samples. The scientists were able to bring them back and found it needed few nutrients to live. The scientists figure their small size helped them so survive trapped so long in the ice. Some studies indicate some bacteria can live suspended in sediments, amber, and halite for millions of years. In 2007 a group of scientists published a paper provided evidence for bacteria surviving in some frozen permafrost samples up to a half a million years. We have seen from other posts the ability for some bacteria and viruses to survive the vacuum of space. In a previous post I reported that even the small, multicellular Water Bear can survive periods in space - including normally deadly doses of ionizing radiation (Water Bears in Space!).

Illustration © European Space Organization

Spacefaring Bacteria?

With Alpha Centauri 101,304 years away (by asteroid) and bacteria that can lie dormant for at least 120,000 years (and especially those that can lie dormant for 1/2 million years), it seems that some unicellular life could theoretically make the trip. The red dwarf planetary system Gliese 581 (with one planet that is warm and terrestrial) is 20.5 light-years away, or around 471,984.5 years away at main belt asteroid velocities. Still within the range of some unicellular creatures. We have seen in earlier posts that there are scenarios where red dwarf systems can be hospitable to life.

Sol's Close Encounters

There is something else to consider as well. Our solar system is not a fixed point in the galaxy. Some researchers feel that the Sun had some close encounters with other solar systems during its 4.6 billion years of existence. The distance that a bacteria hosting extraterrestrial asteroid could have been even smaller than 4.4 light years. Some scientists feel that the Sun may have had a close encounter with another star 4 billion years ago - a very close encounter: the other star may have come as close as 14 to 19 billion miles (Neptune is 4.7 billion miles away from the Sun). That is close enough for major gravitational permutations of each solar system - including the possible exchange of an outer planet. That's right - our solar system could have, in its outermost reaches, a planet from another system left behind from this close encounter.

Let us say the other system already had life established on it. The close encounter with our Sun could cause asteroids to be jostled and sent colliding into the system's life-bearing planet, throwing up chunks of the planet into space. One of those chunks could have been captured by our solar system and eventually made it to Earth (just like some Martian "chunks" have made it to Earth, the result of some asteroid impact on the surface of Mars ejecting Martian rocks into space). Or the other system could already have asteroids with dormant unicellular life on them left over from collisions it had within itself before encountering the Sun, and one or more of those asteroids captured by our solar system.

Conclusion

In conclusion, with regards to panspermia, some stellar distances are not too vast for living organisms to be transverse and end up on Earth. Does not mean it has actually happened - the chances are still probably rather small. But the distances are not too vast, at least for stellar distances of 21 light-years or less.


References:


Coghlan, Andy. "'Resurrection Bug' Revived after 120,000 Years." Life. New Scientist. 15 June 2009. Web. 30 July 2009. <http://www.newscientist.com/article/dn17305-resurrection-bug-revived-after-120000-years.html>

"Did Our Sun Capture Alien Worlds? Close Encounter May Explain Some Objects Beyond Neptune." Science News. ScienceDaily. 9 Dec. 2004. Web. 30 July 2009. <http://www.sciencedaily.com/releases/2004/12/041208235835.htm>

Jordan, Heather. "Astrogenesis Discussion Board." Astrobiology - Life in the Universe. Facebook. 26 Mar. 2008. Web. 30 July 2009. <http://www.facebook.com/s.php?init=srp&sf=r&k=200000010&n=-1&q=life%20in%20the%20universe#/topic.php?uid=19809898338&topic=8155>

Johnson, Sarah S., Martin B. Hebsgaardt, Torben R. Christensen, et. al. "Ancient Bacteria Show Evidence of DNA Repair." PNAS. Proceedings of the National Academy of Sciences of the United States of America. 25 July 2007. Web. 30 July 2009. <http://www.pnas.org/content/104/36/14401.full>

"Novel bacterial species found trapped in Greenland's ice." Penn State Live. Penn State University. 3 June 2008. Web. 30 July 2009. <http://live.psu.edu/story/31052>

Orange Dwarf Stars and Life - Common?

Illustration © European Space Organization

Our Dwarf Sun

Did you know that our own sun is in fact a dwarf star? It is a G type, or yellow dwarf. Next come the smaller K types, or orange dwarfs, followed by even smaller M types, or red dwarfs. While we know life has - at least once - arisen in a yellow dwarf system, could life arise on orange or red dwarf system? While the answer may be yest to both, some think that orange dwarfs may actually make the best place to find life.

Types of Dwarf Stars

• Yellow dwarfs (which are actually white to yellow in color), have surface temperatures of 5,000 - 6,000 K. The average size is a little larger than our sun (110% the size of the sun).

• Orange dwarfs (orange to red in color), have surface temperatures of 3,500 - 5,000 K. Their average size is about 90% that of the sun and are 40 % as luminous as the sun

• Red dwarfs (red in color), have surface temperatures below 3,500 K. The average size is about 40% that of the sun and are 4% as luminous as the sun. Red dwarfs are by far the most common star, accounting for over 75% of all the stars in our galaxy.

Habitable Zones

As you can tell, as the size decreases, the temperature decreases as well as the luminosity. The width of the Habitable Zone (HZ), thus, decreases as well and moves closer to the star (see illustration below) . But HZs still exist. And red dwarfs are extremely long lived - up to 10 trillion years - giving life plenty of time to arise. However, there are other considerations that need to be factored in. First, some tectonic activity is needed to help control the amount of C02 as well as for mixing chemicals - life needs to arise on a chemically dynamic planet. However too much tectonic activity can wipe life out. Planets orbiting in a red dwarf's HZ may experience extreme tidal forces. Another problem with red dwarfs is that being so close to the star there can be problems with radiation bursts from the star - red dwarfs tend to be rather cranky stars that frequently flare up, releasing dangerous bursts of radiation. Since the average HZ for a red dwarf is only 0.1 to 0.2 AU away, the HZ for a red dwarf may actually not be very hospitable. By the way, the HZ for yellow dwarfs, like our sun, is 0.8 AU to 2 AUs.

The average HZ for orange dwarfs is 0.3 to 1 AU away. Its HZ is wider, allowing for planets to be further from the star and thus experience less tidal forces. Also, their flare activity is only slightly more than yellow dwarfs. Another consideration is that orange dwarfs are longer lived than our sun - they have almost twice the life span: almost 20 billion years compare to the 10 billion or so years for our sun. Their light and heat output is much more stable than the sun, fluctuating less over its life and thus making more of its long lifespan useful to life. Orange dwarfs may just give life more chance to originate and thrive than yellow dwarfs like our sun. While not as common as red dwarfs (the most common star type), orange dwarfs are 3 - 4 times more common than yellow dwarfs. We definitely should not overlook orange dwarfs when searching for extraterrestrial life.

Illustration of HZs for Dwarf Stars: dM = Red Dwarfs (M class stars), dK = Orange Dwarfs (K class stars), and dG = Yellow Dwarfs (G class stars).

© Living with a Red Dwarf Program

Red Dwarf Support

Red dwarfs do have their supporters: the "Living with a Red Dwarf" Program, established at Villanova University by E. F. Guinan and S. G. Engle. Guinan and Engle, in their presentation at the 8th Pacific Rim Conference on Stellar Astrophysics in 2008, bring up an interesting consideration: the dangerous flares "are strongly dependent on rotation, and thus age, and diminish as the stars lose angular momentum and spin-down over time via magnetic braking" (Guinan 1). What this means is that the intensity and frequency of a red dwarfs solar flares may diminish over time. Since red dwarfs are extremely long lived, that does crack open just a bit further the door of opportunity for life to find a way to arise and thrive.

Phase Locked

One interesting result of a planet orbiting in an orange or red dwarf's HZ is that it will most likely be phased locked because of the tidal forces; like Mercury is to our Sun, or the Moon is to the Earth, the planet's rotational period and orbital period will be the same, resulting in the same side of the planet always facing the star. This can create a small zone along the terminator line (where, on a phase locked planet, day and night perpetually meet) where life may be able to better survive the radiation bursts.

Related Post

For an interesting related post, see the Color of Life post which tackles the question of what color would plants be on planets circling different types of stars.

References:

Guinan, E. F. and S. G. Engle. "'Living with a Red Dwarf' Program." Summary Paper. Living with a Red Dwarf. Villanova University. n.d. Web. 18 June 2009. <http://www.astronomy.villanova.edu/lward/prcsa2008_LWARD_new.pdf>

Shiga, David. "Orange stars are just right for life." Space. New Scientist. 06 May 2009. Web. 18 June 2009. <http://www.newscientist.com/article/dn17084-orange-stars-are-just-right-for-life.html>.

PhD position at Leiden Observatory on extrasolar planets

© Animation Factory

PhD position at Leiden Observatory on extrasolar planets

A 4-year PhD position is available at Leiden Observatory in the field of extrasolar planets. The student will search for and characterise planets transiting cool red dwarf stars. Planet transits have proven to give unique and extraordinary insights into the physical and atmospheric properties of hot, gaseous giant planets. Transits of much smaller, potentially rocky planets (such as the Earth) can be studied towards red dwarf stars. This is possible due to the significantly smaller size of these cool dwarfs compared to stars of solar type. Several planets have recently been discovered around red dwarfs, including a Super-Earth (possibly within the star's habitable zone), and one transiting hot Neptune. Now is the time to specifically target red dwarfs for transits, and utilise the full potential of the transit method. The student will mainly be working on analysis and follow-up of the WFCAM M-dwarf Transit Survey, which has been awarded 200 nights of observing time on the 4m UKIRT telescope to our international team.

For this project we seek excellent and enthusiastic candidates, who are highly interested in observational astronomy. The astronomy department at Leiden is internationally oriented and hosts about 40 graduate students of several nationalities. Further information about the department can be found at www.strw.leidenuniv.nl.

Applicants should contact Dr. Snellen at the address below for further information. Applicants should have, or soon obtain, a masters degree in astronomy or in physics with a strong astronomy component. Complete applications, including curriculum vitae (with a list of courses and grades), two letters of reference, and a letter explaining your interest in the project, should be sent by the 8st of September 2008 to:

Dr. Ignas Snellen,
Sterrewacht Leiden, PO Box 9512, 2300 RA Leiden, The Netherlands
email: snellen@strw.leidenuniv.nl;
tel: +31 71 527 5838;
fax: +31 71 527 5819
http://www.strw.leidenuniv.nl/~snellen

Posted with permission from Dr. Snellen

Christmas on Omicron Persei 8

During this time of year, my thoughts turn philosophically, sentimentally deeper toward several things: family, the past, spirituality and, of course, life on other planets.

For family, this time of year means additional sentimental thoughts partly because, for the Northern hemisphere, the weather is growing colder, and the nights darker and longer, and so our hearts instinctively look to shorten the distances between loved ones to increase warmth, security, and hope.

For the past, at this time of year, with the New Year approaching, it is a time that we begin to realize that another year has gone, and we begin to look back and take stock of what has happened - sometimes with happiness, sometimes with new knowledge realized, sometimes with anger, sometimes with regret, and sometimes with sadness. If used right, it is a time of extra growth.

For spirituality, this season has strong, and many times somewhat similar, religious meanings for many of the world's theologies. This is in large part because, again for the Northern hemisphere, the Winter solstice brings not only the longest night of the year, but the knowledge that the days will now begin to lengthen again - the Sun returns, and with it renewed warmth and energy filled life. It is the promise of Spring. It is the promise of rebirth, renewal, and resurrection that we rejoice in and are thankful for. It is the promise of death conquered. And connected with looking back to the year that was, and looking close to loved ones, it is a time of year to be thankful yet again for the blessings that loved ones, that love, brings (though for those struggling with a bad year, with abandonment, it can be a very dark time of year indeed).

Of course, too often all of this is ruined by crass commercialism, by the pressures and stresses of false and shallow meanings that have been attached to the season. But that is a topic for other blogs.

For life on other planets, I wonder how they would treat a solstice on their planet? To be high level sentient does one have to be a pattern seeker, to look for the meaning and/or reasons for the patterns? If so, then such sentient beings would see the pattern of solstice and equinox as even our distant ancestors did (from even before Stonehenge) and work to apply a meaning or reason to the pattern (for to find meaning or reason is to find purpose and to be able to make predictions, and maybe even gain some control over - or at least the illusion/delusion of some control).

This, of course, depends on many factors which would affect the severity, or the placidness, of annual weather patterns. Is the planet in a very circular orbit, or a somewhat elliptical one? Is the planet close to its star, and thus with a very short year? Is the planet actually a large habitable moon circling a gas giant? Is there a virtually non-existent tilt to its axis or it is a large tilt? And what of these combined?

If, for instance, the planet is in a very circular orbit, at a close orbit (a red dwarf, for instance, would have a habitable zone much closer to it than a normal G-type star like our own Sun), and with virtually no tilt to its axis, such a planet may have very little differences between its seasons - and seasons that come and go quickly (smaller orbit means, usually, a shorter year). If a longest night is very quickly followed by a longest day (weeks later, i.e.), would there be as much imperative to celebrate the return of the sun's dominance in the sky?

For a planet-moon circling a gas giant, the sun could disappear for days at a time before returning to a "regular" schedule.

Or if the planet-moon is phase locked with its parent gas giant planet, then for the time it is behind the planet there would be, for the far side of the planet-moon there would be constant darkness until the planet-moon came out from behind the gas giant; but then the sun would rise and stay in the sky as it slowly arcs to the opposite horizon as the planet-moon orbits in front of the gas giant. On such a world, a short winter may cover the entire globe while in the shadow of the gas giant, and summer cover the entire globe while in front of the gas giant with extremely short springs and fall at the point the planet-moon is over the terminator line of the gas giant (the line where day and night on the gas giant meet, where one begins and the other ends). Maybe the world's sentient race would view their world as more of a unity than we view our own as on Earth the Northern and Southern hemispheres experience direct opposite seasons at the same time, while on this hypothetical world, both hemispheres experience the same season at the same time.

Anyway, back to the long day and long night, a primitive sentient mind may see that as a mighty heroic epic struggle between day and night. Though if a non-aggressive sentient species, say a slow moving herbivore species on a cool planet, maybe the day and night would represent a sort of "wheel of fortune" - first good luck (sun, warmth, plants taking full advantage) and then bad luck (days long darkness, worsening cold, plants folding up waiting for the sun)?

Additionally, there would be no solstice like we have - there would be no gradual shortening of the night - just one long night, and then one long day, each individual night as long as the night before, separated by an equally long day. Essentially, they would be in eternal equinox. Spring would be morning, summer would be the day, fall would be the evening, and winter would be the night - if you wanted to give them seasons. It may be more accurate to say such a world would have no real seasons at all, only the kind of "seasons" any day-night cycle would have.

If, instead, the planet-moon did have a noticeable tilt to its axis, and a non-circular orbit around its parent gas giant planet, which itself had a non-circular orbit around the central sun, or if the parent planet had a noticeable tilt to its axis with the planet-moon orbiting directly over the parent planet's equator, then the planet-moon, while still retaining non-changing lengths to its day and nights, would gain true seasons. The sun would arc over the sky differently through out the parent planet's year - while the planet-moon's year is the time it takes to orbit around the gas giant, the gas giant has its own year as it orbits its sun.

On such a world, a season would not be different parts of the planet-moon's year, but would be seen year to year. A number of years would be Spring, while another number of years would be Summer, and so forth, repeating itself. What a different kind of zodiac such a world would have! In some ways, it would be similar to a Chinese zodiac calendar (the year of the horse, the year of the dog, etc), except each zodiac would cover a span of years. Their zodiac could contain a zodiac within a zodiac within a zodiac.

Solstice on such a world may not represent so much the return of day, since it is possible that the day and nights would not change in length from year to year, but could represent the point where Winter is half over and thus the return of Spring begins. And maybe, just maybe, the celebration would be a whole year (for the planet-moon).

Of course, this is supposing that all higher level sentient beings feel, in an emotive sense, for in some ways spirituality, and especially sentimentality, depends upon emotion more (at least at times) than reason. Is emotion necessary to higher level of sentience? It seems on Earth, at least, the higher the level of sentience, the more emotion the creature seems to have.

But this is a topic for a future blog.

Comments? Feel free to comment on any post in this blog. Please feel free to disagree with me (just do so respectfully please - even if you think I sin in any or all of my opinions, please recall, if you are Christian, Jesus' attitude toward the adulteress: while he was against what she did, he did not condemn her, and turned away those who would stone her).

Happy Holidays to you and yours (and even to Lrrr, Ruler of Omicron Persei 8, and his wife Nd-Nd. And what the heck, to Robot Santa too!*).

* If Lrrr, Nd-Nd, and Robot Santa mean nothing to you, you need to run, not walk, to the TV and catch an episode of Futurama.

Color of Life

Image credit: Caltech/Doug Cummings

Scientists, including biometerologist Nancy Kiang of NASA's Goddard Institute for Space Studies, have been speculating to the color of alien life in response to the type of star, or even atmosphere, of their planet.

Plant like life would probably be fairly common since starlight is a very useful, and fairly constant source of energy for life to take advantage of. On the Earth, for instance, phytoplankton (microbial plants) are extremely abundant and "provide the basis for most of the marine food chain, half the oxygen in our atmosphere and ultimately much of the life on Earth" ("Breakthrough").

Studying plants on Earth, the scientists discovered something: at first plants seem rather inefficient because they reflect light at its highest energy output - green light. The sun light energy that hits the surface of our planet actually peaks in the green band. However, photosynthesis uses particles (photons) of the light rather than just the energy. The photons peak in the red range. This is because red light penetrates through the atmosphere easier than blue light which gets scattered mainly by atmospheric ozone (which is why the sky looks blue, and the sun appears to be red when it is setting - the light from the setting sun has to travel through more atmosphere than the noon time sun, and the only light that makes it through with the least scattering is red).

But even though blue light is scattered somewhat by our atmosphere, enough still reaches the ground that plants can find it useful; while photosynthesis relies on photons, more energetic photons tend to be more efficient - blue photons are far more energetic than red photons. Though there is a limit as to how much energy a plant can take in. For most Earth plants, concentrating on the peak in the red  range is enough.

By the way, while the sun puts out more light energy in the green band, it looks yellow to us on the surface because, as mentioned above, some of the blue is being scattered by the atmosphere. From space, the sun looks white, but that is because of how our eyes work - when flooded by the entire spectrum, especially from a bright source, our eyes will perceive the source to be white, even if it is not fully white.

Image credit: NASA/Caltech/T. Pyle (SSC)

Using this information about photosynthesis, Nancy Kiang and her fellow scientists speculated what color life would prefer in alien environments. F-type stars, for instance, are hot blue stars that give off more blue photons than photons of other colors, and definitely far more than the sun. On a planet circling such a star, any plant like organisms that finds the chemistry of photosynthesis to be as useful as do Earth plants (*), then such plant like organisms may want to concentrate on absorbing blue particles. They would probably reflect red and orange, since those wavelengths are of little use (not efficient to use them).

Around cooler, and dimmer, red M-type stars, the light may be so little that plant life will need all the particles they can get, and thus they would reflect little to no light back (black plants - a goth planet!). Even if the plant life used chlorophyll that absorbed mostly in the infrared range (scientists have discovered two types of chlorophyll on Earth that absorb in the infrared range), such plants may want to absorb as much heat as possible. Or for a planet or habitable moon circling a gas giant far from the central sun, with a thick atmosphere (reflecting even more of the blue wavelength that our atmosphere), plants on such a planet may need to use all available light as well. (Note: Apparently solitary - not binary - red dwarf M-type stars are the most common in our galaxy).

What would this mean for sentient cultures? Just that each section of their spectrum could easily have rather different cultural significances or cultural or theological metaphors. Think of what yellow means to us: warmth, light, day, energy - it is a positive color. Red is connected to blood, and often means life, and from spilled blood, sacrifice or death. Blue is a color of coolness, water, and sky. And of course green is for food, sustenance, fertility, serenity, and life.

Around different stars, these colors could easily take on other meanings. Around a hot blue star, blue may not be a color of coolness. The sky may very well be blue, with a brighter blue spot for the sun - which could be interesting. Think about what if our sky was yellow? Our yellow sun would be this bright part of the yellow sky, a bright spot that moved. Maybe we wouldn't be able to tell exactly the boundaries of the sun and so not, at first, recognize it as a self contained body circling the Earth, but instead just a brightness that moves across the sky. So too, possibly, for some planets circling a blue star.

On a planet with black plants, black could come to represent, to the primitive sentient mind, life. And if black was food, sustenance, fertility, and thus life - then what of the black night sky?

And what of a planet that had both blue water and blue plants? The color blue could take on such a huge significance. Maybe even some of the animal life would have blue pigmentation (to blend in with the vegetation, for instance). However, Ms. Kiang feels that totally blue is the least likely color for plants, since blue light has very high energy photons.

Speaking of red stars, class M stars tend to flare more than sun, and more strongly. This can cause problems for life as the flare floods the planets with strong radiation. However, life is tenacious, "life always finds a way," and not only are there small life forms on Earth that can survive in outer space, but water is a good shield - life forms 9 to 10 meters below the surface would be protected from the flares while still getting enough life giving photons.

* Because of the universality of the laws of physics and chemistry, it is conceivable that there are universal laws of biology, which are based on physics and chemistry. Not all biologies may discover photosynthesis, as there are many chemical and physical variables within those universal laws, variables that may vary enough that some biologies may not "discover" or even need photosynthesis, or may find alternative versions of photosynthesis that are not needed or were not "discovered" by the biology of our planet. However, chlorophyll is a remarkable molecule; it is a very useful source of energy production for life and so seems highly likely to be popular among life in the universe (though again, that does not rule out exceptions).



References [updated]:
Chen, Min, et. al. "A Red-Shifted Chlorophyll." Science Magazine. 19 August 2010. Web. 21 August 2010. <http://www.sciencemag.org/cgi/content/abstract/science.1191127>

Berman, Bob. "Sky Lights." Discover Magazine. 23 Feb. 2007. Web. 22 Nov. 2007. <http://discovermagazine.com/2003/jun/featsky>.

"Breakthrough Method System for Understanding Ocean Plant Life." Earth Observation News. 1 Mar. 2005. Web. 22 Nov. 2007. <http://news.eoportal.org/research/050301_unicalifornia.html>.

"Extraterrestrial Landscaping." Discover. July 2007. 15. Print.

Kiang, Nancy. "La Couleur des Plantes Extraterrestres." Astrobiologie. Pour la Science. June 2009. Web. 30 July 2009. [Article is in French].

Lada, Charles J. "Stellar Multiplicity and the IMF: Most Stars Are Single." The Astrophysical Journal Letters. 640, L63-L66. Print. Also found at <http://www.cfa.harvard.edu/~clada/pubs_html/binaries.html> (as of 22 November 2007) and reprinted in part at <http://www.sciencedaily.com/releases/2006/02/060206233911.htm> (as of 22 November 2007).

Meadows, Vikki. "Colors of Alien Plants." Astrobiology Magazine. 1 Oct. 2007. Web. 22 Nov. 2007. <http://www.astrobio.net/news/article2477.html>.