Would Life Form Differently Around Cool Stars?
Written by Nancy Atkinson
This artist's conception shows a young, hypothetical planet around a cool star. Credit: JPL
"Life as we know it" seems to be the common caveat in our search for other living things in the Universe. But there's also the possibility of life "as we don't know it." A new study from NASA's Spitzer Space Telescope hints that planets around stars cooler than our sun might possess a different mix of potentially life-forming, or "prebiotic," chemicals. While life on Earth is thought to have arisen from a hot soup of different chemicals, would the same life-generating mix come together around other stars with different temperatures? (And should we call it 'The Gazpacho Effect?') "Prebiotic chemistry may unfold differently on planets around cool stars," said Ilaria Pascucci, lead author of the new study.
Pascussi and her team used Spitzer to examine the planet-forming disks around 17 cool and 44 sun-like stars. The stars are all about one to three million years old, an age when planets are thought to be forming. The astronomers specifically looked for ratios of hydrogen cyanide to a baseline molecule, acetylene. Using Spitzer's infrared spectrograph, an instrument that breaks light apart to reveal the signatures of chemicals, the researchers looked for a prebiotic chemical, called hydrogen cyanide, in the planet-forming material swirling around the stars. Hydrogen cyanide is a component of adenine, which is a basic element of DNA. DNA can be found in every living organism on Earth.
The researchers detected hydrogen cyanide molecules in disks circling 30 percent of the yellow stars like our sun — but found none around cooler and smaller stars, such as the reddish-colored "M-dwarfs" and "brown dwarfs" common throughout the universe.
Cool Stars May Have Different Prebiotic Chemical Mix
The team did detect their baseline molecule, acetylene, around the cool stars, demonstrating that the experiment worked. This is the first time that any kind of molecule has been spotted in the disks around cool stars.
"Perhaps ultraviolet light, which is much stronger around the sun-like stars, may drive a higher production of the hydrogen cyanide," said Pascucci.
Young stars are born inside cocoons of dust and gas, which eventually flatten to disks. Dust and gas in the disks provide the raw material from which planets form. Scientists think the molecules making up the primordial ooze of life on Earth might have formed in such a disk. Prebiotic molecules, such as adenine, are thought to have rained down to our young planet via meteorites that crashed on the surface.
"It is plausible that life on Earth was kick-started by a rich supply of molecules delivered from space," said Pascucci.
The findings have implications for planets that have recently been discovered around M-dwarf stars. Some of these planets are thought to be large versions of Earth, the so-called super Earths, but so far none of them are believed to orbit in the habitable zone, where water would be liquid. If such a planet is discovered, could it sustain life?
Astronomers aren't sure. M-dwarfs have extreme magnetic outbursts that could be disruptive to developing life. But, with the new Spitzer results, they have another piece of data to consider: these planets might be deficient in hydrogen cyanide, a molecule thought to have eventually become a part of us.
Said Douglas Hudgins, the Spitzer program scientist at NASA Headquarters, Washington, "Although scientists have long been aware that the tumultuous nature of many cool stars might present a significant challenge for the development of life, this result begs an even more fundamental question: Do cool star systems even contain the necessary ingredients for the formation of life? If the answer is no then questions about life around cool stars become moot."
Or, could life form differently around cooler stars from anything we know?
Source: JPL
Filed under: Astrobiology, Spitzer
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April 7th, 2009 at 1:53 pm
There are an estimated 70 Sextillion (70,000,000,000,000,000,000,000) stars in the visible universe.
We haven't even begun to understand life or the universe.
"Life as we know it" is analogous to "differential calculus as a newborn baby knows it."
April 7th, 2009 at 1:56 pm
Wow… this is an important result.
It's surprising, though. HCN can be photodissociated by light, so I would have thought there'd be more of it, not less, in the disk of cool stars.
There still might be sources of HCN from comets that are exposed for long periods of time in interstellar space. But it would take a long time for enough HCN to accumulate on a planet orbiting a cool star to have much effect on biochemistry, I'd guess.
Great article, Nancy!
April 7th, 2009 at 2:25 pm
What I find truly amazing is that scientists have not been able to accidentally or purposely create life from all of the various chemicals and elements here on earth. And it is not that they have not tried.
This says to me that at least in our environment, life has a difficult time becoming whatever it has become- And yet you look around us and there is life everywhere. I wonder if we will ever know where the carbon based life originated that permeates the Earth’s ecosystems.
April 7th, 2009 at 2:36 pm
Layman, the conditions on Earth 4 billion years ago were way different than they are now. And it took nature a long time to get life going, then it took even longer to turn it into something bigger than a single cell.
We've had scientific biology for what, a couple centuries at best? People really need to appreciate how short a time it has been since we've actual started to truly understand our world as opposed to rough guesses and superstition.
I am amazed we know as much as we do after all these ages of ignorance and fear.
April 7th, 2009 at 2:54 pm
Looking at our famous first poster ( waves to the troll), ignorance and superstition is still alive and well in this day and age.
April 7th, 2009 at 3:05 pm
My answer to the feeds question:
probably
April 7th, 2009 at 3:28 pm
@huygens- I gave some thought to the fact that the conditions were different 4 billion years ago- They were probably not nearly as conducive for life to begin as they are now and that begs the question of why and how did single celled organisms arise on the primitive Earth. It also leads rational minds to speculate that with so many possible planets that life in one form or another should be common throughout the universe.
April 7th, 2009 at 3:59 pm
My answer to the feeds question (2):
Did you guys really think about that only now?
I don´t see why life should be the same as ours in any place in the universe….
I mean, there´s a lot of chemestry that we dont even imagine…
April 7th, 2009 at 4:02 pm
Ok – who coined the phrase "Gazpacho Effect"? Come on – own up now!
April 7th, 2009 at 4:28 pm
if what this article suggests is true, then life might be even MORE rare than previously thought. this doesn't even include the other neccessary factors that we still have not figured out. ex: local interstellar density.
April 7th, 2009 at 5:18 pm
What pantzov (!?) says is true… cool stars make up 80% of the main sequence stellar population. If planets around such stars can't harbor life, the numbers for the Drake equation may need serious revision…
April 7th, 2009 at 6:24 pm
Humans sometimes have such closed minds and limited scope of thought. Just because we are used to seeing life in a certain light, doesn't mean it's going to be that way everywhere, or anywhere for that matter. Here's kind of a fun challenge: try to imagine a living being that doesn't resemble ANY life on Earth whatsoever. Its more difficult than it sounds.
April 7th, 2009 at 6:24 pm
Saying that we have no idea what other life may look like is borderline sophistry. We know a lot about it. It must be composed of elements that are reactive under the prevailing conditions of the planet or body. The resulting mixture must have a way to accumulate and use energy. It must have a method of replicating. It must have a method for eliminating any waste products it produces. Given those criteria, we can make very educated guesses about life. For example, I think we can pretty much rule out basalt based life forms. Given the apparent near ubiquity of amino acids, under conditions similar to ours, we may well encounter life forms based on similar biology. Body shapes is a whole different issue and not all that relevant.
April 7th, 2009 at 6:28 pm
I have published a book "Can Star Systems Be Explored, The physics of starprobes, "World Scientific, which addresses the question of whether we can send something to other stars. The book is in part a way of presenting mechanics and relativity in a different format. The relativistic rocket, photon sail are the main topics of interest, though I also propose electromagnetically propelled nano-bots. It also does make a point that we might consider in the somewhat distant future sending probes to nearby stars to get a close up look at planetary chemistries and whether there might exist life there. We can't ever know until we look at these things under a microscope. And this requires getting robots with enough sophistication to do the exploration there.
Lawrence B. Crowell
April 7th, 2009 at 8:00 pm
Hydrogen cyanide has been detected in interstellar gas clouds which might seed the planets of cool stars, if enough of it can penetrate the solar wind. This might be a lot weaker than ours in this system.
I'm clutching at straws though. But even if red dwarfs are a non-starter, there are still billions of hot, bright stars to do the business. I mean, who'd want to develop some place you can't get a suntan?
April 7th, 2009 at 9:37 pm
We exist as life consciousness in a very small part of a dimensionally bound electrodynamic spectrum. As a result, we are prejudiced to view life from that biased vantage point. Fortunately we are beginning to explore and understand that there are other energy levels and electromotive realms which might potentially contain life. Cryogenic life with superconducting anatomy anyone?
April 7th, 2009 at 11:13 pm
This finding is problematic for the chances of earth like life developing on these exoplanets. Even if HCN is not being produced by catalytic reactions around the star, there is no guarentee that it cannot be produced on the planets themselves if base elements are present. Lightning, tidal heating and volcanism could proivide the necessary energy. Certainly the molecule would be much less abundant and it would be a limiting factor for he development of Earth-like life, but I don't think this finding excludes the possibility. More remote possibilities for life would be life developing using alternative chemistry other than used by Earth life. Also possible would be life developing via seeding from other solar systems, a wonderfully controversial topic to bring up here. If there is no life to be found on these planets then we may in fact some day bring our form of life there via colonization and terraforming. Older M dwarfs are much more stable and not prone to outbursts and have a very long lifespan compared to yellow dwarfs like the sun.
April 8th, 2009 at 12:53 am
Biologists now define life, i.e., living organisms, in a thermodynamic manner. A living being must maintain itself in a certain physical state over an appreciable length of time; must take in nourishment in the form of matter/energy, excrete waste products, defend itself from danger, and, ultimately, at least on a statistical basis, reproduce itself. That says little or nothing about a particular form or chemical makeup, though, There could be life-forms on Titan whose metabolic functions are made possible by means of enzymes that enable them to take place in a timely enough fashion to support life even in that frigid environment; ditto Pluto. There could be plasma-type life-forms on or in stars that have extremely short life-spans. We might never know if we share the universe with such beings if we don't allow for the possibility that they exist. To completely write off the possibility of such unearthly forms of life would be a terrible mistake.
April 8th, 2009 at 4:05 am
I agreewith Yael. After all,ours is the OnLY example of biosphere we know. It's enormously arrogant to suppose that life MUST be like our own.
April 8th, 2009 at 5:51 am
If we are to seek evidence of life elsewhere how do we start?
answer: we assess life as we know it, for what signs of it that could be detected if it were in the places we choose to look.
To extrapolate the existence of 'exotic other' forms of life is nonsense at this stage.
…and let's get it straight, the "Drake equation" is NOT a number! it is merely an algebraic representation of the factors to be considered.. no numbers have been determined yet. Gathering of evidence such as in this article is the process by which the numbers might eventually be determined, at least to a range of likelihood, and not the uninformed wild guessing and fantast some are presently engaged in.
April 8th, 2009 at 6:04 am
I choose to be arrogant
I reckon that life as we know it should exist throughout our galaxy, and other similar galaxies throughout the Universe. I thought long and hard bout it, and spoke to many people about it. I could (and would need to) write many pages to completely present my case in a cohesive manner.
Life as we know it may indeed be limited to stars like our own Sun – even though it isn't THE most common type of star, there are still enough of them….
The Drake Equation, imo, means so little that ruling out 80% of all stars doesn't change the greater picture at all, really.
Life different from what we know may also exist throughout the Universe, even on Earth, but hasn't been defined (yet) – so it cannot be detected, neither on Earth nor elsewhere.
I rest my case.
April 8th, 2009 at 6:29 am
The wild extremes among the hundreds of thousands of life forms that exist here on earth logically suggests that any life form from planets in orbit around cool stars would unspectacularly blend right in with earth's zoo of life.
April 8th, 2009 at 3:32 pm
Life on Earth developed and evolved to meet the particular conditions found here on this planet. And over time life changed some of the conditions found on the Earth.
I doubt that we will ever find another planet the same as the Earth. With that said it would only be reasonable to conclude that where life exists on other planets, it would develop and evolve to meet their set of conditions.
I hope that there are many types of life out there not just life as we know it.
April 8th, 2009 at 4:57 pm
Yael is in part right. Life is a form of nonequilibrium chemistry which is self-replicating and systaining. So the system needs to operate with a continual influx of free energy which keeps it from an equilibrium condtion. It is certainly possible this happens in other guises than carbon organic chemistry, though it is hard to speculate on those. Low temperatures are more likely than high. High temperature situations, such as in stars, have high entropy and probably destroy any self-replicating system which processes information. Information is erased with heat.
Lawrence B. Crowell
April 9th, 2009 at 10:45 am
Of course, life would be way cooler there!