Scientists have discovered over 500 planets outside our own solar system. However, most of these planets are quite unlike the earth, being much larger and much closer to their parent star. At least part of the reason for the difference is due to the ease of detection of larger planets, since they gravitationally disturb their parent star much more than smaller planets. The recent proclamation by astronomer Steven Vogt that "the chances of life on this planet are 100 percent" has the news media buzzing. However, there are some big assumptions that went into this claim, many of which are certainly false.
Stars and planets are given names according to the following convention. A star's name usually includes some numbers identifying it. For example, the parent star of the newly discovered planet is called Gliese 581 or Gliese 581a, with the "a" designating the star. Subsequent stars and/or planets are given the next letter, in order of discovery. For example, in a binary system (a system containing two stars orbiting each other), the second star would be given the letter "b". If the planetary system has only one star, the first planet discovered will be given the designation "b". So, we know from the name, Gliese 581g, that it is the sixth discovered planet around the star Gliese 581a. A table containing the characteristics of each of the planets of the Gliese 581a system are shown below:
|m sin i (M�)||a (AU)||Mean Anomalya (°)||FAPS|
|b||5.36841 (0.00026)||12.45 (0.21)||15.6 (0.3)||0.0406163 (1.3e-6)||276.1 (4.9)||6.8E-306|
|c||12.9191 (0.0058)||3.30 (0.19)||5.6 (0.3)||0.072993 (2.2e-5)||33 (19)||2.3E-33|
|d||66.87 (0.13)||1.91 (0.22)||5.6 (0.6)||0.21847 (2.8e-4)||56 (27)||0.0000025|
|e||3.14867 (0.00039)||1.66 (0.19)||1.7 (0.2)||0.0284533 (2.3e-6)||267 (40)||1.9E-08|
|f||433 (13)||1.30 (0.22)||7.0 (1.2)||0.758 (0.015)||118 (68)||0.000095|
|g||36.562 (0.052)||1.29 (0.19)||3.1 (0.4)||0.14601 (1.4e-4)||271 (48)||0.0000027|
The star itself is rather typical of stars in our galaxy, being a red dwarf, about one third the mass of our star the Sun. The fact that the star is much smaller than our star has some profound implications regarding possible life on the planet. First, the surface temperature of the star is less than a third that of the Sun.2 This means that the habitable (or Goldilocks) zone is much closer to the star. The small mass and lower temperature means that the star is emitting energy primarily in the longer wavelengths (lower energy). This is why the star appears red (mean radiance at 830 nm), instead of yellow, like the Sun (mean radiance at 530 nm). Light emitted primarily at the red end of the visible spectrum will profoundly affect possible photosynthesis on nearby planets. Photosynthetic pigments of organisms on earth absorb energy in the higher energy wavelengths associated with visible light, that is, violet or blue, and to a lesser extent, red. However, if you try to grow your houseplant in red light it will promptly die.
Although chlorophylls absorb energy down to 700 nm, a dwarf star with mean radiance at 830 nm will find most of its emission unusable by photosynthetic organisms. Is it possible that organisms that evolve around red dwarfs will develop photosynthetic pigments that absorb energy from the red/infrared end of the visible spectrum? Although it is possible, the physics of electromagnetic radiation severely limits the efficiency of such a pigment, since the reduced energy of such light might be insufficient to excite electrons to a higher energy state (during the light reaction phase of photosynthesis). In addition to the photosynthesis problem, red dwarfs suffer from frequent solar flares, which would periodically dowse the planet with high levels of radiation.
By solar standards, Gliese 581a is relatively "metal-poor." In astronomical terms, "metal" does not necessarily refer to things like iron, but to any elements heavier than helium. Initially, during the beginning of the Big Bang, only hydrogen was formed. However, there was a period of time (about three minutes) in which the temperature of the universe was high enough to support nuclear fusion. It was during this time that hydrogen was fused to form helium, which made up about 25% of the universe. The heavier elements that make up rocky planets were formed in the cores of generations of stars preceding the current generation. Large stars use their fuel quickly and end catastrophically as a supernovae. The metals produced by these stars are then incorporated into the next generation of planetary systems. Since Gliese 581a is metal-poor compared with the Sun, it is surprising it has at least 5 rocky planets. However, because of its metallicity, it is likely that those planets are less dense than their solar system equivalents.
Planet Gliese 581g
Although declared to be "earth-like," Gliese 581g is actually at least 3 times more massive than earth. This increased mass likely impacts the atmospheric content of the planet. Planets must be of a certain mass in order to retain an atmosphere. For example, Mars has only 10% the mass of the earth. Extensive evidence indicates that it once had a thicker atmosphere and large bodies of water on its surface. However, because of its reduced gravity, it lost nearly all of that atmosphere and water. The earth originally had a much denser atmosphere that was mostly blasted into space during the collision that formed the Moon. Had it not been for this fortuitous collision, the earth would have had an atmosphere similar to Venus (81% the mass of the earth), which has an atmosphere 80 times denser than earth. One of the assumptions of the paper that reports the discovery of Gliese 581g is that the atmosphere is similar to earth's. This assumption is almost certainly wrong, unless the planet experienced a large collision event, similar to earth's, early in its history. With at least 3 times the mass of earth, the planet would likely have an atmosphere much denser than Venus, making life there extremely unlikely. The problem with such a dense atmosphere is the large greenhouse effect, which would raise temperatures dramatically. The fact that Gliese 581a emits light mostly in the red/infrared end of the spectrum would compound the heating effect.
Because Gliese 581g orbits close to its star (0.15 AU) and the system is at least 7 billion years old, the planet is tidally locked with its star. This means that the planet rotates once every 37 days, the same period over which it revolves around its star. So, one side of Gliese 581g is perpetually in starlight and the other in perpetual darkness. This fact results in severe conditions over the majority of the planet's surface. Assuming an atmosphere similar to earth's, the sunlit side has an average temperature of 160°F, while the dark side has an average temperature of -25°F. Only a small strip of the planet, near the edges between sunlight and darkness would exist at a reasonable temperature for life to exist. However, in these twilight areas, the amount of solar irradiance would be very low, compounding the mean radiance wavelength problem, making photosynthesis all but impossible. The location of the twilight areas of Gliese 581g will not remain stable over time, since all planets tend to wobble around their axis of rotation, causing these "life zones" to migrate over time.
Does Gliese 581g really exist?
Another astronomy team at Geneva Observatory attempted to plug their data on Gliese 581 into computer models and did not see the planet at all, over the random noise seen in the data:
"Simulations on the real data have shown that the probability that such a signal is just produced 'by chance' out of the noise is not negligible, of the order of several percents. Under these conditions we cannot confirm the presence of the announced planet Gliese 581 g."3
The newly discovered planet Gliese 581g has been advertised as being within the "Goldilocks" zone around its star, leading to the claim, "the chances of life on this planet are 100 percent." The reality of the discovery is that the star is a red dwarf, being much dimmer than our Sun. The nearness of the planet to its star insures that the planet is tidally locked with temperatures on the sunny side being 160°F, while the average temperature on the dark side being -25°F. Only small portions of the planet in the twilight zones are at temperatures conducive to the existence of life. However, the emission spectrum of the star averages in the infrared wavelengths, making photosynthesis problematic. The higher mass of the planet virtually guarantees that its atmospheric pressure is quite high, likely resulting in a runaway greenhouse effect. Rather than being a prime candidate for life, Gliese 581g is likely a hot, sterile world devoid of water. Further investigation of the planet is likely, including possible atmospheric spectra, which will reveal the truth about Gliese 581g, if such a planet really exists at all. One must ask whether the odds of life would remain at 100% if the planet is really just noise in the data. Stay tuned, but don't get in your rocket ship to go for a visit!
- Kepler 22b: Why it is Almost Certainly NOT Habitable
- The Incredible Design of the Earth and Our Solar System
- Moons Like Earth's Moon are Rare in the Universe
- God of the Gaps - Do All Christian Apologetics Fall Into This Kind of Argument?
Rare Earth: Why Complex Life is Uncommon in the Universe by Peter D. Ward and Donald Brownlee
A secular book that recognizes the improbable design of the earth. Paleontologist Peter D. Ward and astrobiologist Donald Brownlee examine the unusual characteristics of our galaxy, solar system, star, and Earth and conclude that ET may have no home to go to. Surprisingly, the authors conclude that the amazing "coincidences" are the result of good luck and chance.
A classic book for modern Christian apologetics and science, recently updated with fully one third of the book updated. Dr. Ross presents the latest scientific evidence for intelligent design of our world and an easy to understand introduction to modern cosmology. This is a great book to give agnostics, who have an interest in cosmology and astronomy.
- Vogt, S. S., R. P. Butler, E. J. Rivera, N. Haghighipour, G. W. Henry, and M. H. Williamson. 2010. The Lick-Carnegie Exoplanet Survey: A 3.1M Planet in the Habitable Zone of the Nearby M3V Star Gliese 581. Submitted for publication.
- Gliese 581, Wikipedia.
- Leslie Mullen. 2010. Doubt cast on existence of possibly habitable alien planet, Astrobiology Magazine.
Today's New Reason to Believe
Integrating Science and Faith
- 04/23/2015 02:14 AM
The Proton-Neutron Mass Difference Illustrates Fine-Tuning
Our daily lives depend on neutrons, protons, and electrons. These building blocks of atoms determine how those atoms behave, how long they last, and so many other things. Although protons and neutrons both exceed the mass of electrons by almost a factor of 2,000, the relatively tiny difference in mass between protons and neutrons plays … Continue reading
- 04/20/2015 02:55 AM
Has the Big Bang Gone Bust?
Did the universe begin to exist or has it always existed? RTB argues that strong biblical and scientific evidence point to a beginning. We would say the Bible claims that the universe began to exist and that science can address the assertion. This notion of a beginning represents a significant, testable claim of Christianity, and … Continue reading
- 04/16/2015 02:05 AM
The Human Hand in Creating Superbugs
Superbugs are frightening and the latest news on this medical front isn’t good. Investigators from the Washington University School of Medicine in St. Louis discovered that two genes (dubbed NDM-1 and KPC) that confer resistance to carbapenems—one of the most powerful classes of antibiotics—readily transfer among Escherichia coli, Klebsiella pneumonia, and other members of the … Continue reading
- 04/13/2015 02:30 AM
Darwin’s Problem: The Origin of Language
Language can bind us together and language can separate us. One of the most frustrating things I encountered on a speaking tour in Lima, Peru, last spring was struggling to communicate with my Peruvian audience and hosts, many of whom spoke only Spanish. Whether we speak the same language or not, all human beings possess … Continue reading
- 04/09/2015 02:55 AM
Q&A: Is the Methuselah Star Older Than the Universe?
John from Tennessee I was curious about what effect, if any, an anomaly like HD 140283, commonly know as the Methuselah star, would have on your model. If it were found to be actually 14.5 billion years old, as opposed to falling in the 800-million-year margin for error, what would this mean and could it … Continue reading
- 04/06/2015 02:09 AM
Q&A: Did God Make Time Stand Still for Joshua?
Kristine from Rogers, MN In Joshua 10, Joshua prayed for the Sun to stand still and God answered his prayer and the Sun stopped in the middle of the sky and delayed going down for about a full day. In Isaiah 38, the Lord provided a sign to Hezekiah that he would live longer by … Continue reading
- 03/30/2015 02:07 AM
Soft Tissue in Mollusk Fossils and the Case for a Young Earth
When it comes to science-faith discussions, the age of the earth is one of the most contentious topics among evangelicals and conservative Christians. Most of the scientific debate surrounding this issue centers on astronomy and geology, but young-earth creationists have recently turned to biology to make their case for a young earth. One prominent argument … Continue reading
- 03/26/2015 02:24 AM
How We Keep Our Eyes on Target
They say it’s harder to hit a moving target. The difficulty increases even more if the weapons platform is moving, too. Consider the tank chase scene in Indiana Jones and the Last Crusade. Indy manages to avoid the guns on a lumbering tank by never staying put. Unless on very flat and horizontal terrain, World … Continue reading
- 03/23/2015 02:42 AM
Does Science Make the Case for God, or Not? (Part 1 of 2)
Does science make the case for God, or not? It depends on whom you ask. Author and TV host Eric Metaxas argued the affirmative position in a recent (December 2014) Wall Street Journal piece.1 A month later in response to Metaxas’ article, the New Yorker published an opposite position2 from theoretical physicist Lawrence Krauss. Rather … Continue reading
- 03/19/2015 02:40 AM
Blood Moons: An End-Times Sign? (Part 2 of 2)
Popular Bible preacher John Hagee has authored a book and produced a movie by the same name, Four Blood Moons (in theatres March 23 only). On the film’s website the San Antonio megachurch pastor states, “The heavens are ‘God’s billboard.’ He’s been sending signals to earth, and we haven’t been picking them up.” In part … Continue reading
Last updated October 13, 2010