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Looking for planets in all the wrong places?

red dwarf/NASA

In the ongoing search for life-friendly exoplanets, an interesting observation from the Tokyo Institute of Technology and Tsinghua University, from Nanowerk:

Simulations by researchers at Tokyo Institute of Technology and Tsinghua University indicate that Earth-like planets are more likely to be found orbiting Sun-like stars rather than lower-mass stars that are currently targeted, in terms of water contents of planets.

The search for habitable planets currently focuses on so-called M dwarfs – stars with less than half the mass of the Sun. These stars are thought to have more habitable orbiting planets that are easier to find compared with G dwarfs – stars that have a similar mass to the Sun. However, according to recent simulations by a collaborative research team composed of Shigeru Ida at Tokyo Tech and Feng Tian at Tsinghua University, M dwarf systems may not be the best places to look.

For planets to be habitable, they must orbit stars within the ‘habitable zone’ where it is not too hot or too cold. In addition, recent studies on habitability of planets suggest that the water-land ratio must be similar to the Earth. That is, the water mass fraction should not be far from that of the Earth’s (~0.01wt%): planets with too much water (> 1 wt%)—“ocean planets”—lead to an unstable climate and lack of nutrient supply; and water-poor planets like Venus “dune planets”—become too arid for inhabiting.

Ida and Tian simulated planet distributions around stars with 0.3, 0.5 and 1.0 times the mass of the Sun. They then applied a model for water loss and accounted for the change in luminosity. They found that Earth-mass planets with Earth-like water contents occur 10–100 times less frequently around M dwarfs than around G dwarfs. They conclude, “We suggest that stars close to the size of the Sun should be the primary targets for detecting Earth-like planets.”

Here’s the abstract of the Nature Geoscience paper:

Efforts to identify habitable extrasolar planets have focused on systems around M dwarfs, faint stars with less than half the solar mass. Habitable planets around M dwarfs are thought to be more plentiful and easier to detect than those orbiting Sun-like G dwarfs1, 2, 3, 4. However, unlike G dwarfs, M dwarfs experience a prolonged decline in luminosity early in their history, leading to an inward migration of the habitable zone to where planets may have lost their water through dissociation and hydrodynamic escape. Water-poor planets, such as Venus, are considered uninhabitable. In contrast, planets with too much water (>1 wt%) would lack continents5, leading to climate instability6 and nutrient limitation problems7. Here we combine a numerical planet population synthesis model with a model for water loss to show that the evolution of stellar luminosity leads to two types of planets of Earth-like mass (0.1 to 10 Earth masses) in the habitable zones around M dwarfs: ocean planets without continents, and desert planets, on which there are orders of magnitude less surface water than on Earth. According to our simulations, Earth-mass planets with Earth-like water contents are rare around M dwarfs and occur 10–100 times less frequently than around G dwarfs. We suggest that stars close to the size of the Sun should be the primary targets for detecting Earth-like planets. (paywall)

See also: Don’t let Mars fool you. Those exoplanets teem with life!


How do we grapple with the idea that ET might not be out there?

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A few related notes:
A Renewed Concern: Flares and Astrobiology - January 2011 Excerpt: “Such powerful flares bode ill for any possible biology, life, on any planet that happens to be close to that flaring star. It’s extraordinary to think that the most numerous stars, the smallest ones in our galaxy, pose this threat to life.” http://www.centauri-dreams.org/?p=16327 New Conditions for Life On Other Planets: Tidal Effects Change 'Habitable Zone' Concept - February 2011 Excerpt: Tides can render the so-called "habitable zone" around low-mass stars uninhabitable. This is the main result of a recently published study by a team of astronomers led by René Heller of the Astrophysical Institute Potsdam (AIP).,,, Finally, tides can cause the rotational period of the planet (the planet's "day") to synchronize with the orbital period (the planet's "year"). This situation is identical to the Earth-moon setup: the moon only shows Earth one face, the other side being known as "the dark side of the moon." As a result one half of the exoplanet receives extreme radiation from the star while the other half freezes in eternal darkness. http://www.sciencedaily.com/releases/2011/02/110224091735.htm Overlooked factor suggests fewer habitable planets than thought - Richard A. Lovett - 08 May 2012 Excerpt: There's just one problem with finding habitable planets around such stars (red dwarfs), says Barnes. Because tidal forces vary dramatically with the distance between a planet and its star, closer orbits also result in massively larger tidal forces.,,, A similar tidal process makes Jupiter's moon Io the most volcanic body in the Solar System. "I’m just scaling that Io–Jupiter system up by a factor of 1,000 in mass," Barnes said at the meeting. "It's the same process, on steroids." http://www.nature.com/news/tidal-heating-shrinks-the-goldilocks-zone-1.10601 Notwithstanding What Bill Nye Says, the Sun Is Not an "Unremarkable" Star - Daniel Bakken - December 1, 2014 Excerpt: Another requirement for habitable planets is a strong magnetic field to prevent their atmosphere from being lost to the solar winds. Planets orbiting a red dwarf star are also more affected by the star's tidal effects, slowing the planet's rotation rate. It is thought that strong magnetic fields are generated in part by the planet's rotation.15 If the planet is tidally braked, then any potential for a significant magnetic field is likely to be seriously degraded. This will lead to loss of water and other gases from the planet's atmosphere to the stellar winds.16 We see this in our solar system, where both Mercury and Venus, which orbit closer to the Sun than Earth, have very slow rotation rates, and very modest magnetic fields. Mercury has very little water, and surprisingly, neither does Venus. Even though Venus has a very dense atmosphere, it is very dry. This is due to UV radiation splitting the water molecules when they get high in the atmosphere, and then the hydrogen is lost to space, primarily, again, by solar wind.17,,, etc.. http://www.evolutionnews.org/2014/12/notwithstanding091571.html also of note: Of Gaps, Fine-Tuning and Newton’s Solar System - Cornelius Hunter - July 2011 Excerpt: The new results indicate that the solar system could become unstable if diminutive Mercury, the inner most planet, enters into a dance with Jupiter, the fifth planet from the Sun and the largest of all. The resulting upheaval could leave several planets in rubble, including our own. Using Newton’s model of gravity, the chances of such a catastrophe were estimated to be greater than 50/50 over the next 5 billion years. But interestingly, accounting for Albert Einstein’s minor adjustments (according to his theory of relativity), reduces the chances to just 1%. http://darwins-god.blogspot.com/2011/07/of-gaps-fine-tuning-and-newtons-solar.html Milankovitch Cycle Design - Hugh Ross - August 2011 Excerpt: In all three cases, Waltham proved that the actual Earth/Moon/solar system manifests unusually low Milankovitch levels and frequencies compared to similar alternative systems. ,,, Waltham concluded, “It therefore appears that there has been anthropic selection for slow Milankovitch cycles.” That is, it appears Earth was purposely designed with slow, low-level Milankovitch cycles so as to allow humans to exist and thrive. per reasons org Astrobiology research is revealing the high specificity and interdependence of the local parameters required for a habitable environment. These two features of the universe make it unlikely that environments significantly different from ours will be as habitable. At the same time, physicists and cosmologists have discovered that a change in a global parameter can have multiple local effects. Therefore, the high specificity and interdependence of local tuning and the multiple effects of global tuning together make it unlikely that our tiny island of habitability is part of an archipelago. Our universe is a small target indeed. Astronomer Guillermo Gonzalez - P. 625, The Nature of Nature Does the Probability for ETI = 1? Excerpt; On the Reasons To Believe website we document that the probability a randomly selected planet would possess all the characteristics intelligent life requires is less than 10^-304. A recent update that will be published with my next book, Hidden Purposes: Why the Universe Is the Way It Is, puts that probability at 10^-1054. http://www.reasons.org/does-probability-eti-1 Eric Metaxas - Does Science Argue for or against God? – (2015) video https://www.youtube.com/watch?v=UjGPHF5A6Po Hugh Ross - Multiple Parameters Required For Earth To Support Life - video https://vimeo.com/118304005
I find it strange that the SETI (Search for Extra-Terrestrial Intelligence) organization spends millions of dollars vainly searching for signs of extra-terrestrial life in this universe, when all anyone has to do to make solid contact with THE primary 'extra-terrestrial intelligence' of the entire universe is to pray with a sincere heart. God certainly does not hide from those who sincerely seek Him. Actually communicating with the Creator of the universe is certainly a lot more exciting than not communicating with some little green men that in all realistic probability do not even exist, unless of course, God decided to create them!
Isaiah 45:18-19 For thus says the Lord, who created the heavens, who is God, who formed the earth and made it, who established it, who did not create it in vain, who formed it to be inhabited: “I am the Lord, and there is no other. I have not spoken in secret, in a dark place of the earth; I did not say to the seed of Jacob, ‘seek me in vain’; I, the Lord speak righteousness, I declare things that are right.” JOHNNY LEE ~ LOOKING FOR LOVE [LYRICS] https://www.youtube.com/watch?v=FAyDmJvjxbg
February 18, 2015
06:40 AM

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