Astronomers find first habitable Earth-like planet?

Astronomers find first habitable Earth-like planet, EurekAlert!, 24-Apr-2007, Henri Boffin, European Southern Observatory (ESO) ...

[Above: Artist's impression of red dwarf star Gliese 581's planetary system, EurekAlert!]

Astronomers have discovered the most Earth-like planet outside our Solar System to date, an exoplanet with a radius only 50% larger than the Earth and capable of having liquid water. Using the ESO 3.6-m telescope, a team of Swiss, French and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbour a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses. This exoplanet - as astronomers call planets around a star other than the Sun - is the smallest ever found up to now [1] and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581 [2], is smaller and colder than the Sun - and thus less luminous -the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid! "We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stéphane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result. "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky - like our Earth - or covered with oceans," he adds. "Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X. The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the constellation Libra ("the Scales").

[Right: Loca­tion of red dwarf star Gliese 581 in the constellation Libra, Bits of News]

It has a mass of only one third the mass of the Sun. Such red dwarfs are intrinsically at least 50 times fainter than the Sun ..." [This presumably is the original misleading press release that most, if not all, the news stories are based on, e.g. ABC, BBC, Bits of News, Christian Science Monitor, CNews, National Post, New Scientist, New York Times, San Francisco Chronicle, SPACE.com 1 & 2, Sydney Morning Herald, The Australian, The Independent & USA Today.

While this is a great technical achievement to detect such a small planet, "5 times the mass of the Earth," at such a vast distance, "20.5 light-years away," the press release (and therefore the articles), omits to mention that:

1) A planet "5 times the mass of the Earth" is not "Earth-like." As mentioned in my posts of 22-Feb-06 & 14-Mar-06, even for "planets only a few times heavier than Earth ... the extra gravity ... would crush these [crustal] minerals into ... semi- conductors or metals" resulting in "enhanced heat flow from the planet's core to the surface, which means more volcanoes and more `planetquakes'" (Vergano, D., "Finding 'Super Earth' is a 'Goldilocks' errand," USA Today, February 19, 2006).

2) A "red dwarf" is "far less luminous than our sun, and any planets orbiting them would have to be very close to stay warm enough to allow the existence of liquid water on the surface":

"It is often said that the sun is a typical star, but this is entirely untrue. The mere fact that 95% of all stars are less massive than the sun makes our planetary system quite rare. Less massive stars are important because they are much more common than more massive ones. For stars less massive than the sun, the habitable zones are located farther inward. The most common stars in our galaxy are classified, as M stars; they have only 10% of the mass of the sun. Such stars are far less luminous than our sun, and any planets orbiting them would have to be very close to stay warm enough to allow the existence of liquid water on the surface. However, there is danger in orbiting too close to any celestial body. As planets get closer to a star (or moons to a planet), the gravitational tidal effects from the star induce synchronous rotation, wherein the planet spins on its axis only once each time it orbits the star. Thus the same side of the planet always faces the star. (Such tidal locking keeps one side of the Moon facing Earth at all times.) This synchronous rotation leads to extreme cold on the dark side of a planet and freezes out the atmosphere. It is possible that with a very thick atmosphere, and with little day/night variation, a planet might escape this fate, but unless their atmospheres are exceedingly rich in CO2, planets close to low-mass stars are not likely to be habitable because of atmospheric freeze-out." (Ward, P.D. & Brownlee, D.C., "Rare Earth: Why Complex Life is Uncommon in the Universe," Copernicus/Springer-Verlag: New York NY, 2000, pp.23-24)

as is the case with this planet Gliese 581c which "is 14 times closer to its star than the Earth is from the Sun." But then "As planets get closer to a star ... the gravitational tidal effects from the star induce synchronous rotation, wherein the planet spins on its axis only once each time it orbits the star. Thus the same side of the planet always faces the star. ... This synchronous rotation leads to extreme cold on the dark side of a planet and freezes out the atmosphere" (my emphasis).

3) "M dwarf stars" which Gliese 581 is, "exhibit flares" which "can increase the relative X-ray radiation by a factor of one hundred to one thousand compared with strong flares on the on the Sun" (my emphasis):

"M dwarf stars pose additional problems for life. Like the Sun, they exhibit flares. Some are stronger than solar flares, and because M dwarf stars are far less luminous, a flare's intensity compared with the star is that much greater. A strong flare on an M dwarf star can increase the relative X-ray radiation by a factor of one hundred to one thousand compared with strong flares on the Sun; the resulting increase in the ultraviolet radiation reaching the planet's surface would also be more intense .Not only would such flares threaten surface life, they would probably strip away a planet's atmosphere more quickly as well. The large starspots associated with flares would cause the star's brightness to vary on longer timescales (by about 10 to 40 percent), mimicking an eccentric planetary orbit. Starspots and flares decline steadily as a star ages. So while the passage of time would mitigate these problems, at any age an M dwarf host star will be a less constant source of energy than a star like the Sun." (Gonzalez, G. & Richards, J.W., "The Privileged Planet: How Our Place in the Cosmos is Designed For Discovery," Regnery: Washington DC, 2004, p.134)

which Wikipedia corroborates the above as among the "several factors which may make life difficult on planets around a red dwarf star":

Red dwarf ... Habitability Planetary (Wikipedia) habitability of red dwarf star systems is subject to some debate. In spite of their great numbers and long lifespans, there are several factors which may make life difficult on planets around a red dwarf star. First, planets in the habitable zone of a red dwarf would be so close to the parent star that they likely would be tidally locked. This would mean that one side would be in perpetual daylight and the other in eternal night. This could create enormous temperature variations from one side of the planet to the other, making it difficult for life to evolve. On the other hand, recent theories propose that either a thick atmosphere or planetary ocean could potentially circulate heat around the planet. Another potential problem is that red dwarfs emit most of their radiation as infrared light, while on earth plants use energy mostly in the visible spectrum. But, perhaps the most serious problem may be stellar variability. Red dwarfs are often covered in starspots, reducing stellar output by as much as 40% for months at a time. At other times, some red dwarfs, called flare stars, can emit gigantic flares, doubling their brightness in minutes. This variability may also make it difficult for life to survive near a red dwarf star.

4) Even if astronomers do eventually detect an exoplanet that appears truly Earth-like, i.e. truly Earth-size, is truly an Earth-like distance from its star; which is a single star that is truly a Sun-like G-main sequence star; in a truly near-circular orbit; in a truly Earth-like solar system; at "20.5 light-years away" (i.e. 20 x 63,240 AU = ~1,264,800 times the distance of the Earth from the Sun) yet being "among the 100 closest stars to us," realistically they are never going to know (see "Interstellar travel ...: Interstellar distances," Wikipedia) if it is really is Earth-like.

That is because, "there is more to finding another Earth than detecting a planet the same size and same distance from its star" since if astronomers discovered Venus at that distance they would hail it as the ultimate Earth-like exoplanet, yet close up "Venus has ... hellish conditions ... where 800-degree [Fahrenheit] winds are lashed by sulfuric acid rain":

"But it may not be so easy, suggests University of Minnesota physicist Renata Wentzcovitch and colleagues in the current Science magazine. ... The larger point is there is more to finding another Earth than detecting a planet the same size and same distance from its star, she says. Venus and Earth are very similar, she notes, but have significant differences in their interior chemistry. Venus has a more viscous interior that lead to a planet-sized earthquake hundreds of millions of years ago, she says, and that likely also explains the hellish conditions there, where 800-degree winds are lashed by sulfuric acid rain." (Vergano D., "Finding 'Super Earth' is a 'Goldilocks' errand," USA Today, February 19, 2006).

Quite frankly if these astronomers know all the above (and if they don't then they would be incompetent- which I assume they are not), then according to the late Nobel laureate physicist Richard Feynman's standards of good science, they are lacking "scientific integrity" and "honesty" in seeking to "fool the layman when ... talking as a scientist," by not giving "all of the information to help others to judge the value of" their "contribution; not just the information that leads to judgment in one particular direction" that they favour:

"But there is one feature I notice that is generally missing in cargo cult science. That is the idea that we all hope you have learned in studying science in school-we never explicitly say what this is, but just hope that you catch on by all the examples of scientific investigation. It is interesting, therefore, to bring it out now and speak of it explicitly. It's a kind of scientific integrity, a principle of scientific thought that corresponds to a kind of utter honesty -a kind of leaning over backwards. For example, if you're doing an experiment, you should report everything that you think might make it invalid-not only what you think is right about it: other causes that could possibly explain your results; and things you thought of that you've eliminated by some other experiment, And how they worked-to make sure the other fellow can tell they have been eliminated. Details that could throw doubt on your interpretation must be given, if you know them. you must do the best you can-if you know anything at all wrong, or possibly wrong-to explain it. If you make a theory, for example, and advertise it, or put it out, then you must also put down all the facts that disagree with it, as well as those that agree with it. ... In summary, the idea is to try to give all of the information to help others to judge the value of your contribution; not just the information that leads to judgment in one particular direction or another .... And it's this type of integrity, this kind of care not to fool yourself, that is missing to a large extent in much of the research in cargo cult science. ... But this long history of learning how to not fool ourselves-of having utter scientific integrity-is, I'm sorry to say, something that we haven't specifically included in any particular course that I know of. We just hope you've caught on by osmosis. The first principle is that you must not fool yourself-and you are the easiest person to fool. So you have to be very careful about that. After you've not fooled yourself, it's easy not to fool other scientists. You just have to be honest in a conventional way after that. I would like to add something that's not essential to the science, but something I kind of believe, which is that you should not fool the layman when you're talking as a scientist. ... I'm talking about a specific, extra type of integrity that is not lying, but bending over backwards to show how you're maybe wrong, that you ought to have when acting as a scientist. And this is our responsibility as scientists, certainly to other scientists, and I think to laymen. One example of the principle is this: If you've made up your mind to test a theory, or you want to explain some idea, you should always decide to publish it whichever way it comes out. If we only publish results of a certain kind, we can make the argument look good. We must publish both kinds of results." (Feynman, R.P., "Cargo Cult Science," in "`Surely You're Joking, Mr Feynman!': Adventures of a Curious Character," [1985], Unwin Paperbacks: London, Reprinted, 1990, pp.341-343).

Stephen E. Jones, BSc. (Biology).

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Exodus 23:25-33. ²⁵Worship the LORD your God, and his blessing will be on your food and water. I will take away sickness from among you, ²⁶and none will miscarry or be barren in your land. I will give you a full life span. ²⁷"I will send my terror ahead of you and throw into confusion every nation you encounter. I will make all your enemies turn their backs and run. ²⁸I will send the hornet ahead of you to drive the Hivites, Canaanites and Hittites out of your way. ²⁹But I will not drive them out in a single year, because the land would become desolate and the wild animals too numerous for you. ³⁰Little by little I will drive them out before you, until you have increased enough to take possession of the land. ³¹"I will establish your borders from the Red Sea to the Sea of the Philistines, and from the desert to the River. I will hand over to you the people who live in the land and you will drive them out before you. ³²Do not make a covenant with them or with their gods. ³³Do not let them live in your land, or they will cause you to sin against me, because the worship of their gods will certainly be a snare to you."