PLANETRISE: In an artist's conception, rocky moons orbit a gas giant in a distant planetary system.
Image: NASA
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The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
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In the past two decades, the roster of known planets in the galaxy has mushroomed. Astronomers have added to the handful in our own solar system roughly 450 so-called exoplanets orbiting other stars. Most of those planets are more massive than Saturn, which makes them unpromising from a habitability standpoint—such giants tend to be gaseous bodies without a surface to walk on.
But the giant planets in our solar system—Jupiter, Saturn, Neptune and Uranus—all have moons, some with planetlike features such as atmospheres, magnetic fields or active volcanoes. And although the giant planets roam the cold outer regions of our solar system, other planetary systems feature massive planets in closer, more temperate orbits where life-enabling liquid water could persist. If those planets have satellites, as would be expected, they could provide a real-life counterpart to the Endors and Pandoras of science fiction—livable worlds that are not planets but moons.
No one has yet discovered any extrasolar moons, but some researchers think the capacity to detect them—and even analyze them for habitability—may be just over the horizon. "It's going to happen," says astrophysicist Sara Seager of the Massachusetts Institute of Technology. "It's just a matter of time."
Exoplanets in the habitable zone
Already researchers are locating giant planets far enough from the gravitational pull of their host star to potentially harbor stable satellites. In the May 20 issue of The Astrophysical Journal, a group will report locating a Saturn-mass planet in its star's so-called habitable zone—the temperate ring around a star within which orbiting bodies could harbor liquid water. "It's more than likely the planet has moons," says the study's lead author Nader Haghighipour, a planetary astronomer with the Institute for Astronomy and the NASA Astrobiology Institute at the University of Hawaii–Manoa.
But because the newfound planet, HIP 57050 b, is only Saturn-size rather than, say, the size of Jupiter or larger, any moons it may have are probably rather small and not especially planetlike. "All the things that you need to have a habitable world are not likely" to be found on satellites of HIP 57050 b, Haghighipour says.
Although some moons in our own solar system have been flagged as possible havens for extraterrestrial life, none is as plainly habitable as Earth. That is in part because they orbit on the outskirts of the solar system, making surface temperatures colder, and in part because they are too small to maintain sufficient shielding, in the form of robust atmospheres and magnetic fields, to fend off the charged particles of the solar wind.
But in other planetary systems, moons Earth-size or larger are not out of the question, says astronomer Darren Williams of Penn State Erie. Such large moons could form on their own and later be captured by a more massive planet's gravity to become a satellite. He points to a proposed mechanism by which Neptune may have snagged its moon Triton, in the process ejecting a third object that had been in a binary pairing with Triton. "I've scaled that type of event to something up to a terrestrial mass, and what I've been able to show is you can form something as large as the Earth around a Jupiter by losing a secondary object that is as small as Mars," Williams says.
Exomoon diversity
The incredible menagerie of extrasolar planets already discovered is filled with worlds that look nothing like the denizens of our own solar system. Some are several times the mass of Jupiter; some hug their host stars so tightly that a year on those planets—a full orbital revolution around the star—is shorter than a single day on Earth. So it is not unreasonable to think that extrasolar moons will be a diverse group as well, boasting members that would not fit into the limited sample of solar system satellites. "The possibilities are endless," Seager says. "So far, with exoplanets, nature has been more creative than we are."
Astronomers may soon have observations to back up their hypotheses about lunar companions to extrasolar worlds. In March a team of researchers reported the discovery of COROT 9 b, a planet of about the same mass and size of Jupiter that orbits its star, known as COROT 9, at about the distance Mercury circles the sun. (The names come from the French COROT spacecraft, which spotted the planet.) At that distance the host star's gravitational influence should be sufficiently weak that COROT 9 b could retain stably orbiting moons millions of kilometers from the planet.
On June 17, COROT 9 b will pass in front of its host star from the vantage point of Earth, an event known as a transit, and the hunt will be on for satellites encircling the planet. A mostly France-based team has secured discretionary time on the Spitzer Space Telescope to look for rings and moons around COROT 9 b during the transit. "If they get really lucky this [discovery of extrasolar moons] could happen this year," Seager says. Others have calculated that NASA's Kepler spacecraft, which has been in the exoplanet hunt since 2009, should be able to identify the presence of large lunar companions orbiting the planets it locates.
Whatever the outcome of those campaigns, NASA's massive successor to the Hubble Space Telescope should open up the field of exomoons, assuming they are as abundant as theory predicts. The James Webb Space Telescope (JWST), currently scheduled to launch in 2014, may even be able to resolve atmospheric constituents of those moons, according to a recent analysis by astrophysicist Lisa Kaltenegger of Harvard University. And Williams's research shows that under certain conditions exomoons may be far brighter than their host planets in near infrared wavelengths, to which JWST should be exquisitely sensitive.
But if astronomers manage to turn up an extrasolar moon in the coming years, even a habitable one like those of sci-fi lore, some aspects of Pandora will remain firmly fictional. "What's interesting is Avatar is out of date by about seven years," Seager says. Astronomers have looked for the presence of giant planets in the habitable zone of Alpha Centauri, the nearby star system that is home to Pandora in the film, and have not found one. That's not to say that Alpha Centauri doesn't have a habitable world of some kind—it would just have to be a planet like our own, rather than a moon. "If they had called me or someone else in exoplanet astronomy," Seager says, "we would have advised them to just put an Earth there."
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Add CommentIn the field of space observation and avionics, we are still in our infancy and have a long way to go before we reach the stage of getting through grade school. We have discovered 450 "so-called" exoplanets, why are they so-called planets I don't know why, out of billions that are out there, just in our galaxy alone. Now that we can see just a little bit outside our own crib, we think we are all hot sh*t and a pack of know-it-all's. My feeling is that there are similar characteristics between snow flakes and life on other planets. No two planets and life forms are the same, whether formed on planets or moon does not matter. For we evolve in relations to the evolution of the world that came to be, and no two planets are subjected to the same forces that bring matter and life into existence. We will probably never find ET that look like us, unless we look at our selves in the mirror of life. I do believe, like Carol Sagan, that life flourishes around us, and when the time comes when we are mature enough to accept this fact, then we will find other intelligent life out there among the stars.
Reply | Report Abuse | Link to thisI totally agree with you Kristi276... It is absurd to assume that life can only exist according to our own standards and limitations - there is even a clear example on our own planet of life that exists and breathes nitrates and has no need of sunlight or oxygen - they are called extremophiles and inhabit ice in the bottom of the ocean. As for intelligent life it surely exists in a variety of forms and dimensions. I believe the greatest milestone in human history will be the discovery that we are infact apart of a galactic neighbourhood - but a planet very much in the infancy stages of technological and spiritual progression.
Reply | Report Abuse | Link to thisWe have discovered 450 planets outside our solar system and have rendered judgment on the rest of the galaxy and the universe, while looking for ourselves in the looking glass of life. We are children who look at life from the confines of our crib wondering what life is like in another city in a another state. Armored with the wee-bit-of knowledge we go forward into the pits of darkness creating assumptions that will light our way into the ocean of the galaxy and the universe. I saw myself in the mirror of life and feel in love with my reflection, so life has to be just like the reflection for all life has to be just like me; beautiful and the crown of creation. Carol Sagan stated that life abounds all around us, and I do believe that life exist on planets and moons in the galaxy and the universe. That live is like snow flakes were none two are alike, and that we will not find our counterparts that look like us, talk like us, walk like us and do all the things that we do. Isn't it about we gave up our narcissism and stop making assumptions of how life, to look at the universe with an open mind we will find it at the time we are meant to find it; no sooner and no later. With the eyes of a child go I.
Reply | Report Abuse | Link to thisKristi276 and Peaceful, did either of you actually read the article before attacking it in your ungrammatical diatribes? No one is 'absurdly assuming' that life can only exist as we know it, the scientists quoted are using the phrase 'habitable zone' in reference to life like ours, simply because they are speculating about possible 'earthlike' planets to an audience of human beings, not an audience of extremophile bacteria. No serious scientist has 'rendered judgment on the rest of the galaxy and the universe', and no one expects to find aliens who look like us, think like us, or talk like us. They have to start somewhere, however, and so choose to begin with areas which 'might' support an environment similar to what we are used to.
Reply | Report Abuse | Link to thisStop bashing people who are actually doing research, and appreciate the first, stumbling steps of discovery that we are beginning to take. And while you are at it, learn to type.
RKCampbell6 - I have to wonder why there are so many working in this wonderful field of research, investing so much time and money and so many dreams. Any advanced life forms living more than about 200 light years away would not likely have yet detected any intelligent life on this planet. This galaxy is around 100,000 light years across. Our civilization is a few thousand years old. If we can survive the current global warming, how much longer will we last?
Reply | Report Abuse | Link to thisI don't bemoan that this field of research is being pursued, only that it is not the most promising for its actual return on investment. Many other endeavors would be more enlightening than astronomers' race to find the next New World. It is primarily fueled by competitive astronomy and the fantasies of science fiction.
I think it was odd that they are pessimistic about large moons being around the Saturn-sized planet mentioned when Titan has a thicker atmosphere than the Earth. Titan is practically a planet, and it orbits a Saturn-sized planet, so why should other Saturns not have large moons?
Reply | Report Abuse | Link to thisRegarding the possibility of life on moons, I actually was told by one of the top SETI people at UC Berkeley last week that moons have several advantages over planets as far as life developing, the main disadvantage being that they might not be large enough to hold down an atmosphere, but again, Titan has a thick atmosphere, so it's not impossible.
jtdwyer, I think your final sentence sums it up pretty well, the 'race' to find extrasolar planets feels like both competition and 'science fiction'. I don't know of ANY 'return on investment' we will receive from finding an earthlike planet, given that our current space program can't even manage to get back to our own moon, more than forty years after we first went there. (NASA wanted to take 20 years to do it--after it only took us ten the first time.)
Reply | Report Abuse | Link to thisEven so, if I someday read about the discovery of a roughly earth sized planet (or moon), with what appears to be liquid water and an oxygen atmosphere, my jaw will drop straight to the floor in wonder. Won't yours?
RKCampbell6 - Thanks, but I recommend waiting for confirmation before dropping jaw - any initial report is likely! These observations are highly interpretive...
Reply | Report Abuse | Link to thisWHD2 – Here’s a few issues I’d suggest for additional lines of investigations:
Reply | Report Abuse | Link to this--- The three so-called ‘Generations’ of fermions, increasing in mass, are merely an artifact of the increasing velocity of the detecting experimental conditions. While the resulting estimated effective mass does increase, there is no real distinction in their actual rest mass.
--- Mass is not a characteristic property of fundamental particles but an external field of internally directed energy (potential velocity) which produces the strong force as well as the gravitational effect. It is released by extreme velocity achieved by particle colliders, allowing the decomposition of bound particles. As such there is no mass mediating Higgs Boson. The particle selection function attributed to the Higgs Field is a product of energy density in the initial universe, generally producing decreasingly massive particles as the universe expanded.
--- Black holes actually contain no matter. All ingested matter is converted/decomposed into localized gravitational energy (potential velocity - mass) and expelled fundamental particles.
--- While there is no Dark Energy producing the erroneously reported acceleration of universal expansion, space and time are the product of the initial release of residual energy not converted to matter which still permeates all space and time. It provides the velocity produced as it is contracted by the localized potential energy of accreted objects of mass, which is generally known as the gravitational effect.
There are looking in the wrong places for life, see "Reclassifying the term Habitable Zone" here:
Reply | Report Abuse | Link to thishttp://shineinnovations.com/19312.html
"The one ingredient we find in our outer solar system that these worlds are teaming with is organic chemistry where the inner planets other than earth barely have organic chemicals that can be traced on its surface, this is important because all life on earth are carbon base life forms. This lack of organics is partially blamed on the intense radiation coming from the sun, the earth's magnetosphere blocks most of the solar wind while it atmosphere blocks the intense UVs, low energy neutrons, and x-rays......"
rlb2 - Very good point. However, the key here may be that the outer solar system is where remotely detectable organic chemistry occurs on planets' surfaces because the external energy is not too damaging and water is available. Water is crucial as the universal solvent of biochemistry.
Reply | Report Abuse | Link to thisWhile development of life requires water and organic chemistry, it also requires an energy source. In the 'habitable zone' (or is it the forbidden zone?) there is plenty of external energy for perhaps subsurface biochemistry to develop. In the outer planets organic chemistry is able to develop with fewer destructive (or is it creative) energy sources.
A critical factor in the development of complex lifeforms on Earth seems to be the stabilizing influence of our extremely lucky single large moon. That raises the bar a few orders of magnitude!
I don't think the stabilizing moon and other critical factors are included in what-is-name's supposedly predictive equation for determination of the number of planets with intelligent life...
jtdwyer, you hit the nail right on the head, our life here on earth is very dependant on a substantial atmosphere and magnetosphere, a long term equilibrium must occur over billions of years before life can take hold. With that being said the only place they could find organic chemistry within our inner solar system that isn't buried several meters under the surface is on earth, the reason for this is the high amount of organic splitting UV's our sun kicks out. To be on the inner solar system of local star systems is more of a killer of life than an advantage for it to live long and prosper. However with that being said as mentioned in the paper linked above our outer solar system is teaming with all the necessary ingredients for life to take hold yet it is very cold there.
Reply | Report Abuse | Link to thisUnder the insulating icy surface of Europa and Enceladus that are being mostly heated by tidal forces, lays an ocean of stored water. On earth we find life: on the surface which only recent times in our geological history -- 700 million years life has thrived, in the ocean where life has lived for over 3.5 billion years or under the surface or in the murky soil below the oceans. Finding life in two out of three places such that may exist on Europa and Enceladus isnt bad odds since that is where life first took hold on earth.
A recent finding:
Odd Chemical Found Common in Our Galaxy
A peculiar chemical compound has been found to be ubiquitous in interstellar gas clouds throughout our Milky Way galaxy and may give scientists a better way to track hydrogen across the universe.
This is because hydrogen fluoride molecules can be found in interstellar gas clouds of all sizes, and not just the largest ones. Hydrogen fluoride can sometimes be found on Earth too as a pale yellow gas attached to ash belched by erupting volcanoes, according to the United States Geological Survey.
http://www.space.com/scienceastronomy/odd-chemical-interstellar-clouds-100511.html
Although they explain it a different way on how fluorine and hydrogen gets together in the cold reaches of space, I dont think it is that simple. I think it is due to the tidal heating of cold worlds in interstellar and intergalactic space that create the volcanic gaseous hydrogen fluoride like what IO, a Jovian moon, the most volcanic world in our solar system -- is spewing out around Jupiter and its moons.
This new finding is perplexing the scientific pundits but to me it provides the smoking gun to help prove that our version of a habitable zone should be revised.
rlb2 - I think you may be right about the cold conditions of the outer Solar system favoring the development of organic chemistry, aided by tidal heating.
Reply | Report Abuse | Link to thisI think similar conditions could have occurred, varying at depth under the surface on Earth, especially once the fluid water became available. The presence of water is crucial: it is certainly more abundant now in the outer Solar system, and may have been widely available in the inner Solar system only for a short period as the Sun heated it up. The 'source' of Earth's water (apparently available very early after the moon forming impact) is still uncertain.
Importantly, Earth's unusually persistent magnetic field likely also results from the moon forming impact, as Earth retained most of the combined, reheated iron cores. Earth's iron core may therefore be proportionately unusually large and hot, at least for now.
While the outer planets may favor the production of organic compounds, I suspect the Earth's borderline dangerous, sometimes destructive Solar EM energy is necessary as the final catalyst to produce biochemical processes and mutation dependent evolutionary development from organic compounds. The process is surely delicately balanced... Very interesting - thanks for the info!
In physics of advanced civilization, the Russian astrophysicist Nikolai Kardashev has conjectured that the stages in the development of civilization in the universe could also be ranked by energy consumption.
Reply | Report Abuse | Link to thisUsing the laws of physics, he grouped the possible civilizations into three types.
Type I civilizations: those that harvest the planetary power, utilizing all the sunlight that strikes their planet, and perhaps harness the power of the volcanoes, manipulate the weather, control earthquakes and build cities on the ocean, and all the planetary power is within their control.
Type II civilizations: those that can utilize the entire power of their sun, making them 10 billion times more powerful than a Type I civilizations, also in a sense making them immortal: nothing known to science, such as ice ages, meteor impacts, or even supernovae, can destroy it, (in case their mother star is about to explode, these beings can move to another star system, or perhaps even move their home planet.)
Type III civilizations: those that can utilize the power of an entire galaxy. They are 10 billion times more powerful than a Type II civilization. They have colonized billions of star systems and can exploit the power of the black hole at the center of their galaxy, and they freely roam the space lanes of the galaxy.
Kardashev also estimated, that we are Type O civilization in transition which is wracked with sectarianism, fundamentalism, and racism that typified its rise, and it is not clear whether these tribal and religious passions will overwhelm the transition.
(Perhaps one reason that we don’t see Type I civilization in the galaxy is because they never made the transition, they self-destructed, and one day as we visit other star systems we may find the remains of civilizations that killed themselves in one way or another.)
Yay, finally an intelligent human being.
Reply | Report Abuse | Link to thisPhysicists and astronomers are still far from finding the ingredients of living matter outside our Earth planet. It seems that some inspired genius must be out there to direct research in astronomy to define what life forms are on other planets outside our solar system. Is living matter the same out in the distant galaxies than what exists on earth?
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