So, overall, the planets of Gl 581 are not prime locations in the search for extraterrestrial life. But M-stars in general might be.
* * * *
Data for the planets of Gl 581 (adapted from Udry et al. 2007)
Mass (in Earth masses) [Gl 581b: 15.6] [Gl 581c: 5.06] [Gl 581d: 8.3]
Distance from primary (in AU) [Gl 581b: 0.041] [Gl 581c: 0.073] [Gl 581d: 0.25]
Orbital period (in days) [Gl 581b: 5.3] [1Gl 581c: 2.9] [Gl 581d: 83.6]
Eccentricity of orbit [Gl 581b: 0.02] [Gl 581c: 0.16] [Gl 581d: 0.2]
Larger values of eccentricity imply that the orbit is more oval-shaped
* * * *
M-stars eternal
Another important issue for habitability is that many M-stars are also flare stars. It has been shown that the typical amount of ultraviolet radiation received during one of these flares by a planet at a habitable distance from an M-star can be temporarily as much as ten times the ultraviolet radiation routinely received by the Earth. This may be a particular issue for the early development of a habitable planet around an M-star. Calculations have shown that large flares from a young M-star could entirely remove the atmosphere of a planet at the close distance required for a planet to be habitable. If the planetary atmosphere survives this trauma, though, the solar radiation output of the star is likely to stay the same for a very long period of time, as M-stars then enter a long period of remarkable stability, with energy output changing little over many billions of years, apart from the occasional flare.
But flares can have positive impacts also. Studies have suggested that the usual reddish light of an M-star may not be energetic enough to support photosynthesis. The flares of M-stars may thus supply some badly needed energetic radiation for any life that occurs on planets around them, enabling periodic growth spurts to occur. This is not a new idea: Larry Niven's short story “Flare Time,” part of the Medea volume, has given us a vivid depiction of such an episode. Of course, this assumes that such life-bearing planets around M-stars have been able to develop a protective ozone layer, or that its organisms have found ways to adapt themselves to higher levels of ultraviolet radiation.
M-stars have another advantage in the search for life in the universe. Because M-stars are small, Earth-sized planets are more easily detected in orbit around them than they would be around a bigger star like the Sun. This is because Earth-sized planets can give larger tugs on small M-stars than on big stars, thus making stellar movements easier to detect. This is the method that has been used to detect most extrasolar planets, but other methods that have been employed to date also work better for planets orbiting M-stars. With current techniques, routine detection of planets as small as two Earth masses is possible around M-stars, and even smaller planets can be found under certain conditions. So the first genuine Earth-size, Earth-type planet might well be discovered orbiting an M-star rather than a Sun-like star.
This means that Ribbonland might be discovered sooner rather than later. In fact, because there are many M-stars, Ribbonland may not only exist, it might be quite common. It might not be basking in an endless Arcadian springtime, but the real Ribbonland, windy, stormy and subject to solar flares, might be more than just a strange anomaly among habitable planets: it might be the rule rather than the exception, and Earth might be the anomaly. And M-stars are long-lived. Long after the Sun has ballooned into a red giant, vaporizing all life on Earth, Ribbonland will still be out there, huddling close its small star, its lifeforms scraping by until the next flare, billions of years after Earth has become a cinder.
Copyright © 2009 Kevin Walsh
* * * *
Acknowledgments: The author would like to thank Simbad (simbad.u-strasbg.fr/ simbad/), the Extrasolar Planet Encyclopedia (exoplanet.eu) and the nice compilation of information about nearby stars contained at www.solstation.com.
* * * *
Further Reading
Joshi, M. (2003) “Climate model studies of synchronously rotating planets.” Astrobiology, 3, 415-427.
Scalo, J. et al. (2007) “M stars as targets for terrestrial exoplanet searches and biosignature detection.” Astrobiology, 7, 85-166.
Selsis, F. et al. (2007) “Habitable planets around the star Gliese 581?” Astronomy and Astrophysics. 476, 1373-1387.
Udry, S. et al. (2007): “The HARPS search for southern extrasolar planets. XI. A habitable super-Earth (5 Earth masses) in a 3-planet system.” Astronomy and Astrophysics, 469, 43.
* * * *
About the author
Kevin Walsh is an associate professor in the School of Earth Sciences, University of Melbourne. He has interests in climate change, climate variability, and planetary science.
[Back to Table of Contents]
* * *
Short Story: THE FINAL ELEMENT
by Eric James Stone
Some future crimes will not involve “taking away"....
Waving off the uniformed policeman's offer to help, Dennis Lombardo ducked under the yellow crime-scene tape and hefted the case containing the nuclear resonance scanner over the threshold of the New York brownstone. Slivers of wood from the broken door littered the floor.
“I've lugged this thing all the way from L.A.,” Dennis said to the officer. “I can manage. Just lead the way to where you want me to set up my equipment.”
The officer escorted him to a room dominated by a grand piano. Glass and wood cabinets displaying musical instruments and books lined the walls. At the back of the room, though, stood the thing that had brought him here: the brushed-steel, five-foot cube of a Series 3 nanofactory.
Next to it, on a white-linened table, lay two violins.
Setting down the scanner, Dennis walked over and studied the violins. They were made of fine-grain wood covered with a red lacquer, and to his eye they appeared identical in every respect, except for the NYPD identifying tags. That was to be expected—he would not have been sent here otherwise.
“My most prized possession,” said a voice from the door. “At least, one of them is.”
Dennis turned to see the silver-haired gentleman who had entered the room. “I'm Dennis Lombardo. NanoFaction sent me to detect the fake.”
“Anton Gale.” The man reached out and shook Dennis's hand. “Terence Zhang is an old friend.”
Until last night's phone call ordering him to fly overnight to New York on the corporate jet, Dennis had never spoken to Zhang, NanoFaction's CEO. Gale obviously had connections. “Our company is always happy to help where we can.”
“So what do you think of the Soil?” said Gale.
“Excuse me?”
“The Soil Stradivarius.”
Dennis looked over at the violins. “Oh, this is a Stradivarius? I've heard of those.”
“You are not a violin expert?”
“I'm sorry. I'm familiar with scientific instruments, not musical ones.”
“Ah, of course,” Gale said. “Allow me to introduce you to the instrument of Yehudi Menuhin, Itzhak Perlman, and Yuri Volokh.”
The names sounded familiar, so Dennis decided they must be famous violinists. “Very impressive. I guess that's why someone would steal it and try to dupe it.”
“Not just someone. Leonard Wharton, another collector. This is his house,” Gale said. “You must understand, the Soil Strad is considered the finest violin in the world. I paid fifty-five million at Sotheby's to own it, back in 2027. And the man I outbid was Wharton.”
Dennis raised his eyebrows. “And he stole it from you?”
“Apparently, he planned to ransom the fake and keep the real one for himself. He has been arrested for using an unlicensed nanofactory pattern.” Gale waved a hand dismissively. “I do not wish to press charges against him for the theft, for I understand his obsession. But the police cannot determine which violin is mine and which is the unlicensed copy they need to keep as evidence.”
Dennis nodded. In order to minimize economic disruption, the government had prohibited nanoduplication of
unlicensed patterns. The copy would have to be destroyed when the police were done with it. “Let me just set up my equipment, and I should be able to determine fairly quickly.”
“Your equipment will not damage the violin, I hope.”
Dennis opened up the case and removed a thick-legged tripod. “Nuclear resonance scanning is safe enough you could use it on a baby. I'm not sure why you'd want an atomic map of a baby, but if you needed one...”
He set up the tripod next to the table with the violins, removed the scanner from the case, and attached it to the tripod. Pointing the nose of the scanner at the first violin, he did a five-second preliminary scan for solid objects in the field, then selected the violin. After shrinking the selected volume slightly in order to ignore any surface contamination, he initiated a thorough scan.
“Now we wait,” said Dennis.
“How long?”
“For something this volume, a couple of minutes. And then I should be able to tell you which is the original.”
Gale frowned. “So simple?”
“Yep.”
“I thought your nanofactories built things at the atomic level.”
“They do. Atom by atom, molecule by molecule. And all atoms are equal.” Dennis grinned. “But some are more equal than others.”
“You've lost me, I'm afraid.”
“A little nuclear scanner humor. Atoms of the same element always have the same number of protons in their nucleus. But they can have different numbers of neutrons. The variations are called isotopes, and my scanner here can tell the difference between different isotopes.”
“But even if the ... isotopes of atoms are different between the two violins, how does that show which is my Strad?”
“Some isotopes are much more common than others. Most oxygen atoms, for example, have eight neutrons. Less than one percent have nine or ten. Every nanofactory is programmed to create an isotope ‘signature’ in the items it creates, by varying the levels of different isotopes.”
“I see. By comparing the scans of the two violins, the signature will become apparent.”
“I should be able to tell just from scanning one—if it has the signature, it's the fake; if not, it's your Strad.”
“Amazing.”
“That's my job.”
“You do this all the time?”
“Oh, it's not usually so glamorous as detecting forged violins. Generally it's just scanning things to create new patterns for the—”
The scanner beeped.
“—nanofactories. Sounds like the scan's done.” Dennis checked the readout. A signature pattern would stand out clearly, but the isotope distributions were within the normal range for natural variation. “This one should be your original. I'll scan the other and show you the signature. After that, the cops can come take it as evidence.”
Dennis set up the scan on the second violin.
“It seems such a shame,” said Gale.
“What?”
“People have been trying for centuries to create violins as fine as Antonio Stradivari's. Scientists have studied the wood, the design, the lacquer—every aspect of these violins, looking for the Stradivarius secret. And they have always failed, until now. But the law requires that the copy be destroyed.”
Dennis shrugged. “Law's there for a reason. What would your fifty-five million dollar violin be worth if anyone could buy one from Wal-Mart?”
“What is the worth of every violinist being able to play on so fine an instrument?” Gale sighed. “But you are right. The law prevents economic chaos.”
After a few moments of silence, Dennis said, “The secret still remains. Making a nano-duplicate doesn't explain why a Stradivarius sounds the way it does.”
With a smile, Gale said, “Some believe that a violin becomes better if it is loved and played well. The secret is the great violinists who have loved and played their Strads. And that is something your scanner cannot detect, am I right?”
“You are.” Dennis chuckled. “Although I suppose we could test that theory. Since the copy violin has not been loved and played well, it should not sound as good.”
The scanner beeped. Dennis looked at the readout. There was no signature pattern. As far as his scanner was concerned, both violins were originals. He frowned at the readout. Had he somehow failed to change targets?
“Is there a problem?”
“Yes. I didn't find a signature. So we're back to not knowing which is your Strad.”
“How is that possible?”
“It shouldn't be.” Dennis stepped over to the nanofactory and frowned at it. “Creating an unlicensed pattern is difficult enough, but eliminating the signature would require reprogramming the nanofactory, and that means our source code security has been compromised. The guy who stole your violin isn't a computer genius, by any chance?”
Gale winced. “No, he's a real estate developer.”
“So he must have hired someone to do the hacking for him.” Dennis pulled out his phone. “I have to call my boss.”
After a brief conversation outlining the security issue, Dennis hung up.
“What did your boss say?” asked Gale.
“She said I'd better find a way to detect the dupe.” Dennis let out a long breath through pursed lips.
“We could do as you said—play the violins and see if one sounds different.”
Dennis doubted that atomically identical violins would have different sounds, but allowing Gale to try the experiment wouldn't hurt—and it would give Dennis time to think. “Go ahead.”
After getting a bow from a cabinet, Gale picked up the first violin and positioned it under his chin. He played a few seemingly random notes while adjusting the knobs on the violin. “Tuning up,” he said.
Dennis nodded. He began speculating about possible differences between a real item and a nanoduplicate.
Then Gale began to play. He began slowly, building a melody with the pure tones of the violin. The music floated up the scales, then down again.
Dennis watched as Gale lovingly drew the bow across the strings, sometimes drawing a note out, other times jumping quickly from one note to another.
As the final note faded, Dennis applauded. “Wonderful. Do you give a lot of concerts?”
Gale raised an eyebrow. “Me? No, I am but a practiced amateur. I occasionally loan my violin to truly talented musicians, but...” He lowered the violin and stared at it. “This sounds like my violin. I could tell no difference.”
“Try the other one.”
After carefully laying down the one, Gale picked up the other.
As Gale played, Dennis concentrated on the music, hoping to hear an extra quality or a missing one, to distinguish the violins. But to his ear the music was just as beautiful as before.
Lowering the bow, Gale said, “They are the same.”
“I was afraid of that.” Dennis pursed his lips. “Maybe carbon-14.”
“Carbon-14?”
“We use only stable isotopes for signatures. Carbon-14 decays. How old is this violin?”
“It was made in 1714.”
“So the wood's over three hundred years old.”
“Possibly much more, as Stradivari may have used aged wood.”
“If I focus the scanner on an interior piece of wood, I should get a sample mostly unaffected by any later modifications.” Dennis adjusted the scanner and started it.
“I don't mean to disturb,” said Gale, “but I am curious what you are doing.”
“No problem. About one in a thousand carbon atoms in the air are carbon-14. After something is dead, though, it no longer takes in new carbon atoms. After three-hundred-some-odd years,” Dennis said, checking some numbers on the scanner's computer, “about four percent of the carbon-14 should have decayed into nitrogen. Carbon for nanofactory production generally comes from organic waste, but the carbon-14 levels would reflect things that died recently, not centuries ago.”
“So there should be more carbon-14 in the fake.”
“Exactly.”
The scanner beeped. Dennis set it to scan the equivalent portion on the second violin.
Neither of them spoke as they waited for the scan to finish. When the scanner beeped, Dennis tapped a few keys to bring up a chart comparing the carbon-14 counts.
There was not even a millionth of a percent difference.
Dennis scratched the back of his neck. “Whoever programmed the forgery must have made it duplicate the carbon-14 count. Probably did the same with every isotope of every element. The two violins are the same in every physical way we can measure.”
Gale wrung his hands. “But one of them was played by Menuhin, by Perlman. And one has never been played, except by me. One was fashioned by careful human hand, the other by uncaring machines. There must be a difference.”
“I don't see...” Dennis paused. “There is one element we haven't taken into account yet.”
“Which?”
“The human element. Can you have the police bring what's-his-name here? The collector who stole your violin?” A man as rich as Gale must have some pull with the local police.
“Wharton? I suppose so.”
“And whoever put these police tags on.”
“But why?”
“Because Wharton knows which one is the original.”
* * * *
“After I showed him the warrant,” said the police officer, “he shut the door on us. After we broke down the door, we located him in this room. He was holding one violin. The other was on the table.”
“Can you tell me which violin he was holding?”
The officer leaned over and read the numbers on the tags. “I tagged the one he was holding first, so it's the one on the left.” He pointed.
“Thank you, Officer.” Dennis turned to Wharton, who was seated stiffly in a red leather chair, next to the nanofactory. “Whoever programmed the nanofactory was very clever. Faking the carbon-14 count was a detail few people would have thought of.”
Analog SFF, April 2009 Page 9