Mars, Head and other scientists are finding, has long undergone substantial wobbles in its spin axis—wobbles that have wreaked havoc on its seasons.[16] Working backward in time, he says, it's possible to calculate the effect of perturbations from other Solar System bodies on the tilt of Mars's axis. “You can see it's whipping like a whiplash,” he says.
In the past few million years, he's found, it's ranged from very little tilt to an angle of 35 to 40 degrees. In fact, he says, there's a reasonable chance Mars could practically flip over on its side, tilting by 70 or 80 degrees.[17]
The Earth also sees variations in its tilt, but only by a few degrees. Even these are large enough to launch (or end) ice ages. The difference, Head and others say, is that the Earth's spin is stabilized by the Moon. “Mars has just these two little space potatoes, Phobos and Deimos, which don't really do much,” Head says.
Mischna adds: “Without something like the Moon, essentially locking the Earth into place, the axial tilt tends to wobble back and forth. That's what we see on Mars: a very large wobble. We have only very subtle changes. That keeps the planet pretty much stable relative to Mars."[18]
* * * *
So, what of the future?
In the long run, the Sun is continuing to heat up and eventually Earth's climate will go the way of Venus's.
"Venus shows us what happens to an Earthlike planet when the input of solar radiation gets over a certain threshold,” Grinspoon says.
But there's no hurry building a spacefaring ark: the Sun probably won't get hot enough to boil off the oceans for a billion or more years.
As for our own effects on climate, the good news is that in the million-year long run we're more likely to ruin ourselves than the Earth's climate as a whole. But that doesn't mean it's impossible to do both. “Both Venus and Mars seem to have gone from habitable to uninhabitable,” Grinspoon says. “That should give one pause about messing with one's planetary climate without a complete understanding of the limits of that stability."
Copyright © 2009 Richard A. Lovett
* * * *
1 See R. A. Lovett, “From Fimbulwinter to Dante's Hell: The Strange Saga of Snowball Earth,” Analog, Jan/Feb 2006.
2 Technically, the Earth and Moon aren't quite unique. Pluto’ moon Charon is also large, and other Kuiper Belt objects come in pairs. But none of them are in the habitable zone.
3 For more on this, see an un-bylined article in the online edition of Astrobiology, February 7, 2007.
4 Environmental concerns about acid rain involve another acid, sulfuric acid, produced, in part, by the burning of sulfur-containing fuels.
5 Ideally, we could rely on this process to abate our current climate concerns. Unfortunately, it's slow by human standards, requiring, by most models, thousands of years to remove the extra carbon dioxide we're injecting into the air by burning fossil fuels.
6 See, for example, “Messengers from the Earth's Core? The Great Plume Dabate Heats Up,” Analog, July/August 2006.
7 Press release from the European Space Agency, dated 18 December 2008. Such press releases can be found at www.eurekalert.org.
8 This study was reported at the fall 2008 meeting of the American Geophysical Union. Abstracts for this, and other studies from that meeting, can be found at www.agu.org.
9 The same method has been used to map layers in the Martian ice caps, all the way down to bedrock. See www.nasa.gov/missionpages/MRO/multimedia/phillips-20080515.html.
10 See Richard A. Kerr, “Signs of Plate Tectonics on an Infant Mars,” Science 30 April 1999, pp. 719-722.
11 For a more detailed explanation, see: sunearth.gsfc.nasa.gov/sunearthday/2004/vtdynamoplaentary2004.htm. [Sic: the typo “plaentary” is in the URL.]
12 For more, see www.space.com/scienceastronomy/planetearth/moonwhackside000901.html.
13 See: R. A. Lovett, “Texas-Sized Asteroid Slammed Early Mars,” National Geographic News (online), June 25, 2008.
14 In Roberts’ model, as little as a 1% drop in heat flow from the core can be enough to shut down the dynamo. Restarting it would require the heat flow to rebound by a full 25%.
15 In 2007, for example, seismologists calculated that an enormous mass of squishy rock beneath China contains an amount of water comparable to the Arctic Ocean. See, R. A. Lovett, “Huge Underground ‘Ocean’ Found Beneath Asia,” National Geographic News (online), February 27, 2007.
16 Traces of these cycles appear in several ways. One is in the carving of gullies by what appears to be melting snow, which, Head and coworkers believe, appears to have fallen repeatedly in certain highlands over the past few million years. Only massive climate cycles—the Martian equivalent of ice ages—would allow snow to melt from the ice caps, fall in the highlands, then melt again. Other, more ancient, evidence appears in “layered deposits” in a region called Arabia Terra. In a presentation at the 2008 Lunar and Planetary Science Conference in League City, Texas, Kevin Lewis of CalTech used high-resolution orbital photos to examine these sediments in three dimensions, at one-meter resolution. His team found a regularly repeating succession of layers, indicating that Mars was probably undergoing regular climate cycles even very early in its history, when these sediments were being laid down.
17 See www.planetary.brown.edu/htmlpages/publications.htm.
18 Venus, on the other hand, has no moons but no substantial wobbles, possibly because of its much slower spin (Venus rotates once every 243 Earth days.) Thus, there are spin states, Grinspoon says, that are stable without the presence of a large moon. But in the case of Venus, the price is very long days. Also Venus has no significant axial tilt, which means no seasons.
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Probability Zero: A FLASH OF LIGHTNING by Robert Scherrer
Mr. Schonfield hunched over the chronopod control panel on his desk, checking the settings and taking attendance until the bell rang. “Ladies and gentlemen,” he said, “welcome to Applied History I. We will spend this semester exploring cause and effect in American History prior to the Civil War.” One of the Salem High School students glanced down at his schedule and skulked out of the classroom. Schonfield gestured toward a gleaming metal cylinder propped up against the wall behind his desk. “And of course, the thing that makes it possible for us to tinker with the past is the Weiser chronopod. Before the invention of the Weiser field by Jason Weiser back in ‘33, there were two dominant theories about time travel. Can anyone tell me what those were? Yes, Ms., uh, Bradbury."
Terri Bradbury delicately removed a wad of chewing gum from her mouth and placed it on her desk. “Well,” she said, “there was this one idea that the past couldn't be changed."
"Yes,” said Schonfield. “That was one theory. And the other one was...?"
"Uh...” Terri riffled through the textbook. “Not sure."
"Okay,” said Schonfield, “the other theory was that a tiny change in the past would have huge consequences in the future. People used to talk about a rock thrown in a pond. The ripples spread outward, producing bigger and bigger effects as you move forward in time. And which theory turned out to be correct?"
Terri raised her hand. Schonfield smiled. “Yes, Ms. Bradbury?"
"Is this going to be on the exam?"
Schonfield scowled. “I haven't decided yet. But the answer is that neither theory was correct, as we will see today. I'm going to activate the Weiser field, and we'll take our first trip of the semester, all the way back to the Cretaceous.” Schonfield leaned over his desk and flicked a switch. The walls of the classroom vanished, and hot, humid air buffeted the students.
Terri wrinkled her nose. “Eeew, what is that smell?"
"Rotting vegetation, mostly,” said Schonfield. “The world's future petroleum supply.” The classroom, minus walls and ceiling, nestled in a fern-covered valley, flanked by steep forested hills on all sides. Schonfield pointed to one of the hills. “After school today, I will use the Weiser field to bring a twenty-kiloton nuclear device to the other side of that hill, abo
ut ten miles away. Now, watch and learn.” He pressed a button. Purple-white lightning wreathed the hill, followed by a low rumble that shook the classroom. A few students dived under their desks.
"Relax,” said Schonfield, “it's just an atomic bomb, not an earthquake. We'll be gone before the fallout reaches us. Now, by my calculations, we have exterminated several hundred dinosaurs, thousands of smaller animals, and millions of plants. Let's see how this affects the future."
Schonfield fumbled with the control panel, sliding ahead to the Eocene. A lone Eohippus scurried through the grass. “At this point,” said Schonfield, “we're viewing the newly-altered timeline outside the classroom. But the Weiser field also allows us to display the original, unaltered timeline.” He punched a button and a sepia-colored scene superimposed itself over the outside view. A sepia herd of Megacerops grazed at the rim of a lake. “Note the rather large change we've produced. Our tampering has wiped out those weird-looking rhinos and that lake."
"That's really mean!” said Terri.
"We haven't killed them,” said Schonfield. “They simply never existed in the new timeline we've created."
"It's still mean."
"We'll discuss the ethics of time travel in the spring semester. Now let's make another jump, ahead to nineteenth-century Salem.” Schonfield slapped the switch with his palm, and a handful of rickety wooden buildings appeared, crowding around a rutted dirt road. A dry wind blew dust across the classroom floor.
"Welcome to the Old West,” said Schonfield.
Terri coughed. “Yuck, it smells bad here, too,” she said.
"As we explore history this semester, the one thing you'll have the most trouble getting used to is the smell. As Jason Weiser said, ‘History stinks.’ It's just a consequence of the horse-drawn transportation system."
As if on cue, a rider plodded up the street on a mangy, dirt-colored horse. A woman fluttered out of one of the buildings, arms outstretched to greet him. Schonfield hit a button, and a sepia version of the Old West popped into view. The sepia buildings, along with the horse and rider, tracked their newly altered counterparts, but the woman was nowhere to be seen.
"Note the more subtle changes,” said Schonfield. “The buildings, the horse, the rider appear in exactly the same location, but our distortion of the timeline has added a woman friend. Does that make up for the rhinos, Terri?"
"It's cute,” said Terri. She grinned. “You're a regular matchmaker, Mr. Schonfield."
"Okay,” said Schonfield, “now let's go home.” He flicked the switch, and the classroom popped back to its original space-time coordinates at Salem High. A gaggle of students strolled across the lawn just outside the classroom window. “Let's see how we've changed the present,” said Schonfield. He tapped a button, and a sepia group of students appeared, superimposed exactly over their real counterparts. One of the students stepped a few inches to the right of his sepia doppelganger, crushing a moth in the grass.
"We now know,” said Schonfield, “that neither theory of time travel was correct. We can change the past, but the time stream has its own kind of friction. Colossal changes are slowly damped with time, until—” Schonfield stepped out the classroom door and retrieved the mangled body of the moth “—there are almost no discernable changes at all. Does anybody know what this friction effect is called? Anyone?” The students fidgeted silently. “This will be on the exam,” said Schonfield. He held up the dead moth. “We call it the Butterfly Effect."
Copyright © 2009 Robert Scherrer
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Short Story: THE JOLLY OLD BOYFRIEND by Jerry Oltion
Wherein the Ghost of Christmas Present gets a whole new meaning....
Gina couldn't sleep. She and Todd had been in bed for maybe an hour, but they'd gone there angry after another of their pointless arguments, an argument about how to stack the coffee mugs, of all things, and Gina couldn't put it behind her. Todd had broken two mugs, tipping them out of the cabinet onto the countertop just to prove that they were unstable the way she'd put them in there. Never mind that she'd never broken one in her life, never mind that they were her mugs and this was her apartment.
Worse, tomorrow was Christmas, and she was afraid of what she might find under the tree. She'd been pressuring Todd for an engagement ring. What if he had bought her one? What if he hadn't?
He didn't sleep over every night, but it was getting more common. They'd been talking about him giving up his apartment and moving in. Now she didn't know. She'd thought she wanted that, but after an evening that ended with broken coffee mugs she wasn't sure.
She was running it around and around in her mind when she heard a crash in the living room. A crash, a thump, and “Ow, ow, ow!” in a voice that she thought seemed familiar but couldn't place.
She jerked upward and grabbed the flashlight she kept on the headboard, but she didn't turn it on. No sense attracting trouble. Beside her, Todd raised his head and murmured, “Mmm?"
"Someone's in the living room!” she whispered.
He sat up quickly, overbalanced, and grabbed her arm for support, then turned and fumbled for the can of pepper spray she kept beside the flashlight.
"We're armed!” he shouted, his voice half an octave lower than usual. “Leave now and nobody gets hurt!"
There was another thump in the living room, then a light came on. “I'm sorry,” came a voice, male, definitely familiar. “I'm ... I think I'm lost. I'm not dangerous."
"Who are you?” Gina shouted.
"Dumb!” hissed Todd. “Now he knows there's a woman here."
The intruder had given a name, but she hadn't heard it over Todd's criticism and the beating of her heart.
"Who?” she said again.
"Be quiet!” Todd said, and she missed the name again.
From the living room the voice said, “Where am I?"
Todd shouted, “You're in the wrong place, that's where you are. Get out of our apartment right now."
"Right. Sorry. I don't know how I got here. Sorry about the fireplace. I'll just ... Gina?"
The voice clicked. Her old boyfriend, the one who had dumped her for the sorority girl six months ago.
"Sergei,” she whispered. Here in her apartment. But he was supposed to be dead. She'd gotten email from Christy about it just a couple weeks ago. A car wreck in Kazakhstan or something while he was visiting the homeland with his parents. She'd cried, even though she was still mad at him. But there was no mistaking that voice, that faint hint of a Russian accent even though he'd been born in Wisconsin to second-generation immigrants.
To Todd she said, “Pepper spray the bastard."
"Gladly.” Todd threw the covers aside and rose out of bed, silhouetted against the light coming from down the hallway. He strode out into it like a Greek god, his shoulders wide and his tight little butt rippling with muscle. He made it to the end of the hallway, just out of her line of sight, but instead of the hiss of pepper spray and the howl of anguish Gina had expected, Todd burst into laughter.
"What?” Gina said. She jumped out of bed and grabbed her bathrobe, swirling it on as she rushed out after him to see what could be so funny about Sergei Popovich in her apartment on Christmas Eve.
Todd stood there at the end of the hallway, shaking his head. Across the living room stood Sergei, dressed in a Santa suit and covered with soot and ash from the fireplace. His hat and fake white beard were both askew. He was holding his arms out, hands wide open to show they were empty. At his feet rested a lumpy red cloth bag.
"I'm really sorry,” he said again. “I don't know how I got here.” He stumbled a little and reached for the arm of the couch to support himself, and for a second Gina saw the photos on the mantel right through his chest.
Holy shit, he really was dead. Her heart, already beating hard, took off at a totally new speed.
She stepped past Todd and took a good look at Sergei. “What are you doing here?” she asked.
"I ... I must have unfinished b
usiness,” he said. “The last thing I remember is the front end of a bus coming at me. I'm dead, aren't I?” He sat down heavily on the hearth. The brass handles of the fireplace doors rippled in and out of visibility through his chest.
"All right, this is weird,” Todd said.
"Tell me about it,” Sergei replied. He looked up at Todd, then at Gina, then he took a deep breath and pushed the bag of toys aside and knelt down on the carpet where they had been. “I don't know how long I've got, so let me start with an apology. Gina, I was a total idiot. I treated you badly, and I apologize. I have no excuse and no explanation. If you can ever forgive me, I'll ... I'll rest in peace."
Gina had dreamed of this very moment, of him realizing his mistake and apologizing, and in her daydreams she had always told him to get lost, but now, faced with his returned spirit, she couldn't do it. “Apology accepted,” she said softly.
There was a long moment when nobody breathed. Sergei didn't disappear. After a few seconds he said, “There must be something more.” He stood up, looked to the sack at his feet, picked it up, and untied the cord at the top. “I appeared in your fireplace in a Santa suit with a sack of presents. Maybe I'm supposed to deliver them to you.” He reached into the sack and pulled out a four- or five-inch cubic box wrapped in glossy black paper with a silver metallic bow on top. He read the tag that dangled from the side, and said, “For Todd. That must be you."
He held it out for Todd, and Todd took it gingerly from his hands.
"It's heavy,” Todd said.
"Probably a lump of coal,” Sergei said. “Ha ha. Little joke. Aren't you getting cold?"
Todd looked down at himself, naked as a jaybird, and nodded. “Don't do anything stupid,” he said and retreated into the bedroom.
Gina looked at Sergei. Sergei looked at her. There was something in his eyes, something in his expression, a longing that took her back to the very first days when they'd started going out. They hadn't been able to get enough of each other. The chemistry was obviously still there.
Sergei pulled the fake beard down below his chin. “You look beautiful,” he said.
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