Inside the Boardroom with Alan Bagley - SETI Institute

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Astrobiology Magnetic Field Reversal The Andromeda Galaxy NASA/JPL-Caltech/NOAO Here Comes Andromeda by Laurance Doyle Looking at the last term of the Drake Equation, we see that it relates to the lifetime of technological civilizations – how long they last as technological (meaning interstellar communicating) entities. The three biggest considerations for our civilization at the moment could be characterized as a) getting along with each other, b) getting along with the environment, and c) staying technologically alert for large-scale concerns from space. Some dinosaurs were bipedal, had opposable claws, and were pretty intelligent—so why didn’t they, for example, invent space travel Well, that’s a topic for another essay. Meanwhile, let’s stick to a few of the things we might want to deal with “out there” at various times in the future, from a few thousand to a few billion years from now. The Earth’s magnetic field is thought to be generated by a dynamo effect – that is, the movement of charged particles in its huge iron and nickel core as it spins. Other planets have magnetic fields also, and there seems to be some relationship between the strength of the magnetic field and the size and spin rate of the magnetic core. Jupiter, with a huge core and a 10-day rotation period, generates a massive magnetic field, for example, and spacecraft sent there have to be specially built to withstand this intense field. You may remember the science fiction movie Outland with Sean Connery stranded in a mining colony on Io, one of Jupiter’s moons. However, Io would be uninhabitable since the magnetic field of Jupiter causes a 5 million ampere electric current to flow through it. However, magnetic fields can also be helpful. They can protect the inhabitants of the planet from high energy particles from, for example, the solar wind. (Yes, the Sun has a wind component, one that can be used to power solar-sail spacecraft in the near future.) When the high energy particles from the Sun encounter the Earth’s magnetic field, they are deflected toward the poles, causing beautiful auroral “curtains” of color as they hit the atmosphere. Without the magnetic field of the Earth, these high energy particles could do damage to biology on Earth. When rocks containing magnetite cool from volcanoes or are baked (as in clay pottery), they record the direction of the magnetic field of the Earth at the time of cooling. It turns out, from examining rocks of various ages, that the Earth has reversed its magnetic field many times – the last about 750,000 years ago (the average being about every few hundred thousand years). Recent measurements of ancient pottery and other evidence suggest that the Earth’s magnetic field may be declining – perhaps getting ready for an overdue reversal. This could take place within the next couple of thousand years. If the Earth’s magnetic field is just beginning to reverse, it would certainly be important for us to protect ourselves from the high energy particles of the solar wind and of space. It would not be as devastating an event as, for example, a comet impact, but it does indicate that we do not have the luxury of indulging in another Dark Age over the next thousand years or so. If civilization is to maintain itself, we need to be on our technological “toes” pretty much from now on. 18 SETI Institute Explorer
http://www.oldstarlight.com The Moon absorbs any transfer of orbital to rotational angular moment, preventing the Earth from flipping. Moon Stabilizes Earth’s Rotation The most popular theory for the origin of the moon is that it came from the Earth. We can calculate evolutionary histories of the moon’s orbit as it moved away from the Earth after formation. (It is still moving away due to the Earth’s tidal pull at about one inch per year. The majority of the tidal dragging comes from Earth’s rotational slowdown, with most being caused by waters dragging over the fairly shallow Bering Sea.) In doing some of these kinds of calculations for Mars, it was discovered that the direction of Mars’ rotational axis could flip rather suddenly. Now this is not the normal “precession” (as it is called) of a few degrees that changes, for example, our north star though the millennia. Mars was calculated to have flipped its rotation axis up to 90 degrees in as little as a couple of million years. This was a result of the orbital angular momentum, under certain circumstances, being transferred to the rotational angular momentum and causing a coupling that led to such a flip in rotation axis direction. So why has this not occurred on Earth, whose axis has seemingly not flipped by more than a few degrees The apparent explanation is that the Moon absorbs any transfer of orbital to rotational angular moment, preventing the flip. Would such a flip be important It could get very serious – like the time a couple of hundred million years ago when all the continents were combined into one big continent called “Pangaea”—if the Earth’s rotation axis flipped such that this one big continent became a polar continent like Antarctica. So, it would appear that a moon is required for a stable planet with life. This was perhaps surprising news to folks that would like to see habitable planets widespread in the galaxy requiring, as it does, both an earthlike planet in the circumstellar habitable zone as well as a fairly large satellite. This would seem to rule out habitable planets being very common. However, additional research into the rotational histories of the planets shows that the Earth used to spin a lot faster. If the earth spins faster, that also acts as a protection against flipping of the rotation axis. So, perhaps if the moon had not come off the Earth, our world would still be spinning fast enough to stabilize itself against flipping. Thus there may be many other habitable planets without a large moon, but the inhabitants will have even fewer hours in their day than we do. The moon, of course, is now perfectly placed to exactly cover the solar disk during eclipses. This perfect fit has allowed, for example, a test of General Relativity, the uncovering of the element helium, and the discovery of the solar corona. And clearly the moon has been a great stimulus and practice ground for our first efforts at space travel. However, moving out at an inch a year, in about 1.6 billion years the moon will no longer be able to stabilize our planet’s spin. We’ll have to be ready for a climatologically wild ride by then unless we figure out what to do. Eventually the Earth will have the same rotation period as the moon’s orbit (i.e., the day will equal the month) and then the moon may be expected to fall back toward the Earth, forming a ring perhaps not dissimilar to those around Saturn. It will, no doubt, be a great show. see ANDROMEDA, pg. 20 SAVE THE DATE Sunday September 25, 2005! Join us for the SETI Institute’s Annual TeamSETI Ice Cream Social To sign up for TeamSETI visit: www.seti.org/teamseti Second Quarter 2005 - Celebrating our 20th Anniversary 19
Page 1 and 2: Explorer Second Quarter 2005 Volume
Page 3 and 4: Letter from the CEO July 2005 Dear
Page 5 and 6: Of course, a space program - while
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Page 9 and 10: Astrobiology Perseids © Wally Pach
Page 11 and 12: Figure A - The five Lagrangian poin
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Page 17: COSMIC NEWS NASA/JPL-Caltech/NOAO I
Page 21 and 22: Allen Telescope Array Update David
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