by Paul Gilster | Nov 5, 2004 | Exoplanetary Science
An interesting article in the 30 October New Scientist discusses a new theory on how the solar system began. A team from the Arizona State University led by astronomer Jeff Hester argued last May in Science that isotopic evidence and accumulated astronomical observations argue for a violent, energetic region near high-mass stars as the birthplace of our system.
Image: The Eagle Nebula, as photographed by the Hubble Space Telescope. This famous photo, often known as “The Pillars of Creation,” shows giant nebular clouds being evaporated by the ferocious energy of massive stars, exposing emerging solar systems, much like our own. Credit: NASA/HST/Jeff Hester and Paul Scowen
Forming near a massive, unstable star would have had interesting implications for the appearance of habitable planets. From an ASU press release:
The process leaves a Sun-like star and its surrounding disk sitting in the interior of a low density cavity with a massive star close at hand. Massive stars die young, exploding in violent events called “supernovas.” When a supernova explodes it peppers surrounding infant planetary systems with newly synthesized chemical elements – including short-lived radioactive isotopes such as iron-60.
Hester and company argue that a nearby supernova could have profoundly influenced the habitability of the Earth. Thus planetary habitability may be tied to the interstellar environment that gave birth to particular stars.
From the New Scientist article:
Hester believes it should be possible to look at star-forming regions with massive stars and simply count the number of embryonic stars at a distance from massive stars that would allow them to retain some water and form Earth-like planets.
And citing Alan Boss of the Carnegie Institution (who first proposed that the solar system formed in a region of high-mass stars), the article continues:
Suddenly the search for extraterrestrial life is looking a lot more optimistic. We know that around 90 percent of stars form in regions of high-mass star formation. “If that is where the solar system formed, then the chances of there being planetary systems similar to our own jump by a factor of about 10 compared to the alternative,” Boss says. That makes it 10 times more likely that we’ll find a habitable planet in the neighborhood.
Sources: J. Jeff Hester, Steven J. Desch, et al. “The Cradle of the Solar System.” Science Vol. 304 (21 May 2004): 1116-1117. Marcus Chown, “Hell’s Nursery,” New Scientist 30 October 2004, pp. 61-64. Press release from Arizona State University.
by Paul Gilster | Nov 4, 2004 | Advanced Rocketry |
Fusion is often in the picture when interstellar propulsion systems are discussed, but so far we don’t know how to sustain the process past the breakeven point. Ongoing research is intensive, however, and the latest in inertial confinement fusion (ICF) concepts will be examined in mid-November in Savannah, GA. That’s when the American Physical Society’s Division of Plasma Physics holds its 46th annual meeting.
Inertial confinement fusion works by heating and compressing tiny fuel capsules with laser beams. Significant advances have been reported from the University of Rochester’s Laboratory for Laser Energetics, whose researchers will present the results of their tests of OMEGA, a 60-beam laser facility that is designed for the National Ignition Facility, a fusion laser facility scheduled to be completed later in the decade.
Image: Inertial confinement fusion at the Trident laser facility at Los Alamos National Laboratory.
Here is a description of ICF from Los Alamos National Laboratory: “In an inertial confinement fusion reaction, energy is rapidly applied to the surface of the fusion capsule which causes the solid surface to vaporize or turn into a gas. Upon vaporization this material swiftly moves away from the remaining capsule material in a rocket-like manner. This projection of gas away from the surface creates shock waves that move through the capsule, compressing and heating the interior hydrogen isotopes. Using this technique it is possible to create conditions, similar to that in a star, which are necessary for fusion to occur. As the materials fuse they give off energy, that causes the other hydrogen nuclei to heat up and begin to expand. This expansion is limited by the tendency of the shock waves to continue compressing the material from the outside, otherwise known as inertia. The net result is an inertially confined fusion reaction.” Source: Los Alamos ICF page.
Centauri Dreams‘ take: as far back as the 1970s, the British Interplanetary Society was using a form of intertial confinement fusion to power up its hypothetical Project Daedalus starship, an unmanned probe to Barnard’s Star. Even earlier, in 1966, Dwain Spencer’s paper “Fusion Propulsion for Interstellar Missions” (Annals of the New York Academy of Science 140, December 1966: 407-18) became one of the first to discuss practical fusion concepts in relation to interstellar flight. Spencer described an engine that burned deuterium and helium-3 gases in a combustion chamber ringed with superconducting magnetic coils to keep the hot plasma from contacting the chamber’s walls, a design that could reach three-fifths of the speed of light.
Today ICF concepts are proliferating, with some, like University of Michigan professor Terry Kammash’s Magnetically Insulated Inertial Confinement Fusion, using small amounts of antimatter to light the reaction instead of lasers. Here’s an abstract of “MICF: A fusion propulsion system for interstellar missions,” a paper written by Kammash and Brice Cassenti on MICF. Whatever progress the University of Rochester team can report on other ICF ideas will be well worth noting, and you can bet Centauri Dreams will keep an eye on it.
The gathering, which will be held at the Savannah International Trade and Convention Center from the 15th to the 19th of November, will see 1425 papers covering advances in plasma-based research and technology.
For more on inertial confinement fusion, the General Atomics pages on ICF are here. And here is the Web page for the APS meeting.
by Paul Gilster | Nov 3, 2004 | Deep Sky Astronomy & Telescopes
Recent analysis on more than 100,000 stars studied by the European Space Agency’s Hipparcos satellite showed that about 20 percent of them within 1,000 light years are moving in unusual trajectories. Rather than circular paths around the galactic center, they’re moving toward or away from the core. The cause: so-called ‘density waves’ that compress gas and have a hand in star formation; they also seem to be able to deflect normal stellar motions.
But don’t count on a stellar near miss to give us an easy way to go interstellar, at least not any time soon. The closest encounter with another star won’t occur for another 1.4 million years, when Gliese 710 will pass within 1 light year of the Sun (some 70,000 AU, perhaps within the Oort Cloud of cometary debris). In any case, Gliese 710 does not appear to be one of the stars affected by galactic density waves; its motion around the galactic center seems relatively normal.
Barnard’s Star is approaching us as well, at a speed of 87 miles per second. But the distances will remain daunting. In some 8,000 years, this star, the second closest to the Sun after the Alpha Centauri triple star system, will close to within four light years of the solar system, slightly closer than Centauri is right now.
The Hipparcos work will appear in the European journal Astronomy & Astrophysics. Reference: B. Famaey, A. Jorissen et al, Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data, available here (PDF warning).
ESA’s press release on the Hipparcos findings is here.
by Paul Gilster | Nov 2, 2004 | Breakthrough Propulsion |
The SETI Institute’s Seth Shostak has some things to say about the future of the universe in a recent posting on Space.com, referring to current observations suggesting that the rate of expansion of the cosmos is speeding up. That could make for a long, long night:
After all, most stars are older than the Sun, and the stellar population boom is definitely over. The Galaxy is graying (although the actual color change is to the red). The stars are going out. In about 100 billion years, the once-brightly spangled arms of the Galaxy will be riddled with Sun-sized carbon clinkers, black holes, and quiescent neutron stars – a hundred billion mute, stellar hulks.
The fun will be over, but the decay will go on. Chaotic encounters will eventually strip planets from the corpses of their erstwhile suns, and galaxies will slowly evaporate – spewing their dark and lifeless contents into the ever-expanding void. Even massive black holes will someday melt away, adding their mass to the inert and keenly cold fog that the universe will become.
A depressing, mind-numbing future indeed. Then assistant professor of physics Sean Carroll came along. Carroll and a University of Chicago graduate student named Jennifer Chen have posted a paper on ArXiv (available here in PDF) studying the so-called arrow of time. After all, “…for the most part the fundamental laws of physics don’t distinguish between past and future. They’re time-symmetric,” Carroll said.
A related issue is entropy, which measures the amount of disorder in the universe. Entropy increases with time, as Ludwig Boltzmann noted early in the 20th Century. Is entropy finite, or infinite? And why was entropy initially so small? “In our current universe,” says Carroll, “the entropy is growing and the universe is expanding and becoming emptier.” But is this true everywhere? And how does it tie into the theory of inflation, which says the universe underwent a period of massive expansion almost instantly after the Big Bang?
From a press release from the University of Chicago.
…even empty space has faint traces of energy that fluctuate on the subatomic scale. As suggested previously by Jaume Garriga of Universitat Autonoma de Barcelona and Alexander Vilenkin of Tufts University, these fluctuations can generate their own big bangs in tiny areas of the universe, widely separated in time and space. Carroll and Chen extend this idea in dramatic fashion, suggesting that inflation could start “in reverse” in the distant past of our universe, so that time could appear to run backwards (from our perspective) to observers far in our past.
Regardless of the direction they run in, the new universes created in these big bangs will continue the process of increasing entropy. In this never-ending cycle, the universe never achieves equilibrium. If it did achieve equilibrium, nothing would ever happen. There would be no arrow of time.
So we wind up with a universe that, as Carroll and Chen say in the ArXiv article, “…can be evolved both forward and backward in time,” with energy fluctuations leading to inflation in the distant past and the far future, and the ‘arrow of time’ reversing in each of these periods. Here again from the paper:
Observers in the very far past of our universe will also detect an arrow of time, but one that will be reversed from ours with respect to some (completely unobservable) global time coordinate throughout the entire spacetime. Both sets of observers will think of the others as living in their “past.”
This stuff makes Poul Anderson’s speculations in Tau Zero about driving a Bussard ramscoop into a new universe look tame. The ArXiv paper is tough reading but a fascinating contribution to current theory.
by Paul Gilster | Nov 1, 2004 | Advanced Rocketry, Missions |
Keep an eye on ESA’s SMART-1 mission, which recently completed a four-hour burn of its ion engine to correct its trajectory to the Moon. The next engine burn, lasting 4.5 days, won’t occur until November 15 when the craft has reached lunar orbit. The final operational orbit will be polar elliptical, ranging from 300 to 3,000 kilometres above the Moon’s surface. SMART-1 will perform a six-month survey of chemical elements on the lunar surface by way of examining various theories on how the Moon originally formed.
What’s interesting about SMART-1, in addition to the exotic series of spiraling orbits it is using to reach the moon, is its solar-electric propulsion system. This device uses electricity (generated from sunlight through solar panels) to accelerate xenon ions through an electric grid at huge velocity. So-called ‘ion engines’ like this create low thrust, but their specific impulse (ISP) is high. Their efficiency means a spacecraft can carry less fuel and be outfitted with more scientific instruments.
Image: Artist’s impression of SMART-1. Credit: European Space Agency.
You can’t use an ion engine to lift off from a planetary surface; high-thrust, low ISP chemical engines are better for that. But because it can keep pushing for months or even years, that gentle nudge out the back mounts up. On long missions (as, for example, to the outer planets or the Kuiper Belt), an ion engine can operate almost constantly, allowing such designs to outperform chemical rockets.
The first craft to use an operational ion propulsion system in space was NASA’s Deep Space I mission, launched in October of 1998 (although the principle was tested as far back as 1964 on the SERT 1 satellite). Both Deep Space 1 and SMART-1 use the solar-electric variant of ion propulsion, which works well in the inner solar system where sunlight is plentiful. But to reach the outer planets, nuclear-electric engines will be needed to provide the power to ionize the gas atoms.
The upshot: ion propulsion isn’t powerful enough to get us to another star, but it may develop into an efficient way to launch missions to the outer solar system. And it will take a space-based infrastructure to create our first interstellar probes, making ion propulsion one of the enabling technologies upon which more powerful designs will be built.
ESA maintains good Web materials on SMART-1; its home page is here.
