by Paul Gilster | Dec 16, 2004 | Deep Sky Astronomy & Telescopes
Back when I was a kid gawking at images from the Palomar telescope, it seemed that the only way to see farther and better was to build bigger mirrors. We’ve learned how to do that, of course, but new techniques from adaptive optics to space-borne coronagraphs have made it possible to see things never before revealed. The latest weapon in the astronomers’ arsenal is to me the most fascinating; it’s the use of computers to combine imagery and tease out new information. The National Virtual Observatory is a case in point, creating the tools needed to maintain interoperating databases. “In a few years it will be easier to “dial-up” a part of the sky than wait many months to access a telescope,” according to the NVO’s Web site.
And now we’ve got this remarkable image of 30 Doradus, the Tarantula Nebula. 30 Doradus is located in the Large Magellanic Cloud some 170,000 light years from Earth. A small, irregular galaxy that orbits the Milky Way, the LMC seems to be a region of active star formation; its interactions with the larger galaxy are what apparently energized its star-building activity. The Tarantula Nebula is said to be the largest ‘stellar nursery’ known. This image comes from Hubble data that include more than a thousand observations of the Tarantula Nebula; be sure to click it to call up a higher-resolution version.
And here’s the kicker: this gorgeous depiction is the work of a 23-year old amateur astronomer named Danny LaCrue, who studied the Hubble data and combined 15 of the exposures from Hubble’s Wide Field and Planetary Camera 2. To create this image, LaCrue downloaded and worked with a software tool called FITS Liberator, available at the European Space Agency’s Hubble page. FITS stands for Flexible Image Transport System, a format designed for astronomical images.
You may have read Timothy Ferris’ wonderful Seeing in the Dark (New York: Simon & Schuster, 2003), which recounts the contributions amateur astronomers are making to this worldwide enterprise. It’s clear that digital tools will yield more and more surprises as our computers become more powerful and can tap into data available to all.
The ESO/ST-ECF Science Archive, where LaCrue found his data, is here, if you’d like to try your hand at this kind of work. And here is a thorough backgrounder on the Large Magellanic Cloud.
Image credit: ESA/NASA, ESO and Danny LaCrue.
by Paul Gilster | Dec 15, 2004 | Culture and Society |
Every technology appears in a context, meaning there is a cultural dimension to our creations that will shape and, in turn, be shaped by them. Centauri Dreams occasionally looks at stories, novels and films that have shaped our idea of interstellar flight. Today it’s “Out Around Rigel,” by Robert H. Wilson, which ran in the December, 1931 issue of Astounding Stories. To my knowledge, Wilson published only one science fiction story, but in its day it was a bombshell.
Wilson’s tale is simple enough: two adventurers named Garth and Dunal set out from their home on a terraformed Moon of the future to travel to the star Rigel. Garth’s ship is the ultimate in new tech; he boasts that with it, they can “…go in a year to the end of the universe. But, for a starter, how about a thousand light-years around Rigel in six months?” Taking the bait, a skeptical Dunal goes onboard even as he questions Garth’s science, pointing out that Einsteinian relativity makes it clear nothing can go faster than light.
Wilson may not have understood relativity all that much better than his character Garth, but he knew enough to realize the implications of traveling at near-light speed on his crew. They make the journey to Rigel, experience time dilation without realizing what is happening, and after a series of adventures, Dunal gets back to Earth only to find that a thousand years have passed. In this passage, Dunal figures out what happened:
In our argument as to the possible speed of the Comet, Garth and I had both been right. In our reference frame, the vessel had put on an incredible velocity, and covered the nine-hundred-odd light-years around Rigel in six months. But from the viewpoint of the Moon, it had been unable to attain a velocity greater than that of light. As the accelerating energy pressed the vessel’s speed closer and closer toward that limiting velocity, the mass of the ship and of its contents had increased toward infinity. And trying to move laboriously with such vast mass, our clocks and bodies had been slowed down until to our leaden minds a year of moon time became equivalent to several hours.
It’s creaky stuff today and much of the science is wrong. A modern reader guesses instantly what is going to happen. But in its day, “Out Around Rigel” was electrifying, giving readers of the time a glimpse of how Einstein had re-written our view of the universe. By 1967, when Poul Anderson wrote about a universe-spanning journey in “To Outlive Eternity” (this would become the novel Tau Zero), he knew his readers had long ago absorbed the basic idea of time dilation. Anderson was able to use it to his advantage as he propelled an out of control Bussard ramjet so close to light speed that its crew went through entire galaxies in a time they perceived as mere seconds.
Ask any space scientist with a science fiction interest whether he or she remembers Tau Zero and you’ll get a quick smile of recognition, so pervasive has its influence become. To an earlier generation, “Out Around Rigel” served much the same function, just as science fiction in general has helped to inspire fascination with the cosmos and has nurtured some of today’s most creative scientists. The story has been reprinted twice; the more accessible volume is Damon Knight’s Science Fiction of the 30’s (New York: Bobbs-Merril, 1975).
by Paul Gilster | Dec 14, 2004 | Exoplanetary Science |
More than half of all main sequence stars occur in multiple star systems, and we’ve already found 19 planets in such systems (Tau Bootis and 55 Rho Cancri are examples). But most of our models of planetary formation have been based upon single stars. Are planets common in double star systems?
The answer has huge implications for the number of possible planets, and it’s a fascinating issue because the the nearest stars, the Alpha Centauri triple star system, are now considered capable of sustaining planets. Paul Wiegert and Matt Holman showed in 1997 that stable orbits can exist within 3 AU of Alpha Centauri A or B, and they calculated a habitable zone around Centauri A of 1.2 to 1.3 AU, with a zone around Centauri B of 0.73 to 0.74 AU. Planets at Jupiter-like distances seem to be ruled out around Centauri because of the disruptive effects of the two primary stars; after all, Centauri A and B sometimes close to within 10 AU, roughly the distance of Saturn from the Sun. The red dwarf Proxima Centauri, meanwhile, is far enough away from both (13,000 AU) so as not to affect these calculations significantly.
Jack J. Lissauer at NASA Ames and Elisa V. Quintana (NASA Ames and the University of Michigan), have been working with models of terrestrial planet formation in binary star systems for some time, as this online presentation from March 2004 makes clear. The two have been using mapping methods that have proven effective in studying the long-term behavior of binary systems, and applying them to ‘close binaries’ (stellar systems so close that planets would orbit both stars) and much more widely separated ‘wide binaries,’ where any planets would orbit one or the other of the two stars. The two scientists have simulated the late stages of terrestrial planet growth in such systems.
Applying their methods to Alpha Centauri, Lissauer and Quintana have shown that terrestrial planets may well have formed around both Alpha Centauri A and B, despite their proximity. But a key factor may be the inclination of the circumstellar disk (where any planets would orbit) to the orbital plane of the two stars. If the disk is inclined less than 45 degrees to the binary orbital plane, the simulations produce 3 to 5 terrestrial planets within 2 AU of the primary star in roughly circular orbits. If the disk is at a higher inclination than 45 degrees, most of its mass falls into the primary star.
Assuming planets did form around the Centauri stars, would they be habitable? Quoting Lissauer’s 2004 presentation:
“Probably not. Models for delivery of volatiles…suggest terrestrial planets receive volatiles primarily from the asteroid belt and beyond. In the Alpha Centauri system, orbits >3 AU from Alpha Centauri A or B are very unstable, and material would not form planetesimals in these regions… Alpha Centauri may thus have dry terrestrial planets, devoid of the [carbon and water-based] life which thrives on Earth.”
Findings from the above presentation, which Lissauer made to the Kavli Institute for Theoretical Physics conference on Planet Formation (March 2004) are well worth your time, and you should be aware that a QuickTime file of his talk is available online. See also this abstract from the Second Astrobiology Conference at NASA Ames Research Center (April, 2002).
Lissauer and Quintana have brought their study of close binary systems to the fall meeting of the American Geophysical Union, in a presentation called “Terrestrial Planet Formation Around Close Binary Star Systems.” Updates on this one as information becomes available.
by Paul Gilster | Dec 12, 2004 | Outer Solar System
The outer planets, worthy science targets in their own right, could also be considered something of a dry run for a true interstellar probe. And now details of a nuclear-powered mission to Neptune are beginning to emerge; they’re coming out of a 12-month planning study funded by NASA and led by Boeing Satellite Systems. Particularly intriguing about Neptune is its moon Triton, which many scientists now believe to be a Kuiper Belt object, a planetoid not formed by Neptunian debris but captured long ago by the planet’s gravity. A key part of the mission will be to deploy landers to Triton’s surface.
A December 17 session at the American Geophysical Union fall meeting will be another shakedown of the concept, which the Neptune team has been fine-tuning at various conferences (and how I missed this one in Centauri Dreams‘ earlier story on the AGU is beyond me). The session is “A Neptune/Triton Vision Mission Using Nuclear Electric Propulsion.”
Image: This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow angle camera. The images were taken 4.4 million miles from the planet. The image shows the “Great Dark Spot” and its companion bright smudge. Visible on the west limb are the fast-moving bright feature called “Scooter” and the “Little Dark Spot.” Credit: NASA.
The probe details are fascinating:
Propulsion: Nuclear-electric. After launch by chemical rocket, the probe would be driven by a nuclear fission reactor that would ionize an onboard propellant (presumably xenon gas); the electrically charged ions would be driven out the back to generate thrust. Work on nuclear-electric propulsion is the province of NASA’s Project Prometheus, which is studying power systems that can operate far from the Sun, where solar panels are insufficient.
Sensors: The Neptune mission will use sensors onboard the orbiter to study the composition of Neptune’s atmosphere, which should be more representative of primordial conditions in the Solar System than the inner gas giants Jupiter and Saturn. Atmospheric circulation, meteorology, magnetic fields and planetary chemistry are key areas for study.
Landers: Two Triton landers are being designed to study the strange geysers Voyager saw on the moon’s surface when it flew by Triton in 1989. And three atmospheric entry probes will be dropped onto Neptune itself, in the equatorial, mid-latitude and polar regions. How deep into the atmosphere to deploy these probes is still under investigation.
The so-called ‘ice giants’ are windows on the early Solar System. Says Neptune team member and radio scientist Professor Paul Steffes of the Georgia Institute of Technology:
“Because they are farther out, Neptune and Uranus represent something that contains more of the original – to use a ‘Carl Saganism’ – ‘solar stuff’ or the nebula that condensed to form planets…Neptune is a rawer planet. It is less influenced by near-sun materials, and it’s had fewer collisions with comets and asteroids. It’s more representative of the primordial solar system than Jupiter or Saturn.”
Centauri Dreams‘ take: The Neptune mission is expected to launch between 2016 and 2018, with arrival around 2035. Deep space missions demand a stretching of our time horizons that is utterly out of synch with a ‘do everything now’ society. In that sense, they challenge our perspective towards time and the contribution people make toward futures that seem remote at the time of their work. Now think interstellar: Even at ten percent of light speed, a Centauri probe would need 47 years before Earth-based controllers began receiving data from any planets there. To make things like interstellar probes happen will require changes that are cultural as well as technological, but we have the relatively long time-frames of the Voyager explorations to remind us that the payoff is tremendous.
Also noted from the AGU meeting: Wong, A. and S.K. Atreya, “Clouds of Neptune and Uranus: Implications for Entry Probes,” and Spilker, T.R. and A.P. Ingersoll, “Outstanding Science at Neptune: Aerocapture Implementation of NASA’s ‘Neptune Orbiter With Probes’ Vision Mission.” More on Neptune orbiter developments after the AGU meeting.
Sources: Georgia Institute of Technology; various NASA Web pages; American Geophysical Union 2004 fall meeting database.
by Paul Gilster | Dec 11, 2004 | Culture and Society
“Future historians will give a few paragraphs to the Saturn rockets that took us to the Moon, the shuttle that conquered Low Earth Orbit, and the aerospace plane, but they are likely to spend much more time looking at the underlying principles on which their own civilization was founded. They will know that physical technologies are the vessels for the exploration that takes place in human societies, but are not the essence of the transformations that they engender.”
Frank White, from The Overview Effect: Space Exploration and Human Evolution (Boston: Houghton Mifflin, 1987), p. 161.
