Centauri Dreams

Imagining and Planning Interstellar=20 Exploration

Astrobiology Primer a=20 Gem

November 14th, 2006

Astrobiology, the study of life as a planetary phenomenon, aims to=20 understand the fundamental nature of life on Earth and the possibility = of life=20 elsewhere. To achieve this goal, astrobiologists have initiated = unprecedented=20 communication among the disciplines of astronomy, biology, chemistry, = and=20 geology. Astrobiologists also use insights from information and = systems theory=20 to evaluate how those disciplines function and interact. The = fundamental=20 questions of what =E2=80=9Clife=E2=80=9D means and how it arose have = brought in broad=20 philosophical concerns, while the practical limits of space = exploration have=20 meant that engineering plays an important role as = well.

So goes the introduction to the Astrobiology Primer = now=20 available as a reference tool for those trying to acquire the = fundamentals of=20 this multidisciplinary subject. Ninety researchers contributed insights = and=20 information to the collaborative effort. The work ranges through stellar = formation and evolution, planet detection and characterization to the = evolution=20 of life through time, and it=E2=80=99s hard to imagine a better way to = bone up on the=20 basics. An exotic specialty now, astrobiology will gradually become one = of our=20 most significant disciplines as we continue to find and examine the = worlds that=20 fill the galaxy in their millions.

Posted in Astrobiology=20 and SETI | No Comments = =C2=BB

Minerals, Organics and=20 Early Life

November 14th, 2006

Where did our planet get the stuff from which life is made? The = sources seem=20 surprisingly diverse, and we=E2=80=99re learning more about how organic = materials may=20 have complemented each other in forming life four billion years ago.=20 Extraterrestrial compounds =E2=80=94 biomolecules formed in deep space = and falling to=20 Earth =E2=80=94 probably contributed. And so did lightning and = ultraviolet radiation,=20 along with vulcanism and deep water chemical reactions that could = enhance=20 molecular synthesis.

Now getting new emphasis is the role of mineral surfaces in helping = to=20 activate molecules essential to life, like amino acids (from which = proteins are=20 made) and nucleic acids (think DNA). In a recent s= tudy,=20 Robert Hazen (Carnegie Institution Geophysical Laboratory) described = where we=20 stand at identifying the pairing of molecule and mineral. When molecules = like=20 amino acids adhere to mineral surfaces, a variety of organic reactions = can occur=20 that affect what life can emerge.

=E2=80=9CSome 20 different amino acids form life-essential = proteins,=E2=80=9D Hazen=20 explained. =E2=80=9CIn a quirk of nature, amino acids come in two = mirror-image forms,=20 dubbed left and right-handed, or chiral molecules. Life, it turns out, = uses=20 the left-handed varieties almost exclusively. Non-biological = processes,=20 however, do not usually distinguish between left and right variants. = For a=20 transition to occur between the chemical and biological eras, some = process had=20 to separate and concentrate the left- and right-handed amino acids. = This step,=20 called chiral selection, is crucial to forming the molecules of=20 life.=E2=80=9D

The hunt, then, is to find what mineral surfaces are what Hazen calls = the=20 best =E2=80=98docking stations=E2=80=99 for various biomolecules. The = possibilities are vast=20 considering the number of mineral types and available molecules, but = Hazen=E2=80=99s=20 team is using DNA microarray technology to help. The result is to = overhaul the=20 protocols for doing this work and make the investigation both more = accurate and=20 much faster. The technique allows the team to study these complex = interactions=20 and discover which mineral surfaces and which organic molecules manage = to work=20 together.

Much work lies ahead, but Hazen=E2=80=99s team can now identify a = million types of=20 biomolecules through their interactions with mineral surfaces, and = analyze the=20 results quickly. The goal is an understanding of how specific organics = from the=20 vast number available assembled into early life, and how they were able = to=20 become concentrated enough to begin a basic metabolism. The work, which = draws on=20 biology, chemistry and geology, gives us a glimpse not only of the = primitive=20 Earth but a better understanding of the conditions that may lead to life = on=20 other worlds.

The paper is Hazen, =E2=80=9CMineral surfaces and the prebiotic = selection and=20 organization of biomolecules,=E2=80=9D American Mineralogist = Vol. 91, No. 11-12=20 (November, 2006), pp. 1715-1729.

Posted in Astrobiology=20 and SETI | 1 Comment = =C2=BB

A Hunt = for ET in=20 Binary Systems?

November 13th, 2006=20

An interesting st= ory on=20 Seth Shostak=E2=80=99s recent appearances in Athens, OH ran today in = The Athens=20 News. In a pair of talks Shostak, senior astronomer for the SETI = Institute=20 (Mountain View, CA), explained to a general audience why he thinks=20 extraterrestrial life is out there. He even gave a timeline for its = discovery:=20 within the next two dozen years (he went on to bet each member of the = audience a=20 cup of Starbuck=E2=80=99s coffee on the proposition). Each SETI = experiment, Shostak=20 added, gathers more data than all the previous ones combined.

Deep in the article are two Shostak suggestions for extending the = SETI=20 search. First, focus on the same area of sky for longer periods of time, = instead=20 of today=E2=80=99s common practice of looking at a star for a few = minutes and then=20 moving on. Keep a longer gaze and look for signals of short duration = that may=20 repeat every few hours or days.

The second tactic: work harder on binary systems. These may contain=20 technological civilizations that have explored both sides of their twin = solar=20 systems (inevitably, Centauri A and B come to mind). If two members of a = binary=20 system line up properly from our vantage point =E2=80=94 and if the two = systems are=20 talking to each other =E2=80=94 then there is a possibility for = detecting their=20 powerful, tightly focused communications.

Centauri Dreams=E2=80=98 take: Believing that technological = civilizations=20 are rare in our galaxy (and elsewhere, for that matter), I doubt either = of these=20 strategies will succeed. But I=E2=80=99m all for SETI proponents who say = we won=E2=80=99t know=20 until we try. If ever there was an argument I would be happy to lose, = it=E2=80=99s this=20 one, but I=E2=80=99ll let someone else take Shostak up on that two dozen = year bet.=20

Posted in Astrobiology=20 and SETI | 6 Comments = =C2=BB

A Boost = for Optical=20 Communications

November 13th, 2006=20

Given how tricky it is to pick up accidental radio signals =E2=80=94 = =E2=80=9Cleakage=E2=80=9D =E2=80=94 from=20 extraterrestrial civilizations, how hard would it be to communicate with = our own=20 probes once they=E2=80=99ve reached a system like Alpha Centauri? A = front-runner for=20 interstellar communications is the laser. JPL=E2=80=99s James Lesh = analyzed the problem=20 in a 1996 paper, concluding that a 20-watt laser system with a 3-meter = telescope=20 as the transmitting aperture could beam back all necessary data to = Earth. It=E2=80=99s a=20 system feasible right now.

Right now, that is, if we had some way to get the telescope, just a = bit=20 larger than the Hubble instrument, into Centauri space. But even though=20 propulsion lags well behind laser technology for such a mission, = we=E2=80=99re=20 continuing to study how lasers can help closer to home. Their high = frequencies=20 allow far more data to be packed into the signal, but the highly focused = beam=20 also uses a fraction of the power of radio. Data return becomes less of = a=20 trickle and more of a flood (imagine high-definition moving video from=20 Mars).

How to handle atmospheric effects that can hamper Earth-based = receivers? It=E2=80=99s=20 a problem even on cloud-free days because dust, dirt and water vapor can = still=20 scatter light and deflect parts of the beam. Listen to Penn = State=E2=80=99s Mohsen=20 Kavehrad: =E2=80=9CFree space optical communications offer enormous data = rates but=20 operate much more at the mercy of the environment=E2=80=A6All of the = laser beam photons=20 travel at the speed of light, but different paths make them arrive at = different=20 times.=E2=80=9D

The result: data =E2=80=98echoes=E2=80=99 that confound accurate = reception. But the project=20 Kavehrad is working on, funded through the Defense Advanced Research = Agency,=20 aims at achieving almost 3 gigabytes per second of data over a distance = of 6 to=20 8 miles through the atmosphere. What the Penn State team has done is to = bring=20 digital signal processing methods to bear on laser communications to = make the=20 optical link more reliable. They call their approach free-space = optical=20 communications. Here=E2=80=99s how a Penn State news release describes the = system=E2=80=99s=20 operation:

Using a computer simulation called the atmospheric channel model = developed=20 by Penn State=E2=80=99s CICTR, the researchers first process the = signal to shorten the=20 overlapping data and reduce the number of overlaps. Then the system = processes=20 the remaining signal, picking out parts of the signal to make a whole = and=20 eliminate the remaining echoes. This process must be continuous with = overlap=20 shortening and then filtering so that a high-quality, fiber optic = caliber=20 message arrives at the destination. All this, while one or both of the = sender=20 and receiver are moving.

The system works both for air-to-air and air-to-ground links, and = provides=20 fiber-optic quality signals. But extend the premise to the growing needs = of the=20 Deep Space Network to relieve spectrum overcrowding and provide reliable = high-bandwidth links to spacecraft around the Solar System. = We=E2=80=99re moving toward=20 a future model of networked space vehicles, communicating not only with = Earth=20 but also with each other to coordinate data transfers that will one day = be=20 optical.

The bright future of optical communications relies on resolving = complications=20 like atmospheric distortion. NASA=E2=80=99s Table Mountain = facility in=20 the San Bernadino Mountains houses a one-meter laser telescope used as a = testbed=20 for refining data tracking in future space missions. That and a variety = of=20 space-borne tests have already demonstrated the viability of the = concept. One=20 day we may use it for deep space work and who knows, the reach of the = laser may=20 someday carry data from a distant star.

For those who want more details on the Alpha Centauri communications = paper=20 mentioned above, it=E2=80=99s Lesh et al., =E2=80=9CSpace Communications = Technologies for=20 Interstellar Missions,=E2=80=9D Journal of the British = Interplanetary Society=20 49 (1996): 7=E2=80=9314.

Posted in Communications=20 and Navigation | 1 Comment = =C2=BB

SETI: = Don=E2=80=99t Expect an=20 Alien Sitcom

November 11th, 2006=20

Since we=E2=80=99ve kicked around the idea of searching for SETI = signals in the=20 television bands (as noted in a previous story on Abraham = Loeb and the=20 Mileu= ra=20 Wide-Field Array), it=E2=80=99s interesting to note Seth = Shostak=E2=80=99s thoughts=20 on the subject. Because although planet Earth has been broadcasting TV = signals=20 for some time now, our transmissions are unlikely to be received at any = great=20 distance. And that makes a search for accidental TV-like emissions even = from=20 relatively nearby stars problematic.

Shostak imagines a civilization 55 light years away hoping to pick up = I=20 Love Lucy from Earth. He notes that the non-directional TV signal, = assuming=20 a million watts of transmitter power, will reach this distant world = =E2=80=9C=E2=80=A6with a=20 power density of about 0.3 million million million million millionths of = a watt=20 per square meter=E2=80=A6=E2=80=9D And because only a third of the = transmission power is in the=20 carrier signal =E2=80=94 the most readily detected part of the = transmission =E2=80=94 even that=20 number is too high.

It=E2=80=99s possible to run these numbers against a new facility, = the Low-Frequency=20 Array (LOFAR) now being built in Europe for = radio=20 astronomy work. At VHF television frequencies, LOFAR will have an = effective=20 collecting area similar to that of the Arecibo dish. Says Shostak:

That=E2=80=99s big. That=E2=80=99s brawny. But not brawny enough. = In our SETI experiments=20 at Arecibo, we could find a signal if it were about 0.1 million = million=20 million millionths of a watt per square meter. That number, you will = notice if=20 you count up the words, is a million times bigger than the =E2=80=9CI = Love Lucy=E2=80=9D=20 carrier at 55 light-years. The aliens=E2=80=99 LOFAR would be = inadequate to detect the=20 broadcast by a factor of a million, a not entirely negligible amount. = Simply=20 stated: LOFAR couldn=E2=80=99t hear it.

That=E2=80=99s bad news for our hopes of picking up extraneous = signals from a=20 technological civilization. It doesn=E2=80=99t disqualify these = frequencies from SETI=20 study, but does imply that if we were to find something interesting, it = probably=20 wouldn=E2=80=99t be an extraterrestrial sitcom. If any readers have = references to other=20 work on the strength of such signals at interstellar distances, please = let me=20 know. It=E2=80=99s a question that bears on how visible our own culture = is at the=20 distance of nearby stars. The answer may well be that despite I Love = Lucy, we=E2=80=99re still all but undetectible.

Posted in Astrobiology=20 and SETI | 9 Comments = =C2=BB

Deep = Space Challenge:=20 Shrinking the Tools

November 10th, 2006=20

Shrinking our instrumentation is one of the great hopes for extending = spacecraft missions into the Kuiper Belt and beyond. No matter what kind = of=20 propulsion system we=E2=80=99re talking about, lower payload weight gets = us more bang=20 for the buck. That=E2=80=99s why a new imaging= system=20 out of Rochester Institute of Technology catches my eye this morning. It = will=20 capture images better than anything we can fly today, working at = wavelengths=20 from ultraviolet to mid-infrared.

It also uses a good deal less power, but here=E2=80=99s the real = kicker: The new=20 system shrinks the required hardware on a planetary mission from the = size of a=20 crate down to a chip no bigger than your thumb. The creation of Zeljko=20 Ignjatovic and team (University of Rochester), the detector uses an=20 analog-to-digital converter at each pixel. =E2=80=9CPrevious attempts to = do this=20 on-pixel conversion have required far too many transistors, leaving too = little=20 area to collect light,=E2=80=9D said Ignjatovic. =E2=80=9CFirst tests on = the chip show that it=20 uses 50 times less power than the industry=E2=80=99s current best, which = is especially=20 helpful on deep-space missions where energy is precious.=E2=80=9D

Precious indeed. But imagine the benefits of carrying miniaturization = still=20 further. Nanotechnology pioneer Robert Freitas has speculated = provocatively=20 about space probes shrunk from the bulk of a Galileo or Cassini into a = housing=20 no larger than a sewing needle. Launched by the thousands to nearby = stars, such=20 probes could turn their enclosed nano-scale assemblers loose on the soil = of=20 asteroids or moons in the destination system. They could build a = macro-scale=20 research station, working from the molecular level up to create tools = for=20 continuing investigation and communicating data back to Earth.

The new sensor out of Rochester is a long way from that kind of=20 miniaturization, but surely the dramatic changes in computing over the = past few=20 decades have shown us how potent shrinking our tools =E2=80=94 and = packing more and more=20 capability into them =E2=80=94 can be. And when you=E2=80=99re working = with finite payload=20 weight and can insert a new set of tools because they=E2=80=99re smaller = than before,=20 you=E2=80=99ve dramatically extended what a given space mission can = accomplish. Getting=20 a millimeter-wide needle to Alpha Centauri may not be Star = Trek, but it=20 could be how we start.

Posted in Autonomy and=20 Robotics | 9 Comments = =C2=BB

Probing = Distant=20 Atmospheres for Life

November 9th, 2006=20

Hunting for terrestrial planets is not going to be easy, and even = when we=20 start getting images of such worlds, there will be plenty of questions = to=20 answer. How to detect life on a terrestrial planet was one of the = subjects that=20 came up in September at the Pale = Blue=20 Dot workshop at Adler Planetarium in Chicago. Cassini=E2=80=99s = recent picture of=20 Earth from Saturn space, much like Voyager=E2=80=99s =E2=80=98pale blue = dot=E2=80=99 image of 1990,=20 reminded everyone at the conference of our fragile place in the cosmos. = It also=20 forced the question of how we might find other such worlds.

And finding a blue planet in a star=E2=80=99s habitable zone = isn=E2=80=99t enough. As laid=20 out in this JPL backgro= under,=20 the key will be to gather enough spectral data to make a judgment call = that=20 could change how we view our place in the universe. Breaking down the = light from=20 a distant planet should tell us much about its chemical composition. = Carbon=20 dioxide and water vapor, for example, are both clues to life, their dual = presence suggesting both an atmosphere and an ocean.

But even liquid water isn=E2=80=99t sufficient to make the call. In = reality, we=E2=80=99ll=20 need a combination of things. Oxygen is useful because it suggests plant = life or=20 some kind of living cycle to produce it and keep it in the atmosphere. = Methane=20 likewise suggests life processes at work, though by itself it=E2=80=99s = not sufficient=20 (we can certainly find the stuff in places where life seems less likely, = as=20 witness Titan). So here=E2=80=99s the take from the JPL story:

Scientists say that oxygen is a more reliable sign of life than = methane,=20 but if they found large quantities of both, they=E2=80=99d be more = convinced. =E2=80=9CFinding=20 two of these molecules together would be much better than one. The = more, the=20 better,=E2=80=9D said Dr. Victoria Meadows of NASA=E2=80=99s Spitzer = Science Center, Pasadena,=20 who served as chair of the third Pale Blue Dot conference. = =E2=80=9CFor example, if we=20 found carbon dioxide, oxygen and water vapor, in addition to methane, = then=20 we=E2=80=99d be pretty convinced that we were looking at an = environment like our=20 own.=E2=80=9D

Centauri Dreams=E2=80=99 take: Inevitably, the hunt for = extraterrestrial=20 life looks first for the kind of life we find on Earth. But we may have = to widen=20 that view, and the key is to make as few assumptions as possible. For if = we=E2=80=99ve=20 learned one thing from the 200+ extrasolar planets found thus far, = it=E2=80=99s that=20 solar systems around other stars can be utterly different from anything = we had=20 imagined. Finding that alien blue dot with the right mix of chemicals in = its=20 atmosphere would be profoundly suggestive, but it doesn=E2=80=99t rule = out more bizarre=20 abodes of life that we don=E2=80=99t yet know how to categorize. Not all = those pale,=20 living dots are going to be blue.

Posted in Astrobiology=20 and SETI | 3 Comments = =C2=BB

A = Spectacular View of=20 Orion

November 8th, 2006

Though I hadn=E2=80=99t planned another entry for today, this is just = too beautiful=20 to pass up. We=E2=80=99re looking at the Orion nebula (be sure to click = the image to=20 enlarge) in infrared, ultraviolet and visible light, a composite using = both=20 Hubble and Spitzer data that brings out unheard of detail =E2=80=94 the = green swirls are=20 from Hubble=E2=80=99s ultraviolet and visible light detectors; the red = and orange are=20 Spitzer working in the infrared. This massive star formation region = located in=20 the sword of Orion is home to about 1000 young stars.

Note the set of stars called the Trapezium, identifiable as a bright = area=20 near the center of the image. Each of these massive stars pours out = ultraviolet=20 that heats hydrogen and sulphur in the nebula. The stellar wind from = clusters of=20 stars embedded in the dust and gas helped to create the distinctive = shapes and=20 swirls of this celestial artwork.

Posted in Deep Sky=20 Astronomy | 1 Comment = =C2=BB

Titan=E2=80=99s Haze May Mimic=20 Early Earth=E2=80=99s

November 8th, 2006=20

Titan=E2=80=99s atmosphere may be telling us something about = conditions on the early=20 Earth. It=E2=80=99s thick and filled with interesting things like = organic aerosol=20 particles that form through the reaction of sunlight with methane gas. = Translate=20 that into terrestrial terms and you get a similarly hazy early Earth = whose=20 surface receives more than 100 million tons of organic materials every = year. =E2=80=9CAs=20 these particles settled out of the skies, they would have provided a = global=20 source of food for living organisms,=E2=80=9D said Melissa Trainer = (University of=20 Colorado - Boulder).

3D"Titan

Trainer is principal author of a new paper that examines the chemical = qualities of these aerosol particles in the laboratory, studying their = chemical=20 composition, size and shape. The method: expose a mixture of methane and = nitrogen to ultraviolet light, then add carbon dioxide to see if organic = haze=20 forms. And indeed, the haze forms readily in a wide range of methane and = carbon=20 dioxide concentrations. That smoggy sky over Titan may be similar to the = haze=20 that hung over the Earth for millions of years as the conditions for = life=20 emerged.

Image: As Cassini approached Titan on Aug. 21, 2005, = it=20 captured this natural color view of the moon=E2=80=99s orange, global = smog. Images taken=20 with the wide-angle camera using red, green and blue spectral filters = were=20 combined to create this color view. Credit: NASA/JPL/Space Science=20 Institute.

Another benefit of the haze layer would be protection, shielding = primitive=20 organisms from ultraviolet light from the Sun and helping to stabilize = the early=20 climate. =E2=80=9CIt=E2=80=99s somewhat similar to the smog in Los = Angeles,=E2=80=9D adds Trainer.=20 =E2=80=9CToday=E2=80=99s haze on Earth is also created photochemically, = which means sunlight=20 powers chemical reactions in the atmosphere. However, the early = atmosphere of=20 Earth had different gases present, so chemical composition of the early = haze is=20 very different than the haze we have today. There also would have been a = lot=20 more of it.=E2=80=9D

The paper is Trainer et al., =E2=80=9COrganic Haze on Titan and the = Early Earth,=E2=80=9D=20 accepted for publication in Proceedings of the National Academy of=20 Sciences. The study was performed for NASA=E2=80=99s Astrobiology=20 Institute.

Posted in Astrobiology=20 and SETI, Outer Solar=20 System | 1 Comment = =C2=BB

Flares, = Asteroids and=20 Extinctions

November 7th, 2006

Imagine our Sun spewing out a flare 100 million times stronger than = usual,=20 releasing the energy of 50 million trillion atomic bombs. The effect on = our=20 planet would be catastrophic. Fortunately, what the Swift satellite has = spotted=20 occurred a bit further away in a binary system called II Pegasi, some = 135 light=20 years from Earth. Swift is designed to detect gamma-ray bursts =E2=80=94 = the most=20 powerful of all explosions =E2=80=94 and this=20 flare was energetic enough to produce a false alarm for such a = burst.

NOTE: The original entry here referenced the power of =E2=80=98fifty = trillion=E2=80=99 atomic=20 bombs; the actual figure used by NASA was corrected, as above, to = =E2=80=98fifty million=20 trillion.=E2=80=99 Thanks to Robin Goodfellow for catching the typo.

II Pegasi is an interesting system. The flare star is 0.8 times the = mass of=20 the Sun; its companion is 0.4 solar masses, and the stars are separated = by only=20 a few stellar radii. That produces fast rotation on both stars, and = while II=20 Pegasi may be a billion years older than the Sun, the tight orbit has = something=20 to do with the flare activity. =E2=80=9CThe tight binary orbit in II = Pegasi acts as a=20 fountain of youth, enabling older stars to spin and flare as strongly as = young=20 stars,=E2=80=9D said Steve Drake of NASA Goddard, a co-author with = Rachel Osten of an=20 upcoming Astrophysical Journal paper.

3D"Solar

The cosmos is both a life-giving and a life-taking place. Some = believe that=20 stellar outbursts like this one may be a factor in conditioning = interstellar=20 dust that will later form into planets, immense violence that eventually = produces life. But such a flare could be a civilization-ender if it = occurred on=20 a star like ours. The x-ray outpouring would produce climate change and, = doubtless, mass extinction. X-ray emissions from II Pegasi lasted for = several=20 hours; a normal solar flare produces emissions that may last a few = minutes.

Image: A typical solar flare from our sun, from = September=20 2005, captured in the X-ray waveband by NASA=E2=80=99s TRACE satellite. = Note the bright=20 magnetic loops of matter. The twisting and reconnecting of these loops = initiate=20 the flare. NASA=E2=80=99s Swift satellite detected a similar flare from = a star system=20 called II Pegasi 135 light-years from Earth=E2=80=A6 except it was one = hundred million=20 times more energetic than the sun=E2=80=99s typical solar flare. Had it = been from our=20 sun, it would have triggered a mass extinction on Earth. The II Pegasi = flare was=20 too distant (fortunately) to image in detail. Credit: NASA/LMSAL.

Flares aren=E2=80=99t on the agenda, but extinction events of a more = localized sort=20 will be discussed at the 2007= =20 Planetary Defense Conference, to be held next March 5-8 at George = Washington=20 University in Washington, DC. The objective of the conference is to = create a=20 white paper that analyzes the current state of the art in detection and = tracking=20 of near Earth objects (NEOs), and the methods we might use to defend = ourselves=20 against them. Registration opens in December; let=E2=80=99s hope the = conference gets=20 plenty of press coverage.

And finally, a 48-minute documentary=20 with the same name =E2=80=94 =E2=80=9CPlanetary Defense=E2=80=9D = =E2=80=94 is now being produced to depict the=20 various efforts at detection and deflection of asteroids and comets with = Earth-crossing orbits. Numerous experts in the field are said to be = involved,=20 along with science fiction legend Arthur C. Clarke, who began his 1973 = novel=20 Rendezvous with Rama with a major asteroid impact (on a = September 11,=20 no less, though one set 75 years in the book=E2=80=99s future). Project = Spaceguard is=20 the result, a determined response to incoming objects that, we must = hope, will=20 one day become reality in the form of a robust space-based = infrastructure=20 throughout our Solar System.

Posted in Deep Sky=20 Astronomy | 5 Comments = =C2=BB

=C2=AB = Previous=20 Entries

=20
Charter

Centauri Dreams is a review of research issues in deep = space=20 exploration, with an eye toward interstellar possibilities. In the = image=20 above, the leftmost star is Alpha Centauri, a triple system closer to = our Sun=20 than any other star, and surely a primary target for early = interstellar=20 probes. To its right is Beta Centauri (not a part of the Alpha = Centauri=20 system), with Beta Crucis, one of the stars forming the Southern = Cross,=20 visible at the far right. Image credit: Marco Lorenzi.
Pages
- About Centauri = Dreams=20
- Contact=20
- Errata=20
- Tau Zero = Foundation=20
Recent Comments:
- Alexander<= /A>:=20 >If two members of a binary system line up properly from our = vantage=20 >point =E2=80=94 and if the two...=20
- Joseph = Baneth=20 Allen: Putting an exact timeline on the discovery of = extraterrestrial=20 life is a risky proposition....=20
- Administra= tor:=20 Actually, stable orbits turn out to be quite possible in binary = systems,=20 something we used to think...=20
- JD: I = guess=20 the binary hypothesis could be possible. I'd hate to think of how = many times=20 evolution would have "reset"...=20
- Adam: = Hi Ron=20 Good point about confusing a starship source of radiation with the = origin=20 point, presumably a star. I...=20
- Administra= tor:=20 I had the same thought, Ron, though I suppose that by specifying = short=20 duration, he could be talking...=20
- Adam: = Hi=20 Kevin Wow! Those power densities are incredible. What would their = in-space=20 survivability be like though...=20
- Ron = S: "Deep=20 in the article are two Shostak suggestions for extending the SETI = search.=20 First, focus on the same area...=20
- Ron = S: Adam,=20 Sorry that I misunderstand you. In fact after I made my comment I = realized=20 that I had no idea where the...=20
- Kevin = Reed:=20 Hello, Interesting disussion. We have made 9.5% efficency, 6 micron=20 thickness solar cells with record...
Archives
- November = 2006=20
- October 2006 =
- September = 2006=20
- August 2006=20
- July 2006=20
- June 2006=20
- May=20 2006=20
- April 2006=20
- March 2006=20
- February = 2006=20
- January 2006 =
- December = 2005=20
- November = 2005=20
- October 2005 =
- September = 2005=20
- August 2005=20
- July 2005=20
- June 2005=20
- May=20 2005=20
- April 2005=20
- March 2005=20
- February = 2005=20
- January 2005 =
- December = 2004=20
- November = 2004=20
- October 2004 =
- September = 2004=20
- August 2004=20
Categories
- Administrative = (10)=20
- Advanced = Rocketry (23)=20
- Antimatter (17) =
- Astrobiology and = SETI (85)=20
- Autonomy and = Robotics (24)=20
- Breakthrough = Propulsion=20 (38)=20
- Communications and=20 Navigation (14)=20
- Culture and = Society (72)=20
- Deep Sky = Astronomy (114)=20
- Exoplanetary = Science (191)=20
- Exotic Physics = (9)=20
- Interstellar = Medium (21)=20
- Missions (63)=20
- Outer Solar = System (149)=20
- Research Tools = (13)=20
- Sail Concepts = (49)=20
- Tau Zero = Foundation (7)=20
Clippings
- Moving=20 Beyond String Theory=20
- Outer = Space=20 Nurseries=20
- The=20 Inelegant Universe=20
- T= he=20 Energy of Empty Space that Isn't Zero=20
- Searching=20 for Aliens=20
- A=20 Life, the Universes, and Everything=20
- Has=20 String Theory Tied Up Better Ideas in Physics?=20
- But=20 What If No One's Out There at All?=20
- One = Big=20 Bang, or Were There Many?=20
- A = Universal=20 Constant on the Move=20
- W= hat=20 Lies Beneath=20
- Beyond=20 the Standard Model (reviews)=20
- Why = We=20 Explore=20
- Peer = Review=20 and 'Media Science'=20
- One=20 Universe or Many?=20
- Light Shed = on=20 Mysterious Particle=20
- Civilized Life in the Universe (review)=20
- The=20 Gods of Cosmology=20
- If the Universe Were a=20 Computer=20
- Science=20 Friday: What Dreams May Come=20
- Bubble= =20 Fusion: Silencing the Hype=20
- Secrets of the Cosmos (review)=20
- Astronomers = Agog=20 Over Stellar Explosion=20
- Infinite Worlds = (review)=20
- Galactic = Glow=20 Gleaned
Weblogs, Discussions, Commentaries
- Advanced = Nanotechnology=20
- Airminded=20
- Anthonares=20
- Apparent Brightness=20
- Astrobiology Magazine=20
- Astronomy = Blog=20
- Astroprof's Page=20
- Atlas of the = Universe=20
- Bad Astronomy=20
- Benford & Rose=20
- Cosmic Variance=20
- CosmoCoffee=20
- Dick's Rocket = Dungeon=20
- Eternal Golden = Braid=20
- European Federation of Biophysics=20
- Fly Me to the Moon=20
- Futurismic=20
- Habitable Zone=20
- Leaves on the Line=20
- Long Bets Foundation=20
- Long Now Foundation=20
- Meme Therapy=20
- Meridiani = Journal=20
- Music of the Spheres=20
- NASA Watch=20
- Not Even = Wrong=20
- Occasional Randomness=20
- Out of the Cradle=20
- peregrinus = interstellar=20
- Physics Comments=20
- Rick Costello Space = Art=20
- Science Gate=20
- Scitizen=20
- SolStation=20
- Space for Commerce=20
- Space Law Probe=20
- Space Politics=20
- Space Pragmatism=20
- Space Review=20
- Space Transport News =
- Star Spangled Cosmos=20
- Studi Galileiani=20
- Systemic=20
- Tales of the=20 Heliosphere=20
- Tangled Bank=20
- This Week's Finds in = Mathematical Physics=20
- Tom's Astronomy Blog=20
- Universe Today=20
- Unmanned=20 Spaceflight=20
- Velcro City Tourist Board =
- Watered Down = Physics=20
- Woodward Effect=20
- Woodward Home = Page=20
- Worlds of David = Darling=20
- Xenoarchaeology =
Enter your email address:

Delivered by FeedBurner
Meta
- Register=20
- Login=20
- Valid XHTML=20
- XFN=20
- WordPress =

Centauri Dreams is powered by WordPress
Entries = (RSS) and Commen= ts=20 (RSS).

Charter

Pages

Recent Comments:

Archives

Categories

Clippings

Weblogs, Discussions, Commentaries

Meta