The Hunt for Centauri Planets

by Paul Gilster on May 20, 2009

Finding Earth-like planets around any star would be a stunning feat, and either Kepler or CoRoT may deliver such news before too long. But how much more exciting still if we find a planet like this around a star as close as Centauri B? After all, the Centauri stars are our closest stellar neighbors, close enough (a mere 40 trillion kilometers!) to conjure up the possibility of a robotic mission there and, if we play our propulsion cards right in the future, perhaps a manned trip as well.

A Radial Velocity Long Shot

But can we pick up the faint signature of a terrestrial world in this system, given that it would be akin to ‘detecting a bacterium orbiting a meter from a sand grain — from a distance of 10 kilometers’? The phrase is Lee Billings’, from his fine essay in SEED called The Long Shot, on an ongoing project to do just that. Most radial velocity surveys are spread out over numerous stars, picking off close-in worlds whose traces should be obvious in short periods of time.

Gregory Laughlin (UC-Santa Cruz), on the other hand, armed with a planet hunter’s insights, a passion for the Centauri system, and a realization that patience could tease out faint signals like these, traded ideas with Debra Fischer (San Francisco State) on the possibility of devoting years to an Alpha Centauri search. Fischer is now hard at work, using a telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. She works with a decommissioned spectrometer and other vintage equipment. Call it ‘Alpha Centauri on the cheap.’

fischer

It may take promising early data to get even this modest setup funded after National Science Foundation funds run out in November, but we’ll take the funding problem one step at a time. For now, the precision work continues, with software Fischer herself coded being used to filter out distortions of weather, instrumentation and stellar activity on the target stars to hunt for the minute shifts in wavelength that could signal the breakthrough discovery. If she pulls this off, Fischer’s patience may become legendary.

Image: Centauri planet-hunter Debra Fischer. Credit: NASA.

A Parallel Hunt, and Controversy

We may be talking three to five years here, and in the meantime, Fischer’s work is being paralleled by Michel Mayor and Stéphane Udry using the High Accuracy Radial velocity Planet Searcher (HARPS) at the European Southern Observatory facilities at nearby La Silla. But ‘matched’ isn’t the best word — Mayor’s team isn’t as fixated on Alpha Centauri as Fischer’s because HARPS can’t be committed to a single, intensive project. If we’re talking an Earth-mass planet in Centauri B’s habitable zone, Fischer should find it first. A larger world may be claimed by Mayor.

You must read this essay. Billings is a wonderful writer whose scientific clarity is matched by a novelist’s eye for detail. And he’s working with a fascinating bunch of scientists, including Philippe Thébault, whose recent papers, discussed in these pages, have made the case that planets could not form around Centauri A and B because the relative velocities of planetesimals there would prevent their further growth. You have to love a scientist who speaks so openly about his own results, which differ sharply from Greg Laughlin’s conclusions on the Centauri system. Here’s Thébault on the matter, as quoted by Billings:

“If you ask a doctor about a fatal diagnosis he makes for a cancer patient, of course he wishes he is wrong. It is the same for me. It appears to be very difficult to form planets around close binary stars. I don’t wish for such a universe—I wish for another universe where planet formation is always very easy. I hope that Greg is right and that I’m wrong.”

We won’t know for a while, but it’s interesting that the binary system HD196885, a close match to Alpha Centauri, has a known gas giant at 3.5 AU. With refreshing candor, Thébault says he can’t explain that result: “…It shouldn’t be there.” On the flip side, the astronomer Peter van de Kamp spent decades looking for planets around Barnard’s Star, only to learn that the effect he was observing was an aberration in his instruments. The hunt continues in search of hard data.

alpha

Image: Alpha Centauri in context. Note that the three Centauri stars appear here as a single light source. Credit: Akira Fujii/David Malin.

What Centauri Means

Billings has his own thoughts on the significance of a find, and he also asks planet hunter Geoff Marcy for his take on the project:

The discovery of habitable worlds around any star would be front-page news, but finding them around our next-door neighbors would catalyze a scientific and cultural revolution, an immense rising wave of effort to learn whether our sister stars’ habitable planets were in fact inhabited. The ripples would spread beyond science to touch and change our literature and art, our politics and religion, perhaps even aiding our struggles to unite, survive, and expand as a species. The chain of chance that brought us into existence would swing to point outward to the stars, strengthening our resolve to someday reach them.

“If planets are found around Alpha Centauri, it’s very clear to me what will happen,” Marcy said. “NASA will immediately convene a committee of its most thoughtful space propulsion experts, and they’ll attempt to ascertain whether they can get a probe there, something scarcely more than a digital camera, at let’s say a tenth the speed of light. They’ll plan the first-ever mission to the stars.”

Well, maybe. Or maybe we’ll start with something closer to home, such as putting new emphasis on a planet hunter mission that can get spectroscopic observations of planetary atmospheres around these stars, a hellishly difficult challenge, but considerably less expensive than a one-shot flyby. That’s a question that can only be resolved by technical advances in coming years. While we work on the relevant technologies, what an encouraging thought that early in the next decade, we should have hard evidence for the presence or absence of Centauri planets. Billings again:

Alpha Centauri is today what the Moon and Mars were to prior generations—something almost insurmountably far away, but still close enough to beckon the aspirational few who seek to dramatically extend the frontiers of human knowledge and achievement. For centuries, it has been a canonical target of the scientific quest to learn whether life and intelligence exist elsewhere. The history of that search is littered with cautionary tales of dreamers whose optimism blinded them to the humbling, frightful notion of a universe inscrutable, abandoned, and silent.

Let’s hope today’s dreamers will be vindicated in their hopes for planets in this fascinating system. The confirmation of a terrestrial world there would add robustly to our theories of planetary formation. The study of its atmosphere could tell us whether our nearest neighbor also sheltered life. And what was true decades ago still holds: As an inspirational target driving propulsion research for the ultimate next generation mission, there’s nothing like Centauri.

tacitus May 20, 2009 at 17:07

I agree that it’s way too premature to be designing missions to Alpha Centauri should we find a habitable world in that system, despite the temptation and public pressure there will be to come up with something.

For one thing, we will continue to get orders of magnitude better return on investment by putting our efforts into building bigger and more powerful planet hunting telescopes that can characterize dozens, even hundreds of worlds in a matter of weeks or months. We have barely scratched the surface of what space-telescopes will be able to find out about exoplanets in the next 100 years, and until we start hitting up against physical limitations (like being hindered by the zodiacal light surrounding the innermost planets in their solar system) it should be full speed ahead on this type of mission, money and resources permitting.

I think Marcy does have one thing right, though. The 40-50 year duration (1/10th speed of light) of an interstellar mission is one that can be completed (just) within the lifetime of the designers (or the youngsters in the team anyway — you have to add another 4.37 years for the data to be returned!). I think this is going to be a hard limit to overcome, in the sense that scientists (and the funding politicians) are going to be very reluctant to pursue any mission that is longer than a working lifetime (40-50 years). The psychological hurdle will simply be too great, unless there is a driving force (like pending extinction!) behind it.

You might be able to stretch that out to 100 years by including important intermediate objectives, like studying the Oort Cloud or characterizing the true, interstellar environment, but that’s probably about it until and unless we find a way to vastly increase our lifespan (biologically or cryogenically).

Gregory Benford May 21, 2009 at 0:48

Of course, extending the mean human lifetime might well happen on this time scale. The technology is advancing rapidly. See: genescient.com

Adam May 21, 2009 at 2:35

Hi Paul

This time of year the Pointers are aimed at my house when I step off the train of an evening… a nice little cosmic signpost and a reminder of Bigger Things than little human concerns. Alpha would be an amazing place to find terrestrial planets, even if they were analogues of Venus or Mars.

JD May 21, 2009 at 5:39

Hi,

I still have a question about starships which may get us to Centauri. Fusion is our best bet at the moment, right?

But before we even start thinking about fusion propulsion, shouldn’t we achieve net gain fusion here on Earth first? I read about the Winterberg starship in an article here and apparently he came up with a method to ignite a D-D pulse reaction on a starship. But would this even work with current technology? Or do we have to find a method to achieve a net gain in energy first?

philw1776 May 21, 2009 at 14:29

JD, none of these Fusion technologies have been engineered to work (net gain) even in the lab never mind space ready, and that’s with decades of effort and tens of billions of dollars.

Were HZ plante(s) detected around Alpha Centauri A and/or B, there are plenty of good practical space telescope engineering efforts that could produce spectroscopic data capable of detecting biomarkers and later continental resolution images, given 2-3 decades.

kurt9 May 21, 2009 at 15:15

We’re not going to get interstellar travel before we get radical life extension and other developments like fusion power. We certainly will not have manned interstellar travel anytime in the near future (unless some wild card like Heim theory turns up). In any case, it is pointless to attempt interstellar travel until you have the technology to make the trip in 30-40 years or less.

James M. Essig May 21, 2009 at 17:09

Hi Folks;

While we are on the subject of 30 to 40 year time frame trips to the Centauri System under nuclear power, perhaps the following computations can make the case for a electrodynamically breaked manned nuclear rocket mission to our nearest 10 or 20 stellar neighboors, most especially the closest one of the Centauri System.

Take the relativistic rocket equation delta V = C tanh [(Isp/C) ln(Mo/M1)] where C is the speed of lght, Mo is the initial mass of the fueled weight of the vehicle, and M1 is the dry weight of the vehicle or final payload rest mass.

We will let M0/M1 = a hefty 1,000 which might be doable for vehicles having tanks made of metallic hydrogen that could be scavenged for use as fusion fuel. The maximum theoretical Isp of hydrogen to helium is .119 C. Note that these equations assume constant Isp output.

The result is delta V = C tanh [(.119C/C) ln 1,000] = .6762 C. For Mo/M1 = 10,000, we have delta V = C tanh [(.119C/C) ln 10,000] = .79907 C, and for M0/M1 = 100,000, we have delta V = C tanh [(.119C/C) ln 100,000] = .87870 C which corresponds to a gamma factor of about 2. This bad boy could put any star system within a 60 lightyears in range of Earth for a healthy young robust crew. Without medical life span enhancement, child birth and rearing could happen enroute. A medically enhanced life expectancy of 1,000 years could permit crews to arrive at stars that are 1,900 lightyears distant yet still allow the crew members an average of most of a century to live out the rest of their lives on the new home.

For a perhaps more reasonable, M0/M1 = 100, we have delta V = C tanh [(.119C/C) ln 100]= .49899 C, and for a very reasonable M0/M1, we have delta V = C tanh [(.119C/C) ln 10] = .2673 C.

Now for a maximum Isp of 0.04C for nuclear fission fuel, and a very reasonable M0/M1 = 10, we have delta V = C tanh [(.04C/C) ln 10] = 0.0918 C. For Mo/M1 = 100, we have delta V = C tanh [(0.04C/C) ln 100] = 1.821C.
For Mo/M1 = 1,000 we have delta V = C tanh [(0.04C/C) ln 1,000] = .2694 C.
For Mo/M1 = 10,000 we have delta V = C tanh [(0.04C/C) ln 10,000] = .35259 C, and for a still plausible Mo/M1 = 100,000 we have delta V = C tanh [(0.04C/C) ln 100,000] = .4305 C.

The point is, we can get to the stars under nuclear power and reactionary propulsion mechanisms that by far out do Project Daedalus. I would love to be the commander of such a nuclear vessel radioing back to Earth, “Underway on nuclear power”, just as someone else did when the first nuclear powered submarine was launched by the U.S. Navy.

If we find an Earth like planet within the Centuari System, I think there will be a huge effort to develop nuclear propulsion methods with operational paramenters simmilar to the values calculates above in order to reach this system, and this discovery could happen any year now.

Enzo May 22, 2009 at 0:58

I really do not think that the discovery of Earth like planets around the Centauri system will start any effort to get there.
First of all, it depends on how much Earth like. A clone with oceans, clouds and continents would generate interest for sure, but enough to get there ?
I don’t know, certainly enough to build some serious telescope and study it, but beyond that…..

We have in our solar system a world which is very likely to have an ocean. It is one of the best targets we have for extraterrestrial life and, still, the first orbiter will get there in 20 YEARS if we are lucky.
Just scale that to Alpha Centauri.

Athena Andreadis May 22, 2009 at 9:47

Some great public works took more than the lifetime of their designers and engineers, but they still undertook them on the wings of collective desire to accomplish them. A fifty-year mission to the Centauri system if it is discovered to harbor earth-like planets will be worthwhile, even if it were to be later overtaken by a faster one.

Marc Millis May 22, 2009 at 10:14

To James M. Essig;

Can you also provide us the calculated energy and power requirements that go along with your ∆v figures?

Thanks,

Marc

James M. Essig May 22, 2009 at 13:06

Hi Marc;

Note that the power actually delivered to the rocket is dependent on rocket velocity in accordance to the equation Int (F dot x) dt = Int (Fx Cos 0)dt for thrust stream velocity anti parallel to the rocket velocity vector.

For fusion fuel with an Isp of 0.119 C, an Mo/M1 value of 10 and an M0 = 1 million metric tons and thus an M1 value of 100,000 metric tons, assumming 1 kilogram of fuel is fully fusioned per second ship time , the energy released within the exhaust stream per second ship time is 0.007156 kg [C EXP 2] = 6.4404 x 10 EXP 14 Joules. The exhaust stream power output ships reference frame is 644 Terawatts. The time required to expend the entire supply of fuel ship’s time is 900 million seconds or about 30 years. For fuel burn at 10 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3 years. Not that 10 kilograms of fully fused fusion fuel is equal to about 1.5 megatons of TNT.

For fusion fuel with an Isp of 0.119 C, an Mo/M1 value of 100 and an M0 = 1 million metric tons and thus an M1 value of 10,000 metric tons, assumming 1 kilogram of fuel is fully fusioned per second ship time , the energy released within the exhaust stream per second ship time is 0.007156 kg [C EXP 2] = 6.4404 x 10 EXP 14 Joules. The exhaust stream power output ships reference frame is 644 Terawatts. The time required to expend the entire supply of fuel ship’s time is 990 million seconds or about 31 years. For fuel burn at 10 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3.1 years.

For fusion fuel with an Isp of 0.119 C, an Mo/M1 value of 1,000 and an M0 = 1 million metric tons and thus an M1 value of 1,000 metric tons, assumming 1 kilogram of fuel is fully fusioned per second ship time , the energy released within the exhaust stream per second ship time is 0.007156 kg [C EXP 2] = 6.4404 x 10 EXP 14 Joules. The exhaust stream power output ships reference frame is 644 Terawatts. The time required to expend the entire supply of fuel ship’s time is 999 million seconds or about 31 years. For fuel burn at 10 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3.1 years.

For fusion fuel with an Isp of 0.119 C, an Mo/M1 value of 10,000 and an M0 = 10 million metric tons and thus an M1 value of 1,000 metric tons, assumming 10 kilogram of fuel is fully fusioned per second ship time , the energy released within the exhaust stream per second ship time is 0.07156 kg [C EXP 2] = 6.4404 x 10 EXP 15 Joules. The exhaust stream power output ships reference frame is 6,440 Terawatts. The time required to expend the entire supply of fuel ship’s time is 999 million seconds or about 31 years. For fuel burn at 100 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3.1 years.

For fusion fuel with an Isp of 0.119 C, an Mo/M1 value of 100,000 and an M0 = 100 million metric tons and thus an M1 value of 1,000 metric tons, assumming 100 kilograms of fuel is fully fussioned per second ship time , the energy released within the exhaust stream per second ship time is 0.7156 kg [C EXP 2] = 6.4404 x 10 EXP 16 Joules. The exhaust stream power output ships reference frame is 64.40 Petawatts. The time required to expend the entire supply of fuel ship’s time is 999 million seconds or about 31 years. The yield of 100 kilograms of high end performance fusion fuel is a whopping 15 megatons. Note however, that with this craft, relativistic time dilation would be an important consideration for journies to stars dozens of light years from Earth.

James M. Essig May 22, 2009 at 13:08

Hi Marc;

Here are some numbers for fission powered rockets.

For fission fuel with an Isp of 0.04 C, an Mo/M1 value of 10 and an M0 = 1 million metric tons and thus an M1 value of 100,000 metric tons, assuming 1 kilogram of fuel is fully fissioned per second ship time , the energy released within the exhaust stream per second ship time is 0.0008 kg [C EXP 2] = 7.208 x 10 EXP 13 Joules. The exhaust stream power output ships reference frame is 72.08 Terawatts. The time required to expend the entire supply of fuel ship’s time is 900 million seconds or about 30 years. For fuel burn at 10 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3 years. Note that 10 kilograms of fully fissioned fission fuel is equal to about 200 kilotons of TNT.

For fission fuel with an Isp of 0.04 C, an Mo/M1 value of 100 and an M0 = 1 million metric tons and thus an M1 value of 10,000 metric tons, assuming 1 kilogram of fuel is fully fissioned per second ship time , the energy released within the exhaust stream per second ship time is 0.0008 kg [C EXP 2] = 7.208 x 10 EXP 13 Joules. The exhaust stream power output ships reference frame is 72.08 Terawatts. The time required to expend the entire supply of fuel ship’s time is 990 million seconds or about 31 years. For fuel burn at 10 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3.1 years.

For fission fuel with an Isp of 0.04 C, an Mo/M1 , an Mo/M1 value of 1,000 and an M0 = 1 million metric tons and thus an M1 value of 1,000 metric tons, assuming 1 kilogram of fuel is fully fissioned per second ship time , the energy released within the exhaust stream per second ship time is 0.0008 kg [C EXP 2] = 7.208 x 10 EXP 13 Joules. The exhaust stream power output ships reference frame is 72.08 Terawatts. The time required to expend the entire supply of fuel ship’s time is 999 million seconds or about 31 years. For fuel burn at 10 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3.1 years.

For fission fuel with an Isp of 0.04 C, an Mo/M1 value of 10,000 and an M0 = 10 million metric tons and thus an M1 value of 1,000 metric tons, assuming 10 kilogram of fuel is fully fissioned per second ship time , the energy released within the exhaust stream per second ship time is 0.008 kg [C EXP 2] = 7.208 x 10 EXP 14 Joules.. The exhaust stream power output ships reference frame is 720.8 Terawatts. The time required to expend the entire supply of fuel ship’s time is 999 million seconds or about 31 years. For fuel burn at 100 kilograms per second ship time, the fuel burn time ships reference frame time would be a mere 3.1 years.

For fission fuel with an Isp of 0.04 C, an Mo/M1 value of 100,000 and an M0 = 100 million metric tons and thus an M1 value of 1,000 metric tons, assuming 100 kilograms of fuel is fully fissioned per second ship time , the energy released within the exhaust stream per second ship time is 0.08 kg [C EXP 2] = 7.208 x 10 EXP 15 Joules The exhaust stream power output ships reference frame is 7.208 Petawatts. The time required to expend the entire supply of fuel ship’s time is 999 million seconds or about 31 years. The yield of 100 kilograms of high end performance fission fuel is a whopping 2 megatons. Note however, that with this craft, relativistic time dilation would be an important consideration for journeys to stars dozens of light years from Earth.

Note that for the mildly relativistic ship cases, one second ship time is approximately one second Earth time. Even at the speed of 0.5 C, the gamma factor is only 1.1547 and time is only dilated about 15 percent. Therefore the rate of fuel consumption in terms of kilograms per second is fairly close in both the Earth’s reference frame and the ships reference frame for velocities less than 0.5 C

JD May 22, 2009 at 14:03

Hi,

Interesting numbers.

I don’t think really high mass ratios will be possible for D-He3 fusion rockets, since you need to factor in tankange. The tanks will not only have to keep the Deuterium and Helium cool enough (not that much of a problem in interstellar space) but also provide micrometeroid shielding and of course withstand the internal pressure the fuel exerts on the tank structure.

And the ISP number is probably too high. According to NASA reports a magnetic nozzle would be about 80% efficient in channelling exhaust.

15% to 20% c is by far the most I can see for D-He3 fusion propulsion.

It may be a different story with p-Li fusion. It offers a lower exhaust velocity, but since the proton is “recycled” in the reaction the only fuel we need to bring along is lithium. Since lithium is metallic there would be no need for tankage. A p-Li starship could essentially be a fusion reactor attached to a huge ball of litihium, allowing for very good mass ratios, like Enzmann starships.

Anyway, fusion propulsion is probably not an option unless we achieve power generation by fusion here on Earth. Perhaps the polywell is a promising candidate? It may lead to the development of QED fusion drives, as described by Bussard.

I don’t think it is realistic to construct fission starships capable of reaching a significant fraction of the speed of light. Reactor power levels are too high and the amount of fissionable materials required by such a mission would simply be stunning, probably exceeding the known reserves of Uranium on Earth.

spaceman May 22, 2009 at 14:58

I have a few thoughts on this subject, one of them being that all of the evidence thus far points to the fact planet formation is a very robust process that takes place in multiple stellar environments, and, if anything, we should be more cautious about saying where we think planets CANNOT be found then where we say planets can be found. The very existence of the planets in the HD196885 and Gamma Cephei systems, as our boy Thébault himself admits, casts a shadow of doubt on his team’s pessimistic conclusion regarding Centauri planets.

So, time will tell whether or not there are terrestrial planets in the Centauri A & B region. However, very few people seem to realize that the Kepler mission will undoubtly look at multiple star systems with configurations more or less similar to Centauri A & B. I am optimistic that Kepler will find evidence of terrestrial planets in close binary systems thereby increasing our confidence that planets may exist in the Centauri system.

I think the Kepler mission website states it quite well indeed:
“Estimate how many planets there are in multiple-star systems…”

Marc Millis May 22, 2009 at 18:26

James Essig, JD, et al;

Thanks for the numbers and other comments. I’ve been struggling for an effective way to capture such information – across the span of possibilities – so that when we make comparisons there is a common baseline and the critical issues are brought to the surface. My intent is not to pick THE winner (way too soon), but to draw attention to today’s to-do-list – those challenges that are the easiest to make progress on now.

For example, with the vehicle idea put forth, which of the required ‘miracles’ could be addressed by real research today – to actually improve the prospects. Is it finding another source of fissionable materials? Ultra efficient magnetic nozzles? ‘Consumable’ propellant tanks?

Another thought from the prior discussion – the potential need to mine fissionable materials from non-Earth sources might find its way onto a list of interim learning missions – interstellar precursors. At this point, this is just a raw thought, but offered to illustrate other things we’ll need to solve along the way.

At some time in the not-to-distant future, I might ask you folks to resubmit your information (like that above) and the supporting references, but configured into an outline that I still have to devise – an outline to offer more evenly considered comparisons and put all our required ‘miracles’ into fair terms.

Thanks,
Marc

James M. Essig May 22, 2009 at 21:58

Hi Marc;

Thanks for the kind words.

One notion of fissionable materials I would like to consider here, and I am really going out on a limb here, is the science fiction concept of the proton bomb. The idea here is that somehow the quarks within protons would somehow liberate their binding energy, an energy which is about 2 orders of magnitude greater than the rest mass of the quarks.

Obviously, QCD models of hadrons composed of up and down quarks such as the proton and the neutron indicate that finding a lone or isolated up or down quark is at least next to impossible. However, reports of the observation of an isolated heavier flavor of quark have surfaced.

Perhaps with the LHC and/or the proposed ILC, a planned TeV electron collider in the design phases, we will discover an energy source under the umbrella of better understood QCD physics or perhaps the discovery of an additional nuclear force which might pave the way for higher mass specific energy density fuels than nuclear fusion but which does not involve the combersome problem of producing large quantities of antimatter.

Regarding fission fuel resources, one thing I have become interested in as of late is breeder reactor technology which could be used to produce traditional fission fuels from much more plentiful natural isotopic stocks.

Perhaps we should really be looking at asteriods, the Moon, and Mars much more closely as a supply of such fission fuels or fission reactor breed stock.

Regards;

Jim

spaceman May 23, 2009 at 12:27

I don’t want to engage in nay-saying and I hope my concern over this is unfounded, but has anyone worked out the consequences of a pebble-sized piece of dust or ice hitting a starship that is traveling at 10-15% light speed? I mean, if a small pebble can crack my windshield at 40 MPH and the infamous “space junk” could bring down a space shuttle, then just think of the destruction even a small particle hitting a spaceship traveling at 10-15% light-speed could cause. And if shielding is used to protect against this, assuming a denseresilient heavy material, the mass of the ship is increased to the point that it becomes hard to reach such enormous velocities to begin with.

Upon further thought, I guess it would depend to some extent the general size and spatial distribution of interstellar matter. Is there any data on the size and spatial distribution of interstellar particles from astronomical observations? If there isn’t any such data, then before any fast missions are developed, this data will be a must.

Administrator May 23, 2009 at 13:24

spaceman, interstellar dust is a significant issue. Here’s the most recent thing I’ve done on it:

http://www.centauri-dreams.org/?p=7065

and here’s one that’s more closely focused on small particles:

http://www.centauri-dreams.org/?p=5994

but you might want to search the archives for older stories dealing with the problem of encounters like this. Shielding is a major problem; the people behind the Project Daedalus design worked out a variety of options for providing protection, but all have drawbacks due to the mass they add.

JD May 23, 2009 at 16:06

Wouldn’t it be possible to generate a magnetic field which shields at least the habitable compartments from radiation?

Mark May 23, 2009 at 20:12

I think before we send a manned mission to the stars, we should really take a page from the space race of the 60′s. I vote we send a dog first, then if that succeeds, we send a monkey. The monkey could be trained to point the digital camera at any planets it finds and then hook up a USB cable and key a transmitter to return the images. Monkeys are easier to transport through space because they are physically smaller and do not require much in the way of complicated menus or sophisticated entertainment. They eat bananas and coconuts and can entertain themselves for hours by just grooming themselves, hooting, jumping, throwing feces, and scratching themselves. If we really push it, we can do better than 0.1c, say 0.2c. Then we could get a dog there and back in 40 years, do a complete physical on it, then if all checks out, we send in the monkey. By that time we should be able to reach 0.5c and we can get the monkey there and back in only 16 years. When he gets back we should be good for 0.9c or better, very likely even FTL and in that case we can send a large manned crew, who will arrive there several years before they are launched. They will return also FTL, arriving before we even launch the dog. In this manner we will have explored the region even without constructing a single ship. The key is to plan it out and get started. FTL time paradox will take care of the rest.

Athena Andreadis May 25, 2009 at 10:50

Water is a good radiation shield. So is food (and its metabolites…) as Zubrin pointed out in his Mars proposal.

Mark, both dogs and monkeys are deeply social animals. Sending an isolated monkey in a tin can for an extended period time won’t yield much information because the animal will go mad very soon without company. Primates do require stimulation and sophisticated environments — they don’t do terribly well in zoos, that’s why they resort to throwing feces around (as do human prisoners, when they riot).

amphiox May 28, 2009 at 20:47

Mark, notwithstanding the social animal issues, what breed of dog, and what species of monkey, lives for 40 years?

amphiox May 28, 2009 at 20:49

At any rate, by the time we develop 0.1-0.2c propulsion, it is highly likely we will also have developed AI functioning at least at a level equivalent to a well trained dog, and sufficiently sophisticated biological analogs to do the appropriate life support testing.

spaceman June 3, 2009 at 7:26

Does anyone know if nulling interferometers and/or SIM are scheduled to look for planets around Alpha Centauri A and B? If so, what is the minimum planet size that a TPF or Darwin could detect around either or both of these stars?

ljk August 13, 2009 at 10:36

Five planets and an independent confirmation of HD 196885Ab from Lick Observatory

Authors: D. A. Fischer, P. Driscoll, H. Isaacson, M. Giguere, G. W. Marcy, J. A. Valenti, J. T. Wright, G. W. Henry, J. A. Johnson, A. W. Howard, K. M. G. Peek, C. McCarthy

(Submitted on 11 Aug 2009)

Abstract: We present time series Doppler data from Lick Observatory that reveal the presence of long-period planetary companions orbiting nearby stars. The typical eccentricity of these massive planets are greater than the mean eccentricity of known exoplanets.

HD30562b has Msini = 1.29 Mjup, with semi-major axis of 2.3 AU and eccentricity 0.76. The host star has a spectral type F8V and is metal rich. HD86264b has Msini = 7.0 Mjup, arel = 2.86 AU, an eccentricity, e = 0.7 and orbits a metal-rich, F7V star. HD87883b has Msini = 1.78 Mjup, arel = 3.6 AU, e = 0.53 and orbits a metal-rich K0V star. HD89307b has Msini = 1.78 Mjup, arel = 3.3 AU, e = 0.24 and orbits a G0V star with slightly subsolar metallicity. HD148427b has Msini = 0.96 Mjup, arel = 0.93 AU, eccentricity of 0.16 and orbits a metal rich K0 subgiant.

We also present velocities for a planet orbiting the F8V metal-rich binary star, HD196885A. The planet has Msini = 2.58 Mjup, arel = 2.37 AU, and orbital eccentricity of 0.48, in agreement with the independent discovery by Correia et al. 2008.

Comments: 12 figures, 8 tables, accepted ApJ

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:0908.1596v1 [astro-ph.EP]

Submission history

From: Debra A. Fischer [view email]

[v1] Tue, 11 Aug 2009 23:43:14 GMT (1880kb)

http://arxiv.org/abs/0908.1596

ljk August 13, 2009 at 10:38

Two Exoplanets Discovered at Keck Observatory

Authors: J. A. Valenti, D. A. Fischer, G. W. Marcy, J. A. Johnson, G. W. Henry, J. T. Wright, A. W. Howard, M. Giguere, H. Isaacson

(Submitted on 12 Aug 2009)

Abstract: We present two exoplanets detected at Keck Observatory. HD 179079 is a G5 subgiant that hosts a hot Neptune planet with Msini = 27.5 M_earth in a 14.48 d, low-eccentricity orbit. The stellar reflex velocity induced by this planet has a semiamplitude of K = 6.6 m/s.

HD 73534 is a G5 subgiant with a Jupiter-like planet of Msini = 1.1 M_jup and K = 16 m/s in a nearly circular 4.85 yr orbit. Both stars are chromospherically inactive and metal-rich.

We discuss a known, classical bias in measuring eccentricities for orbits with velocity semiamplitudes, K, comparable to the radial velocity uncertainties. For exoplanets with periods longer than 10 days, the observed exoplanet eccentricity distribution is nearly flat for large amplitude systems (K > 80 m/s), but rises linearly toward low eccentricity for lower amplitude systems (K > 20 m/s).

Comments: 8 figures, 6 tables, accepted, ApJ

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:0908.1612v1 [astro-ph.EP]

Submission history

From: Debra A. Fischer [view email]

[v1] Wed, 12 Aug 2009 04:32:34 GMT (89kb)

http://arxiv.org/abs/0908.1612

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