Potential ‘Goldilocks’ Planet Found

by Nancy Atkinson on February 2, 2012

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The newly discovered planet is depicted in this artist's conception, showing the host star as part of a triple-star system. The diagram below shows the orbits of the detected planets around the host star in relation to the habitable zone. Images courtesy of Guillem Anglada-Escudé, Carnegie Institution.

A new-found planet is in a ‘just-right’ location around its star where liquid water could possibly exist on the planet’s surface. A team of international astronomers have discovered a potentially habitable super-Earth orbiting a nearby star in a habitable zone, where it isn’t too hot or too cold for liquid water to exist. The planet, GJ 667Cc, has an orbital period of about 28 days and with a mass about 4.5 times that of the Earth. The star that it orbits is quite interesting. It is an M-class dwarf star and is a member of a triple star system and appears to be quite different from our Sun, relatively lacking in metallic elements.

The team said this discovery demonstrates that habitable planets could form in a greater variety of environments than previously believed.

“This was expected to be a rather unlikely star to host planets,” said Steven Vogt from UC Santa Cruz, one of the scientists involved in the discovery. “Yet there they are, around a very nearby, metal-poor example of the most common type of star in our galaxy. The detection of this planet, this nearby and this soon, implies that our galaxy must be teeming with billions of potentially habitable rocky planets.”

“This planet is the new best candidate to support liquid water and, perhaps, life as we know it,” said Guillem Anglada-Escudé, from the University of Gottingen in Germany. He was with the Carnegie Institute for Science when the planet was first discovered.

The planet orbits quite close to its parent star at 0.12 astronomical units, which is much closer than Mercury to the Sun. However, the Planetary Habitability Laboratory says the star is much dimmer and provides enough energy for the planet to possibly maintain similar terrestrial temperatures. There’s a caveat, though, that astronomers aren’t sure what the planet’s composition is, because they have not been able to measure its size; therefore, it could be a either a rocky or a gas planet. I would need to have a radius between about 1.7 and 2.2 Earth radii to be a rocky world.

The team used public data from the European Southern Observatory combined with observations from the Keck Observatory in Hawaii and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope in Chile. To follow up and verify the findings, the team used the radial velocity method to measures the small wobbles in the star’s motion caused by the gravitational tug of a planet.

“With the advent of a new generation of instruments, researchers will be able to survey many M dwarf stars for similar planets and eventually look for spectroscopic signatures of life in one of these worlds,” said Anglada-Escudé.

The star, GJ 667C is 22 light years away. It has much lower abundance of elements heavier than helium, such as iron, carbon, and silicon, as does our Sun. The other two stars (GJ 667A and B) are a pair of orange K dwarfs, with a concentration of heavy elements only 25% that of our Sun’s. Such elements are the building blocks of terrestrial planets so it was thought to be unusual for metal-depleted star systems to have an abundance of low mass planets.

Diagram of the planets orbiting the star GJ 667C. Credit: UC Santa Cruz

GJ 667C had previously been observed to have another super-Earth (GJ 667Cb) with a period of 7.2 days, although this finding was never published. This orbit is too tight, and thus hot, to support life. The new study started with the aim of obtaining the orbital parameters of this super-Earth, and came to find an additional planet.

The new planet receives 90% of the light that Earth receives. However, because most of its incoming light is in the infrared, a higher percentage of this incoming energy should be absorbed by the planet. When both these effects are taken into account, the planet is expected to absorb about the same amount of energy from its star that the Earth absorbs from the Sun. This would allow surface temperatures similar to Earth and perhaps liquid water, but this extreme cannot be confirmed without further information on the planet’s atmosphere.

The team said there is a possibility of other planets in the system, potentially a gas-giant planet and an additional super-Earth with an orbital period of 75 days. However, further observations are needed to confirm these two possibilities.

This is the fourth potentially habitiable extrasolar planet. Three were found in 2011: Gliese 581d, which scientists say is likely a rocky world about 20 ight-years away; HD 85512 b, another planet orbiting in a habitable zone is about 36 light-years away from Earth; and Kepler 22b, about 600 light-years away. Vogt was involved in the discovery of another planet in 2010 (Gliese 581g) in which he said the “chances of life on this planet are 100%,” but other astronomers have cast doubt on whether that planet even exists.

Papers:
The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample, and A planetary system around the nearby M dwarf GJ 667C with at least one super-Earth in its habitable zone (will add link when it becomes available)

Sources: UC Santa Cruz, Carnegie Institute for Science, Planetary Habitability Laboratory

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Anonymous February 2, 2012 at 6:21 PM

nice, but i think that kepler 22b is a far better candidate for life. We do not really now if a red dwarf is good to support life. maby we should first investigate that.

Anonymous February 2, 2012 at 11:47 PM

The only problem is that it is a flare star, the planet needs a powerful magnetic field in order to keep its magnetic field intact. It’s larger than the Earth and the orbital period should not be so long as to stop a dynamo effect from occurring.

Torbjörn Larsson February 2, 2012 at 7:20 PM

Keep them coming!

The planet is a bit on the heavy side, so it is unclear if it is a neptune or a terrestrial. Also it has to have a tad light atmosphere to be habitable. At the modeled Earth atmosphere pressure it would not protect as much against the more serious CMEs a young M star tend to give.

It would be interesting to know the age of the star, but I can’t find it.

I’m not sure why they speculate in that metal-poor star has fewer planets. As I remember it smaller stars on average has more terrestrials but metal-poor stars are believed to have less jupiters.

Another speculation often heard is that M stars, which are most numerous and are expected to have many planets AFAIK, would be poor habitables for life or complex life.

But all the negatives can be mooted or are speculative. Initial CMEs and/or later lack of magnetic field can be shielded by a denser atmosphere, tidal locks of close orbiting habitable planets are not necessarily resulting in a lack of magnetic field (see our Moon’s initial field right after its creation and rapid lock), oxygenating photosynthesis is possible in the near IR max spectra of an M star (chlorophyll f), et cetera.

If one plays the number game, it is possible that the population of M stars are at least as good as the population of G stars as regard potential habitability in a galaxy.

Anonymous February 2, 2012 at 7:44 PM

If the planet has a composition similar to Earth its surface gravity would be around 1.65g. If the radius is 1.7R_earth then is surface gravity is 1.55g and for 2.2R_earth it surface gravity would be .93g.

This planet is just within the range I think which could be explored with interstellar probes. A photon sail, driven by a collimated beam of solar light directed by a large Fresnel lens, could reach ? = 1.5, or with ? = 1/sqrt{1 – (v/c)^2} a velocity v ~ .75c, which might reach the star in about 40 years and transmit data back in 22 years. That means people starting the project might actually live to see data returned.

This planet is likely tidally locked, which carries all those implications. This planet will have about 4 times the surface area Earth has, and the annulus where solar radiation is 0 to 20 degrees to the horizon means there is 1.3 times the Earth’s surface which could be “comfortable.” This would require enough atmosphere to maintain pressure and to equilibrate temperatures moderately, but not too much. The planet could has a very thin atmosphere or be another Venus-like body. Then again as the article points out it could be a gas planet.

There is a plausible chance for life there.

LC

Anonymous February 2, 2012 at 11:27 PM

From the diagram it looks like GJ 667 Cc is in the region of the habitable zone where the Earth is located. That might make it habitable for many components of the terrestrial biosphere. Looks like a good candidate for settlement, it’s only 22.1 ly away.

Anonymous February 3, 2012 at 12:38 AM

A mission to send a probe to GJ 66 would be a huge endeavor. I don’t think we will have the ability to send a robotic spacecraft there until the second half of this century at the earliest. Honestly I suspect interstellar probes may not be sent until the 22nd century, and this assumes our species or civilization has not sh*t canned itself by various possible means. Sending human travelers to other stars would be orders of magnitude larger in scale and complexity.

We have found an array of planets in this galactic neighborhood; some which we know are very different from anything in our solar system. I read a while back about a hot rocky planet orbiting close to its star. As I recall there was a spectral signature of water, where the thinking is this is an ocean planet with superheated water under enormous pressure. That is very different from anything in our solar system. The data is revealing a huge range of diversity of possible planetary systems and planetary environments. Some of these rocky planets in the habitable zone are likely to be radically different from Earth. These planets near dwarf stars might hold life in some cases, but chances are excellent they would be hostile to human life.

The surface gravity of this planet is 1.5g, which means walking around there would be like carrying an 80 pound pack all the time. The added weight and pull on blood would put much greater strain on the heart. Even if this planet has an oxygen atmosphere, liquid water, balmy temperatures and so forth, it is likely we could not live there. If there is biology there it would be problematic to interact directly with it.

LC

Anonymous February 3, 2012 at 5:51 AM

I agree with you. But what I’m saying is that it would be relatively easier to send a probe to this planet than to, say, Kepler-22b 600 light-years away. As for living there, I’m pretty sure that you could live on GJ 667 Cc, but it would be incredibly difficult. Not that you’d die early or anything, you’d just need to be in good physical shape and willing to withstand stress.

People would anyway probably do less physical activity as a result of being on that planet, if we ever colonized it. But in any event, obese people are able to stand on Earth. It would require more exertion like that, but an able-bodied colonist should be able to do it. And the biological effects of obesity (atherosclerosis etc) would not come. However, there would be health problems (such as osteoarthritis) which would result from bearing 1.5 Gs on bones designed for 1.

Could humans colonize it? Yes.
Would it be advisable if you’re not able-bodied? No.

Torbjörn Larsson February 3, 2012 at 10:55 PM

Some of those effects would be the first years, the skeleton would remodel et cetera, as well as first generations.

Unless development is seriously affected (can or has been tested in centrifuges here I would bet, at least on insects), some of those effects may go away within the first generation or two. The rest would be under heavy selection, and who knows how much will go away.

Anonymous February 4, 2012 at 6:12 AM

I’d have to contest this idea that the planet makes a decent candidate for colonization. Remember it is tidally locked. This causes huge imbalances in temperature between the star facing side and it’s counterpart.

Depending on how thick the atmosphere is, you could be up against some pretty ferocious planetary winds. It’s quite possible these winds would make living on the surface impossible (or reaching it for that matter).

Anonymous February 3, 2012 at 10:04 PM

Laying aside the Fresnel lens possibility, I think a raw sail can still achieve better than 2% of the speed of light (I’d love to get your book some day to see if my calculations are anywhere near yours – if the price comes down) and the main advantage then is that slowing down uses the symmetrical process of course. Looking at what Rice University is doing with nano- vehicles, self maintenance and self replication may be possible before the end of this century. Aluminium on a carbon nanotube and graphene structural frame could make a very high lightness sail.

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=13528&SnID=1581437466

Julian Sloop February 3, 2012 at 1:02 AM

What do you think about the possibility of life forming in liquid methane? All that talk about life possibly existing on Titan, couldn’t we monitor the flux in Titan’s atmospheric composition and determine the answer to that question?

Torbjörn Larsson February 3, 2012 at 10:48 PM

That is exactly how the speculations got amplified, the surface has a deficit of hydrogen, and a surplus of acetylene IIRC, which can’t yet be explained by astrophysical models. Hydrogen to acetylene metabolism could be one explanation, or something else interesting associated with the surface.

Julian Sloop February 3, 2012 at 11:31 PM

I find this amazing. How wild would it be if humanity discovered such a life form! Could you imagine the possible uses for such organisms? I really hope that America decides to stop half-assing space exploration, if not the scientific community could soon be moving to china, lol.

Torbjörn Larsson February 4, 2012 at 12:55 PM

Possibilities for methanogenic life in liquid methane
on the surface of Titan”
, McKay et al. (Icarus 2005, so not the latest on the atmosphere measurements and modeling.)

“If bacteria are consuming complex hydrocarbons at the surface of Titan, the observable effects might include: complete consumption of C2H2 at the surface, reduction in C2H6 and organic solids at the surface compared to the
accumulation expected from photolysis alone, and a sink of hydrogen at the surface creating a gradient in the hydrogen mixing ratio with altitude. All of these effects may be detected and measured by the Huygens probe.”

What is Consuming Hydrogen and Acetylene on Titan?“:

“Two new papers based on data from NASA’s Cassini spacecraft scrutinize the complex chemical activity on the surface of Saturn’s moon Titan. While non-biological chemistry offers one possible explanation, some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan’s surface. According to one theory put forth by astrobiologists, the signatures fulfill two important conditions necessary for a hypothesized “methane-based life.”

One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan’s atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.”

Oops – McKay et al speculated in deficits of simple hydrocarbons from a hydrogen metabolism, what was observed was a surface deficit. I got that backwards.

Mind that everything observed can be more parsimoniously predicted by some surface mechanism. But what that is remains uncertain, while putative life is more “known”. Well, sort of…

Anonymous February 4, 2012 at 3:31 AM

There might be some complex chemistry. However, at those very cold temperatures ~ -170C on Titan the rate chemical activity takes place is much lower. There might be complex self-adaptive chemical processes, but they might not be exactly what we call life.

LC

Anonymous February 3, 2012 at 4:20 AM

Yes, but it might take hundreds (thousands?) of years for humans to get to the point where we can build such a lens (“large” is a bit of an understatement) , if we don’t kill ourselves in the mean time.

Anonymous February 4, 2012 at 4:01 AM

If you look up how a Fresnel lens work you see this does not have to be a huge thick lens of material. It would be more like a huge thing sheet.

LC

Anonymous February 7, 2012 at 7:29 PM

I have looked it up. I never said it would have to thick, I was just responding to your comment about it being a “large” Fresnel lens. It would have to cover a large area (again, an understatement) in order to focus enough of the light to make the spacecraft travel fast enough to be meaningful and we are very far away from the technology to be able to build such a lens, not to mention the economics of doing it. .

Gore Gogore February 3, 2012 at 11:00 PM

I don`t believe in the capacity of a spaceship to gather data from a star system (like our solar system) while flying at 0.75c, nor photos. Also i don`t believe in our capacity to receive signal from a small spaceship 20 light years away.

Anonymous February 4, 2012 at 3:10 AM

The solar sail is a disk of reflecting nanometer thin material. There would of course be a mast assembly and so forth which holds a shape and anchors the spacecraft to it. The sail would have a radius of 10km or so. The Fresnel lens would be this material in a fine grained pattern similar to those old overhead projectors base. That is a Fresnel lens. This too would be huge. The craft would accelerate by photon pressure up to maximum velocity. When it gets close to its destination the collimated beam of light again reaches the sail, but now a small central disk detaches. These photons reflect off the main sail, now an annulus and reach the small disk. This accelerates the small disk in the opposite direction and decelerates it. The central spacecraft, something maybe the size of a city bus, then enters the extra solar system at velocities comparable to spacecraft we send in our solar system. It may even have landing probes with rovers to explore one or more of the planets.

LC

Anonymous February 4, 2012 at 3:48 AM

I’ve heard and read about the solar sail concept before and it seems interesting, but 2 questions always come to mind. Firstly, will the craft be able to obtain enough light to reach maximum velocity while continuously moving away from it’s source (i.e. the Sun), and second, with such a delicate structure, what is to prevent the sail and craft from being damaged by things like interstellar dust and debris? Clearing the Oort cloud alone, with all it’s asteroids and rocks, would be difficult without some sort of “deflector” set up a la Star Trek. Then there’s the question of what lies beyond the Heliopause insofar as small or large obstructions is concerned. With 10km square of sail only nanometers thick and the craft moving so fast (at even 1% the speed of light, it’d be going!), any collisions might be catastrophic, no?

Anonymous February 4, 2012 at 4:03 AM

That is the point of the Fresnel lens optics. This collimates a beam onto the photon sail far out into space.

As for impact damage, the major concern is with the core spacecraft. The sail is just nanometer thin material. Any tiny piece of material will just pass right through. It would be best to select target stars which are not in line with the ecliptic to avoid much of this problem.

LC

Anonymous February 5, 2012 at 2:20 PM

The light falls off as the inverse square of distance so you need to get as close as possible to the Sun with a plain sail. That is temperature limited (assume a near black body rear side) but rotating the sail to grazing incidence (sail surface aligned with the limb of the Sun) can give a useful improvement.

The Fresnel Lens approach means you create a very low divergence beam so can use much lower thrust for a longer time. It still becomes inverse square beyond the Rayleigh Distance though. To lose half the energy sending a beam to Alpha Centauri for slowing the sail would require a lens 50km in diameter using visible light. That size and the power required then set the maximum distance of the lens from the Sun. There is also the technical problem of aiming the beam, just pointing at the target star isn’t good enough when the beam is ~70km in diameter at the destination and you have to illuminate the sail evenly. Perhaps a bigger problem though is political, a lens that size turned on a spot on Earth could be an effective weapon so getting international agreement for such a capability would be almost impossible.

Colloision avoidance isn’t feasible because transverse acceleration in deep space would be very slow and there is no power source to maintain a radar capable of giving sufficient advance warning of sub-millimetre dust. Since the sail side is illuminated at high power levels, any payload must be on the rear side and pushed so tethers cannot be used to spread the load. Using a distributed control model with sub-milligram processing nodes on a centimetre scale grid or smaller gives enormous redundancy so control core damage and even major attrition are not issues.

Using the simple sail approach, speeds are lower but the project can become truly “fire and forget” until you get a signal from the far end. You need an on-board repair system to avoid mission loss through attrition which can use rotational kinetic energy extracted using the galactic magnetic field for power. Very slight transverse acceleration for course correction might be possible using the same magnetic interaction but I haven’t done the numbers on these aspects.

The repair system would also allow for probe replication at the destination (using starlight for energy of course) if asteroid material or zodiacal dust could be used, just split the sail into quarters and allow each to repair themselves back to full size.

One is reconfigured as a sphere and stays to act as a communications hub using synthetic the aperture technique with metre scale plates each transmitting at the 1kW level. A 10km diameter sphere could transmit 80GW total continuous ERP.

The other sails would launch themselves towards the next tranche of stars to repeat the process so it is all fire and forget. We could span the galaxy in less than 15 million years (or any alien technological civilisation will already have done so). The Fresnel Lens approach reduces that to under 200,000 years but they don’t need to be exclusive, plain sails could be launched first and faster version launched later would just catch and pass them.

Anonymous February 2, 2012 at 10:36 PM

Goldilocks still doesn’t mean much =

Anonymous February 3, 2012 at 3:03 PM

Eric,
Yes it does.

Anonymous February 3, 2012 at 10:27 PM

What can it actually tell us though? I’ve seldom heard an astrobiologist speak in those kind of terms. Mars and Venus are ‘Goldilocks’ planets too, they remind us.

Torbjörn Larsson February 3, 2012 at 10:43 PM

I am not sure what you mean here. The astronomical program is quite clear cut and often presented.

- Kepler and others are surveying stars for exoplanets.

- From such surveys that one can design targeted missions for characterizing exoplanets.
This helps constrain models of planetary systems and their formation.

The similar astrobiological program is at least partway solidified.

- From exoplanet characterization one can hopefully find and characterize inhabited planets, with oxygen and nitrogen oxides in the atmosphere as biosphere indicators. This helps constrain models of biospheres and their formation (aka abiogenesis).

In as much as abiogenesis is a phenomena too large and too long to easily fit in a lab, nature can help us with finding out how life gets started.

Anonymous February 3, 2012 at 11:13 PM

I was suggesting that people may miss the point when they hear the term “goldilocks”. Given that so many variables play into our habitability, I believe that this term is giving some of the public a very narrow view of how scientists may characterize planets/moons.

Cheers
E

Ari Rosenbach February 3, 2012 at 12:46 AM

“GJ 667C had previously been observed to have another super-Earth (GJ 667Cb) with a period of 7.2 days, although this finding was never published.”

Amazing how far we’ve come. 15 years ago, that would’ve been among the most interesting stories of the year, now it’s so commonplace it’s scarcely worth publishing

Anonymous February 3, 2012 at 9:40 AM

Does anyone know any work on possibility that planet avoids being tidal locked to it’s star because of influences of other stars in a multistar system? I believe this may not be the case at present star system, having wobbling ~1M at 50-200 AU distance is not enough to avoid bleeding angular momentum, but I’m wondering about general case.

Anonymous February 3, 2012 at 10:17 PM

“GJ 667C had previously been observed to have another super-Earth (GJ 667Cb) with a period of 7.2 days, although this finding was never published.”

Actually, it was: http://arxiv.org/abs/1111.5019

Anonymous February 4, 2012 at 4:41 AM

It’s only 4.5 times the mass of Earth (-: . Has no metal. Has three suns. Hey I’m ready to go now. Why do we continue to hear excitement about “earth like” planets that are nothing like the earth? What is exciting about that?

Glenn

Torbjörn Larsson February 4, 2012 at 1:13 PM

I’ll point you to my first reply to EricEdwin below. It is exciting for knowing more on planetary formation but mostly IMO more on abiogenesis!

Anonymous February 7, 2012 at 2:51 AM

Planetary formation is extremely fascinating. So why not say it’s about planetary formation instead of hipping it as our new home? Couldn’t they say almost earth like planet? Isn’t honesty important in science? Hipe is not good for science. Thanks for your reply.

JFeral

________________________________
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To: g.nile@yahoo.com
Sent: Saturday, February 4, 2012 8:13 AM
Subject: [universetoday] Re: Potential ‘Goldilocks’ Planet Found

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Torbjörn Larsson wrote, in response to jferal:
I’ll point you to my first reply to EricEdwin below. It is exciting for knowing more on planetary formation but mostly IMO more on abiogenesis! Link to comment

Anonymous February 4, 2012 at 10:40 AM

4.5 time the mass of earth. No metal. 3 Suns. Hey I’m ready to go now. Why do scientist continue to get excited about planets like this and call them “Earth like” Is there a part of the earth I have yet to hear about?

Anonymous February 4, 2012 at 4:17 AM

Small objects just passing through makes sense, but what about something larger? What kind of control systems will a spacecraft like this be able to have? Or is it more a “set it and forget it” deal? If a big piece of debris rips the sail, or somehow tangles the supports (ostensibly, in order to produce the maximum reflectivity, one has to assume there wouldn’t be a massive support system which would obscure the sail) will that render the craft useless? Again, really interesting concept. Just curious about it’s feasibility.

Anonymous February 4, 2012 at 5:59 AM

In my understanding, there wouldn’t be any tangling or ripping. Any object would punch it’s way through, as their would be a huge speed difference between interstellar debris and the craft. Perhaps LC can elaborate on this.

Anonymous February 5, 2012 at 12:35 AM

Nothing is certain. If the photon sail craft crashes into a large enough of an object it could be destroyed. The central craft could suffer an impact, and even if the object were submillimeter in size the energy released would be equivalent to several pounds of explosives. If that just hits the sail the explosive energy just expends itself behind the path of the craft.

LC

Anonymous February 7, 2012 at 7:34 PM

There are materials being developed now that have self-healing properties. It would be awesome to have a self-healing solar sail.

Torbjörn Larsson February 4, 2012 at 1:09 PM

Ah, yes, that is also very sensible.

Actually I have seen “Goldilocks” mentioned as a description of the last refuge survival zone ~ 1 km down the crust that shows up in models of Late Heavy Bombardment survivability.

Maybe also for the Galactic Habitable Zone? But it is populated by (religious or not) Rare Earthers, so is suspect as a propaganda tool.

Which is the point really, what does it mean? That gets into the similar discussion on habitability measures, Earth analogs measures, et cetera.

It is context dependent as these are relative measures based on a sensitivity idea – how much different can a planet be and still have a possibility of life? So you start out simple, surface radiation balance liquid water zone for an estimate, atmospheric model liquid water zone for a realistic measure, et cetera.

I agree, Goldilocks doesn’t mean much (or too much). But it is a convenient figure of speech, maybe too convenient.

Anonymous February 5, 2012 at 12:54 AM

I guess what it ultimately comes down to is if there are any other more practical solutions feasible. Probably not until a new propultion system is designed, which may be tomorrow or a thousand years from now. Wouldn’t it be something if this world was inhabited, and with intelligent life? Imagine their surprise to see something obviously made on another coming careening through space toward their planet through the cosmos. Wouldn’t it be surreal if after all the UFO theories, movies, science fiction novels… If WE ended up being the visiting extra-terrestrials… Surreal

Anonymous February 5, 2012 at 9:29 AM

It would be nice, but improbable given the current climate for large-scale scientific projects.

LC’s Fresnel sail is probably the best method for obtaining relativistic speeds this century. It is better then Fusion Impulse, or Nuclear Pulse Propulsion – both of which are less efficient and require decades of development anyway.

It is rather unlikely we will come across another HEI (human equivalent intelligence). By this I mean a intelligence similar to our own that adapts it’s environment through the use of tools. We can give a very rough estimate of this type of life form given our Keplar findings and extrapolating from our own Earth history.

We have gone over this issue extensively in other postings. In summary, the time scales are so vast, and the distances so great, it is likely (given our best current estimates and datasets) that HEI are about 1 per major galaxy or 1 per local cluster at any given point in time.

Anonymous February 5, 2012 at 2:46 PM

I appreciate “Goldilocks” for precisely what it means. No more, no less. It puts a planet in a POTENTIAL zone. The rest of the information is not available. We don’t know about the depth of atmosphere, whether or not there is a magnetosphere, or much else at all. Therefore, we widen the scope of the G-zone to accomodate oddball planets of extreme likelihoods and assuming liquid water is a necessity, give each star it’s halo of probability. Since having all the ingredients for life AWKI is a far more complex question then just orbital placement we hardly expect most of these planets to be inhabitable or inhabited so it’s no surprise at all that in our own solar system, only one of four in the G-zone actually harbours life.

Anonymous February 7, 2012 at 7:40 PM

Could you not use the focussed sunlight to power the systems on the spacecraft? Attach a solar panel to the solar sail and you have power. That sunlight would be very concentrated and would make the panels much more efficient than the ones currently deployed in space, although I guess the efficiency would decrease dramatically with time. Alternatively, you could use a thermal electric system, also using the concentrated sunlight. Maybe this would stand the test of time better than solar electric?

Anonymous February 10, 2012 at 4:32 PM

Yes it could but even then the power available would be quite small so it’s doubtful what use it would be. Sending signals back needs lots of power which would be more readily available from the target star if the craft were in range to make measurements. The spin method gives free energy (since the spin comes from the incident thrust) and doesn’t need any infrastructure at the sending end.

Actually, I made an error in my calculations, the numbers I gave are for RF sources where a synthetic aperture antenna can produce a collimated beam. Lawrence’s optical Fresnel lens cannot do that because the Sun is an extended source. To create a well collimated beam, you have to start with something close to a point source otherwise you just create an image of the source.

It’s different for the StarWisp concept where a microwave source can produce the necessary Gaussian cross-section plane wave source.

The basic problem I see is that the peak thrust can be reduced from that required for a raw solar sail if it can be applied longer, i.e. by collimating the beam by whatever method. If the same method is to be used to slow down the craft at the destination, the illumination needs to be comparable at that end. The limiting factor will be how long the annulus can maintain the focus on the payload section once they separate. The annulus is pushed away from us while the payload is pushed back towards us so the distance between them would grow rapidly so I think a few months would be an optimistic limit. Since the outside diameter of the annulus would be of the order of tens of km, the beam width by the time it reaches the destination system could not be much more. That rules out a simple lens in favour of a coherent source. Even if the beam were only 6 times the diameter, at the target star, that would reduce the illumination by a factor of 36 so a deceleration phase of a few months would equate to an acceleration over a few days, and that is not a great improvement over raw sunlight. Raw sunlight is limited to ~2% of c because anything higher melts the sail so I don’t believe the method would work. Another factor that needs to be considered is that the light reflected from the annulus would be twice Doppler shifted. As the payload slow , the annulus accelerates so the thrust of the reflected light would be significantly reduced.

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