Alpha Centauri and the New Astronomy

by Paul Gilster on October 16, 2012

For much longer than the nine years Centauri Dreams has been in existence, I’ve been waiting for the announcement of a planetary discovery around Centauri B. And I’m delighted to turn the first announcement on this site over to Lee Billings, one of the most gifted science writers of our time (and author of a highly regarded piece on the Centauri stars called The Long Shot). Lee puts the find into the broader context of exoplanet research as we turn our gaze to the nearest stars, those that would be the first targets of any future interstellar probes. On Thursday I’ll follow up with specifics, digging into the discovery paper with more on the planet itself and the reasons why Centauri B was a better target than nearby Centauri A. I’ll also be offering my own take on the significance of the find, which I think is considerable.

by Lee Billings

For much of the past century, astronomy has been consumed by a quest to gaze ever deeper out in space and time, in pursuit of the universe’s fundamental origins and ultimate fate. This Old Astronomy has given us a cosmological creation story, one which tells us we live in but one of innumerable galaxies, each populated with hundreds of billions of stars, all in an expanding, accelerating universe that began 13.7 billion years ago and that may endure eternally. It’s an epic, compelling tale, yet something has been missing: us. Lost somewhere in between the universe’s dawn and destiny, passed over and compressed beyond recognition, is the remarkable fact that 4.5 billion years ago our Sun and its worlds were birthed from stardust, and starlight began incubating the planetary ball of rock and iron we call Earth.

Somehow, life emerged and evolved here, eventually producing human beings, creatures with the intellectual capacity to wonder where they came from and the technological capability to determine where they will go. Uniquely among the worlds in our solar system, the Earth has given birth to life that may before the Sun goes dim reach out to touch the stars. Perhaps, on other worlds circling other suns, other curious minds gaze at their night skies and wonder as we do whether they are alone. In this coming century, a New Astronomy is rising, one that focuses not on the edge of space and the beginning of time but on the nearest stars and the uncharted worlds they likely hold. It will be this New Astronomy, rather than the Old, that will at last complete the quest to place our existence on Earth within a cosmic context.

In a major leap forward in this enterprise, today a European planet-hunting team announced their discovery of an alien world about the same mass as Earth. This alone would be noteworthy, for of all the “exoplanets” now known beyond our solar system, only a very few, and very recently, have been shown to at all resemble our own. But there is more to the story. This particular exoplanet resides in a three-day orbit around the dusky orange star Alpha Centauri B, a member of the Sun’s closest neighboring stellar system. There are two other stars in the system as well, the yellow Sun-like star Alpha Centauri A and the red dwarf star Proxima Centauri.

Astronomers began discovering exoplanets about two decades ago, finding at first a few per year. Since then, the pace of discovery has dramatically accelerated. Today there are more than 750 confirmed exoplanets, and a single NASA mission, the Kepler spacecraft, has detected more than 2,300 additional candidates that await confirmation. Most of these exoplanets are far too large, too hot, or too cold to support life as we know it, but a handful appear to be “Goldilocks” worlds the right size and the right distance from their stars where liquid water could flow in streams and pool in seas, worlds where carbon-based organisms could potentially thrive. The discovery of more Goldilocks worlds appears inevitable — statistics from the Kepler mission and other sources suggest that somewhere between ten to thirty percent of stars harbor potentially habitable planets. Among the planet-hunters, the question is no longer whether life exists elsewhere in the universe, but rather how far removed the next-nearest living world might be.

At a distance of just over 4.3 light years, the stars of Alpha Centauri are only a cosmic stone’s throw away. To reach Alpha Centauri B b, as this new world is called, would require a journey of some 25 trillion miles. For comparison, the next-nearest known exoplanet is a gas giant orbiting the orange star Epsilon Eridani, more than twice as far away. But don’t pack your bags quite yet. With a probable surface temperature well above a thousand degrees Fahrenheit, Alpha Centauri B b is no Goldilocks world. Still, its presence is promising: Planets tend to come in packs, and some theorists had believed no planets at all could form in multi-star systems like Alpha Centauri, which are more common than singleton suns throughout our galaxy. It seems increasingly likely that small planets exist around most if not all stars, near and far alike, and that Alpha Centauri B may possess additional worlds further out in clement, habitable orbits, tantalizingly within reach.

Anyone in the Southern Hemisphere can look up on a clear night and easily see Alpha Centauri — to the naked eye, the three suns merge into one of the brightest stars in Earth’s sky, a single golden point piercing the foot of the constellation Centaurus, a few degrees away from the Southern Cross. In galactic terms, the new planet we’ve found there is so very near our own that its night sky shares most of Earth’s constellations. From the planet’s broiling surface, one could see familiar sights such as the Big Dipper and Orion the Hunter, looking just as they do to our eyes here. One of the few major differences would be in the constellation Cassiopeia, which from Earth appears as a 5-starred “W” in the northern sky. Looking out from Alpha Centauri B b and any other planets in that system, Cassiopeia would gain a sixth star, six times brighter than the other five, becoming not a W but a sinuous snake or a winding river. Cassiopeia’s sixth bright point of light would be our Sun and its entire planetary system.

Image: Alpha Centauri as seen by the Cassini orbiter above the limb of Saturn. Credit: NASA/JPL/Space Science Institute.

Despite its close proximity, as with nearly all other known exoplanets, Alpha Centauri B b is as yet unseen. It was detected indirectly, via a periodic 50-centimeter-per-second wobble its orbit raises in the motions of its star, in a painstaking process that took four years of nightly monitoring and careful analysis. The wildly successful Kepler mission finds the bulk of its candidates by a different technique, looking for the minuscule diminution of a star’s light when, by chance, a planet in its orbit transits across the star’s face and casts a shadow toward Earth. Both of these discovery methods can constrain the most basic properties of a planet: its orbit, its mass, and perhaps its size and bulk composition. But neither can readily reveal whether or not any potentially habitable planet is actually a place much like Earth. To do that really requires taking a planet’s picture. Even if that picture amounted to only a meager clump of pixels, astronomers might discern within it a planet’s rotational period — the length of its days — as well as clouds, oceans, and continents. The reflected planetary light would also contain spectroscopic signatures of atmospheric gases. Carbon dioxide would suggest a rocky planet, and water vapor would hint at oceans or seas. Detecting oxygen and methane — gases produced on Earth by living things — would further suggest that the distant planet was not only habitable, but inhabited.

Viewed over interstellar distances in visible light, the Earth is some ten billion times fainter than the Sun, meaning that for every photon bouncing off Earth’s atmosphere or surface, ten billion more are flying out from our star. About the same ratio would apply for any habitable planet around Alpha Centauri’s stars. Distinguishing such faint planetary light from that powerful stellar glare is rather like spotting a firefly hovering a centimeter away from the world’s most powerful spotlight, when the spotlight is in Los Angeles and you are in New York. To see the firefly, that overwhelming ten-billion-to-one background light must be suppressed.

Amazingly, on paper and in laboratory studies, astronomers have already devised multiple ways to do exactly this for potentially Earth-like planets that may exist around nearby stars. Most of these methods require an entirely new multi-billion-dollar space telescope, though a few proposals exist to augment NASA’s upcoming James Webb Space Telescope with starlight-suppressing technology at an estimated cost of $700 million. Considering that three years ago a film about life on Alpha Centauri’s planets — James Cameron’s Avatar — grossed some $2 billion in box-office receipts, it stands to reason there is public appetite to spend at least that much on space telescopes to search for the real thing.

Matt Mountain, the director of the Space Telescope Science Institute in Baltimore, Maryland, likes to quip that the discovery of life beyond our solar system could be to this coming century what Neil Armstrong’s lunar footprints were to the last. Yet today NASA is not seriously funding any life-finding telescopes, and has no real plans to do so in the future. The agency instead is spread thin and lacking any unified direction, strapped for cash and struggling to avoid obsolescence while it maintains the International Space Station, builds a new fleet of rockets to replace the retired Space Shuttles, and completes the James Webb Space Telescope. Yet obsolescence is precisely what NASA will embrace if it fails to invest now in the next giant leap required for this New Astronomy. Of all the scientific institutions and agencies upon this planet, at present NASA alone has the resources to build a telescope capable of directly imaging and characterizing any Earth-like planets around nearby stars. Unless it does so, as the list of potentially habitable planets grows long in years to come, all that shall grow along with it will be our ignorance of what those distant worlds are actually like and what may live upon them.

Meanwhile powerful, influential Old Astronomy, which has revolutionized our understanding of the universe at its largest scales, is wary of the New, and at times has acted quite deliberately against it. Alas, government-funded Big Science is too often a zero-sum game, one in which money that could go toward looking for life on exoplanets around nearby stars would be taken from cosmological efforts to study far-distant galactic clusters and the expansion of the universe. In a perfect world we would fully fund both quests simultaneously. But our world — with its economic instabilities, rising temperatures, growing populations, and plummeting biodiversity — seems to grow more imperfect by the day, in ways that no knowledge of dark energy or dark matter is likely to ever assuage. The New Astronomy is different. We do not yet know whether planets like ours and creatures like us are in fact common or rare in the cosmos, but by trying to find out, we will unavoidably learn just how precious our planet truly is. Perhaps, with luck, discoveries following from today’s announcement will help us finally kick off from our small blue footstool, and find our way among the stars.

Lee Billings is working on a book about the search for other Earth-like planets, forthcoming from Penguin/Current next fall.

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Angelo Genovese October 17, 2012 at 17:05

Finally a Centauri Planet!
Now let’s push Obama and NASA for a real Planet Finder in space, I am sure there is much more lurking out there!

lorq October 17, 2012 at 17:26

This unquestionably wins the prize for most wonderful recent space news, and in these already exciting times of discovery, that’s saying something.

Enzo October 17, 2012 at 17:55

@FrankH

A mission like ESA’s NEAT is a class M mission (I believe capped at 470 M euros). This will survey (all ?) the K, G and F star systems within 15 pc down to earth mass.
This is amazing value for money.

A coronograph like DAVinci :
http://exep.jpl.nasa.gov/files/exep/DAViNCI_ASMCS_Report-external-2011-04-07.pdf

will cost twice as much. Lower cost also means higher probability of actually flying.
I don’t know about the occulter cost but they are both incapable of looking very close to the star. If Kepler statistic hold for nearby systems, there will be a lot of “compact” system that cannot be observed by coronograph or by occulter.

It would be safer to survey nearby systems first to see what’s observable. If anything a mission like NEAT should be extended to M stars (as many as economically possible). This way there would be a good idea of what is out there and specific instruments could be designed.

The only reason of going ahead with the occulter now is that JWST is flying and it’ll be ages until the next one follows so one might as well take the opportunity when it comes.

Ronald October 17, 2012 at 18:36

And this is just a first discovery, not surprisingly because of the technology used, an innermost, the system’s own ‘Mercury’.
I expect more planets to be discovered in wider orbits around B, and maybe also A, in the near future.
However, I would also not be surprised if those planets will appear to be significantly larger than earthlike (super-earths), because of Alpha Centauri’s much higher metallicity than our sun’s (about 60% higher) and because compact systems consisting of large planets (super-earths and Neptunes) seem to be the norm anyway.
On the other hand, Holger rightly mentioned the already detected absence of planets > 4 Me within about 0.85 AU of Alph Cen B. Which may be very good news or very bad: there are no (sub)giant planets in the HZ of B, but there may be no planets there at all.
BTW, I do not share FrankH’s concern about this planet being a hot gas giants core: a Jupiter core would probably be closer to 8 – 10 Me, not just 1.

Ronald October 17, 2012 at 18:38

I wonder: could the planned E-ELT detect (more) planets around Alph Cen B? Either through RV, astrometry or even direct imaging?

An Infinitude of Tortoises October 17, 2012 at 18:48

James Jason Wentworth: True, but remember that this planet is neither the one discovered via that “series of deep-thrust telescopic probes” (no doubt prompted by the theories of planetary habitability developed by Dr. Donald West) and hence the destination of the Jupiter Project nor the world Priplanus, first [crash-]landing site of the Jupiter 2. It is, as mentioned, merely the beginning.

And for all we know, extremophiles simply love the place.

wojciech October 17, 2012 at 19:18

Years ago, the writer at oklo.org made some simulations,
interestingly one of them was quite spot on regarding current detection

http://www.oklo.org/wp-content/images/alphacenbsims.gif

spaceman October 17, 2012 at 22:13

Wow, a Centauri planet at last, sometimes dreams do come true! An amazing discovery made in a historical blink of an eye, as I can remember being a child in the 1980s and thinking how strange it was that we still didn’t know of any other planetary systems at the time let alone one “next door”!

FrankH October 17, 2012 at 23:46

@Ronald
A large gas giant like Jupiter can slowly dissolve its core (see http://phys.org/news/2011-12-jupiter-core-liquefying.html).

I feel better about this system now, though. I went to Exoplanet Data Explorer (http://exoplanets.org/plots) and plotted star mass vs planetary orbit semi-major axis and colored the data according to the number of components found in each system.

There are several multiple planet systems with primaries similar in mass to Alpha Cent. B (0.9 Sun) that have planets orbiting at about the same distance as Bb.
55 Cnc is a good example – 5 planets within 5.74AU

I’ll be happy with just one more planet – an Alpha Centauri Bc at about 0.7AU with a mass between 0.9 and 1.25 Earths.

ljk October 17, 2012 at 23:51

Scott G. said on October 17, 2012 at 16:20:

“If you ask around, you find that this is what people generally want in a space program. We all want to see a picture of another blue world out there in our lifetimes.”

And any native life forms that might come with it.

Excellent article, BTW. I remember an article from I think NSS’s publication circa 1990 which said we might find an alien planet circling some star by the year 2000 or so. We beat it by five years if you count 51 Pegasi b or eight years if you count the first detected pulsar planets.

I also agree with the article author that NASA should use this discovery as a focus for its future space projects. First with exoplanet detection telescopes, then ones that can image said planets, then a probe mission. Otherwise why claim to be a space program if all we are going to do is circle Earth and keep visiting the same old local worlds?

Martyn Fogg October 18, 2012 at 0:13

I am surprised that so many people think that half a million dollars is a small amount of money. It doesn’t seem so to researchers on grants who work on the discoveries we crave, or to enthusiasts who are self-funded. But forgive me for introducing such a squalid topic of hoarding much needed support funds… How about this instead?

One fascinating thought is the possibility of synchronous rotation. If that is the case we would have a scorching hot day side, but what about the night side? If volatile endowment was modest for this planet, or they have not all been blasted into space, it’s possible that atmospheric collapse could have occurred forming an ice cap on the dark side. In permanent shadow the dark side would be cold. But how cold? There would surely be some conduction of heat from the torrid illuminated side through to the unlit side through the solid body of the planet.

Martyn Fogg October 18, 2012 at 0:18

In another place, James Essig made the point that not so long ago it was routine to rule out the chances of surviving planets in binary star systems. Here’s some of the history of that…

That was just a byproduct of conservative manipulations of the Drake equation originally. Eliminating binary stars as a block subtraction from f_p was just one convenient way of reducing N down to ‘sensible’ looking numbers. Then there was the paper by Heppenheimer in the seventies that predicted that stellar perturbations would excite planetesimals such that collisions would result in fragmentation, rather than growth. That was overturned by Marzari and Scholl in 2000 when they showed that gas drag would have the effect of drawing eccentric planetesimal orbits into a common alignment, which would reduce mutual impact velocities, improving the chances of growth. Then in 2002, Quintana et al. published simulations of planetary systems about Star A showing that, if accretion can make it to the oligarchic growth phase, then full sized planetary systems could form around both Stars A and B, out to the stability boundary of ~ 2.5 AU in each case.

Planet formation probably is more difficult in a medium separation, high-e, binary such as this, but how much more difficult remains unclear. At least we now know that the dynamical relaxation which must have sculpted the present arrangement of the AB pair was not so violent that it drove all planet-forming material into their primaries. But whether we have full-sized systems in each case is still an open question.

The presence of Planet Bb at a star-grazing 0.04 AU orbit is ominous in the sense that if it didn’t get there via gentle disk-planet migration, it might have been scattered there and then had its orbit tidally circularised. The second of these possibilities would not bode well for the presence of much surviving material at greater distances.

henk October 18, 2012 at 3:53

Years ago, the writer at oklo.org made some simulations,
interestingly one of them was quite spot on regarding current detection

http://www.oklo.org/wp-content/images/alphacenbsims.gif

none of those came close to 3.2 days orbit. The closest one in that model was a little close than Mercury, and that one have also a smaller mass.

bigdan201 October 18, 2012 at 6:00

This is incredible news! Even if it is a lavaball, this is a big step forward. There may well be more planets there, and only time will tell what they’ll be like.

As I’ve said, finding an earth analogue in the Centauri system would be like a blessing from the space gods. But even if there isn’t, I feel very optimistic about future exoplanet discoveries.

If we’ve found such a boon of exoplanets already, I imagine that we’ll discover many more with expanded equipment and methods. And we haven’t even gotten a glimpse of the details, such as surface conditions and possible exomoons. There is much science to be done.

ljk October 18, 2012 at 9:34

Martyn Fogg said on October 18, 2012 at 0:18:

“In another place, James Essig made the point that not so long ago it was routine to rule out the chances of surviving planets in binary star systems. Here’s some of the history of that…

“That was just a byproduct of conservative manipulations of the Drake equation originally. Eliminating binary stars as a block subtraction from f_p was just one convenient way of reducing N down to ‘sensible’ looking numbers.”

The Drake Equation was primarily designed to make a guesstimate at how many ETI might be out there who could contact us. While the original view was that multiple star systems would disrupt any worlds around them from even having life let alone smart ones that could build radio telescopes and the like, it may not be out of bounds to assume that the early practitioners of the DE thought that some such exoworlds could have organisms, but that conditions would keep them from becoming advanced enough to talk to us across interstellar distances.

Mathieu October 18, 2012 at 12:15

Dear Lee,

I greatly enjoyed your piece and find most of what you say to be true. The funding crisis of most agencies is affecting more than we know the future of our research, and is indeed sad to see governments lacking the will to do such things, which means the private sector has to step up. (SpaceX or the recent RedBull Stratos achievment)

I would like to add to your article and perhaps rectify a couple of points. Forgive me if I’m deliberately Europe-oriented in this, as this is my area of expertise, no doubt the Russian and Chinese initiatives are equally worth mentioning.

Kepler is one of the most incredible tools we have at our disposal and has indeed discovered most of the planet “candidates” we know of, although the particularity of Kepler means these worlds are quite often far-off, and need to be confirmed via other methods. Let us not forget HARPS (on the 3.6-m telescope at ESO’s La Silla observatory in Chile) which made this very discovery, and so many others of significance. Indeed the same Swiss team using the Coralie spectrograph and the likes discovered the 1st ever exoplanet around a main sequence star. We could also mention the French-built space telescope CoRoT.

More importantly, I would like to rectify the statement that NASA is the only agency with the resources to build a telescope capable of imaging and characterizing Earth-like exoplanets around nearby stars. This is in fact erroneous as the European Southern Observatory (ESO, whose telescopes discovered Alpha Centauri Bb) is preparing to build the European Extremely Large Telescope in Chile. With a 40-m primary mirror, one of its main scientific goals, clearly stated, is to image and characterize exoplanets, and its resolution will indeed enable it to “reach” Earth-sized planets. The design study has been completed and construction has been approved, with an expected completion date around 2023, for a cost of around 1 billion USD, (compare that to the JWST’s 8 billion USD). ESO is a European intergovernmental research organisation, like CERN, which is funded by 15 member countries)

This goes to show that it is not necessary to build just space-telescopes (which by definition cost many more billions) and that other agencies in the world have the resources AND the political will to do this sort of research.

I agree the pace is definitely too slow and we could do much more, but it is important to remind the public that this research is still going forward and that many groups/institutions/countries around the world are working and getting together to build these machines and achieve these goals (another example being the Canada-UK-Australia-India-China Square Kilometer Array telescope, or the US-Japan-ESO ALMA telescope in Chile).

In my opinion, the funding crisis American science is going through means NASA and the NSF should perhaps lobby to join these international projects rather than look to build giant telescopes alone. In cash-strapped economies, and with such expensive research, international cooperation seems to be the only sensible future of research.

John M October 18, 2012 at 12:36

WOW ! Centauri Dreams is no longer dream. Some questions (with apologies in advance – being an amateur in the fullest sense of the word – HBSc. – Astrophysics 1973 – now a tax accountant). I presume that “b” could not have formed at its present distance with the gravitional distruption affect of B during its accretion (assuming it is not a core of gas giant – yes, I understand the discussion about gas giant formation in the previous comments); and therefore could this mean that there could be terrestial-size planet migrations resuluting in a “hot earths” (yes – aware of “hot super earths”) ? Or could this a “tight” capture i.e. “b” formed further out where terrestrial planets would otherwise form but as a result of the high “e” of A-B’s orbits which excited “b” into a very high “e” orbit where it was ultimately captured much more tightly by B into its present oribital distance ?

Lee Billings October 18, 2012 at 15:37

Mathieu:

Thank you for reading, and for pointing out the importance of not being too centered on one space agency (NASA) or one country (the USA). Indeed, I think it’s fair to say that in terms of precision radial-velocity work and progress toward an ELT, Europe is currently trouncing the USA, and that NASA and the NSF could greatly benefit from adopting some of the funding mechanisms employed by ESA and ESO.

I’m intrigued by your assessment of the prospects for ground-based Extremely Large Telescopes to characterize Earth-like planets around nearby stars. Whichever continent they’re on and no matter how big they are, they are still below the atmosphere, and even with sophisticated extreme adaptive optics that seems to be a showstopper for direct imaging and spectroscopy. Transits, of course, offer some hope, but even there I have seen no material that makes me confident any of these next-generation ELTs will be capable of detecting atmospheric biosignatures via transmission spectroscopy of a potentially habitable transiting planet. Maybe this is just because all the folks I’ve talked with are pushing for the space-based route, but the general consensus I’ve encountered is that you simply can’t do this from the ground.

Could you direct me to some authoritative sources saying otherwise?

N.Oberg October 18, 2012 at 17:54

Mr. Billings,

In regards to your question “Could you direct me to some authoritative sources saying otherwise?”; I recall passing by this some time ago: http://www.toomanyparsecs.info/2012/06/brief-outlook-on-e-elts-wonders.html

This material is from “The E-ELT Construction Proposal, ESO, December 9, 2011″ which can be found here http://www.eso.org/public/products/books/e-elt_constrproposal/

Inside is stated:

Alternatively, exoplanet atmospheres can be observed during transits in the optical and near-infrared. Ground- and space-based facilities (such as the CoRoT and Kepler missions) are accumulating target stars for which an exoplanet, as seen from Earth, transits in front of its parent star. During these events, which last a few hours every few months or years, spectral features of the exoplanet’s atmosphere, back-lit by their parent star, can be seen in the spectrum of the system. Such measurements are barely feasible at present from the ground and space, but lie well within reach of the E-ELT, which will be able to sample several important chemical diagnostic lines.

Rob Henry October 18, 2012 at 18:12

Why not come right out and say it Martyn Fogg. This might be a great base for human operations in the Centauri system, if it has volatiles on its night side.

If operations are near the terminator we might has accesses to enough shade to eliminate the need for active cooling mechanisms, yet also have access to bright sunlight to supply our power needs.

To me we can, for the first time, bring some shape to our personal dreams of Centauri.

FrankH October 18, 2012 at 18:18

@Lee Billings:
I don’t know if this is the article Mathieu is referring, but this ESO PR release:
http://www.publicservice.co.uk/news_story.asp?id=12811
claims that the E-ELT:

“Speaking to Public Service Review, Tim De Zeeuw, ESO director general said: “The light gathering power of the ELT should allow us to measure the properties of the atmospheres of some exoplanets.

“Today this is only possible for giant, bright planets like Jupiter. The ELT should allow us to do this for planets that are the size of the Earth, or a little bigger, and are sure to be rocky.”

Here’s a technical article (PDF):

https://www.eso.org/sci/libraries/SPIE2010/7735-84.pdf

Rob Henry October 18, 2012 at 19:14

What a wonderful article! However, I am disturbed by Lee Billings claim the constellations would look more or less the same from the Centauri system. To me, this is like claiming that people would still be recognisable if the scrambling was such that most of their features were displaced by less than their body length.

Take some of these very bright examples: Sirius, Procyon, Altair, Vega and Fomalhaut. These average 17.4 light years from us, and thus, are displaced an average of 4.36/17.4 sini radians, that is 14 sini degrees. Even supergiants such as Betelgeuse (and taking its Wikipedia distance) would be 0.4 sini degrees off.

Lee Billings October 19, 2012 at 11:04

FrankH:

Hmm. From the technical article you linked:

“Figure 6 demonstrates that Gliese 581 d, a rocky planet in the HZ with a separation of 35 mas and an approximate contrast ratio to the star of about 2.5 x 10-8, would be readily observable with the EPICS IFS in about 20 hrs. The EPICS contrasts shown in Figure 4 (top row) would in principle even allow for the detection of an Earth analog around a G2 star at 5pc (1AU corresponds to 0.20 angular separation). However, there are only a handful of stars that are bright enough to be observed at ~2e-10 contrast, alpha Cen being the most promising.”

That’s more than I thought could be done, and it may be worth noting that this analysis does not seem to address how these measurements will counter the spectral contamination caused by telluric lines. Gliese 581 d has frankly a borderline case for habitability. The claims re: an Earth analog around Alpha Cen are much more interesting, though the qualifier “in principle” should not be discounted. It would be nice to get a second opinion on these statements from someone involved with independent current ground-based direct-imaging projects like Gemini Planet Imager. I’ve been pitching a story about this around for a while, now — if and when someone commissions it you can bet I’ll address this.

Point being, it looks like the best-case scenario here is that for a handful of cases a ground-based ELT with an instrument like EPICS could — maybe — characterize some potentially habitable planets. An 8-meter space telescope outfitted with a coronagraph or an occulter could perform even better investigations for hundreds of stars, without question. I know where I’d prefer to invest…

Lee Billings October 19, 2012 at 11:15

Rob Henry:

Don’t take my word for it. Feel free to load up your preferred space-sim like Celestia and view the Centauri sky for yourself. You’ll recognize a lot.

andy October 19, 2012 at 18:50

The presence of Planet Bb at a star-grazing 0.04 AU orbit is ominous in the sense that if it didn’t get there via gentle disk-planet migration, it might have been scattered there and then had its orbit tidally circularised. The second of these possibilities would not bode well for the presence of much surviving material at greater distances.

Migration might also be ominous – there isn’t all that much room in the system outside the habitable zone, it could be that all the planets in outer orbits all ended up migrating through the habitable zone and into the inner system where they would be too hot.

Essentially with Alpha Centauri we are looking at a new scenario of planet formation that hasn’t been seen before (low-mass planet in a close binary). Whether the properties of the low-mass planetary systems found around single stars still apply remains to be seen. Alpha Centauri Bb itself is located close to the star, which puts it in the accretion-friendly zone. The habitable zone could still have been accretion-hostile. This would still be compatible with the observations of gas giants at relatively large separations in systems similar to Alpha Centauri (e.g. Gamma Cephei or HD 196885) if we assume that they formed rapidly by the gravitational instability mechanism.

FrankH October 20, 2012 at 10:52

@Lee Billings – I’m a bit skeptical of the ground based resolution claims; it read like a lot of PR. I’m with you – an 8m telescope in orbit would be better, but in the current anti-science, anti-reason era, it’ll be many decades before something like that flies.
@Rob Henry – Fire up a sky simulator; the sky from Alpha Centauri looks hardly different, and if you showed it to the average Joe on the street, they wouldn’t notice the difference.

Koichi Ito October 20, 2012 at 11:15

Alpha Centauri Bb Planet must be like hot Io (Moon of Jupiter)? It must be hot and volcanic planet.

Aksel October 20, 2012 at 21:41

Build the Enterprise!

ljk October 22, 2012 at 10:56

Lee Billings said on October 19, 2012 at 11:15:

“Rob Henry: Don’t take my word for it. Feel free to load up your preferred space-sim like Celestia and view the Centauri sky for yourself. You’ll recognize a lot.”

Carl Sagan described how he created the view of the galaxy from Alpha Centauri in his famous 1973 book The Cosmic Connection. Or rather, he asked for the assistance of one David Wallace at the Laboratory for Planetary Sciences at Cornell who was proficient with an “electronic computer” to simulate the sky as seen from our neighboring star system.

This was back in the day when recreating such a scene required a lot more than just Googling it from your laptop, which would have been rather hard to do in the early 1970s in any case.

And I quote from Chapter 2 of the book:

We now ask the computer to draw us the sky from the nearest star to our own, Alpha Centauri, a triple-star system, about 4.3 light-years from Earth. In terms of the scale of our Milky Way Galaxy, this is such a short distance that our perspectives remain almost exactly the same. From α Cen the Big Dipper appears just as it does from Earth. Almost all the other constellations are similarly unchanged.

There is one striking exception, however, and that is the constellation Cassiopeia. Cassiopeia, the queen of an ancient kingdom, mother of Andromeda and mother-in-law of Perseus, is mainly a set of five stars arranged as a W or an M, depending on which way the sky has turned. From Alpha Centauri, however, there is one extra jog in the M; a sixth star appears in Cassiopeia, one significantly brighter than the other five. That star is the Sun.

From the vantage point of the nearest star, our Sun is a relatively bright but unprepossessing point in the night sky. There is no way to tell by looking at Cassiopeia from the sky of a hypothetical planet of Alpha Centauri that there are planets going around the Sun, that on the third of these planets there are life forms, and that one of these life forms considers itself to be of quite considerable intelligence. If this is the case for the sixth star in Cassiopeia, might it not also be the case for innumerable millions of other stars in the night sky?

One of the two stars that Project Ozma examined a decade ago [1960] for possible extraterrestrial intelligent signals was Tau Ceti, in the constellation (as seen from Earth) of Cetus, the whale [the other was Epsilon Eridiani]. In the accompanying figure, the computer has drawn the sky as seen from a hypothetical planet of T Cet. We are now a little more than eleven light-years away from the Sun. The perspective has changed somewhat more. The relative orientation of the stars has varied, and we are free to invent new constellations – a psychological projective test for the Cetians.

I asked my wife, Linda, who is an artist, to draw a constellation of a unicorn the Cetian sky. There is already a unicorn in our sky, called Monoceros, but I wanted this to be a larger and more elegant unicorn – and also one slightly different from common terrestrial unicorns – with six legs, say, rather than four. [Shades of Avatar!]

She invented quite a handsome beast. Contrary to my expectation that he would have three pairs of legs, he is quite proudly galloping on two clusters of three legs each, one fore and one aft. It seems quite a believable gallop. There is a tiny star that is just barely seen at the point where the unicorn’s tail joins the rest of his body. That faint and un-inspiringly positioned star is the Sun. The Cetians may consider it an amusing speculation that a race of intelligent beings lives on a planet circling the star that joins the unicorn to his tail.

When we move to greater distances from the Sun than Tau Ceti – to forty or fifty light-years – the Sun dwindles still further in brightness until it is invisible to an unaided human eye. Long interstellar voyages – if they are ever undertaken – will not use dead-reckoning on the Sun. Our mighty star, on which all life on Earth depends, our Sun, which is so bright that we risk blindness by prolonged direct viewing, cannot be seen at all at a distance of a few dozen light-years – a thousandth of the distance to the center of our Galaxy.

Kavanna October 23, 2012 at 14:28

The Universe is a very big place :)

New versus old astronomy seems a little overdrawn. The “old” astronomy was once new, after all. A better contrast is between Big and Little Science, as Lee mentions in passing. Big Science is great when it starts, but keeping it going is draining and always puts a damper on smaller projects.

Astronomy is blessed, like medical research, in that a large fraction of its funding comes from private sources. (In contrast, high-energy physics is essentially all government-funded.) For smaller science, private funding is increasingly going to be the future.

Ironically, for NASA, the biggest drain is not scientific research at all, but the manned space program. The gradual privatization of space travel and research is slowly starting to happen, just not fast enough. NASA spent 20 years blocking it.

Roland Buck December 4, 2012 at 7:37

“Astronomy is blessed, like medical research, in that a large fraction of its funding comes from private sources.”
The research on Alpha Centauri by the Marcy-Fischer team is obtaining funding from the Planetary Society which has been soliciting contributions for this from its members. My own contribution pays for about 1/2 hour of telescope time.

Roland Buck December 4, 2012 at 7:43

The picture of Alpha Centauri from Cassini is especially impressive in that it actually shows two separate stars that are tiny disks.

Roland Buck December 4, 2012 at 7:45

This may be a stupid question since I am very amateur. But have observations excluded the possibility of a gas giant, like the one Pandora orbits?

Lee Billings December 14, 2012 at 15:03

Roland Buck:

Yeah, if I recall correctly RV work several years ago ruled out gas giants within a few AU of either Alpha Cen A and B. I can’t immediately recall the exact study, but there you go.

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