Alpha Centauri Hunt Intensifies

by Paul Gilster on June 9, 2009

I love Greg Laughlin’s remark to the Washington Post‘s Joel Achenbach in last week’s article Astronomers Seek New Home Closer to Home. Having discussed Debra Fischer’s ongoing search for Alpha Centauri planets and his own theories on planet formation around binary stars, Laughlin points out where we stand today: “We have what is to all appearances by far the best planet in the galaxy. And we have no workable backup plan.”

The Washington Post article doubtless draws on Lee Billings’ earlier piece in SEED Magazine called The Long Shot, which discusses with an elegance rare in science writing the attempt to find planets around the Centauri stars by Fischer as well as Michel Mayor’s Geneva team. Mayor has been using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at La Silla, the Cadillac of radial velocity instrumentation (and boy does that auto industry reference date me!). Competition can work wonders, and having two teams on the case can only bode well for quick results.

Not that those results will necessarily reveal planets, but we can hope for the best. Laughlin writes about the search in Alpha Centauri: Market Outperform, noting that “…when HARPS is working full bore on a bright quiet star, it can drill right down into the habitable zone.” Note, too, that Alpha Centauri is visible almost year-round from La Silla. Laughlin plugs in values for Centauri B’s habitable zone and creates data sets for differing values of planetary mass in the system. He then extrapolates from this to determine where the Geneva team might be now that it has upped its frequency of observations.

The results: A 4.6 Earth-mass planet in an optimally habitable orbit around Centauri B might be “…on the verge of current ‘announceability.'” A smaller 2.3 Earth-mass planet in the same zone would not be visible yet, requiring another year and a half of observations. If we’re anxious to find not a ‘super Earth’ but a true Earth analog, then, silence on the Centauri front for another eighteen months may, as Laughlin suggests, be good news.

But back to Laughlin’s comment to Joel Achenbach. At present, Earth’s lack of a backup plan is obvious, a matter of little concern to most unless we one day discover an asteroid in a dangerous, intersecting orbit. What technologies do we have today that could move quickly to reach an object potentially far out in the Solar System, allowing us to change its trajectory? Making sure we have the tools is part one of the backup plan, and that puts an emphasis on observation and propulsion studies.

Part two is building the infrastructure for a continuing human presence off-planet, and for ensuring that future asteroid or comet encounters are better anticipated. Part three is finding out whether continuing work on interstellar propulsion will one day produce the energies we need to push a payload to the nearest stars in time frames that human crews can survive. The answer will determine whether our backup plan is system-wide or extends to habitable planets around suns other than our own.

John Hunt June 9, 2009 at 11:48

A fascinating quote from that SEED article:

“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.”

tacitus June 9, 2009 at 19:41

“We have what is to all appearances by far the best planet in the galaxy. And we have no workable backup plan.”

I understand the sentiment of this remark, but we haven’t a clue whether we have “by far the best planet in the galaxy” (except in the obvious sense that we evolved here and thus there is probably no better place suited for us).

NASA will immediately convene a committee of its most thoughtful space propulsion experts… [and] they’ll plan the first-ever mission to the stars.

I really hope this isn’t the first thing they do. Sure, there’s no harm in using the discovery of a nearby planet to boost interest into researching interstellar drive technology, but the money and manpower would be best directed to boosting the Terrestrial Planet Finder program (which has already been subject to cuts in funding) and future high-powered planet-finding scopes.

From a purely selfish point of view (but I suspect most astronomers feel the same way), there is absolutely no way I would be alive after the 60 years (or more likely at least 100 years) it will take to design and execute a mission to Alpha Centauri. On the other hand, there is every chance that I could still be around after the 20 – 30 years it will probably take to design and execute a series of missions that we not only produce clear images of any planets around Alpha Centauri, but perhaps images of dozens of other planets in our local corner of the galaxy.

Lee Billings June 9, 2009 at 22:58

Good point, Tacitus. The fact is, if any planets are detected around Alpha Centauri, they’ll have to be properly characterized before a reasonable argument could be made for sending a probe there. Imagine if after all the effort and spending, the probe arrived only to discover the equivalent of Mars or Venus.

The chances of any putative planets yielding viewable transits from our perspective are quite slim, so getting anything like light curves or atmospheric spectra will almost certainly require direct-imaging missions like TPF or Darwin.

Marcy knows this… I should say in his defense that the quote may be taken slightly out of context, since it was culled from a much longer conversation. He’s certainly thinking more of the “end game,” the scenario that may occur if any Alpha Centauri planets are shown to have characteristics of habitable/inhabited worlds. Given such data, it would be challenging to argue against attempting a robotic interstellar mission of some sort.

Adam June 10, 2009 at 6:41

Alpha Centauri guides me home at night and Scorpio is sitting on the horizon in the rough direction it’s pointing (with Beta Cen defining the direction with it that is.) Crux Australis is towards the zenith from them, and then I run out of constellations I know and can see clearly in all the City sky-glow. Personally I’d like to see matters interstellar propulsion wise develop out of solar power satellites first providing gigawatts of power for us on earth, in space, then for lasers powerful enough to shove a light-sail on a quick trip to Alpha Cen. But I wouldn’t say no to a mini-probe in the near-term. Just quicker than 0.1 c, please!

philw1776 June 10, 2009 at 9:18

I’m firmly in the camp of extrasolar spectroscopy and imaging. Such technologies are a matter of improving engineering, unlike most physics fantasy propulsion systems, which even if feasible would require tens of billions and decades of continued funding to implement, and that’s if they really worked. Remember, we’re a space exploring society that after 50+ years has flown something like one ion propelled spacecraft mission and where even solid engineering propulsion concepts like VASIMIR have yet to fly.

Given the public’s short attention span enthusiasm followed by steady state fickle indifference on space exploration, I’m not sure that support for funding a multi-year development 10-11 figure development and flight cost spectroscopy and imaging program would last even if HZ planets were detected.

Luca June 10, 2009 at 10:18

The discover of a terrestrial planet around Alpha Centaury or some other near Earth star may be the only chance to save TPF from imminent budget haircut.

ljk June 10, 2009 at 12:55

Wanting to examine in detail an Earthlike world, especially if it is in the
Alpha Centauri system, is definitely understandable and desirable.

However, these discussions on what to do about an alien world that
resembles our planet always lead to a desire not just to visit that world
but to eventually colonize it as well.

I know such a thing is a long way off, even if we found a suitable Earth-
type planet circling Alpha Centauri A tomorrow, but we must not assume
such a place is ours for the taking, even if the highest life forms on it turn
out to be flowers.

I know this may not be the way things work in the Universe, that other
intelligent species just move into new worlds whether there is someone
comparable at home or not, but I hope we will be more careful and
respectful. Besides, an alien world’s occupants may not be big on having
permanent houseguests.

kurt9 June 10, 2009 at 13:31

If Earth-sized planets are found around Alpha Centauri, it makes more sense to build a great big humoungus telescope in space to directly image those planets than it would be to send a probe there. A reflector, perhaps around 1 kilometer is diameter, might be big enough to image such planets.

amphiox June 10, 2009 at 22:29

With regards to extra-terrestrial ‘Plan B’s’ regarding colonizing other habitable planets, I have this suspicion that by the time we develop the requisite technologies in propulsion, energy production and life support to contemplate sending a colony ship to any such world, we would have simultaneously reached the technology level where habitable planets are no longer required. (ie we will have the tech to build self-sustaining fully artificial colonies, which is basically a colony ship with the big engines optional)

Ronald June 11, 2009 at 5:54

I fully agree with philw1776 and kurt9, that direct imaging and spectroscopy make by far the most sense as a follow-up action to discovery of (an) earthlike planet(s) near AC, also because the same technologies could be used for other sunlike stars and their planetary systems. Therefore, I think that any such discovery would first and foremost trigger a major development in that field. And not only ground-based on earth and space-based, but probably also moon-based, because it is possible to build truly large observatories on the moon.

I agree with ljk that we should always excercise the utmost respect and care with regard to planets with present alien life, any life. Interestingly, such a discovery would probably trigger an entirely new kind of ethical discussion: when, where, under which conditions and to what extent is it allowable to settle and transform a planet? Only uninhabited? Or also those with merely ‘primitive’ (single-celled) life? Simple multi-celled? Also those with more complex life, but only with (very) limited changes to the planet? Etc.

In that respect, as I have argued before, terraformable terrestrial planets might be better picks for colonization, especially in combination with genetic engineering.

I can even imagine advanced civilizations having sort of galactic agreements, prime directives and the like, with regard to non-intervention/limited intervention on inhabited planets.

ljk June 11, 2009 at 10:36

In regards to planetary protection policies, going back to the early days of Sol system exploration, the first priority was to ensure that all missions intended to land on another world in one form or another were thoroughly sterilized of Earth microorganisms.

This rule even applied to the Moon, when scientists thought some kind of life might exist under the lunar surface. This is one reason the early Ranger hard landers failed, as the sterilization process apparently messed with their electronics.

Note that these rules applied only to NASA spacecraft; the West was not entirely certain how much the Soviets decontaminated their lunar and planetary probes, if at all.

However, once we learned whether or not there was alien life in our Sol system, it was just assumed that future missions would not be careful with the natives and that the chances of their being reduced or exterminated through general interaction were fairly good. As one example, Richard Greenberg’s new book on Europa describes how the space agency’s plans for exploring that Galilean moon include finding and examining any native organisms in their “pure” state before being contaminated or destroyed by the visitors from Earth.

There is an “amusing” report from circa 1964 about a plan for a manned Mars mission where one of the human explorers’ objectives was to secure Martian life forms to see if they were edible to supplement their diets!

http://beyondapollo.blogspot.com/2009/02/philco-aeronutronic-mem-1964.html

Perhaps worrying about usurping the life forms of other worlds is a moot point, as there may not be another planet that matches what we would need to live on. Terraforming “dead” worlds or the distinct possibility that our descendants will not be like our current selves and not need an Earth-type planet are other factors to consider.

But please keep this in mind as we consider finding Earthlike worlds and sending spacecraft to them: If we were merely interested in discovering alien planets for the mere sake of finding other worlds, then we might be content with long-distance exploration via powerful space telescopes. However, we want to go to these places directly with the main intent of seeing if they have life forms or not, which would imply that we could live their as well.

Unless something drastic happens to Earth and our society which requires our escape (and we would need plenty of warning to mount such a project), we should have the next century or so to be able to map out the local regions of our galaxy and plan any expeditions/colonization efforts with a minimum or none at all of intrusion into other ecosystems.

Imagine how our species would feel and respond if an alien ship appeared in our Sol system and the crew declared their intent to colonize Earth, even if they had the most peaceful of intentions.

Whether anymore means or realizes it or not, there is an underlying feeling going far back in our history that makes us think we are the most important things in the Universe. Several centuries of realizing just how small and off-center we truly are compared to the rest of the vast Cosmos has not erased this kind of thinking, as relatively few people have ventured past low Earth orbit.

While we have a right and duty to protect and preserve our species and society, these actions must include ending our self-centered perspective, or we may get quite the wakeup call from another species who also thinks the Universe is preordained for them. This is something to seriously consider as we plan and build our first true interstellar missions.

kurt9 June 11, 2009 at 11:56

The early Mars stuff is a hoot! Indeed, up until the mariner 4 flyby in summer of 1965, Mars was commonly believed to have lots of plant life. There were papers published in the scientific journals up until the mid 60’s about “Martian” biology and there was a lot of media hype while Mariner 4 was en rout to Mars about how it was going to take “spectacular” photos of the Martian biology.

David Grinspoon’s book “Lonely Planets” has a particularly entertaining chapter about early Mars observations. The part he wrote about Percival Lowell is absolutely hilarious! I highly recommend this book.

It is true that the Mariner 4 flyby was a shock and disappointment to scientists and the general public alike. I, along with many others, believe the discovery of a very non Earth-like Mars did more than anything else to kill public enthusiasm for space.

Unless a wild card like a Heim drive turns up, we will most certainly develop O’neill space colonies and related technologies (material science and biological) long before we go to the stars.

ljk June 11, 2009 at 13:25

I try not to laugh too much at the old views of Mars, because I have the
feeling we may have equally amusing and off views of life on other worlds
in the rest of the galaxy, where we have even less data.

If you read Percivall Lowell’s books on Mars, it is amazing how relevant
they sound even today – if you replace Mars with anyplace else in the
Universe.

If Mariner 4 had imaged say Tharis or Valles Marineris and with better
images to boot, I wonder if our exploration of the Red Planet might
not have been so curtailed?

Ronald June 12, 2009 at 4:32

Amphiox and kurt9, ref. “self-sustaining artificial space colonies” and the like: I strongly disagree, for the much mentioned and discussed fundamental physical reason, that shit happens, or to put it a bit more academically, small habitats have (exponentially) greater risks of being struck by an all-out stochastic (= chance) disaster, be it internal (malfunction) or external. This basic concept of island biology is also the reason that small island habitats are much more prone to major disasters and extinction, and are therefore much species poorer, than large continental habitats.
Relatively small space colonies will always need relatively (very) large investments and intensive maintenance and management. It is no conicidence that we were born on a decently sized planet, instead of an asteroid.

Therefore, I believe, when it comes to settling anything outside earth, we will first settle on Mars, first in self-sustaining mini-colonies (like domes), then terraforming.

Spacecraft will always (or at least into the foreseeable future) be something for transport and research.

But I do admit there is a degree of wishful thinking here: I want to go to the stars and other planetary systems, as much as dolphins want to swim in the sea.

ljk June 11, 2009 at 10:36: fully agree, particularly last paragraph: I actually believe that exactly this will determine our future expansion into the galaxy and beyond: the presence of other advanced intelligence/civilization and the resulting galactic pecking order. Our species and civ will theoretically be able to keep expanding (as species and civs do) until we run into something else (someone else) who does the same. This limitation can (theoretically) be galactic neighborhood, galactic, Local Group, or even Local Supercluster.

ljk June 12, 2009 at 19:11

Relevant to the last few items in this thread, here is the section
from Mars and Beyond released by Walt Disney in 1957, depicting
what were then considered plausible life forms on Mars:

http://www.youtube.com/watch?v=d76fiWRobU4

Now maybe in the Alpha Centauri system….

Torbjörn Larsson, OM June 14, 2009 at 15:23

Old thread, but interesting. I’ll pitch in with those who lauds the remote sensing and notes the difficulty of life adapted for one world to expand into another biosphere. I get all excited thinking of the possible knowledge gained on biospheres and abiogenesis by having fair statistics here.

“Earth’s lack of a backup plan”

More precisely, human culture’s lack of backup plan. Life has weathered all these risks well, and life has been found to be robust. It has survived one recent impactor, and last week or so there was a paper showing that life could probably survive the late heavy bombardment.

Btw, which would both explain why genome studies give that the first proteins were developed at decent temperatures of ~ 20 Celsius, while later bacteria protein and DNA all went through a ~ 70 Celsius bottleneck.

This coincides neatly with two other thermometers (of isotopes) in cherts, where the first surviving rocks after the LHB and the development of a more modern green house atmosphere at 3.5 Ga shows ~ 70 Celsius sea temperatures before slowly decreasing to decent temperatures at the start of the Cambrian.

This is precisely the temperature that allow for the bacterial oxygenating photosynthesis that later opened up for multicellular life. Life has probably survived and developed under atrocious conditions for most of its existence.

As they say, life will take a licking and keep on ticking.

“Our species and civ will theoretically be able to keep expanding”

If I’m not mistaken, the typical species lifetime is ~ 10^5 years. Humans aren’t exempt but in fact extra vulnerable for evolution, as the population explosion increased selection efficiency measurably 2 orders of magnitude. (Ref: John Hawks et al research.)

So while a colonization front may potentially be able to explore relativistic effects to remain static enough, the core worlds will be changed beyond recognition before a species settled a galaxy. (Even considering the, rather benign I think, assumption of culture lifetime on the order of species lifetime.)

In all probability there will never be any galactic cultures. Less so considering that information may be the only commodity which can later be economically traded between star systems.

Mike C June 16, 2009 at 11:19

If we found a planet or planets in the habitable zones around AC A or B I think it would definitely take 100% proof of some kind of life or presence of oceans from images taken of the atmospheres of those planets in order for the public to consider a trip or mission to send a probe there. Not to be too pessimistic, but I believe we are at least 50 years from attaining the ability to send anything .10C or greater. The only source we know of that could send a probe that fast is antimatter. I don’t think even fusion power can get us there that quick. We must be able to produce more antimatter than we currently do and design better traps to harness the antimatter in order to create a supply large enough to power a ship or probe or whatever. From all of the research into antimatter that I have read….. advancement is slow and the costs are extremely high. I guess all of this matters not if planets are not detected.

ljk August 20, 2009 at 12:37

Accurate masses and radii of normal stars: modern results and applications

Authors: G. Torres (CfA), J. Andersen (NBIA, Denmark; NOTSA, Spain), A. Gimenez (CSIC/INTA, Spain)

(Submitted on 18 Aug 2009)

Abstract: This paper presents and discusses a critical compilation of accurate, fundamental determinations of stellar masses and radii. We have identified 95 detached binary systems containing 190 stars (94 eclipsing systems, and alpha Centauri) that satisfy our criterion that the mass and radius of both stars be known to 3% or better.

To these we add interstellar reddening, effective temperature, metal abundance, rotational velocity and apsidal motion determinations when available, and we compute a number of other physical parameters, notably luminosity and distance.

We discuss the use of this information for testing models of stellar evolution. The amount and quality of the data also allow us to analyse the tidal evolution of the systems in considerable depth, testing prescriptions of rotational synchronisation and orbital circularisation in greater detail than possible before.

The new data also enable us to derive empirical calibrations of M and R for single (post-) main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff), log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.

Excellent agreement is found with independent determinations for host stars of transiting extrasolar planets, and good agreement with determinations of M and R from stellar models as constrained by trigonometric parallaxes and spectroscopic values of T(eff) and [Fe/H].

Finally, we list a set of 23 interferometric binaries with masses known to better than 3%, but without fundamental radius determinations (except alpha Aur). We discuss the prospects for improving these and other stellar parameters in the near future.

Comments: 56 pages including figures and tables. To appear in The Astronomy and Astrophysics Review. Ascii versions of the tables will appear in the online version of the article

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Galaxy Astrophysics (astro-ph.GA)

DOI: 10.1007/s00159-009-0025-1

Cite as: arXiv:0908.2624v1 [astro-ph.SR]

Submission history

From: Guillermo Torres [view email]

[v1] Tue, 18 Aug 2009 20:00:01 GMT (676kb)

http://arxiv.org/abs/0908.2624

Koichi Ito July 21, 2010 at 6:26

Alpha Centauri A and B are very similar to our Sun because of size and brightness of stars. Since Alpha Centauri A is slightly brighter than Sun and Alpha Centauri B is slightly dimmer than Sun. So Alpha Centauri is most likely place find Earthlike Planets going around both stars of Alpha Centauri.

Bearfax June 12, 2012 at 8:13

How fortunate are we that two of the three closest stars are almost identical to our sun. And according to research done these stars have high metalicity, are at least 6 billion years old and are both stable orbs. Only Tau Ceti is in close range to our sun with similar characteristics and its believed to have a lower metalicity.

What this of course means is that both stars, A and B, are capable of developping planets and the likelihood of one or two of these being in the goldilocks region of both planets suggests the strongest chance of finding an earth type planet within perhaps dozens of light years.

Of course the problem is their proximity, given that A and B come as close as Saturn’s orbit in our system. Can a planet develop under those gravitational circumstances, or would orbits be too unstable. Theoretically its possible for planets to be within about 2 AU of each star (at best). Under such circumstances though, would there be an extensive and volatile asteroid belt at the extremes of each stars gravitationally unstable points, such as has occurred in our Solar System thanks to Jupiter, and would such bodies be a far greater threat to planets in Alpha Centauri orbits than in our own.

As for travelling there, such as with the Daedalus proposal, at this stage it would be way too expensive even for the smallest of crafts, and the energy required to get it there within a hundred years is not yet available to us…wait for a few centuries I think.

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