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Earth-mass Exoplanets and Their Uses

What would it take to energize the public about interstellar flight? The answer seems obvious: Discover an Earth-type planet around another star. As happened with Gliese 581 c, once thought to be potentially habitable, the media would quickly focus on the question of how to get there. Interviewed by the BBC on that topic, I found myself explaining that a star over twenty light years away was an impossible target at our current level of technology, but the discussion quickly opened up into what we could do about that, and what methods might evolve to allow star travel.


The point is to get people thinking not only about distances but methods. Right now we’re still in the ‘build a better rocket’ mindset, one that doesn’t comprehend the realities of adding more fuel just to push still more additional fuel. The equations are inexorable: Rockets can’t do the job when we’re talking about crossing light years, so we look for ways to leave the propellant at home. And because even fast solar sails are numbingly slow at Centauri distances, we consider beamed propulsion via lasers, microwaves and particle beams, and look into the possibilities of antimatter through near-term technologies like Steve Howe’s antimatter catalyzed sail. And, of course, we hope for breakthroughs beyond.

Image: Or maybe an interstellar ramjet? Like other interstellar technologies, the idea has severe problems and may not be workable. But getting the public energized about these issues is one way to ensure that research continues and new ideas emerge. Credit: Manchu/ITSF.

Now comes the news that a planet discovered through microlensing — MOA-2007-BLG-192-L b — orbits not a brown dwarf, as originally believed, but an M-class dwarf, a larger star whose mass in turn suggests that the planet is smaller than first thought. MOA-2007-BLG-192-L b, in fact, could weigh in at about 1.4 Earths, and that, as this New Scientist story explains, would make it unusually interesting (but see the addendum below). The magazine quotes Scott Gaudi (Ohio State):

“The result is important because this is the lowest-mass planet yet detected, and is extremely close to the mass of the Earth,” he says. “Obviously, finding a true Earth-mass planet is one of the biggest goals of searches for exoplanets. We are very close to that goal now.”


Gaudi is not himself a member of this team, which is led by Jean-Philippe Beaulieu (Paris Astrophysical Institute); Beaulieu recently reported on the new findings at a meeting of the Royal Astronomical Society in London. Following up that story led me to the microlensing team Beaulieu heads. Called HOLMES (Hunting fOr Low Mass Extrasolar planetS), its stated goal is “…the discovery of low mass planets (1 – 15 Earth masses) within 1 – 5 AU of the most common stars in our Galaxy by microlensing effects in order to measure their frequency.”

Surely Scott Gaudi is right that we are close to finding an Earth-mass planet, and one day after that, a team like Beaulieu’s may turn up one in the habitable zone of its star. An intense round of media interest will inevitably follow.

The question: Will the discovery of an Earth-analog elsewhere in the galaxy be a one-day event, to be eclipsed by still more ‘breaking news’ in the perpetually overheated reporting cycle? Chances are it will, but my hope is that each intriguing exoplanet discovery will give us a brief window to work on public awareness of Earth’s place in the cosmos. If we choose to become a star-faring species, it will be because on the broadest possible level we will have placed ourselves in the context of a galaxy that may well be aswarm with living worlds. The key is to get people thinking, one story, one idea, one planet at a time.

Addendum: Re the mass of MOA-2007-BLG-192-L b, be sure to read David Blank’s message below. New Scientist‘s story was in error — the true mass seems to be 3.3 (+4.9 / – 1.8) Earth masses.

Comments on this entry are closed.

  • James M. Essig January 20, 2009, 23:02

    Hi Paul;

    This is a very interesting thread.

    This is the first time I read of an antimatter catalyzed sail. Does anyone know what the upper theoretical velocity limit is for Steve Howe’s antimatter catalyzed sail? I am rather intrigued by this concept. Perhaps electrodynamic breaking could be used to slow the craft down so that it would not need to carry fuel onboard for breaking and thus be able to obtain higher velocities than it would otherwise for practical manned interstellar missions.



  • Paul Titze January 21, 2009, 3:31

    > What would it take to energize the public about interstellar flight?
    > The answer seems obvious: Discover an Earth-type planet around another
    > star.

    2) Faced with certain extinction (a planet killer asteroid inbound for Earth), people usually start thinking hard and fast about their options.

    3) A breakthrough in Physics which would allow interstellar flight to be practical and economical.

    It will be a while before we can show to the public a photo of another livable Earth (this is what is required to convince the majority of the public), hopefully 2) won’t happen this century, my money’s on new Physics:


    Cheers, Paul.

  • Colin Weaver January 21, 2009, 19:27

    As an aside, to me the beautiful illustration of an interstellar ramjet against the disc of the galaxy strongly brings to mind the Larry Niven story “The Ethics of Madness”.


  • John Hunt January 21, 2009, 20:58

    2) Faced with certain extinction (a planet killer asteroid inbound for Earth), people usually start thinking hard and fast about their options.

    If you take a look at this graph it might suggest that most of the really big, easily detected asteroids have already been discovered. As we detect smaller ones, we will be able to evacuate people to another part of the region (e.g. Tunguska-sized). It doesn’t seem likely to me that a killer asteroid is going to get us to establish another base in the solar system much less an interstellar mission.

    I think that there are much more likely existential risks in the form of self-replicating technology by mid-century. Unfortunately, I think people are not going to get around to doing anything about it until we already have the technology to produce such things. By that time the proverbial genie will be out of the bottle!

  • John Hunt January 21, 2009, 21:07

    If there’s anyone who doubts that we’ll be creating self-replicating chemicals in the near future, this article, should be very informative.

    The line that got my attention was:

    the most fit replicators growing in number to dominate the mixture

    I’m just glad that they didn’t report “dominate the biosphere”!

  • Adam January 21, 2009, 23:38

    Hi again

    Without my youngest grabbing the keyboard this time.

    John, rest easy when it comes to such lab replicators – they require prepackaged energy inputs to work. Life has been exploring the chemical structure space of RNA/DNA for 4 billion or more years and it still hasn’t produced a “grey goo” catastrophe. There are trillions of trillions of RNA/DNA variants in existence at any one time and none dominate. I suspect that means none can be created or stumbled across by a random search – and we have no hint of an algorithm for a directed search either.

  • Adam January 21, 2009, 23:44

    To clarify:

    by “none can be created or stumbled across by a random search” I meant a grey goo replicator NOT any sort of replicator at all. Replicators most definitely can be found by such searches – that’s how they get made in labs. But they’re not super capable beasties like a grey goo style replicator would have to be.

  • Colin Weaver January 21, 2009, 23:57

    We have already experienced the dangers of self replicating technology, albeit in virtual form. In its purest form, a computer virus is a self replicator dedicated to its own propagation and continued existence. Even in this form it can cause damage by consumption of resources (memory, disc space, network bandwidth). Add to the package mission coals that have malicious intent behind them, and suddenly they can be dangerous indeed. Add a primitive form of genetic variability so they can mutate and it gets worse still – self mutating viruses already exist, using self modification of code as a survival strategy by changing their digital signature. (As an aside, there is quite a significant overlap between virus technology and code generation in a language compiler. Viruses are already using techniques from main stream computer science, e.g. register selection algorithms for code generators, to change their binary image at each propagation step).

    Besides showing the the dangers inherent in anything that self replicates, the other lesson taught us by computer viruses is that once something becomes technically feasible, its use by someone, somewhere, is almost inevitable. Try and control it as much as you might, and someone – for their own reasons – will try to release it “into the wild”.

  • Colin Weaver January 21, 2009, 23:58

    Sorry – for “coals” above, read “goals”.

  • Paul Titze January 22, 2009, 3:25

    Re: John Hunt

    > If you take a look at this graph it might suggest that most of the really big,
    > easily detected asteroids have already been discovered.

    #2 Scenario is highly unlikely however it is a possiblity. From p171 from the Motion Mountain textbook http://www.motionmountain.net/

    “Incidentally, discovering objects hitting the Earth is not at all easy. Astronomers like to point out that an asteroid as large as the one that led to the extinction of the dinosaurs could hit the Earth without any astronomer noticing in advance, if the direction is slightly unusual, such as from the south, where few telescopes are located.”

    Cheers, Paul.

  • James M. Essig January 22, 2009, 10:04

    Hi Folks;

    I find the above artistic depiction of the interstellar space craft very beautiful and inspirational. The depiction of some sort of reactionary thrust exhuast leads me to think that perhaps unlimited gamma factors might be possible, as a mathematical and logical limit in the event the FTL travel proves impossible.

    Even if such FTL might prove impossible, imagine all the mattergy in an infinite universe that is available for propulsion and infrastructure building.

    I think mankind will definately journey ever further out into the cosmos. Artists will no doubt have a role to play in this eternal endeaver especially with such beautiful illustrations such as that of the above space craft. I have had to look at that depiction about 10 times yesterday as I find it inspiring even on the spiritual level.



  • ljk January 22, 2009, 16:10

    Colin, I think a planet full of coal might be an admirable goal
    for an interstellar mission, too. :^)

  • David January 22, 2009, 16:56

    Hi All,

    I got an email from David Bennett stating that New Scientist made an error in stating that the mass of MOA-2007-BLG-192-L b is 1.5 Earth masses. The correct estimate remains 3.3 (+4.9 / – 1.8) Earth masses which while still lower than any other exoplanet, aside from the pulsar planets, none the less overlaps with estimates of a few others when one considers the uncertainties. The misunderstanding apparently arose because the writer gave what the mass would be if it was orbiting an M dwarf, rather than a brown dwarf.

  • James M. Essig January 22, 2009, 17:02

    Hi Folks;

    I can imagine Steve Howe’s antimatter catalyzed sail being used to propell a huge world ship to about 1,200 km/sec. More appropriate perhaps would be a very large colony ship with a mass of about 100 trillion metric tons for 10,000 year flights to stars 20 to 30 lightyears distant. The ship could have nuclear fission reactor based power production for dailly living and could have a dewar style multilevel hull for insolation from radiative thermal energy losses.
    This bad boy could have its own permanent magnet-based “geomagnetic field” for shielding against cosmic rays.

    The main point is that the plethora of propulsion systems using well extablished physics can allow us to get to the stars with todays technology albiet with improved low Earth orbit transport for ship construction purposes.



  • Administrator January 22, 2009, 17:09

    David wrote:

    I got an email from David Bennett stating that New Scientist made an error in stating that the mass of MOA-2007-BLG-192-L b is 1.5 Earth masses.

    David, thanks for passing this along! I’ve added this information to the original post.

  • ljk January 22, 2009, 23:22

    The following post is quoted from the blog Exoplanetology:


    Wednesday, January 21, 2009

    MOA-192 b remains at 3.3 Earth Masses

    Bummer. There was an error.

    The flood of news reporting that the mass of exoplanet MOA-2007-BLG-192L b (MOA-192 b) was revised to 1.5 or 1.4 Earth masses was an error.

    Officially, the correct mass of MOA-192 b is still 3.3 Earth masses, and NOT 1.5 Earth masses as reported in the news yesterday.

    Lest I myself err in that regard, I am posting the exact message today from David Bennett who wrote to the exoplanet mailing list I am subscribed to.

    “The New Scientist and perhaps other media outlets are reporting that the mass of MOA-2007-BLG-192Lb has been revised down to 1.5 Earth masses, but these reports are in error. The reporter has been confused by a report of one of my colleagues regarding a revision in the mass estimate that would be possible if the host star was confirmed to be a ~0.09 solar mass M-dwarf instead of a brown dwarf. The correct mass estimate remains 3.3 (+4.9 / – 1.8) Earth masses. This is currently the lowest mass estimate for an exoplanet except for PSR 1257+12 b, but the error bars have large overlap with a number of other planets detected by both radial velocities and microlensing.”

    – David Bennett, for the MOA, OGLE, and PLANET collaborations

    Thus, MOA-2007-BLG-192L b remains as a Super-earth. And Earth-like Worlds remain elusive. But with the launch of Kepler this coming March 2009, true Earth-like worlds will even come closer to being discovered.

    I can hardly wait.

  • george scaglione January 29, 2009, 10:45

    hello all,yes i have said myself,if we found an earth like planet,what a shot in the arm that would be for the popularity of space! people would forget all the arguments and SIMPLY WANT to go there!!!!!!!! ahem ahem the fact that this place might be 95 light years away,small problem lol just needs a ‘little” engineering/physics! anyway,thank you all your friend george

  • ljk February 3, 2009, 10:12

    While of course finding an Earthlike planet will be great, we
    better make sure nobody is home on it before we send out a
    big colonizing expedition.

    And seeing as this will be an alien world with alien creatures,
    defining who or what is there in terms of intelligence and
    society compared to the equivalent of “just” animals and
    plants is a whole matter in itself.

    Imagine if someone else out there just discovered Earth
    and thinks it might make for a nice new home.

  • george scaglione February 4, 2009, 16:03

    ljk,nobody could have put that better my friend! we would not have the moral right to steal what we wished to steal by any stretch of the imagination.just ask the american indian or the buffalo!!!!!! but i can some it up in an old quote i have always remembered….”if we go out into space and act like children we may find people perfectly capable of treating us like children”! very respectfully to all my tau zero friends,george scaglione