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Musings on SETI and Nearby Brown Dwarfs

There is enough going on at the Royal Astronomical Society’s 2010 meeting to keep us occupied for some time, but I don’t want to go any farther without circling back to UGPS 0722-05, an unusually cool brown dwarf now thought to be the seventh closest star to the Sun. The parallax measurements of its distance are still being refined, but the dwarf is currently thought to be some 9.6 light years from Earth, roughly twice the distance of Proxima Centauri. With a temperature between 130 and 230 degrees Celsius, this is the coolest brown dwarf ever observed, its mass ranging somewhere between five and thirty times that of Jupiter.

A number of readers sent links to this discovery, for which many thanks, and I note how interest seems to be growing in the idea that a brown dwarf may exist closer to us than the Alpha Centauri stars. Brown dwarfs are now thought to be relatively common in the galaxy, perhaps as common as normal stars, which suggests that missions like WISE may well discover brown dwarfs even closer in the neighborhood. In this case, we can thank the United Kingdom Infrared Telescope on Mauna Kea for the find, with follow-up spectra from the Gemini North Telescope.

For more on this dwarf, the paper is Lucas, et al., “Discovery of a very cool brown dwarf amongst the ten nearest stars to the Solar System,” submitted to Nature and available as a preprint. Science News has a good story on the dwarf, as does New Scientist. I’m bemused by the fact that I baked a loaf of bread last night in a tiled oven that was in the same temperature range as calculated for this object, which is cool enough that it may represent the first of a new class of ultra-low temperature dwarfs. The suspicion grows that objects in this temperature range would be dim enough to have lurked within a few light years and remained unnoticed.

What other surprises are out there? At the RAS meeting in Glasgow, recent talk has focused on discovering things with new instrumentation, in this case the Low Frequency Array that will, when completed, be made up of 44 independent stations spread across the Netherlands, Germany, Sweden, France and the UK. LOFAR will study radio emitting galaxies from the early universe and look into astrophysical phenomena from cosmic rays to pulsars. But it’s intriguing to note that the project also has a SETI component, the first phase of which will be to study how to filter out contamination from Earth-based transmitters and improve the system’s sensitivity.

After that, an extended SETI effort is planned, says Alan Penny, who presented the LOFAR SETI program to an audience in Glasgow:

“LOFAR will scan nearby stars searching for radio emissions which could only be produced by artificial means — a sign that there is a civilization there and that we are not alone. Previous investigations of these stars have concentrated on higher frequencies but, as we do not know at which frequencies an extraterrestrial civilization might choose to emit radio waves, LOFAR will fill an important gap in the search. It is particularly exciting that this is being done by a European team with a pan-European telescope.”

We know comparatively little about the universe at the very low energy wavelengths LOFAR will examine, but that should change quickly as the final stations of LOFAR are completed this summer. Check the sensitivity available in the imagery below:

Image: A comparison of the LOFAR image with the results from other radio telescopes at various observing frequencies. The Very Large Array image at 74 MHz and Westerbork Synthesis Radio telescope image at 325 MHz, shown to the same scales, provided the previous state-of-the-art images at low frequencies. The image quality with LOFAR at 173 MHz is well beyond what has been done before in terms of sensitivity and resolution. Credit: van Weeren/ASTRON.

LOFAR functions in a range from 10 to 240 MHz (compare this to the 0.4 to 3 GHz range of typical radio telescopes), and offers baselines across Europe on the order of 1500 kilometers, with the bulk of the aperture array stations being located in the Netherlands. The frequencies involved are so choked with terrestrial traffic that separating signal from local noise has to be the top priority, as anyone who has worked the SWL or ham bands above 10 MHz can testify. But opening up a new frequency range invariably promises surprises down the road. Whether those surprises are all astrophysical or might involve SETI should soon become apparent.

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Comments on this entry are closed.

  • Eniac April 15, 2010, 9:19

    A temperature as low as 130-230 degrees Celsius opens the possibility for liquid water. Perhaps there could be life on a “star” like that?

  • kzb April 15, 2010, 13:43

    This survey has so far covered only about 6% of the sky, so to find this amongst the 10 nearest stellar systems raises my hopes that one or more will be found closer than the Centauri system, perhaps by WISE.

  • James M. Essig April 15, 2010, 13:43

    Hi Enaic;

    Interesting possibility. I started thinking of the Jovian floaters and sinkers that Carl Sagan discussed in his “Cosmos”. Any habitable moon size worlds in close orbit around such a brown dwarf might also have life forms.

  • bigdan201 April 15, 2010, 17:49

    This quote from the OC bible in the Dune series comes to mind:

    Think you of the fact that a deaf person cannot hear. Then, what deafness may we not all possess? What senses do we lack that we cannot see and cannot hear another world all around us?

    When observing the cosmos, it’s important to have a wide observation window. The general trend is that the more we look, the more we discover, so making the effort to observe in lower frequencies will definitely turn up more stuff.

    If there was a terrestrial planet orbiting a brown dwarf, how close would the habitable zone be? I imagine that it would have to be a very close orbit. And how bright are brown dwarfs? A quick search doesnt really answer these questions.

  • spaceman April 15, 2010, 17:49

    It just goes to show how much progress has been made in astronomy in past 15-20 years, as I remember Carl Sagan mentioning brown dwarfs as just a possibility in his 1994 book “Pale Blue Dot.”

  • Adam April 15, 2010, 21:51

    Of course further down the mass scale are free-floating interstellar planets, some probably ejected Ice Giants and the like from late-stage migration and similar upsets that new systems under go. Finding them will be quite a neat trick. David Stevenson suggests scanning for radio emissions from their very large magnetospheres.

  • Greg April 16, 2010, 17:40

    Personally I’m excited to see what LOFAR might dig up. I think it is the surest way to detect other civilizations.

  • bigdan201 April 17, 2010, 2:19

    Of course further down the mass scale are free-floating interstellar planets, some probably ejected Ice Giants and the like from late-stage migration and similar upsets that new systems under go. Finding them will be quite a neat trick. David Stevenson suggests scanning for radio emissions from their very large magnetospheres.

    the thought of interstellar planets is intriguing. They’re probably out there – all it would take is for a terrestrial planet to get tossed by a gas giant, or for a planet to break orbit during a stellar event.

    And of course there’s the possibility of life. If they do have strong magnetospheres, as suggested, that would shield life from gamma rays/interstellar radiation and could provide a suitable habitat. An even wilder thought would be to colonize such a planet – perhaps using fusion and/or the planets’ interior heat. That’d be one way to travel through space…

  • Lionel W April 17, 2010, 19:31

    @bigdan201 – great quote.

    regarding interstellar planets, as far as i know current simulations of solar system evolution do indeed involve dramatic incidents of smaller planets getting flung out of the system by gas giants migrating about. so perhaps for each star that is formed, many ejected interstellar planets also result.

    a rocky interstellar planet with a magnetosphere would be an attractive destination for colonisation i think. shielding from interstellar radiation is a huge asset. but in the freezing cold of deep space, what kind molecules could exist in the atmosphere?

    having a magnetosphere would probably mean a convecting core, probably requiring geological activity. this perhaps holds some hope for providing a source of molecules and a bit of heat for the atmosphere. but i’m really unable to speculate what kind of temperatures or molecules could form an atmosphere in, say, a geologically active interstellar planet between 1 – 5 earth masses.

    finding interstellar planets, as Adam says, will be a neat trick – i guess many decades away – since the recently discovered TNOs like Eris and Sedna are a mere 0.0015 light years from here!

    again perhaps a geologically active interstellar planet might help us out with infra-red emissions from an eruption

  • Lionel W April 17, 2010, 20:09

    Ah! Just read David Stevenson’s article which Adam posted, which amoungst other things contains analysis of some of the issues I just wrote about above! A few points from the paper:

    -Many rocky planets may have been scattered from our solar system by protoJupiter and protoSaturn. “Planet formation may be quite
    inefficient in the sense that more solid material is ejected than retained… excessive scattering may prevent terrestrial planet formation…” Perhaps then the 4 terrestrial planets of our solar system may be the minority of those which have been created, the majority were ejected into deep space (and some destroyed in collisions)

    -These Interstellar planets as a destination for life and surface water. On page 6 “We thus see that bodies with water oceans are possible in interstellar space. The “just right” conditions are plausibly at an earth mass or slightly less, fortuitously similar to the expected masses of ejected embryos during giant planet formation.”

    -Concludes “It is even conceivable that these are the most common sites of life in the Universe.”

  • ljk April 19, 2010, 23:25

    The Entropy Principle and the Influence of Sociological Pressures on SETI

    Authors: Vladimir Bozhilov, Duncan H. Forgan

    (Submitted on 11 Apr 2010)

    Abstract: We begin with the premise that the law of entropy could prove to be fundamental for the evolution of intelligent life and the advent of technological civilization. Building on recent theoretical results, we combine a modern approach to evolutionary theory with Monte Carlo Realization Techniques.

    A numerical test for a proposed significance of the law of entropy within the evolution of intelligent species is performed and results are compared with a neutral test hypothesis. Some clarifying aspects on the emergence of intelligent species arise and are discussed in the framework of contemporary astrobiology.

    Comments: 11 pages, 5 figures, accepted for publication in the International Journal of Astrobiology

    Subjects: Popular Physics (physics.pop-ph); Earth and Planetary Astrophysics (astro-ph.EP)

    Cite as: arXiv:1004.1822v1 [physics.pop-ph]

    Submission history

    From: Vladimir Bozhilov Mr. [view email]

    [v1] Sun, 11 Apr 2010 17:17:19 GMT (39kb)

    http://arxiv.org/abs/1004.1822

  • Eniac April 20, 2010, 14:14

    It makes sense that a rocky planet further from the sun than 1 AU will retain much more water than Earth, and since the Earth’s interior is a lot hotter than its surface, there will be a layer somewhere with ambient temperature just right for life, even without any light at all. Most likely, such a layer will have liquid water. What does that do to the concept of the “habitable zone”? Do we need to open it up to encompass everything further than 1 AU, including interstellar space?

    I don’t think the presence of a magnetosphere matters much, since life on a sunless planet will have to be deep under the surface anyhow, where radiation cannot reach. The magnetosphere may be implied by the necessary hot core, but it may not be necessary itself.

    If there were a very large number of Earth-like planets floating around in interstellar space, would we have noticed? I understand that the brown dwarf density is constrained by lensing studies, are these studies also sensitive to much smaller bodies?

    Perhaps interstellar space is filled with prime destinations for advanced ice-fishing….

  • Lionel W April 20, 2010, 17:56

    Indeed, if liquid water can exist on an interstellar planet, then I think the habitable zone should have no upper limit.

    Regarding lensing, I believe diffraction is proportional to the mass of the object, so the lensing resulting from a terrestrial planet will be hundreds of thousands of times less than that from a star. The focal point will also be orders of magnitude further away than the focal point of a star. No idea how capable our instruments would be in detecting these.

    I wonder if any of the gravitation lensing experts, Claudio Maccone perhaps, have worked out where the Earth’s focal point would be (I am sure they have). I think that the distance where the focal point begins will be a function of both mass and radius of the object.

    It would be interesting to know far away terrestrial size objects need to be for us to be in range of their gravitational lenses. Would we be in the range of any planets closer than the centauri stars? Perhaps this will be the way that the first interstellar planets are found.

  • andy June 23, 2010, 15:37

    Distance of UGPS J0722-05 has been revised upwards, paper has been withdrawn from Nature and a revised version of the paper has been submitted to MNRAS. New version of arXiv paper here.