As promised, we now have the infrared sky at a new level of detail thanks to the labors of the Wide-Field Infrared Survey Explorer (WISE) mission, which has now mapped (with a few slight glitches) more than half a billion objects, from galaxies to stars to asteroids and comets. We can now expect a new wave of papers from the more than 2.7 million images WISE has delivered at four infrared wavelengths and can explore the WISE atlas of some 18,000 images ourselves.
The Big Picture
But first, I want to step back and look at astronomical discovery in context, a thought spurred by Larry Klaes, who sent me a note originally posted on the HASTRO-L mailing list (by Rich Sanderson, of the Springfield Science Museum in Massachusetts). Every now and then I read something that wraps back into the past and yet implies future things, generating a sense of connection with what the enterprise is all about. Such is the case in this passage Sanderson quotes from an 1875 book by Richard Proctor that looks at 19th Century transits of Venus. Remember, these are rare phenomena, occurring in pairs spaced eight years apart which are then separated by gaps of 121.5 years and 105.5 years. Listen to Proctor:
We cannot doubt that when the transits of 2004 and 2012 are approaching, astronomers will look back with interest on the operations conducted during the present “transit season;” and although in those times in all probability the determination of the sun’s distance by other methods…. will far surpass in accuracy those now obtained by such methods, yet we may reasonably believe that great weight will even then be attached to the determinations obtained during the approaching transits. I think the astronomers of the first years of the twenty-first century, looking back over the long transitless period which will then have passed, will understand the anxiety of astronomers in our own time to utilise to the full whatever opportunities the coming transits may afford; and I venture to hope that should there then be found, among old volumes in their book-stalls, the essays and charts by which I have endeavored to aid in securing that end (perhaps even this little book in which I record the history of the matter), they will not be disposed to judge over-harshly what some in our own day may have regarded as an excess of zeal.
Thus the past regards us, and in his own comment, Sanderson goes on to speculate about what’s ahead:
As Proctor had hoped, a copy of his little book did appear on a “book-stall” I visited in Ithaca, New York, from which it made the journey to Massachusetts to take up residence in my library. I wonder whose fingers will be caressing its pages in 2117.
For we do have a transit coming up on June 6, but after that, it will be December of 2117 before the next, and we can only wonder not only how astronomers of that day will observe it, but also about the techniques they will then be using to study planets around other stars. We can also wonder at the kind of nearby objects we will be considering as fair game for future space probes, given the results of missions like WISE. We’re learning that ‘rogue’ planets may be out there in huge numbers, and that brown dwarfs are interesting targets in their own right. Perhaps in the new WISE data we’ll find a few objects like these to put on our exploratory wish list, even as we imagine future astronomers looking back and marveling at our primitive equipment.
Analysis and Papers Ahead
But as we begin to dig into what WISE has produced, we’ve already learned that the mission has now identified, according to NEOWISE principal investigator Amy Mainzer, some 93 percent of the near-Earth asteroids larger than 1 kilometer, thus satisfying the congressional mandate for the SpaceGuard project.
NEOWISE is the asteroid-hunting portion of the WISE mission. Its efforts have also found fewer mid-size objects among near-Earth asteroids than used to be thought were there. The recent discovery of 2010 TK7, the first known Earth Trojan asteroid, underscores the capabilities of NEOWISE. Trojans are asteroids that share an orbit with a planet, circling the Sun in front of or behind the planet — they circle around the stable gravity wells called Lagrange points. 2010 TK7’s orbit is well known over the next 10,000 years, showing that at no time during that period will it approach any closer than 20 million kilometers to the Earth.
WISE is, of course, equally attuned to the study of distant objects, as in the image below, which shows the ‘light echo’ of the supernova event associated with Cassiopeia A, one of the most powerful radio sources in the sky. The light from the explosion reached the Earth around 1667 AD but seems to have gone unnoticed, probably because dust between the event and the Earth would have dimmed the explosion so as to make it all but invisible to the naked eye.
Image: The light echo of the explosion that produced Cassiopeia A. The central bright cloud of dust is the blast wave moving through interstellar space heating up dust as it goes. The blast wave travels fast – at an average speed of about 18,000 kilometers per second (11,000 miles per second) – but that is still only about 6% of the speed of light. The blast has expanded out to about a distance of 21 light-years from the original explosion. The flash of light from the explosion traveled faster – at the speed of light – covering over 300 light-years at the time that WISE took this picture. The orange-colored echoes further out from the central remnant are from dust heated as the supernova flash reached the dust centuries after the original explosion. Credit: NASA/JPL-Caltech/WISE Team.
Among the many discoveries of WISE are the Y-class brown dwarfs that are the coolest known class of stars. We now wait as the astronomical community sifts through the 15 trillion bytes of returned data in search of brown dwarfs and other interesting IR signatures in nearby space. The WISE all-sky archive with catalog and image data is available online along with instructions.
I went online yesterday and had some fun with the data base. They have an excellent help service available via Email and I got some detailed instructions. I was able to find both Uranus and Neptune burning bright in the infrared ( more at longer wavelengths).
I was expecting more announcements to accompany the release yesterday but there is a LOT of work in progress. If you rummage around some of the frames you soon realize what a big job it is to sort things out. I emailed Rolf Scholtz ( an author on a recent Brown dwarf paper using WISE data) about updates and he gave me some further references. From looking a these there are hundred(s) of candidate brown dwarfs many of which are virtually certain, to be interesting, but without more observation with larger scopes at different times it is hard to figure out important info like the spectra, and distances, overall brightness, mass estimates etc. BUT at least we know Where and HOW to look! As far as other “planets in the outer solar system… well I think we have to wait just a bit longer to see the search definitive out to say, 1000AU ( ~20 times the distance to Neptune and Pluto) There could be just about anything short of a brown dwarf out there, and it is hiding in plain site in this data.
The importance of the previous transits was the accurate determination of the astronomical unit. In this age of solar-orbiting spacecraft and L1 observatories, what new discovery could the current transits offer?
One fascinating thing about WISE is that it can turn out to be a great SETI instrument…
If a Neptune-sized object would be seen at hundreds AU, Jupiter-sized one – at many thousands, and a rogue super-jupiter at several light years, than a Dyson Sphere, which is supposed to be several thousand times wider than a super-jupiter, would be detectable at 10000 – 20000 light-years as far as energy conservation isn’t broken and the energy output of the central star, after having been used by a type II civilisation, is re-emitted in thermal infrared.
So, as we possibly haven’t any other types of objects, which look like a point source of thermal infrared, but have luminosity of a star, it would be very distinctive object… At least, the following observation with more powerful telescopes would be able to tell this is not a close brown dwarf (by telling there aren’t any CH4 and other atmospheric gases absorption lines and figuring out that it’s much more distant and luminous), and not an extremely massive and compact protoplanetary disk, because even a partial Dyson sphere would have much higher thermal infrared excess than a flat disk. And even a Dyson swarm at the early stage of construction, which intercepts no more light than an ordinary protoplanetary disk, would possibly have a very peculiar spectrum.
So, the hunt for Dyson spheres in our half of Milky Way begins?
Here is a Web site with images from Richard Proctor’s book on the transit of Venus – true works of art:
http://www.transitofvenus.org/history/1874-1882/210-book-by-richard-proctor
I saw the 2004 Venus transit and I cannot say enough about how fortunate I was to do so, not just because they are so rare. I will never forget seeing the Sun rise in the east as a huge red ball with that surprisingly large black dot on its face, which I could see without binoculars (the Sun was dim enough to do this safely at the horizon).
Regarding the Proctor quote (thank you for using it, Paul): I wonder if in 2117 people will be asking “What’s a book?” “What is a book stall?” “What are fingers?”
Who knows, they may even be asking “What’s Venus? Oh yes, it was the second planet from Sol – before it was turned into our Dyson Shell along with the rest of the system.” :^)
Torque_xtr,
Quite a few searches have already begun. Visit http://home.fnal.gov/~carrigan/infrared_astronomy/infrared_astronomy_master.htm and note the links at the bottom of the page.
2010TK7, being a Trojan of Earth, means that Earth has not cleared its orbit. Thus, Earth is officially a dwarf planet.
torque_xtr writes:
Re recent searches for Dyson spheres, see our discussion of Richard Carrigan’s work here:
https://centauri-dreams.org/?p=4397
and more recently here:
https://centauri-dreams.org/?p=12153
Martin J Sallberg March 16, 2012 at 8:23
“2010TK7, being a Trojan of Earth, means that Earth has not cleared its orbit. Thus, Earth is officially a dwarf planet.”
Good one. By those standards Jupiter is also a dwarf planet. The IAU did a really crappy job attempting to define planets and exclude Pluto. Not that I can do better.
torque_xtr, searching WISE data for Dyson surface signatures is a great suggestion. While I expect the search to turn up negative, because I estimate the number of ETI per galaxy to be far less than one, I’d be happy to be proven wrong.
What would be particularly useful would be a thorough search that would, if it turned up negative, rule out, for up a significant fraction of the Milky Way, a wide range of objects by their size and thermal signature in these four wavelengths (or just their temperature as implied by these). For example, just picking numbers out of the air, rule out the existence of any object within 10,000 ly of more than 0.5AU diameter with surface temperature of over 150K. Closer in, within 2,000ly, rule out the existence of any object of more than 0.1AU diameter with a surface temperature of over 150K. And so on. (These criteria would have to be more carefully defined to not include natural objects such as dust belts).
As also suggested, detecting a candidate Dyson surface would be just the first step. These objects would then have to then be much more carefully studied through spectroscopy (well beyond the scope of the WISE data, but a good future use of the JWST or similar) to detect signatures of engineered surfaces or illumination methods, to rule out the possibility of previous undiscovered natural phenomena — and of course to learn more about such a very advanced civilization should it prove to be that!
If somebody wants to program software for the above suggested computerized search of the WISE data and post it on this forum, I have programming experience and I’d love to volunteer to help.
I’ve thought of another way to look for Dyson surfaces, analogous to the transit technique Kepler is using. Such an artificial star-surrounding surface, like a thick dust cloud or dust belt inclined with respect to us, will sometimes eclipse other galaxies as it orbits in the Milky Way. The data set would be repeated observations of the billions of visible galaxies, looking for total eclipses of them (i.e. looking for the galaxies to disappear and then re-appear). Or, if these eclipses occur very slowly, looking for the said galaxies (this requires a fewer number of galaxies that aren’t just point sources) to oddly increase or decrease in size as the eclipse grows larger or smaller.
Possibly this kind of search has already been done looking for dust belts around stars inclined to us. Possibly the Kepler data could be mined for transits of the closer-in stars, but the search would be far more productive (by searching a far larger volume of space) against more distant stars or galaxies. I’d be interested in learning what data sets would be the most suitable for this kind of search.
I was wondering at what scale it would be practical to deploy a Dyson Sphere using realistic materials. One of the first principles of engineering I learned when working on automated lab systems was not to rely on ” unobtainium”.
There is in fact a CONTINUUM of structure sizes available, varying by size of the contained object and the diameter of the enclosing structure: thus a simple plastic bag filled with gas will enclose an asteroid, while a star the size of Sirus might require a inconceivably strong shell a light year in diameter.
What about enclosing a dwarf planet ( ceres?) what about enclosing a planet that generates a mild amount of heat ( earth or neptune)- If such aplanet were a nomad not orbiting a star enclosing it might make it interesting to support a civilization.
IF we are to start looking for dyson spheres we should be able to project at least the engineering requirements to enclose a brown dwarf ( say 30 times the mass of jupiter,) or what is the point? You might was well posit the idea of a civilization inside a star as one encircling one on a sphere made of magic materials ( hey – David Brin wrote a very fun novel , Sundiver, on the subject)
Could a realistic shell be build to contain a brown dwarf? The surface area to strength problem is much more manageable it might seem. plenty of heat available if it is all trapped! what would such a shell look like in the infrared?
a surface temperature of maybe 100 to 200K with a very large surface area?
it would look like a dust enshrouded brown dwarf but with some strange features in the spectrum…
jkittle: “I was wondering at what scale it would be practical to deploy a Dyson Sphere using realistic materials.”
This is a red herring. Dyson’s idea was not about a particular structure — it was about an emergent process of economic growth, per the Malthusian imperative, that would efficiently use more and more of a star’s power, until it was completely obscured and all we could see were artificial surfaces — primarily radiators, presumably radiating in the infrared after having efficiently used that power.
I call this idea a “Dyson surface” to remain agnostic about what is speculative and not directly observable — the underlying structure(s) — and focus on what we would observe — the surface. These surfaces would more than likely, due to the “unobtainium” problem you cite, be those of billions or trillions of independently orbiting structures rather than of one. Like trees in a forest, they would compete to collect photons until nearly all the photons were collected by them. Dyson’s idea is about the forest, not the trees.
Thus the overall size of a Dyson surface is limited not by the size of a single structure, but simply by the mass available in a star system, the ETI’s ability to manipulate it, and the equilibrium emergent distance from the star we might expect based on energy efficiency and how the competition for being in view of the star is handled. (cf. the disputes between those with shade-casting trees and buildings and people with rooftop solar collectors here on earth, then throw in orbital mechanics and the distribution of the existing population of other Dyson surface objects to see what percentage of time the star would be in view from a given orbit).
That said, your idea is nevertheless of smaller Dyson surfaces is intriguing insofar as an advanced civilization is probably not limited to merely the fusion power going on inside their star. Thus I posit a second category of radiating surface to look for — one that radiates far more power than can be accounted for by the fusion of a star alone — one that reflects instead a civilization that harnesses an even greater amount of artificially induced fusion power. These varieties of radiating surfaces might indeed be much smaller than a circumstellar Dyson surface. And they might be more easily distinguished from natural objects by their unnaturally large yet low-frequency power output densities.
Sorry, But Please more Science and less Science Fiction like this Dyson Spheres.
Please tell more about nearby Brown dwarf and “free floating Planets” like Jupiter, is there any sign of how abundant this worlds are in solar neighborhood?