by Paul Gilster | Jul 19, 2010 | Culture and Society |
WISE Completes First Full Survey
The WISE mission completed its first survey of the entire sky on July 17, generating more than a million images, of which one of the most beautiful is surely the image of the Pleiades cluster below. We’re looking in the infrared at a mosaic of several hundred image frames with the combined light of WISE’s four detectors working in a range of wavelengths. The cluster of stars in seen in a dense latticework of dust in an area covering seven square degrees, equivalent to about 35 full moons.
Image: In this infrared view of the Pleiades from WISE, the cluster is seen surrounded by an immense cloud of dust. When this cloud was first observed, it was thought to be leftover material from the formation of the cluster. However, studies have found the cluster to be about 100 million years old — any dust left over from its formation would have long dissipated by this time, from radiation and winds from the most massive stars. The cluster is therefore probably just passing through the cloud seen here, heating it up and making it glow. Credit: NASA/JPL-Caltech/UCLA.
In addition to sights like these, WISE has thus far rung up 100,000 asteroids, 25,000 of which were previously undetected. Because Centauri Dreams readers have been concerned about data release (after our discussions of the Kepler policy on these matters), it’s worth noting that the first release of WISE data covering some 80 percent of the sky will be offered in May of next year. WISE goes on to map half the sky again, operating until its solid hydrogen coolant runs out. An extension to the mission using two infrared wavelengths without coolant hasn’t been ruled out.
And as we wait for possible brown dwarf detections, the recent paper by Adrian Melott and Richard Bambach comes to mind. You’ll recall in our discussion of the paper that the researchers found a repetitive 27-million year cycle in extinction events going back some 500 million years, and argued that this weighed against the idea of a dark companion to the Sun (‘Nemesis’) because the orbit of the latter object would be more variable than the extinction cycle. Comments here and on other sites make it clear that the 27-million year cycle may not be as robust as the authors believe, leaving the status of a dark companion unresolved.
Will WISE find a brown dwarf or a gas giant somewhere in the Oort Cloud? Let’s hope the data the mission produces either finds the object or puts ‘Nemesis’ to rest.
Interstellar Ideas at Solar Sail Conference
Tau Zero practitioner Pat Galea will be presenting a paper at the upcoming Second International Symposium on Solar Sailing (ISSS 2010), which convenes at the New York City College of Technology of the City University of New York tomorrow. A member of the Project Icarus team, which is at work designing a fusion-based successor to the Project Daedalus design, Pat will be examining the possible uses of solar sail technology in the mission. How to combine fusion and sail? Here’s the abstract:
Project Icarus is an in-depth theoretical engineering design study of a mission to another star, following on from the historically successful Project Daedalus. While the terms of reference for the project specify that the spacecraft propulsion system will be mainly fusion-based, aspects of the mission and overall architecture could be implemented or assisted by the use of solar sails. This discussion paper gives a brief overview of the aims of Project Icarus, and examines the potential application of solar sails in several areas of the mission. This includes: assisted boosting of the Icarus probe out of our solar system; deploying sub-probes in the target solar system for exploring local planets and other objects of interest; deploying a relay station at the Sun’s gravitational focus to receive transmissions from the distant Icarus craft. This paper discusses some of the engineering requirements for these potential roles as well as any potential performance enhancements to the mission.
You’ll find the full program for this timely meeting online. I call it timely because of the recent success of JAXA’s IKAROS sail and the upcoming LightSail mission sponsored by the Planetary Society. JAXA’s Osamu Mori, project leader for IKAROS, will be a speaker at the session, as will the Planetary Society’s Lou Friedman, along with sail luminaries from ESA and NASA. Have a look at the program to see how rich this conference should be. I hate to miss any of it, but will particularly regret not hearing Ed Belbruno, Les Johnson, Roman Kezerashvili and Greg Matloff.
Calendar watchers will also note that the International Astronautical Congress 2010 is coming up this September in Prague, during which meeting Pat Galea will be discussing the possibility of using gravitational lensing for communications with an Icarus-style craft. I’ll publish the abstract to that talk as we get closer to the event, but I do want to note that Tau Zero founding architect Marc Millis will be presenting four papers of his own in Prague as part of a robust Tau Zero presence at the meeting (I know Claudio Maccone is going, as is Tibor Pacher, and I’m sure Greg Matloff will be in attendance along with a number of Project Icarus team members including Kelvin Long).
Farside Protection at Ames (and a Lensing Find)
Speaking of Claudio Maccone, the good doctor tells me in a recent email that he will be discussing lunar farside protection this Tuesday at NASA Ames. You’ll recall our recent examination of creating a ‘quiet zone’ on the farside that would keep the area pristine for radio astronomy and SETI work. Maccone is suggesting that the 80-kilometer Daedalus Crater would be an ideal location for a scientific installation, shielded from Earth-made radio pollution. His talk is part of the 3rd annual NASA Lunar Science Forum, which runs through the 22nd at the NASA Ames Conference Center.
Thoughts of the FOCAL mission to the Sun’s gravitational lens are never far when discussing Claudio Maccone, and the recent news out of Caltech and the Ecole Polytechnique Federale de Lausanne (EPFL) instantly caught my eye. Researchers have found the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens. We know about hundreds of gravitationally lensed quasars, magnified by a foreground galaxy, but this is the first example of a background galaxy lensed by the host galaxy of a foreground quasar.
Image: The quasar SDSS J0013+1523 (blue), bracketed by the lensed images of the background galaxy (red), obtained with the W. M. Keck Observatory’s 10-m telescope and Adaptive Optics. Credit: Caltech/EPFL.
I also found the lensing diagram available via Caltech to be helpful:
This ‘reverse lensing’ is extremely useful because quasars, thought to be powered by supermassive black holes in the centers of galaxies, can be a thousand times brighter than the galaxy in which they are embedded. That makes studying the host galaxies quite difficult — EPFL’s Frederic Courbin likens it to staring into car headlights and trying to figure out the color of their rims. But lensing, he adds, changes things: “We now can measure the masses of these quasar host galaxies and overcome this difficulty.”
If quasars are a useful probe of galaxy formation and evolution, as Caltech’s S. George Djorgovski says in this news release, the lensing method itself is away of probing distant astronomical objects as well as those closer to home. Maccone’s FOCAL mission would use the Sun’s gravitational lens at 550 AU to study a variety of astrophysical issues, and could conceivably be used for close study of nearby solar systems. More exotic applications in SETI and, as Pat Galea will describe at the IAC, in communications, may well follow.
by Paul Gilster | Jul 16, 2010 | Exoplanetary Science |
The exoplanet HD 209458b is the subject of such intense scrutiny that the discovery of a comet-like ‘tail’ is almost anti-climactic. After all, this transiting ‘hot Jupiter’ has given us plentiful information about its atmosphere (including the presence of a massive storm), and its tight orbit around its primary, orbiting that star in 3.5 days, would imply an atmosphere in continual turmoil. Now we learn that some of the atmosphere is indeed escaping into space, with the result that stellar winds evidently push the cast-off material into a long stream behind the planet.
Jeffrey Linsky (University of Colorado in Boulder) explains the observations:
“Since 2003 scientists have theorized the lost mass is being pushed back into a tail, and they have even calculated what it looks like. We think we have the best observational evidence to support that theory. We have measured gas coming off the planet at specific speeds, some coming toward Earth. The most likely interpretation is that we have measured the velocity of material in a tail.”
The observations were made with the Hubble Space Telescope’s Cosmic Origins Spectrograph, which revealed carbon and silicon in the atmosphere, an indication that heavier elements are being heated and are escaping from the planet. As a large portion of the escaping gas was flowing at the same speed (some 35,000 kilometers per hour), the presence of the comet-like tail seems a reasonable conclusion. The work confirms earlier observations by Hubble’s Space Telescope Imaging Spectrograph from 2003, which showed an evaporating atmosphere and suggested a comet-tail structure as a possibility.
There have been a number of papers in the past few years looking at how a gas giant close to its star loses mass and investigating the lifetime of such a world, and in fact the first suggestion that such a planet would have a comet-like tail goes back to 1998. The researchers conclude in the paper on this work that the mass-loss rate in the planet’s outflow is in a range of (8-40) x 1010 g s-1, a formidable flow but one that would take, according to Linksy, a trillion years to cause the planet to evaporate. HD 209458b, some 153 light years from Earth, will be around for quite a while, and this usefully transiting world doubtless has much more to teach us.
The paper is Linsky et al., “Observations of Mass Loss from the Transiting Exoplanet HD 209458b,” Astrophysical Journal Vol. 717, No. 2 (10 July 2010), p. 1291 (abstract / preprint).
by Paul Gilster | Jul 15, 2010 | Outer Solar System |
We learned in May that Jupiter’s South Equatorial Belt (SEB) had disappeared, an event that still has skywatchers puzzled, though it’s not without precedent. In fact, the SEB fades out every now and then, with recent fadings in 1989, 1993 and 2010, and we can expect an outburst of storms and vortices when the enigmatic belt returns, probably within the next two years, based on historical precedent. All of which puts the spotlight on Juno, a Jupiter mission intended for launch in August of 2011. Juno is all about the giant planet’s core, its magnetic field, its auroras and the amount of water and ammonia in its atmosphere.
Juno’s Jovian Science
Maybe Juno will tell us whether the disappearance of the South Equatorial Belt is the result of ammonia cirrus forming on top and hiding the belt from view. But there is much more to learn. Hydrogen gas deep in Jupiter’s atmosphere is pressed into metallic hydrogen, a fluid that acts like an electrically conducting metal and is thought to be the source of the planet’s intense magnetic field. Juno will, among other things, sample the charged particles and fields near Jupiter’s poles while observing the brightest auroras in the Solar System, caused by charged particles moving into the planet’s atmosphere.
For that matter, does Jupiter actually have a core? Juno should help us find out, pointing to one among two possible formation models. Either a massive planetary core formed early and captured Jupiter’s hydrogen and helium, or an unstable region inside the huge cloud of gas and dust from which our system formed collapsed to create the gas giant. Juno will measure Jupiter’s gravitational and magnetic fields by way of probing its interior structure.
A Hostile Place for Electronics
But what an environment to operate in. Scott Bolton (SwRI), Juno principal investigator, calls the spacecraft “an armored tank going to Jupiter,” a nod toward the protective radiation vault that will house its electronics, protecting these systems from the planet’s vast radiation belts, which circle the planet’s equatorial region and extend past Europa, some 650,000 kilometers from the cloud tops.
“For the 15 months Juno orbits Jupiter, the spacecraft will have to withstand the equivalent of more than 100 million dental X-rays,” said Bill McAlpine, Juno’s radiation control manager, based at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “In the same way human beings need to protect their organs during an X-ray exam, we have to protect Juno’s brain and heart.”
All that radiation is why a future human presence on a place like Europa is so deeply problematic. For Juno, Lockheed Martin Space Systems built a radiation vault out of titanium, each wall measuring close to a square meter in area, a centimeter thick and massing 18 kilograms each. Inside go the spacecraft’s command and data handling box, power and data distribution unit and numerous other electronic assemblies, with a total mass of about 200 kilograms.
Image: Juno’s specially designed radiation vault protects the spacecraft’s electronic brain and heart from Jupiter’s harsh radiation environment. The vault will dramatically slow down the aging effect radiation has on the electronics for the duration of the mission. The image was taken on June 14, 2010, as Juno was being assembled in a clean room at Lockheed Martin Space Systems, Denver. Credit: NASA/JPL-Caltech/LMSS.
It’s going to be fascinating to see how this assembly does, but the Juno team also plans an orbit around Jupiter’s poles to lower the amount of time spent in the worst of the radiation around its equator. JPL has tested the vault in a high radiation environment, a lead-lined testing unit in which spacecraft parts were subjected to gamma rays from radioactive cobalt pellets. More tests await when the spacecraft is completely assembled — the vault is already on Juno’s propulsion module, with complete assembly to be accomplished next spring.
Future Mission to Ganymede and Europa?
Meanwhile, we can forget the image of the team in spacesuits drilling through Europa’s ice. This is one hostile environment for living beings as well as electronics, and unless we find breakthroughs in lightweight radiation shielding, chances are future Europa investigations will have to proceed with our machine proxies. Such proxies would be part of the proposed Europa Jupiter System Mission (EJSM), an international effort involving a Europan orbiter from NASA and a Ganymede orbiter built by the European Space Agency. The two craft would study both moons and return data on the entire Jovian system.
Can it be done? The mission is certainly feasible and it’s a candidate for a flagship mission. But Europa and Mars may conflict at a time when a major Mars sample return effort is also under consideration. We might be able to fund both missions, at the expense of a host of smaller yet worthwhile efforts, but we won’t know how the committee drawing up NASA’s mission goals (for the National Research Council’s Planetary Science Decadal Survey, 2013-2022) will come down on the matter until it makes its draft recommendations in late September.
My guess: We’ll get Europa and, depending on ESA’s decisions, Ganymede as well at the expense of the incredibly complex Mars sample return, a choice that will leave many unhappy, and one that highlights the steep financial constraints we labor under. But it will leave open the possibility of funding much less expensive Discovery-class and New Frontiers-class missions like Juno and New Horizons at the same time we explore Europa and Ganymede.
by Paul Gilster | Jul 14, 2010 | Outer Solar System |
The idea of ‘Nemesis,’ a hypothetical dark companion to the Sun, won’t quite go away, and it’s possible that the WISE mission may help us either identify such an object or else demonstrate that it’s not there. The idea is simple enough: Sol’s companion would perturb the Oort Cloud in its orbit, causing comets to enter the inner Solar System, thus increasing the likelihood of an impact with the Earth. Throw in an apparent periodicity in extinction events first described back in 1984 and you have an intriguing case.
But Adrian Melott (University of Kansas) and Richard Bambach (Smithsonian Institution) have reconsidered Nemesis in terms of extinction events in a new paper, one that looks at the timing of these incidents in light of the movements of Nemesis over time. They extend the original 26 million year extinction periodicity slightly, to 27 million years, and are careful to note that there is no consensus on the matter among paleontologists. But the real question they tackle is whether the apparent cycle really can be explained by the actions of a distant, massive object.
This is a useful contribution to the discussion particularly because the authors stretch the span over which periodic extinction events are studied to 500 million years. What they find is that the events seem to occur too regularly over that period to be tied to Nemesis. If that seems counterintuitive, realize that the effects of such an object depend upon the stability of its orbit. Two major causes of perturbation to that orbit have been considered, one the galactic tidal gravitational field, the other the effect of passing stars. Both carry a punch. From the paper:
Hut (1984) was specific that irregularity of the period of revolution of such an object over the past 250 My should be about 20% due to perturbation from the Galaxy tidal gravitational field and by passing stars, and sharp peaks should not be expected in Fourier analysis. Torbett & Smoluchowski (1984) reached the same conclusion, but with a somewhat larger estimate of the fluctuations from the Galactic tide alone, dependent on the inclination of the Nemesis orbit with respect to the Galactic disk. Hills (1984) estimated a period change of 4% per Nemesis orbital period from the effects of passing stars. Using a t1/2 amplitude scaling expected from a random walk, the orbital period should drift by 15 to 30% over the last 500 My. This change in the period will broaden or split any spectral peak in a time series frequency spectrum, so Nemesis as an extinction driver is inconsistent with a sharp peak.
So how sharp is the peak? Sharp enough for the authors to conclude that there is 99 percent confidence in rejecting the hypothesis that there is no association of mass extinctions with the 27 million year cycle. The periodicity is demonstrated for a much longer period of time, its timing revised to roughly 27 million years (over the previous 26 million) and the confidence level in the results has gone from 95% to 99%, surely a confirmation of a cycle, but what is causing the extinctions?
It’s not likely to be Nemesis, argue the researchers:
Fossil data, which motivated the idea of Nemesis, now militate against it and suggest another mechanism is needed to explain extinction periodicity. An attempt to associate the periodicity with passage through the Galactic mid-plane …has its own set of problems: 54 My is rather too short for most estimates of the period of the Sun normal to the plane, and our passage within the last My or so of the mid-plane… is inconsistent with the phase of the 27 My signal we have detected, with its recent maximum at 11 My ago.
This is a fascinating finding. On the one hand, we do see the expected timing for extinction events, but the very regularity of that timing argues against its being the result of Oort Cloud perturbations caused by a Nemesis-like object. Nemesis’ orbit couldn’t be that stable. We are left to ponder the cause of these events, now measured over a span of some 500 million years and found to meet the confidence levels of three different statistical tests.
The paper is Melott and Bambach, “Nemesis Reconsidered,” accepted by Monthly Notices of the Royal Astronomical Society and available as a preprint.
by Paul Gilster | Jul 13, 2010 | Astrobiology and SETI |
by James Benford
We recently looked at a paper by Duncan Forgan and Robert Nichol on the question of detecting extraneous emissions from an extraterrestrial civilization using technology like the Square Kilometer Array. James Benford (Microwave Sciences) has some thoughts on the issue growing out of his own work with brother Gregory on interstellar beacons and SETI reception in general. No one has put the question of interstellar beacons to tighter scrutiny than the Benfords, with particular regard to bringing the SETI discussion, as Jim puts it, “onto a quantitative basis, as opposed to rampant speculation, as is typical of the playing-tennis-without-a-net approach taken previously.” The Benfords’ work on interstellar beacons appears this month in Astrobiology. I give full citations at the end of this post.
The Forgan & Nichol paper on detection of leakage radiation does neglect our continuing use of microwave beams not only for radar, but also for likely future beaming of power for space purposes, such as power transfer. This has been noted by several others in their comments to this website.
Understanding Leakage Radiation
I feel that leakage radiation should include both what we have generated, such as TV and radar, but should also include future likely radiation for power beaming.
Examples of applications that have been studied are transferring energy from Earth-to-space, space-to-Earth, and space-to-space using high power microwave beams. Such beams have been quantified for spacecraft launch to orbit, orbit raising to GEO, launch from orbit into interplanetary and interstellar space, and deployment of large space structures (see “Space Applications of High Power Microwaves”, James Benford, IEEE Trans. on Plasma Sci., 36, pg. 569, 2008). For example, even a single microwave beam powered launcher of Kevin Parkin would produce an increase of the effective isotropic radiated power (EIRP) of Earth by five orders of magnitude beyond that of Arecibo, our present highest EIRP radar. I feel that in the future we will be radiating in the microwave in these ways, not just as leakage from communication channels.
Strategies for Detection
Should we observe such activities by ETI, the signals would appear to us, Thomas Hair points out, as transient events. But such quick, powerful bursts would be verifiable by a ‘staring’ strategy, with smaller dishes looking continuously at the skies, most profitably at the galactic plane. Once such a burst appears, watching time can be focused on such possible sites, perhaps with some dishes linked so their effect could be coherent, raising the detection capacity of the network.
Project Argus, led by the SETI League, is the right direction to go. They’ll need short integration times to spot such transients. I would expect the transients would recur as ETI’s launches, transfers and such repeat. But even a frequent launcher aims at different parts of the sky, as planets rotate. So, we must be patient.
Distance, Receptivity and Cost
I also found that the distances Forgan & Nichol give, which are taken from the Leob & Zaldarriaga paper, although portrayed as discouraging for detecting leakage from ETI, are in fact overly optimistic for conventional TV and radar. Their work assumes that receivers are going to be integrating over hours-days-months. That doesn’t work when the TV station you are observing is transmitting in your direction only for a time typically ~hour, before it disappears around the limb of the Earth, as shown by Sullivan in his seminal paper. There is also a confusion in both papers over the distinction between transmitter power and EIRP. Forgan & Nichol misunderstand the EIRP quantity, saying on their page 1 that radars produce ‘isotropic radiation with billons of watts’. Although EIRP, the product of radiated power and the antenna gain, is that high, the radiated power is of order megawatts, since the gain is ~1000. The problem of observing leakage due to TV stations is identical to that of detecting a single strong station, as shown by Sullivan, so their estimates of detectability of leakage in these papers are systematically high.
One important implication of this is that the case made by advocates of sending messages to the stars (METI), who argue the ‘we’ve already announced ourselves’ is wrong. We have not been noticed at interstellar range by societies of our order of magnitude of technical and economic capability. One might argue that aliens will be far richer, so will have vastly larger antennas. But if so, why are they not radiating at oxygen-obvious planets like ours?
Michael Simmons, who suggests a phased array radiating rapidly cycling, short, high-powered transmissions directed at millions of nearby stars, might look at my cost equations to estimate what the expense will be (see “Messaging with Cost Optimized Interstellar Beacons,” referenced below). Hint: they won’t be cheap.
To follow the latest Benford thoughts on SETI matters, see James Benford, Gregory Benford and Dominic Benford, “Messaging with Cost-Optimized Interstellar Beacons,” Astrobiology Vol. 10, No. 5, pp. 475-490 (abstract / preprint), and the same authors’ “Searching for Cost-Optimized Interstellar Beacons,” Astrobiology Vol. 10, No. 5, pp. 491-498 (abstract / preprint).
