by Paul Gilster | May 26, 2008 | Exoplanetary Science |
Yesterday’s high-tension arrival on Mars raises inescapable thoughts about future missions. Even the fastest spacecraft we can build today take years to reach the outer planets (New Horizons won’t reach Pluto/Charon until 2015), and targets deep in the Kuiper Belt, much less the Oort Cloud, conjure up potential missions longer than a human lifetime. Imagine the arrival of a robotic interstellar probe around, say, Epsilon Eridani, not a few years after launch, but a few generations. How would the team feel that took that final handoff from previous researchers, people who had invested their lives in a mission whose end they knew they would never see?
Thus we make the segue back into interstellar matters, with today’s Phoenix operations still very much in mind. And I want to go quickly to the recent COROT announcement, for the doughty spacecraft has been hard at work observing its sixth star field, a sweep of some 12,000 stars that began in early May. The team presented two new planets at the IAU symposium on transiting planets in Boston, which just concluded on Friday the 23rd. Both are gas giants in the ‘hot Jupiter’ category, but two other COROT objects are even more interesting (and thanks to Vincenzo Liguori for another early heads-up on COROT news).
For the object called COROT-exo-3b may well be a cross between a brown dwarf and a planet. With a mass some twenty times Jupiter’s (based on ground-based follow-up observations) and a radius somewhat less than Jupiter’s, it is said to be twice as dense as platinum. Another potential signature may mark the existence of an exoplanet a mere 1.7 times Earth’s radius, although that one has yet to be confirmed.
Based on all the Boston results, you have to believe that what Greg Laughlin calls ‘transit fever’ is catching hold. Here I have to quote the UC-Santa Cruz astronomer, recently back from the abovementioned IAU meeting. Calling this the most exciting conference he ever attended, Laughlin adds:
Planetary transits are no longer the big deal of the future. They’re the big deal of the right here right now. Spitzer, Epoxi, MOST, HST and CoRoT are firing on all cylinders. The ground-based surveys are delivering bizarre worlds by the dozen. And we’re clearly in the midst of very rapid improvement of our understanding of the atmospheres and interiors of the planets that are being discovered.
The HARPS planet survey alone, tracking solar-type stars of classes F, G and K, has not only been accumulating data and tightening the profiles of existing planets, but has forty-five additional candidates in the hopper, not counting red dwarf possibilities. I’ve often said that we are in the golden age of planetary discovery, but it’s clearly an age that is only beginning as we not only tighten up our transit methods but improve our radial velocity techniques to find ever less massive worlds. Can a terrestrial-class world around a Sun-like star be that many years away?
by Paul Gilster | May 24, 2008 | Culture and Society |
I usually point readers to articles on interstellar issues when the weekly Carnival of Space comes out. But this time, with the polar regions of Mars on everyone’s mind, I’ll focus instead on the Red Planet. Todd Flowerday, who hosts the current Carnival at his Catholic Sensibility site, obviously shares my predilection. Todd’s been following space issues on his blog for quite some time and is a long-term correspondent, so it’s good to see him involved with the Carnival. He leads the parade this week with Cumbrian Sky‘s helpful compilation of information and links related to the flight of the Phoenix. Today, of course, is the big day.
We can all, I think, understand the apprehension and anticipation of Cumbrian Sky‘s post, as so well conveyed in this passage:
…during the landing itself I’ll be watching TWO monitors, not just one; my laptop is going to be… displaying the amazing real-time JPL animation/simulation of Phoenix’s Entry, Descent and Landing. I’ll start that playing at the appropriate time, and that will allow me to imagine I’m actually flying alongside Phoenix in a “chase plane” as she drops, screaming, through the thin Martian atmosphere, counting off the minutes then seconds then moments until landing… If I feel nervous now, how am I going to feel on Sunday night, when we’re so close to Mars after all the waiting? What kind of a state are my guts going to be in as thoughts of how many ways the landing can go wrong run through my head? I’m going to be an absolute nervous wreck!!
I’ve poached Stuart’s illustration to use in this post because it’s so evocative, especially for those who recall the last attempt to land at a Martian pole. Be sure to run through Cumbrian Sky‘s list of links to make sure you have what you need for the upcoming event. I also want to point you to Emily Lakdawalla’s post on the search for the missing Mars Polar Lander via imagery from orbit, including how previous landing sites have looked to the Mars Reconnaissance Orbiter’s HiRISE camera. This is interesting stuff, for as Emily notes, “Mars Polar Lander is the missing lander whose crash site is most narrowly constrained, so the search requires a manageable number of HiRISE images.” Volunteer searchers can help out with this investigation; contact Emily for more.
Addendum: Well done!
by Paul Gilster | May 23, 2008 | Exoplanetary Science |
From the standpoint of planetary detections, the small red stars called M dwarfs are all but ideal. Their size is an advantage because radial velocity and transit methods should find it easier to pull the signature of smaller planets out of the statistical noise. Not so long ago, that wouldn’t have seemed important because the search for terrestrial worlds seemed confined to G- and K-class stars not too different from our Sun. But more and more theory is piling up as to why a terrestrial-sized planet in the habitable zone of an M dwarf could harbor life.
So these are important stars, especially when you add in the fact that they account for 75 percent or so of all the stars in the Milky Way (that statistic is admittedly subject to change as we learn more about other stars, especially brown dwarfs). And that makes the recent flare on EV Lacertae quite interesting. Some sixteen light years from Earth, the star is young (300 million years), dim (shining with one percent of Sol’s light) and small (its mass and diameter being a third that of the Sun). And although far too dim to pick out with the naked eye under normal circumstances, the recent monster flare it emited would have made it easy to see.
Once again we can thank the Swift satellite for the detection. Although intended to hunt gamma ray bursts (GRBs), Swift often does double duty, as in the recent case of a supernova caught just as it exploded. When the satellite detected the EV Lacertae flare, detailed measurements followed. The flare was thousands of times stronger than solar flares in our own system, of a magnitude that Rachel Olsten (NASA GSFC) calls “unprecedented.” Osten adds: “This star has a record of producing flares, but this one takes the cake.”
Image : An artist’s depiction of the incredibly powerful flare that erupted from the red dwarf star EV Lacertae. Credit: Casey Reed/NASA.
So now we are developing the ability to watch flares on other stars as they develop, with the help of Swift and other space-based resources like Chandra and XMM-Newton. That’s useful data as we ponder life’s chances around M dwarfs, where intense magnetic activity can generate flares like this one, capable of damaging a planetary atmosphere. This seems to be the thorniest issue of all, for although we can develop plausible scenarios for habitable climates on such worlds, their sheer proximity to their parent star could make frequent flares an evolutionary wildcard, if not prohibiting the development of life altogether. The range of flare activity possible on M dwarfs — some are far more benign than others — should be a factor as we fine-tune our target lists for future space-based observatories.
by Paul Gilster | May 22, 2008 | Astrobiology and SETI |
SETI quite naturally started with the assumption that we should look in the realm of photons for signals from other stars. After all, radio or optical wavelengths were things we understood, and the interest in radio and attendant theorizing about ‘waterhole’ frequencies and interstellar beacons continues to be worth examining. But a truly advanced civilization might be using methods we haven’t yet managed to exploit. Of these, a singularly interesting choice is communication by neutrino.
John Learned (University of Hawaii) and colleagues take on this issue in a new paper just posted to the arXiv site, looking at the advantages of the notoriously elusive neutrino. A major plus is that the signal to noise problem is tricky for radio and optical methods, especially in the galactic plane, whereas neutrinos, depending on their energy levels, can offer an essentially noise-free band. We also run into severe problems with photons as we look at line of sight communications anywhere near the galactic center, intervening materials causing signals to be attenuated.
But neutrinos show up with little attenuation from almost any direction, and are free of photon scattering that introduces jitter in arrival time and direction. The paper looks at the neutrino energies best suited for galactic communication, noting that low energy neutrinos are a problem because natural sources (like supernovae) produce emissions that can obscure a signal. The paper runs through the factors considered in choosing a high energy level near 6.3 PeV “…such that it would be clear at once that it is an artifical source such as ETI and not some random background.”
Given the distances and times involved, the question of when an extraterrestrial civilization might choose to send a message becomes intricate. Although it’s a digression from the neutrino beam technology considered in the rest of the paper, the discussion is provocative:
We presume that the ETIs, though in our galaxy, are remote. Even if an ETI has been observing us, it may be a long while (timescale of thousands of years) before they would send us an introductory message. So if they want to send a message in advance, saying hello and welcome to the galactic network, they are going to have to speculate about when to bother to transmit. From the jittering of advances in speciation, with the great die offs, it seems clear that evolution is a stochastic process, with ?uctuations on a timescale of many millions of years. The evolution of technology may ?uctuate over a timescale of thousands of years, as exempli?ed by the long periods of lack of technological progress in post-Roman Europe, China and India. One must reason that no useful prediction could be made as to when the industrial revolution would take off and high technology would arise. Thus the ETI would have to be transmitting speculatively over a long period.
The possibility of two stages of communication arises, the first stage being an ‘attention-getter’ signal, the second the sending of information. Artifacts could be more efficient than transmitting data, and could be sent to promising star systems with the assumption of later discovery by the inhabitants there. So a message from the stars might simply be short and to the point, a set of instructions telling us where to find the alien object.
Producing the needed neutrino beam goes beyond our current technology, but making neutrino beams in this energy range may well be feasible for a sufficiently advanced culture:
…we do not know the methods that may be available to advanced civilizations to make a neutrino (or any other) beam. We have direct evidence in the 1020 eV cosmic rays, the gamma ray bursts (GRBs), the micro-Quasars, and the amazingly collimated jets from active galactic nuclei (AGN), so that we might suspect that we do not yet understand some fundamental issues on particle acceleration. For example, how does one get an earth mass accelerated to a gamma of 1000 in a distance of a few light seconds, as has been inferred for gamma ray burst jets or “cannonballs”? So, for present purposes, we shall assume that an ETI would ?nd it affordable and worthwhile to expend such resources to communicate with our TES [Technically Emergent Society].
The beauty of directed beams of neutrinos at the energy levels considered here is that their signal would clearly signal the presence of an extraterrestrial civilization, there being no known natural mechanism for making neutrinos in only this energy range. The authors estimate that properly encoded data could accumulate at a rate of roughly 1000 pages per year. If any civilizations have taken this course and are actively transmitting to us, we can sit back and wait for the result, for the neutrino detectors coming online should soon discover their signatures.
The paper is Learned, Pakvasa and Zee, “Galactic Neutrino Communication,” available online.
by Paul Gilster | May 21, 2008 | Deep Sky Astronomy & Telescopes |
If the pace of discovery seems to be accelerating, that’s surely because of the network of tools we’re putting into place, able to work with each other both in space and on the ground to ferret out new information. Thus the collaborative effort that followed the remarkable observation of a new supernova, one caught so early in the process that it was found before visible light from the blast had begun to become apparent.
We have such tools as the Swift satellite to thank for this. Its ongoing observations of a supernova in the spiral galaxy NGC 2770, ninety million light years from Earth in the constellation called the Lynx, caught a three-minute, 40 second x-ray burst from the same galaxy, another supernova in the process of happening. What Swift seems to have uncovered was the shock wave of kinetic energy heating gas in the star’s outer layers to the temperatures that produce X-ray emissions. Such an event would be undetectable at optical wavelengths, which is where most supernovae have thus far been discovered.
Swift’s job is to use its wide-angle instruments to target interesting phenomena like the supernova now known as SN 2008D, at which point it puts other, more sensitive instruments on the alert. Both Hubble and the Chandra X-ray Observatory went to work, but so did numerous sites on Earth, including the Very Large Array, the Palomar Observatory, the Keck I telescope in Hawaii and too many others to list here.
Image: Scientists had planned on studying Supernova 2007uy in the galaxy NGC2770, which was already several weeks old when seen in this visual, ultraviolet image (upper left) taken on January 7, 2008, by NASA’s Swift satellite. A close-up, X-ray image of that supernova is beneath. At the right, you can see SN 2008D, shown in ultraviolet imagery (top) and at X-ray wavelengths (below). Credit: NASA Swift team.
Alicia Soderberg (Princeton University), leader of the team studying this event, calls the new supernova “…the Rosetta stone of supernova studies for years to come,” a reasonable statement given that the ‘shock breakout’ of X-rays, triggered by the compression and ensuing rebound of the newly formed neutron star produced by the massive star’s collapse, has never been observed before. The team’s paper on the event shows that the energy and pattern of the X-ray burst are consistent with its origin in the exploding star. And note this:
“A fascinating conclusion from the theoretical modeling of this outburst is that a thin outer layer must have been ejected at velocities up to about 70-percent the speed of light. This speed is much higher than previously known for the bulk of the stellar envelope, which moves at only up to 10-percent the speed of light,” said Peter Meszaros, Holder of the Eberly Family Chair in Astronomy and Astrophysics and Professor of Physics at Penn State and leader of the theory team for Swift. “The relatively higher-energy X-rays observed can now be understood as the usual optical photons emitted by the supernova being boosted up to X-ray energies as they are batted back and forth between the slower envelope and the faster outer shell.”
Thus we gain plentiful data about how supernovae occur, which should help us tune the existing model. Current thinking is that stars far more massive than the Sun produce supernova explosions when they exhaust their resources for thermonuclear reactions. When the core of the star stops producing the needed energy, the core collapses, causing the rebound that blasts stellar materials into space. Either a neutron star or a black hole is left behind. If most supernovae show an X-ray outburst like this one, hundreds should be detectable per year with the space-based instruments we currently have in the planning stage.
And here’s something I didn’t know: Ninety-nine percent of the energy of a supernova is carried away in the form of neutrinos (this is from David Pooley at the University of Wisconsin-Madison). Pooley leads a quick-reaction team for the Chandra X-ray Observatory program and is one of the authors of the paper on this work. He sees our ability to study future supernovae as useful for future instruments like the IceCube neutrino detector being built at the South Pole. “If we have better and more accurate knowledge of when and where these happen, that would let an instrument like IceCube be more sensitive,” says Pooley.
Which could offer a natural segue into the uses of neutrinos, but I’ll put that discussion off until tomorrow. For now, the supernova paper is Soderberg et al., “An extremely luminous X-ray outburst at the birth of a supernova,” Nature 453 (22 May 2008), pp. 469-474. Available online.
