Just off the phone with Seth Shostak, I can report that the KTVU story discussed below about a possible SETI reception is bogus. Apparently the reporter involved misinterpreted the conversation, as we had surmised. We may get a successful reception of an extraterrestrial civilization’s signal one of these days, but this wasn’t it.
We spend so much time talking about the Arecibo radio telescope with regard to planetary radar that it’s nice to come back to its applications in deep space. Thus the news that astronomers using the instrument have found key ingredients of amino acids in a galaxy 250 million light years from Earth in the constellation Serpens. The molecules are methanimine and hydrogen cyanide which, with the addition of water, form the amino acid glycine, considered a key ingredient in life on Earth.
Arp 220 is known for a high rate of new star formation, and recent Hubble work has discovered more than 200 star clusters at its heart. Observing it at a range of frequencies and using the wide-band mode of the main spectrometer, the team, led by Arecibo astronomer Christopher Salter, found the characteristic emission of the molecules clearly evident. Says Emmanuel Momjian (NRAO), “The fact that we can observe these substances at such a vast distance means that there are huge amounts of them in Arp 220. It is indeed very intriguing to find that the ingredients of life appear in large quantities where new stars and planets are born.” This Cornell news release has more.
Image: The galaxy Arp 220, where the recent finds were made. The Hubble Space Telescope’s Advanced Camera for Surveys has uncovered more than 200 mammoth star clusters in its heart. The clusters are the bluish-white dots scattered throughout the image. The heftiest Arp 220 cluster — about 10 million solar masses — is twice as massive as any comparable star cluster in the Milky Way. Arp 220 collided with another galaxy about 700 million years ago, fueling the frenzy of star birth in a small region about 5,000 light-years across. The galaxy is a nearby example of the aftermath of two colliding galaxies. Credit: Credit: NASA, ESA, and C. Wilson (McMaster University, Hamilton, Ontario, Canada).
Bear in mind that Arecibo has recently been ugraded with new receivers, thus allowing the 800-MHz wide-band study the team performed on Arp 220. The galaxy itself has been the subject of intense scrutiny. Classed as an ultra-luminous infrared galaxy (ULIRG), it seems to have an active galactic nucleus (AGN) at its core. The high level of new star formation is thought to be related to a collision between two galaxies, making Arp 220 the brightest of the three galactic mergers closest to Earth. The star formation itself is occurring in a region about 5000 light years across, where gas and dust are dense enough to equal all gas and dust in the Milky Way. More on the latter finding in this Hubble news release.
This looks like a case of extremely poor science reporting, but because I’ve already received e-mail about it, I will point you to a report from KTVU, a San Francisco television station, claiming that a mystery signal has been received at Arecibo, with obvious SETI implications. Cosmic Variance has also picked up on this and seems as skeptical as I am. A quick call to the SETI Institute revealed there is absolutely no buzz about any sort of successful reception making the rounds there. I have a voicemail in to Seth Shostak in hopes of a comment.
I’m late getting to this one, because I wanted to get Mike Gruntman’s paper on interstellar instrumentation finished. But for exoplanet enthusiasts like myself, the best news to come out of the recent American Astronomical Society meeting may have been the announcement of a new planet around the star HD 74156. So let’s talk about it, an interesting find because we haven’t had a new planet turn up just where predicted since Urbain Le Verrier and John C. Adams (independently) worked out the existence of Neptune by noting its effects on the motion of Uranus. Thus were calculations turned into observations and thence discovery.
Rory Barnes (University of Arizona) has been working on a theory that led to the HD 74156 discovery for some time. His computer simulations (begun with Thomas Quinn while both were at the University of Washington) on the stability of extrasolar planetary systems showed a key fact: All systems whose planets were close enough to affect each other gravitationally were on the edge of instability. All it would take would be a slight change in orbits to lead to disruptions. Astrophysicist Steven Soter explained the implications in an article last summer:
This remarkable result might seem surprising. But the prevalence of such marginally stable systems makes sense, Barnes and Quinn concluded, if planets form within unstable systems that become more stable by ejecting massive bodies. The investigators remarked, “As unsettling as it may be, it seems that a large fraction of planetary systems, including our own, lie dangerously close to instability.”
Mature planetary systems hold about as many planets as they can, spaced as closely as is consistent with stability. Think of an evolving planetary system as one that ejects disruptive elements before settling into its mature stage, a process of self-organization. If that hypothesis works, it becomes a useful predictor, as Barnes, Quinn and Sean Raymond (University of Colorado) saw. HD 74156’s two known planets were a test case, because the gap between them suggested the presence of a third. It took observations by Jacob Bean and team at the University of Texas to observe the system and make the actual discovery.
The question is, are the processes that proved so successful at HD 74156 likely to be universal? If so, we have a useful predictor of planets around other stars, helping us probe more deeply into systems we’ve already begun to study. Now comes word that another team has found a planet where the ‘packed planetary system’ theory suggested it would be around the star 55 Cancri. Thank you Debra Fischer and team.
55 Cancri f turns out to exist at the inner region of a large stable zone, suggesting the possibility of still further planets in this most interesting system. More on this from the 55 Cnc f discovery paper:
This ?fth planet apparently resides in the previously identi?ed gap between 0.24-5.8 AU, and it remains between 0.73 AU (periastron) and 0.84 AU (apastron), preventing orbit crossings with both the next inner planet, “c”, whose apastron is at 0.26 AU and the outer planet, “d”, whose periastron is at 5.5 AU, ensuring dynamical stability that is demonstrated numerically by N-body simulations. As the star’s luminosity is L = 0.60 L? (from its effective temperature and radius), this ?fth planet resides within the classical habitable zone. With a minimum mass of 45 MEarth, we speculate that it contains a substantial amount of hydrogen and helium, not unlike Saturn (M = 95 MEarth ) in the solar system.
The kind of calculations Barnes and team have employed also call for a planet in a stable region around HD 38529, although that one awaits confirmation. As we continue to explore the interesting hypothesis of ‘packed’ planetary systems, it begins to appear that efficiency is the watchword. If there is room for a planet to form without destabilizing gravitational effects, it does. And that tells us something about the ubiquity of celestial real estate.
The discovery paper is Bean et al., “Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope,” accepted by The Astrophysical Journal and available online. The 55 Cancri paper is Fischer et al., “Five Planets Orbiting 55 Cancri,” also accepted by The Astrophysical Journal and available here. Thanks to Dave Moore for helpful background links as this story developed, and to other Centauri Dreams readers who passed the story along and asked for comment.
Addendum: Be sure to check andy’s comment re a paper that may cast HD 74156 d into doubt.
It’s a long-term conundrum in interstellar studies: When do you launch a mission, knowing that faster methods may make your spacecraft obsolete? We might think about this problem again in light of Mike Gruntman’s paper on a precursor interstellar mission to the local interstellar medium (LISM). As we saw on Friday, Gruntman (USC) has examined a probe to 400 AU, a region well outside the heliosphere where interstellar space is thought to be unperturbed by the Sun’s influence.
Keeping to technologies that are close to the required readiness level (he considers solar sails and nuclear electric propulsion), Gruntman works out a nominal escape velocity of 75 kilometers per second. To those who argue that a twenty-year mission to the 400 AU target is sure to be superseded by faster spacecraft, the counter-argument is clear: If we wait for a breakthrough, how do we know its timing? What if, Apollo-style, political decisions slow the development of sound alternatives? Incremental missions like these take us the needed next step beyond Voyager and New Horizons to create the first dedicated interstellar spacecraft, from which the learning opportunities will be priceless.
Innovative Interstellar Explorer is the current project incorporating these concepts. Gruntman works on its team, and would be the first to note that the idea of IIE has changed since the 2004 paper we’ve been considering (the IIE site has mission details, including a shorter-range target of 200 AU, and an interesting new take on propulsion). But the instrumentation question is still a lively one. Get a probe into true interstellar space and you want to learn such things as the composition of interstellar matter in gaseous and dust forms, the nature of the interstellar magnetic field, the status of low-energy cosmic rays that cannot reach the inner heliosphere, and the characterization of any organic matter that may exist in this medium.
Image: Concept study for a mission beyond the heliopause. Credit: NASA/Johns Hopkins University Applied Physics Laboratory.
That’s just the beginning, of course, because we also have much work to do while crossing the interface between heliosphere and the LISM, not to mention a whole series of remote observations related to the density of neutral hydrogen in the nearby interstellar environment, and study of the distribution of objects in the Edgeworth/Kuiper belt. What gets tricky here is not just the number of needed instruments but the high speed of the spacecraft. With the probe moving in the ‘upwind’ direction (in relation to the interstellar wind), the relative velocity of interstellar matter with respect to the spacecraft approaches 100 kilometers per second.
New instrumentation concepts are called for. From the paper:
It is not clear, for example, what is the best way of analyzing complex organic molecules in interstellar gas and plasma. The high energy of such molecules, 52 eV/nucleon, would likely destroy their molecular bonds (complicating identi?cation) when captured on a surface for a subsequent analysis. On the other hand, the molecule velocity and energy would not be sufficient for analysis in conventional thin foil-based time-of-?ight instruments….Interpretation of dust grain measurements and search for traces of organic matter in the grains would also be complicated by an exceptionally high speed of grains with respect to the spacecraft. The grain velocities would be even higher than those at the Comet Halley ?ybys by the Giotto and Vega spacecraft.
So we need to start thinking in non-traditional ways, trying to tease out basic information about plasma, dust and fields. Dust particles bombarding the spacecraft, for example, can be characterized by measuring the effects of hot plasma produced by the impacts — the whole spacecraft, in other words, becomes the detector. Moreover, the new instruments developed for the mission, heavy on miniaturization and autonomy, will require low energy solid state particle detectors.
But the opportunities are vast, including interesting analysis of physical effects. Gruntman proposes using a precursor interstellar mission as a testbed for the Pioneer effect, the anomalous acceleration of both Pioneer spacecraft whose origin is still unknown. And how about the ‘look back’ effect:
As our ?rst interstellar spacecraft leaves the solar system, a ‘‘look back’’ would provide us with an unusual view of our home stellar system, a view from the outside. A view back will provide a unique opportunity for a global study of the heliosphere, a vast essentially 3-D region governed by the sun. This view back would also be a glimpse of what a truly interstellar mission of the distant future would encounter in approaching a target star. A combination of obtaining images from two vantage points, one from the outside of a stellar system and one from inside, would allow the characterization of an astrosphere.
Image: Looking back, a long way from home. Credit: NASA/Johns Hopkins University Applied Physics Laboratory.
Keep your eye on Innovative Interstellar Explorer as this mission concept continues to evolve. We’re asking basic questions about the nature of space outside the heliosphere, what the IIE team calls the ‘undiscovered country’ through which future, much faster missions will one day journey. With a penchant for Latin mottoes, I like IIE’s: “Si requiritis futurum nostrum, spectate astra!” Translation: ‘If you seek our future, look to the stars!’ IIE would be the first mission to do that free of the Sun’s effective influence. Learning how to design it is part of the incremental process of making our way, step by step, toward a true star-faring civilization.
