Best wishes to all for a wonderful 2008, and thanks beyond the telling to the numerous readers who participated in our discussions in the year past. There will be no post on New Year’s day, but we’ll get back to the normal schedule on the afternoon of January 2. Have a wonderful holiday.
Apropos of Saturday’s article on the Subaru Telescope — and the optical improvements that may help it detect an exoplanet image — comes news that scattered light from a planet orbiting another star has been detected by an international team. The planet is our old friend HD189733b, some sixty light years away in the constellation Vulpecula. The transiting world is a ‘hot Jupiter,’ orbiting its star in 2.2 days at a blindingly close 0.03 AU.
Thanks to Hans Bausewein for passing along the link to a news release on this work. The scientists involved — Svetlana Berdyugina (ETH Zurich & Tuorla Observatory), Andrei Berdyugin and Vilppu Piirola (Tuorla Observatory), and Dominique Fluri (ETH Zurich) did their study using polarimetry, examining starlight that is scattered in the distant planet’s atmosphere. Polarimetry measures the angle of rotation of the plane of polarized light that occurs when it moves through particular materials. It’s a useful technique for exoplanetary work because such detections tell us about the chemistry and thermodynamics at play within that atmosphere.
Using the remotely controlled KVA telescope on La Palma (Spain), the team will report in its upcoming paper that the atmosphere under study consists of particles smaller than half a micron, scattering light in the blue, like Earth’s atmosphere. Such findings are consistent with water vapor or tiny dust grains. The work also allows us to see the shape of the planet’s orbit, a determination that can be made because as the planet moves around its star, the scattering angle changes. From the paper:
The observed polarization variability should thus, in principle, exhibit the orbital period of the planet and reveal the inclination, eccentricity, and orientation of the orbit, and, if detected with high enough polarimetric accuracy, also the nature of scattering particles in the planetary atmosphere.
The image below shows the result.
Image: The orbit of HD189733b as projected on the sky. Solid and dashed lines indicate parts of the orbit in front of and behind the sky plane, respectively. The orange circle in the center depicts the star and the blue circle on the orbit the planet. Credit: Svetlana Berdyugina. For more background, see Dr. Berdyugina’s description of this work.
Hot Jupiters, it turns out, are the best candidates for this kind of work because they are so close to their star that they develop extended hydrogen haloes. That makes for effective scattering of the star’s light, especially in the blue wavelengths. The authors are calling this the first direct detection of an extrasolar planet in visible light. But they argue that polarimetric techniques have significance for future planet studies not just of hot Jupiters but a wide variety of worlds:
Our ?ndings open the door to new opportunities for direct detections of extrasolar planets, both hot Jupiters and Earth-like, to a large degree independently of their mass and gravitational effect on the host star. Furthermore, until now probing exoplanetary atmospheres was largely limited to systems with transits, which are relatively rare events. Polarimetry provides us with the new prospect of detecting directly the light from the planetary atmosphere outside transits. Thus, with polarimetric accuracy approaching the photon noise limit, direct studies of exoplanetary atmospheres in the visible at any orbital inclination become reality.
The paper is Berdyugina, S.V. et al., “First detection of polarized scattered light from an exoplanetary atmosphere,” in press at Astrophysical Journal Letters and available online.
How likely is it that we will begin to image extrasolar planets from observatories on the ground? The prospect seems all but certain if we grant a long enough lead time to get certain advanced telescope designs built, but it may happen sooner than we think if the news from the Subaru Telescope is factored in. The instrument, an 8.2 meter optical/infrared telescope, is located at the summit of Mauna Kea (Hawaii), from which vantage it has already produced intriguing results like spin-orbit alignment measurements for the exoplanet TrES-1.
But Subaru astronomer Ryuji Suzuki is ready to go to the next step. Noting the installation of the HiCIAO camera (High Contrast Instrument for the Subaru Next Generation Adaptive Optics), Dr. Suzuki points out that “…the unique instrument was primarily designed for the direct detection of extrasolar planets and disks.” Indeed, the Subaru team is hopeful that they will be the first to directly observe a planet orbiting a star other than our own (we’ll discuss the possible detection of visible light from a planetary atmosphere by another team on Monday).
Image: Not much like the Hawaii most of us imagine, this is the summit of Mauna Kea. Will instruments here and in other locations be able to snare direct images of exoplanets with upgrades to their technologies? Credit: National Astronomical Observatory of Japan.
HiCIAO replaces an older imager that also uses coronagraphic techniques to filter out direct light from a star to make faint objects near it more viewable. But the new system offers contrast 10 to 100 times better than than the old. Its other trump card: A significantly upgraded adaptive optics system that increases the clarity of what Subaru sees by a factor of ten. The latter uses a deformable mirror to effectively remove atmospheric distortion and a new laser guide star system, so that the instrument is not limited in terms of where it can look.
If nothing else, the new instrument should provide impressive results in the study of brown dwarfs, as well as dust disks around nearby stars. But a direct image of a planet — not a brown dwarf — would be a historic first. ‘First light’ use of the new instrument, which occured on December 3, is a reminder of how much ground-based astronomy has improved in the unceasing quest for better seeing conditions, to the point where objects once thought visible only from space are now within its legitimate domain.
When it comes to understanding possible extraterrestrial civilizations, I’m with Freeman Dyson, who had this to say:
“Our business as scientists is to search the universe and find out what is there. What is there may conform to our moral sense or it may not…It is just as unscientific to impute to remote intelligences wisdom and serenity as it is to impute to them irrational and murderous impulses. We must be prepared for either possibility and conduct our searches accordingly.”
As quoted in a 2005 essay by Michael Michaud, Dyson saw two alternatives: Intelligent races may rule their domains with benign intelligence, occasionally passing along the knowledge they have accumulated to a universe eager to listen. Or intelligence may be purely exploitative, consuming what it encounters. We don’t know which of these alternatives prevails, if either, and that’s one reason that Michaud, a former diplomat who became deputy assistant secretary of state for science and technology, resigned from the International Academy of Astronautics’ Permanent Study Group dedicated to SETI in September. The issue: Active SETI, not just listening but beaming signals at will to other stars.
If you want to have a good look at the controversy, read David Grinspoon’s article “Who Speaks for Earth,” as comprehensive a look at the issue as I’ve seen. Grinspoon is a scientist at the Southwest Research Institute (Boulder, CO) as well as the author of Lonely Planets: The Natural Philosophy of Alien Life (Harper, 2004). Two years ago we looked at his provocative ideas about life on Titan in a Centauri Dreams posting.
Image: M31, the Andromeda Galaxy. Are ‘cities of stars’ like these home to benign species exchanging information, or are there threats we know nothing of that make silence a better choice? Credit: NASA.
Running in SEED Magazine, Grinspoon’s latest article should receive plenty of attention, a good thing given the fact that most people either don’t know that signals have already been sent (not just from Arecibo but to nearby stars from the Evpatoria planetary radar site in the Crimea), or else think that sending signals is a harmless exercise, because surely extraterrestrial civilizations are, though entertaining, pure science fiction.
And perhaps they are — people like me think they’re vanishingly rare — but the point is that we have nothing more than speculation to work with. Meanwhile, what would we do if we ever did receive an actual SETI signal? The First SETI Protocol was drawn up in the 1980s to address the issue, laying down procedures that begin with notifying the worldwide SETI community, verifying the potential alien signal, then announcing it to the public. No reply would be sent without first establishing a global consensus.
That latter, of course, is the sticking point. As Grinspoon explains, a Second SETI Protocol should have tuned up our policy for sending messages from Earth, but arguments over whether it should only affect responses to received messages — or messages sent before any extraterrestrial signal was detected — have complicated the picture. Language calling for international consultations before we make further deliberate transmissions was deleted from Michaud’s draft of the Protocol when the Permanent Study Group of the SETI subcommittee of the IAA met last year in Valencia.
Grinspoon’s article is a calm assessment of the current situation, and I recommend it to you. He discusses the work of Alexander Zaitsev at Evpatoria, whose team has sent a series of messages toward nearby stars. Remember that Frank Drake’s Arecibo message of 1974, the first active SETI attempt I know of, was aimed at the globular cluster M13, some 25,000 light years away, and was thus something of a scientific exercise rather than a active attempt to open a communications channel. But the stars reached by the Evpatoria messages are between 45 and 70 light years from Earth, more or less in our back yard.
Discussions between the two camps continue. But two Grinspoon points merit special attention. One is that the kind of facilities that can make active SETI broadcasts are today largely in the hands of national governments or large organizations answerable to public opinion. Will it always be so? Grinspoon says no:
…seemingly inevitable trends are placing increasingly powerful technologies in the hands of small groups or eager individuals with their own agendas and no oversight. Today, on the entire planet, there are only a few mavericks like Zaitsev who are able and willing to unilaterally represent humanity and effectively reveal our presence. In the future, there could be one in every neighborhood.
Which is one reason why public indifference to the question of broadcasting to the stars may not last much longer. In fact, the Grinspoon article may be a watershed event in changing awareness. The issues are clearly large. As David Brin has been pointing out since the 1980s, one possible answer to our failure to detect other civilizations is that there may be a reason why such civilizations would want to remain silent. Is there a threat to emerging intelligence that could make our attempt to draw attention to ourselves a dangerous mistake? We can’t know at this juncture, which makes deliberate broadcasts something of a shot in the dark. And that dark is quite impenetrable at present.
Grinspoon also makes the point that the entire discussion on active SETI may in itself be a good thing for our own understanding. Let me quote him again:
…even if no one else is out there and we are ultimately alone, the idea of communicating with truly alien cultures forces us to consider ourselves from an entirely new, and perhaps timely, perspective. Even if we never make contact, any attempt to act and speak as one planet is not a misguided endeavor: Our impulsive industrial transformation of our home planet is starting to catch up to us, and the nations of the world are struggling with existential threats like anthropogenic climate change and weapons of mass destruction. Whether or not we develop a mechanism for anticipating, discussing, and acting on long-term planetary dangers such as these before they become catastrophes remains to be seen. But the unified global outlook required to face them would certainly be a welcome development.
These are welcome words, highlighting the fact that the issues we confront as we look for extraterrestrial civilizations are just as significant for our own dealings here on Earth, where other cultures can sometimes seem as inscrutably alien as anything we might find through a radio telescope search. And Grinspoon is surely right about the proliferation of technologies expanding active SETI in the future. We need to be raising public consciousness on this issue and getting the entire active SETI question into broader forums, where people from a wide range of backgrounds, in and out of the sciences, can address it. We need to do that so we act not as individuals but as a species, looking out into a universe that may or may not welcome us as friends.
Cassopeia A is a supernova remnant some 11,000 light years away. Turning the attention of the Spitzer Space Telescope on this object allows us to examine the different elements within it, a useful exercise because it helps to answer a question about the early universe: Where did the interstellar dust so essential for the formation of stars and planets — not to mention the creatures that live on planets like ours — come from?
Despite the ubiquity of space dust, the question has persisted because the first stars, so-called Population III, are the only ones to have formed without dust. We can see dust being pumped out by dying solar-type stars in the nearby universe, but in the infancy of the cosmos, such stars weren’t old enough to perform the job. So massive Population III stars are thought to have contributed dust in their violent death as supernovae, a theory in support of which Cassiopeia A provides data.
Jeonghee Rho (Spitzer Science Center, Caltech) seems certain of the result: “Now we can say unambiguously that dust – and lots of it – was formed in the ejecta of the Cassiopeia A explosion. This finding was possible because Cassiopeia A is in our own galaxy, where it is close enough to study in detail.” That’s helpful to know, but it doesn’t limit dust formation to supernovae alone. Other avenues exist for dust formation, including highly energetic black holes, whose role remains to be clarified.
Image (click to enlarge): The upper left panel is a composite made up of three infrared views shown in the remaining panels. The bottom left view shows argon gas (green) that was synthesized as it was ejected from the star. The bottom right view shows a collection of dust (red), including proto-silicates, silicate dioxide and iron oxide. The fact that these two features line up (as seen in yellow in the combined view) tells astronomers that the dust, together with the gas, was created in the explosion. The upper right panel shows silicon gas (blue) deep in the interior of the remnant. This cooler gas, called the unshocked ejecta, was also synthesized in the supernova blast. Credit: NASA/JPL-Caltech.
The mapping of Cassopeia A generates data on proto-silicates, silicon dioxide, iron oxide, pyroxene, carbon, aluminium oxide and other compounds. A close match between dust and ejecta expelled in the explosion ties the formation of the dust to the stellar blast. Rho’s team believes the dust would form days to months after the explosion, when the temperature of the gas in the ejecta has had the chance to cool. And although enough dust to form 10,000 Earths has been located in Cassopeia A, the quantity involved still doesn’t completely explain early dust formation, though it comes close. As the paper notes, “The freshly formed dust mass derived from Cas A is sufficient from SNe [supernovae] to explain the lower limit on the dust masses in high redshift galaxies.”
Next for such work: Studies of other supernovae at a range of distances, and better models for understanding how dust is destroyed. The paper is Rho et al., “Freshly Formed Dust in the Cassiopeia A Supernova Remnant as Revealed by the Spitzer Space Telescope,” accepted by The Astrophysical Journal (abstract).