Centauri Dreams
Imagining and Planning Interstellar Exploration
Cassini’s Latest from Hyperion
We can thank the British astronomer John Herschel (1792-1871) for giving the moons of Saturn their classical theme, resulting in the familiar names Mimas, Dione, Enceladus, Tethys, Titan, Rhea, and Iapetus for the seven moons known to him when he wrote his Results of Astronomical Observations Made at the Royal Observatory, Cape of Good Hope (1847). It was a natural, then, that the moon discovered shortly thereafter would get a name like Hyperion (although it wasn’t Herschel but merchant and astronomer Willam Lassell who suggested the name). Hyperion was an elder brother of Cronos (Saturn), and was associated with watchfulness and observation.
Only recently have we discovered just how unusual Hyperion turns out to be, as the unprocessed image from the Cassini mission below clearly demonstrates. Its shape is irregular, indicating it may be the remnant of a larger body broken by some ancient impact. Its low density indicates large amounts of water ice mixing with small amounts of rock. Its low albedo suggests a layer of dark material that may be associated with Saturn’s moon Phoebe, much of which seems to have wound up on Iapetus. And it resembles nothing so much as an enormous sponge.
Image: NASA’s Cassini spacecraft obtained this unprocessed image of Saturn’s moon Hyperion on Aug. 25, 2011. Image credit: NASA/JPL-Caltech/Space Science Institute.
You can see more images of Hyperion from the encounter here. The image above was made as the spacecraft flew past Hyperion at some 25,000 kilometers. We’re looking at a very small place, some 270 kilometers across, and a world that tumbles chaotically in its orbit around Saturn, the motion making it difficult for scientists to predict what Cassini would see as it set about imaging the moon on this flyby. Color measurements made during this observation run will tell us much about the moon’s brightness as lighting changes, which in turn should offer some insight into its surface texture.
Back in 2007 the analysis of data from a 2005 Cassini flyby pointed to a surface composition of water and carbon dioxide ices along with the hitherto mentioned dark material that Dale Cruikshank (NASA Ames), lead author of the paper on that study, found interesting:
“Of special interest is the presence on Hyperion of hydrocarbons — combinations of carbon and hydrogen atoms that are found in comets, meteorites, and the dust in our galaxy. These molecules, when embedded in ice and exposed to ultraviolet light, form new molecules of biological significance. This doesn’t mean that we have found life, but it is a further indication that the basic chemistry needed for life is widespread in the universe.”
Many of Hyperion’s craters appear to be crisply defined, evidently the result of the moon’s low density. Just half as dense as water, Hyperion is porous enough to compress when struck by debris, but the ejecta of an impact often fails to return to the surface because of the moon’s low gravity. Denser worlds usually lack a large population of craters with such crisp visual definition.
Two papers on that earlier Hyperion work go into detail on all this. They are Cruikshank et al., “Surface composition of Hyperion,” Nature 448 (5 July 2007), pp. 54-56 (abstract) and Thomas et al., “Hyperion’s sponge-like appearance,” Nature 448 (5 July 2007), pp. 50-56 (abstract). A slightly later summary of the dark coating we see on various Saturnian moons can be found in Saturn’s Dark Materials, a Centauri Dreams article in which I look at research from 2008.
In the Sky with Diamonds
The idea of a planet around a pulsar is so bizarre that we often forget that three planets around the pulsar PSR B1257+12 were the first exoplanets ever detected. This pulsar is the remnant of a once massive star in the constellation Virgo that became a supernova, and the planets there — detected by Alex Wolszczan (Penn State) — were the first new planets discovered since the era when Clyde Tombaugh was putting the blink comparator through its paces at Lowell Observatory, an effort that led to the discovery of Pluto in 1930. And these are tiny worlds at that. A newly found fourth planet in the B1257+12 system is thought to be no more than one-fifth the mass of Pluto itself. We can find worlds like this because the beam of electromagnetic radiation pulsars emit is extraordinarily regular, making planetary signatures apparent.
Now another pulsar — PSR J1719-1438, some 4,000 light years away in the constellation Serpens (the Snake) — is in the news because of the discovery that its own pulses are being affected by the gravitational pull of a small planet. What we are learning about the new planet is highly interesting. It is slightly more massive than Jupiter, and orbits the pulsar at a distance of about 600,000 kilometers, racing around its primary in a scant two hours and ten minutes. The pulsar rotates more than 10,000 times per minute and has a mass about 1.4 times that of our Sun, but is only 20 kilometers in radius. At 600,000 kilometers out, a planet larger than 60,000 kilometers (five times Earth’s diameter) would be pulled apart by the pulsar’s gravity.
This must be, then, a small planet with a great deal of mass, which is why this story stands out. For what Matthew Bailes (Swinburne University of Technology, Melbourne) and colleagues are reporting is a planet that may itself be the remains of a massive star. The pulsar and its companion are close enough that the planet must in fact be what’s left of a white dwarf that has lost over 99.9 percent of its original mass. And that leaves us with an interesting relic, a remnant of carbon and oxygen at such high density that the star may be made largely of diamond.
The paper on this work states the matter clearly:
PSR J1719?1438 demonstrates that special circumstances can conspire during binary pulsar evolution that allows neutron star stellar companions to be transformed into exotic planets unlike those likely to be found anywhere else in the Universe. The chemical composition, pressure and dimensions of the companion make it certain to be crystallized (ie diamond).
Image: Artistic reproduction of an extrasolar planet around a pulsar. Copyright : Paris Observatory/UF.
Most of the mass of the so-called ‘diamond planet’ would have been drawn toward the pulsar. Interestingly enough, very fast-spinning pulsars like this one — astronomers call them millisecond pulsars — normally have companions of some kind. In fact, as many as 70 percent of them do. According to this CSIRO news release, some astronomers believe that such companions, when burning as a star, would be responsible for transferring matter to the pulsar and spinning it up to its high speed. The result over time: A millisecond pulsar keeping company with a white dwarf.
This configuration of pulsar and white dwarf makes sense, but finding former white dwarfs that have survived destruction only to become crystalline planets is not likely to be common:
“The ultimate fate of the binary is determined by the mass and orbital period of the donor star at the time of mass transfer. The rarity of millisecond pulsars with planet-mass companions means that producing such exotic planets is the exception rather than the rule, and requires special circumstances,” said Dr. Benjamin Stappers (University of Manchester).
We should learn a great deal more about pulsars from the project this work grew out of, a search for pulsars that is the largest and most sensitive of its type ever attempted. It will doubtless identify more pulsar planets, and probably more intriguing circumstellar disks of the kind already found around the pulsar 4U 0142+61. Planets, as we’re realizing more and more, seem to find myriad ways to form even after events as massive as a supernova. The paper is Bailes et al., “Transformation of a Star into a Planet in a Millisecond Pulsar Binary,” published online in Science Express August 25 2011 (abstract).
WISE: Coolest Brown Dwarfs Yet
The WISE mission has again come through, this time in the form of a discovery we’ve been more or less anticipating but now see confirmed. The Wide-field Infrared Survey Explorer works at infrared wavelengths ideal for spotting things we just can’t find with ground-based telescopes. WISE has now turned up six Y dwarfs, stars so cool that you could set your office thermostat to match them without real discomfort. The Y dwarfs range from nine to 40 light years away.
Consider them the coldest class of brown dwarfs, completely incapable of reaching the temperatures needed to induce stable fusion at the core, their light gradually fading with time. And if the line between gas giant planets and brown dwarfs was ever malleable, it’s here. The atmosphere of these stars is similar to that of Jupiter, and one of them, WISE 1828+2650, now becomes the coldest brown dwarf known, its estimated atmospheric temperature something less than 25 degrees Celsius. Says WISE science team member Davy Kirkpatrick (Caltech):
“The brown dwarfs we were turning up before this discovery were more like the temperature of your oven. With the discovery of Y dwarfs, we’ve moved out of the kitchen and into the cooler parts of the house.”
Look closely at the center of the image below and you’ll see WISE 1828+2650.
Image: NASA’s Wide-field Infrared Survey Explorer, or WISE, has uncovered the coldest brown dwarf known so far (green dot in very center of this infrared image). Called WISE 1828+2650, this chilly star-like body isn’t even as warm as a human body, at less than about 80 degrees Fahrenheit (25 degrees Celsius). Like other brown dwarfs, it began life like a star, collapsing under its own weight into a dense ball of gas. But, unlike a star, it didn’t have enough mass to fuse atoms at its core, and shine steadily with starlight. Instead, it has continued to cool and fade since its birth, and now gives off only a feeble amount of infrared light. WISE’s highly sensitive infrared detectors were able to catch the glow of this object during its all-sky scan, which lasted from Jan. 2010 to Feb. 2011. WISE 1828+2650 is located in the constellation Lyra. The blue dots are a mix of stars and galaxies. Credit: NASA/JPL-Caltech/UCLA.
But it’s Michael Cushing (JPL), who is lead author of the Y dwarf paper in the Astrophysical Journal, who gets my attention. He’s taking note of the fact that one of the Y dwarfs, WISE 1541-2250, may move past Ross 154 to become the seventh closest star system known, at approximately nine light years out. And Cushing is thinking the data harvest is hardly over:
“Finding brown dwarfs near our sun is like discovering there’s a hidden house on your block that you didn’t know about,” Cushing said. “It’s thrilling to me to know we’ve got neighbors out there yet to be discovered. With WISE, we may even find a brown dwarf closer to us than our closest known star.”
There’s that thought again, a brown dwarf closer than Proxima Centauri, and it’s still a possibility. But whether such a star exists or not, the Y dwarfs we’re now finding should be useful in their own right. From the paper:
Independent of their spectral morphology, the study of these ultracool brown dwarfs will provide important insights into both ultracool atmospheric physics and the low-mass end of the stellar mass function. Because brown dwarfs and exoplanets have similar atmospheric conditions, ultracool brown dwarfs are also excellent exoplanet analogs that can be used as benchmarks for model atmospheres. The study of these ultracool brown dwarfs will therefore directly inform the interpretation and characterization of exoplanets detected with the next generation of high-contrast imagers…
It’s interesting to reflect on how the brown dwarf story has developed. The existence of this category of star was predicted in the early 1960s, but it took projects like the Two Micron All Sky Survey (2MASS), the Sloan Digital Sky Survey and the the Deep Near-Infrared Southern Sky Survey to start turning them up in bulk. But as the paper on the Y dwarf discovery notes, these successes still left a gap of almost 400 K between the coolest brown dwarfs then known (with an effective temperature of 500 K) and Jupiter (approximately 124 K). The existence of a cooler Y class to follow on to the brown dwarf spectral classes L and T seemed more and more likely, and now we have hard evidence for objects too cool to be detected by the earlier surveys.
The paper is Cushing et al., “The Discovery of Y Dwarfs Using Data from the Wide-field Infrared Survey Explorer (WISE),” accepted for publication in the Astrophysical Journal (preprint). You’ll also want to see Kirkpatrick et al., “The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE),” accepted for publication in the Astrophysical Journal Supplement Series (preprint).
Changing Face of an Icy Dwarf
2007 OR10 is an innocuous enough designation (discoverer Mike Brown calls it ‘an official license plate number’ based on date of discovery), but ‘Snow White’ isn’t. The dwarf planet that acquired the latter monniker from Caltech astronomer and KBO-hunter Brown seemed to deserve its name because at the time, Brown thought it was an icy chunk that had broken off from the dwarf planet Haumea. Ice in the outer system is almost always white, and that’s what you would expect on a world called ‘Snow White.’ But recent spectral analysis has revealed that while ‘Snow White’ is indeed covered in water ice, it’s not white at all. In fact, it is one of the reddest objects in the Solar System, about half the size of Pluto in its orbit at system’s edge.
What to make of this? It turns out that another dwarf planet fits the same characteristics, in being both red and covered with water ice. Although a bit smaller than Snow White, Quaoar is thought to have had an atmosphere and to have once been covered with ice-spewing volcanoes. As this Caltech news release points out, being smaller than the big dwarf planets Eris and Pluto, Quaoar could not hold on to volatile compounds like methane, carbon monoxide or nitrogen for long time frames. All that’s left at this point in our system’s history is methane, which over time and exposure to radiation would have been turned into reddish hydrocarbon chains.
Image: Caltech’s Mike Brown. Credit: California Institute of Technology.
So Quaoar, and possibly Snow White, are covered with irradiated methane, accounting for their hue. “You get to see this nice picture of what once was an active little world with water volcanoes and an atmosphere, and it’s now just frozen, dead, with an atmosphere that’s slowly slipping away,” adds Brown. It’s a view being pieced together with an instrument called the Folded-port Infrared Echellette (FIRE), used with the 6.5-meter Magellan Baade Telescope in Chile. The instrument’s spectral analysis revealing water ice told Brown just what he needed to know.:
“That combination—red and water—says to me, ‘methane,'” Brown explains. “We’re basically looking at the last gasp of Snow White. For four and a half billion years, Snow White has been sitting out there, slowly losing its atmosphere, and now there’s just a little bit left.”
Brown also talks about Snow White in a series of posts on Mike Brown’s Planets, from which this:
I love this spectrum of Snow White, since it tells a long complex history of a little icy world all in one glance. Snow White formed 4.5 billion years ago in the chaos that was the outer solar system. It had an evaporating atmosphere and a surface that was slowly gunking up from all of the frosts sitting in the sunlight on the surface. It would have been a cold, dark, uneventful place, until suddenly water burst out from the interior and began its slow slush flow on the surface before quickly freezing up. The volcanic period probably didn’t last long, and most of the atmosphere didn’t last much longer. The nitrogen went first, then the carbon monoxide. And finally, today, when we look at Snow White we see the very last gasps of a dying atmosphere covering a once dynamic but now dead and frozen world.
The methane finding will have to be confirmed as part of the larger study of volatile loss and retention on these distant objects. Volatiles have also been discovered on the surfaces of Eris, Makemake and Sedna. In fact, a model for volatile retention that has successfully explained the situation on these worlds seems to hold for every large KBO except Haumea, which is the parent body of a family of collision-born objects, and thus has a history more varied than most of its neighbors. From the paper on the spectral analysis, a clear view of where to go next:
While the size of 2007 OR10 has yet to be measured, the simple assumption that it has an identical albedo to Quaoar – the object whose spectrum its spectrum most resembles – places 2007 OR10 into a regime where it would be expected to retain trace amounts of methane on its surface. Such an object would be expected to have red optical coloration from methane irradiation, which both Quaoar and 2007 OR10 do have. In addition, such an object should have detectable signatures of methane if observed at sufficient signal-to-noise. Such methane signatures have been detected on Quaoar, but require higher signal-to-noise to positively identify on 2007 OR10. While additional measurements of the size and spectrum of 2007 OR10 are clearly required, we conclude that volatile retention models (Schaller & Brown 2007b) appear to continue to flawlessly predict both the presence and absence of volatiles on all objects in the Kuiper belt which have been observed to date.
Assuming that confirmation proceeds as planned, Snow White and Quaoar will stand apart from the vast majority of KBOs as being large enough to hold on to volatile compounds, a trait that helps us to analyze their subsequent history. The paper is Brown et al., “The surface composition of large Kuiper Belt Object 2007 OR10,” accepted by Astrophysical Journal Letters (preprint).
HARPS: Hunting for Nearby Earth-like Planets
Ever more refined radial velocity searches for exoplanets are reaching into the domain of lower and lower mass targets. It’s natural enough that we’re most interested in planets of Earth mass and even smaller, but as a new paper on the work of the European Southern Observatory’s HARPS instrument reminds us, one of the great values of this work is that we’re getting a broad view of how exoplanets form and evolve in their systems, no matter what their size. Characterizing not just planets but entire systems is becoming a profitable investigation.
But small worlds continue to fascinate us, particularly in the hopes of finding possible abodes for life. HARPS’ involvement in the hunt now includes an intense campaign to monitor ten stars that are relatively near our Sun, all of them slowly rotating and quiet solar-type stars. Mounted on ESO’s 3.6-meter instrument at La Silla Observatory in Chile, HARPS (High Accuracy Radial Velocity Planet Searcher) has produced more than 100 exoplanet candidates in its first eight years of operation, including not just Neptune-mass planets but super-Earths and intriguing systems like Gliese 581, with two possibly rocky planets near the habitable zone.
Moreover, from the system-wide point of view, the system around HD 10180 includes seven low-mass planets including the 1.5 Earth mass HD 10180 b. So when HARPS talks, we listen, and I want to quote this from the paper at the outset (internal references omitted for brevity):
… a recent investigation of the HARPS high-precision sample has shown that about 1/3 of all sample stars exhibit RV variations indicating the presence of super-Earths or ice giants… Indeed, planet formation models… show that only a small fraction (of the order of 10%) of all existing embryos will be able to grow and become giant planets. Hence, we expect that the majority of solar-type stars will be surrounded by low-mass planets.
Good news for small planets! If this is the case, we would expect that even a small sample like the current ten solar-type stars now under intense investigation by HARPS will turn up several Earth-like planets (i.e., rocky worlds in the inner system), and the new paper does not let us down. Three of the host stars involved in this program have already produced detections; these are HD 20794, HD 85512 and HD 192310. There are no giant planets here but study of the three stars has thus far yielded six low-mass planets, including three super-Earths around HD 20794 (82 Eridani), with semi-major axes of the planetary orbits measured as 0.12AU, 0.20AU and 0.35AU. The semi-major axis measures the radius of an orbit taken at the orbit’s two most distant points.
No habitable zone planets here, though, with even the furthermost planet reaching likely equilibrium temperatures of 388 K, which works out to about 115 degrees Celsius. Remember that equilibrium temperature is not the same thing as temperature at the surface. The equilibrium temperature of the Earth without an atmosphere is 255 K ( -18 degrees Celsius), but adding in the various effects of our atmosphere we come to an average of 288 K (15 degrees Celsius), so it’s clear how careful we have to be with these numbers, given how little we know about the planets in question. The surface temperature of a planet with a dense atmosphere will depend upon our atmospheric models.
That issue applies to the system around HD 85512 as well, which is described as the most stable of the stars in the HARPS sample. This star is found to have a possible super-Earth in an interesting orbit indeed, with a semi-major axis of 0.26 AU and a computed equilibrium temperature of 298 K, one that could place this potentially rocky world within the inner edge of the habitable zone. As my friend Ronald Botterweg reminds me in one of the comments to an earlier post, this equilibrium temperature is not far from that of southern France about now, but again, that has to be adjusted for atmospheric effects (for a paper analyzing different atmospheric models for this planet, see Kaltenegger et al., linked to at the end of this post).
In fact, let me go ahead and quote from the Kaltenegger paper, which calls HD 85512 b “…with Gl 581 d, the best candidate for habitability known to date.”:
We focus our analysis on HD 85512 b. We show the influence of the measurement uncertainties on its location in the Habitable Zone as well as its potential habitability. We find that HD 85512 b could be potentially habitable if the planet exhibits more than 50% cloud coverage. A planetary albedo of 0.48 +/- 0.05 for a circular orbit, and an albedo of 0.52 for e=0.11 is needed to keep the equilibrium temperature below 270K and the planet potentially habitable.
And this:
If clouds were increasing the albedo of HD 85512 b, its surface could remain cool enough to allow for liquid water if present. HD 85512 b is a planet on the edge of habitability.
But back to the original HARPS paper. HD 192310 has been under investigation for several seasons following the earlier discovery of a Neptune-mass planet there. HARPS confirms that earlier discovery and adds another possibly Neptune-class world, the two semi-major axes being 0.32 AU and 1.18 AU. According to the paper, we’re again bracketing the habitable zone, with equilibrium temperatures on the order of 355 K and 185 K — possibly at the very inner and outer edges of the habitable zone, respectively.
So far, then, three of the ten stars observed in this program have yielded low-mass planets. From the paper:
Although statistics is poor over only ten targets, it is interesting to note that this 30% value was already announced by Lovis et al. (2009) who based their analysis on the larger (< 200 stars) HARPS high-precision program. Theoretical works by Mordasini et al. (2009) actually forecasted that the frequency of small Neptunes and super-Earths on short and intermediated orbits would be considerably higher than that of Saturns and Jupiters. The recent amazing discoveries made by the KEPLER satellite using the transit technique further strengthen this fact. Borucki et al. (2011) report that the probability of finding low-mass planets is considerably higher than for Jupiter or Saturn-mass planets. Furthermore, when summing up the frequency of finding a planet of any mass, they end up with a probability of about 30%, again in perfect agreement with the results of Lovis et al. (2009).
All good news for finding Earth-class worlds as we push the radial velocity method into this mass range. It’s interesting, too, to look at what this paper has to say about Alpha Centauri, Centauri B being one of the ten targets on the HARPS list for the study. As the work continues, the researchers have to contend with the bright magnitude of the Centauri stars, which “may result in poorer RV precision due to incomplete light scrambling across the spectrograph’s entrance slit.” Another major issue: Alpha Centauri B is a member of a triple star system, which means the radial velocity analysis must include a complete and precise orbital model. All of this is tricky but a thorough reading of the paper yields the conviction that HARPS is up to the task.
Tau Ceti is also a member of the list — this is one of the two stars from the original Project Ozma that Frank Drake made famous back in 1960 (the other being Epsilon Eridani). Tau Ceti as yet shows no planetary signatures, and again I’m going to turn to Centauri Dreams regular Ronald Botterweg, who has been in the thick of our ongoing exoplanet discussions for many years. Ronald analyzed the metallicity of the ten stars in the HARPS sample and found that eight of them have lower metallicity than the Sun (seven, in fact, have considerably lower metallicity than Sol). Which leads Ronald to quote a recent Greg Laughlin post on systemic:
“First, among host stars with masses similar to the Sun that harbor giant planets, there’s a strong preference for metal-rich stars. This is the classic planet-stellar metallicity effect. Second, among low-mass stars, there’s a dearth of giant planet candidates. This is the known giant planet-stellar mass effect.”
Interesting stuff, and I’m pleased at the way readers here have been digging into these papers, which not only alerts me to new work but points to issues I might otherwise have missed. Solar-type stars of low metallicity are places where we find few giant planets, the latter seeming to favor high-metallicity stars of solar size and larger. Meanwhile, the relatively high metallicity content of Centauri B, which might lead us to expect a gas giant, is presumably offset by its position as a close binary. We’ll now wait with great interest to see how the HARPS work continues on the vital and fascinating question of smaller worlds in the Alpha Centauri system. With two other teams also on the case, I suspect we won’t have to wait too much longer before we learn something definitive about the planetary situation around our nearest neighbor.
The paper is Pepe et al., “The HARPS search for Earth-like planets in the habitable zone: I — Very low-mass planets around HD20794, HD85512 and HD192310,” accepted by Astronomy & Astrophysics (preprint). See also Kaltenegger et al., “A Habitable Planet around HD 85512?” submitted to Astronomy & Astrophysics (preprint).
Catching Up with New Horizons
New Horizons continues on its inexorable way to Pluto/Charon, now some 21 AU out, which places it between the orbits of Uranus and Neptune. The latest report from principal investigator Alan Stern tells us that the 2011 checkout of the spacecraft was completed on July 1, a two-month process that included a test of the REX radio occultation experiment, coordinating with the Deep Space Network as the Moon interrupted a radio signal from Earth. According to Stern, spacecraft tracking over May and June shows New Horizons on a ‘perfect course’ toward the distant world, one that will demand no course correction until, at the earliest, 2013.
I wanted to bring Stern’s report into play here because of the image below, which shows Pluto’s newly discovered moon P4 along with the other moons now known in the system. The fact that I hadn’t yet run it told me that it was time to do some catching up with this impressive mission.
Image: These two images, taken about a week apart by NASA’s Hubble Space Telescope, show four moons orbiting the distant, icy dwarf planet Pluto. The green circle in both snapshots marks the newly discovered moon, temporarily dubbed P4, found by Hubble in June. The new moon lies between the orbits of Nix and Hydra, two satellites discovered by Hubble in 2005. It completes an orbit around Pluto roughly every 31 days. Credit: NASA, ESA, and M. Showalter (SETI Institute)
P4 (the name is temporary) was found during a search for rings around Pluto. At an estimated diameter of 13 to 34 kilometers, it’s the smallest moon yet discovered in this system. Obviously, the more we learn about Pluto/Charon, the better the New Horizons team will be able to plan for its brief period of close up observations. And it’s likely we’ll find still more tiny moons in a system that is thought to have been formed by a collision between Pluto and another large body in the early Solar System. P4 was found with Hubble’s Wide Field Camera 3 on June 28 and later confirmed through subsequent imagery. Still no signs of any Plutonian rings, however.
Meanwhile, John Spencer, a member of the New Horizons mission science team, has posted an interesting look at the effort to find a Kuiper Belt object that New Horizons will study after the encounter with Pluto/Charon. We’ve talked before about the Ice Hunters project, where volunteers can help pursue the search using the power of networked computers at home. Hunter now reports on his trip to Hawaii, which provided the chance to work with the Subaru telescope on the summit of Mauna Kea, an experience would-be astronomers can only envy. Spencer talks about recapturing ‘the romance of the old way of connecting with the universe,’ something many working astronomers seldom do these days, and describes the trip to the top:
After a night and a day of acclimatization, adjusting our bodies to the thin air, we climbed into 4WD vehicles and made the half-hour drive to the summit as sunset approached. It is always an amazing transition from the relative domesticity of Hale Pohaku and its mamane trees to the vast, alien, apparently lifeless landscape of the summit and its giant telescopes. This was the first time at Subaru for some in our group, so Josh Williams, the telescope operator, gave us a quick tour of the darkened, cathedral-like space of the dome, almost filled by the huge bulk of the telescope with its 8-meter diameter mirror. We also made quick trip around the catwalk outside the dome, to admire the fabulous view, before returning to the warmth and comfort of the control room, where we were to spend the night.
The work involved calibration observations, warm-up tests using near-Earth asteoids, and finally the acquisition of the images that might lead to KBO finds. But toward the end of the observing period, a broken coolant hose ended operations (and kept Subaru down for another three weeks). Spencer says the team left with 70 percent of what they were there for, in any case, and his laptop hard disk returned from the journey with data that will appear soon on Ice Hunters.
Image: The Subaru dome (left) is silhouetted by the Milky Way, as the telescope searches for KBOs. The search area is among the star clouds in the upper left of the image. (Credit: John Spencer).
Whether or not New Horizons gets to make that flyby of a distant Kuiper Belt object depends upon a number of things, among them NASA approval of an extended mission (it’s hard to see how this could be turned down given the rarity of our getting a spacecraft this far from the Sun), as well as the discovery of an appropriate KBO. The New Horizons team is looking for an object at least 50 kilometers across for a flyby and high resolution imagery, as well as spectroscopic investigations and study of possible moons or traces of an atmosphere. I can only echo Spencer’s invitation for those of you who haven’t yet done so to join the Ice Hunters search today. Remember, although we’ve found more than 1000 objects beyond Neptune’s orbit, it’s estimated that there may be half a million objects bigger than 30 kilometers across out there.
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