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STEREO: Closing on the Lagrange Points

by Paul Gilster | Aug 14, 2009 | Asteroid and Comet Deflection | 20 Comments

A note the other day from astrodynamics wizard Edward Belbruno (Princeton University) has put me in mind of the ongoing study of the L4 and L5 points being conducted by the STEREO mission. STEREO is a two-spacecraft observatory designed to study solar activity, but in September and October the craft will be making their closest approach to the two gravitational wells at L4 and L5, and it's possible we'll discover a resident population of asteroids in the process. If so, we may be looking at material from the birthplace of a long-gone planet. Call this hypothetical world, as Belbruno does, Theia. We looked at this secondary mission for STEREO last February, but as Belbruno passed along a link to the 2005 paper on the subject of Theia for which he was lead author, it's time to revisit it. The paper is a lively piece of work, noting that current thinking is that our Moon was the result of a giant impactor, a planetary-sized object that hit the Earth and produced debris that eventually...

WASP-17b: Unusual World Bloated by Tides

by Paul Gilster | Aug 13, 2009 | Exoplanetary Science | 11 Comments

Why some planets are the size they are remains something of a mystery. I'm looking at the discovery paper for a planet called WASP-17b, which is said to be twice Jupiter's size but only half its mass. That raises questions about the mechanisms at work, for you can't explain the bloated nature of this world with the models of planetary evolution we're now working with without factoring in massive tidal effects. In one sense, WASP-17b is completely anomalous. In addition to its size, it orbits its star in retrograde fashion, opposite the direction of the star's spin. But in other important respects, the new planet joins the ranks of other bloated worlds like HD209458b (the first such world to be discovered), and a flock of other huge planets that includes TrES-4, WASP-12b, XO-3b and HAT-P-1b. TrES-4 shows a density about fifteen percent that of Jupiter, with a radius 1.78 times larger than Jupiter's. Image: Orbiting close to its parent star, WASP-17b may look something like this, a...

In Praise of K-class Stars

by Paul Gilster | Aug 12, 2009 | Astrobiology and SETI | 26 Comments

When it comes to exoplanet speculations, we're still in the era when data are few and dominated by selection effect, which is why we began by finding so many 'hot Jupiters' -- such planets seem made to order for relatively short-term radial velocity detections. It's a golden age for speculation, with the promise of new instrumentation and a boatload of information from missions like Kepler and CoRoT to be delivered within a few years. What an extraordinary time to be doing exoplanetary science. The big questions can't be answered yet, but it shouldn't be long before we have an inkling about what kind of stars are most likely to produce terrestrial planets. And maybe a qualification is in order. M-dwarfs are so common in our galaxy -- some estimates run to seventy percent of all stars and up -- that finding habitable worlds around them would hugely increase the possible venues for life. But is there any way we could call planets around M-dwarfs 'Earth-like?' Maybe in terms of...

A Massive Extrasolar Collision

by Paul Gilster | Aug 11, 2009 | Exoplanetary Science | 2 Comments

It doesn't take much observation to realize that the early Solar System was a violent place. Mercury seems stripped of its outer crust, doubtless the result of a massive impact, while Uranus was knocked to one side at some point in its history, aligning its spin axis with the plane of the ecliptic. Venus was hit so violently that it rotates clockwise as seen from above, opposite to the other planets. At least, a collision is one of several theories that may explain Venus' retrograde rotation, and it's more than plausible. 100 light years from Earth is a place that reminds us of the impact that produced Earth's own moon billions of years ago. HD 172555 is a young star in the southern constellation Pavo (the Peacock), its twelve-million year old system in its infancy. Spectral analysis from the Spitzer Space Telescope shows clear evidence of a collision much like that between the Earth and that early, Mars-sized object that once struck it. Image: This artist's concept shows a celestial...

Titan: A ‘Fishing License’ to Broaden the Hunt for Life

by Paul Gilster | Aug 10, 2009 | Astrobiology and SETI | 26 Comments

An exotic planetary environment right here in the Solar System may be a useful test for answering the key question of how common life is in the universe. So argues Jonathan Lunine (University of Arizona) in an upcoming paper. Lunine believes there is a plausible case for life to form on Titan, and that if we were to find it there, its very dissimilarity from Earth would make it a test-case for life in other extreme environments of the sort that may be common in the cosmos. We'd like to answer this question locally because it may be some time before we can answer it around other stars. After all, the best spectral signatures we can hope to get from the atmospheres of Earth-analogues elsewhere are quite possibly going to be ambiguous. Molecular oxygen can be a sign of photosynthesis but also of the abiotic escape of water from the upper atmosphere. Methane in the same atmosphere makes biology more likely but may be, Lunine thinks, difficult to detect from Earth. Image: One way to...

Sharp Early Returns from Kepler

by Paul Gilster | Aug 7, 2009 | Exoplanetary Science | 18 Comments

Unlike the Cassini Saturn orbiter, which we looked at yesterday in the context of cryovolcanism on Titan, the Kepler spacecraft has but a single scientific instrument. It's a photometer based on a Schmidt telescope design with a 95 cm aperture and a field of view larger than 100 square degrees. Measuring brightness variations for over 100,000 stars, Kepler is the first mission that should be able to detect Earth-size planets in the habitable zones of their stars. That made yesterday's news conference an eagerly anticipated event, but we have to remember that it's going to be a while before we start talking about terrestrial planet detections. It takes multiple transits and much data analysis to make that possible, and a transiting world at roughly Earth-like distance from its star will demand several years of work. Kepler's baseline mission is three and a half years, more than enough to make such detections, and the good news is that the instrument works. Image: Magnified Kepler...

Notes & Queries 8/6/09

by Paul Gilster | Aug 6, 2009 | Culture and Society | 14 Comments

Propulsion Book Discussion Available Give a look, and then a listen, to David Livingston's August 3rd Space Show. Livingston talked to Tau Zero founder Marc Millis and Eric Davis (Institute for Advanced Studies at Austin) about the recently published Frontiers of Propulsion Science, calling it "the ultimate research and reference book to have for advanced and out-of-the-box space propulsion science" and adding: "As you will hear me say over and over again, this is a must own and a must read book. It is also a very valuable research and reference book for anyone wanting to know propulsion and physics facts regarding space travel and related issues." Knowing how much time and effort Marc and Eric spent coordinating the many contributions from leading authorities that went into this book, it's a pleasure to see Frontiers of Propulsion Science achieving this kind of acclaim. At 739 pages and stuffed with technical and scientific papers aimed at scientists and university students, the...

Tuning Up Ion Propulsion

by Paul Gilster | Aug 5, 2009 | Advanced Rocketry | 21 Comments

A story on MIT's Technology Review site looks at ion propulsion, and specifically at improvements made in the technology at Glenn Research Center. Comparing the recent work to the engines used in the Deep Space 1 and Dawn missions, the story quotes GRC's Michael Patterson as saying, "We made it physically bigger, but lighter, reduced the system's complexity to extend its lifetime, and, overall, improved its efficiency." That's good news, of course, and Patterson presented it to the AIAA's Joint Propulsion Conference & Exhibit this week in Denver. With sessions on everything from Electric Propulsion Thruster Wear and Life Assessment to Advanced Propulsion Concepts, Denver was clearly the place to be for propulsion mavens. An entire session was devoted to the new ion thrust work, which goes under the name NASA's Evolutionary Xenon Thruster (NEXT). Quoting from an abstract of one of the talks: The NASA NEXT thruster is engineered to be extremely flexible in terms of input power and...

Anomalies and Their Uses

by Paul Gilster | Aug 4, 2009 | Exotic Physics | 19 Comments

Anomalies in scientific data can sometimes lead to a richer understanding of the underlying principles involved. Einstein was able to explain the difference between the Newtonian description of Mercury's orbit and subsequent observations by applying his developing theory of General Relativity. Add the curvature of spacetime to the Newtonian picture and the problem of a tiny discrepancy in Mercury's perihelion precession can be resolved. This anomaly briefly changed our view of the Solar System. Originally, the astronomer Urbain Le Verrier had thought it could be explained by the presence of another planet -- Vulcan -- closer than Mercury to the Sun, but reported sightings of Vulcan were found to be spurious. Einstein's work solved the precession problem. In a letter to his close friend Michele Angelo Besso, Einstein would write: "In these last months I had great success in my work. Generally covariant gravitation equations. Perihelion motions explained quantitatively… you will...

On the Nuclear Imperative

by Paul Gilster | Jul 31, 2009 | Advanced Rocketry | 39 Comments

Sometimes our concerns about the human future are eerily like those of our ancestors. Giancarlo Genta (Politecnico di Torino) likes to quote an ancient Assyrian tablet on the matter, one said to have been rendered around 2800 BC: Our Earth is degenerate in these latter days; bribery and corruption are common; children no longer obey their parents; every man wants to write a book and the end of the world is evidently approaching. Marvelous as it is, the quote may be apocryphal, as Genta noted in his recent talk at the deep space conference in Aosta. In fact, I suspect it is, unless the bit about every man wanting to write a book was literally written 'every man wants to keep his household accounts on a clay tablet' or some such. But whatever the case, the quote echoes similar sentiments found throughout history, thoughts that evoke a golden age when things were just plain better than they are in the present and the future did not seem so dark. Which is not to say we don't have serious...

Cometary Catastrophe? Not So Fast…

by Paul Gilster | Jul 30, 2009 | Asteroid and Comet Deflection | 14 Comments

Once again we're asked to reconsider our views about the outer Solar System. In this case, the area in question is the Oort Cloud, which begins at roughly 1000 AU and continues, by some estimates, as far as three light years from the Sun. It's a spherical cloud of comets, probably numbering in the billions of objects, most of which will never be observed because of their distance and faint signature. Getting comets into the inner Solar System is necessary for closer observation, but it's also risky for living beings. At least, that's been the prevailing belief, given that comet collisions with Earth could theoretically produce extinction events. New research, however, has begun to challenge this view. Nathan Kaib (University of Washington) and doctoral adviser Thomas Quinn have developed computer models to study how comet clouds behave. The simulations trace the evolution of comets over a 1.2 billion year period and allow the team to estimate the highest number of comets possible in...

Enceladus: More Evidence of Liquid Water

by Paul Gilster | Jul 29, 2009 | Outer Solar System | 13 Comments

I'm pushed for time this morning but do want to catch up with Cassini news, in particular the recent findings from Enceladus. The plumes of water vapor and ice particles erupting from the moon continue to capture the imagination. Cassini's Ion and Neutral Mass Spectrometer was used during Enceladus flybys in July and October of 2008, with results just released in Nature. Out of all this we get this interesting find, as discussed by Hunter Waite (SwRI), who is lead scientist on the instrument involved: "When Cassini flew through the plume erupting from Enceladus on October 8 of last year, our spectrometer was able to sniff out many complex chemicals, including organic ones, in the vapor and icy particles. One of the chemicals definitively identified was ammonia." William McKinnon (Washington University, St. Louis) calls ammonia "sort of a holy grail for icy volcanism," noting that this is our first unambiguous detection of ammonia on an icy satellite of a giant planet. Finding it is...

Notes & Queries 7/27/09

by Paul Gilster | Jul 28, 2009 | Culture and Society | 4 Comments

Tau Zero in the Press Edinburgh-based journalist Ian Brown offers up an overview of interstellar issues in Scotland's Sunday Herald. The core of the story is an interview Brown conducted with Tau Zero founder Marc Millis, who as Brown notes was formerly the manager of NASA's Breakthrough Propulsion Physics project. The Tau Zero Foundation grows out of that work (though it retains no NASA connection), and it's good to see us getting publicity in a popular science story that captures TZF's imaginative spirit while avoiding sensationalism. Brown calls us "a grass-roots network of physicists, mathematicians, engineers and science journalists," an accurate description. Here's a snippet quoting Millis on the nature of interstellar striving: "How much we accomplish is, of course, tied to the resources we acquire. The focus will be on making incremental progress rather than big projects." As a physicist, he knows the sheer immensity of the challenge. Many scientists believe we will never...

Galactic Life in Context

by Paul Gilster | Jul 27, 2009 | Astrobiology and SETI | 35 Comments

Does complex life emerge at a gradual, uniform rate? If so, we can come up with one answer to the Fermi paradox: We have not detected signs of extraterrestrial life because the time needed for complex life to appear generally exceeds the life of a star on the main sequence. But the assumption that intelligence appears over time with a gradual inevitability -- a key tenet of work by Brandon Carter, Frank Tipler and others in the 1980s, may not in fact be true. Solar system-wide events connect life with its stellar environment, while galaxy-wide events provide yet another context. Punctuated Evolution Among the Stars Milan ?irkovi? (Astronomical Observatory, Belgrade) and colleagues have much to say about this in a new paper in Astrobiology. It's a rich treatment of our older assumptions and newer thinking about punctuated evolution, the idea that life actually evolves in spasms rather than smooth ascents. Species remain relatively stable for long periods but endure sudden changes that...

Updating the Gravitational Focus Mission

by Paul Gilster | Jul 24, 2009 | Outer Solar System | 23 Comments

If you'll examine the cover of Claudio Maccone's new book carefully, you'll see an interesting object at the lower right. It's a spacecraft with two deployed antennae connected by a tether. The book is Maccone's Deep Space Flight and Communications, whose subtitle -- 'Exploiting the Sun as a Gravitational Lens' -- tells us much about the author's view of how early interstellar missions should proceed. And Maccone devoted a session at the recent conference in Aosta to these matters, making the case for taking advantage of this natural phenomenon. Uses of Gravitational Lensing We've looked at the Sun's gravitational lens, and the FOCAL mission Maccone champions to exploit it, many times here on Centauri Dreams. But for newcomers, gravitational focusing has been an active astronomical tool since 1978, when a 'twin' image of a quasar was found by the British astronomer Dennis Walsh. The gravitational field of a galaxy between the Earth and the quasar had bent the light from the more...

Habitable Exomoons Should Be Detectable

by Paul Gilster | Jul 23, 2009 | Exoplanetary Science | 15 Comments

The hunt for exomoons -- satellites of planets around other stars -- gets more interesting all the time. This morning I received a note from David Kipping (University College London), who has been studying methods for finding such objects. Kipping and colleagues have a paper soon to be published by Monthly Notices of the Royal Astronomical Society that discusses how to detect habitable exomoons using Kepler-class instrumentation. And it turns out that finding such worlds is well within our present capabilities. A bit of background: Kipping's method is to analyze two useful sets of signals. Transit timing variations (TTV) are variations in the time it takes a planet to transit its star. Kipping and team acquire these data and then weave the TTV information together with what is called transit duration variation (TDV). The latter is detectable because as the planet and its moon orbit their common center of mass, velocity changes can be observed over time. Put TTV and TDV together and...

A New Jovian Impact

by Paul Gilster | Jul 22, 2009 | Asteroid and Comet Deflection | 12 Comments

It's a lively Solar System indeed. In yet another confirmation of the value of amateur astronomy, Australia's Anthony Wesley tipped off scientists on July 19 that a new object had struck Jupiter and observatories around the world zeroed in on the event. It comes exactly fifteen years after the 'string of pearls' comet Shoemaker-Levy 9 struck the giant planet. Infrared images show a likely impact point near the south polar region, visible in the image below. Image: A large impact shown on the bottom left on Jupiter's south polar region captured on July 20, 2009, by NASA's Infrared Telescope Facility in Mauna Kea, Hawaii. Image credit: NASA/JPL/Infrared Telescope Facility. Unlike Shoemaker-Levy 9, this event may have been caused by a single object. UC Berkeley and SETI Institute astronomer Franck Marchis explains: "The analysis of the shape and brightness of the feature will help in determining the energy and the origin of the impactor. We don't see other bright features along the same...

Chinese Test of Eclipse Anomaly

by Paul Gilster | Jul 21, 2009 | Exotic Physics | 11 Comments

Tibor Pacher has been kind enough to publish the text of my public lecture in Aosta, Italy on his PI Club site. The lecture took place at the Aosta town hall and wasn't part of the ongoing conference just down the street, although some conference participants attended. It's a broad overview of earlier work on interstellar flight. My intention was to acquaint non-scientists with the fact that the subject has been under study for decades in ways that do not violate the laws of known physics. A major challenge is how to scale some of the colossal engineering involved down to realistic levels. Although I only touched upon it in the lecture, I often talk about the twin tracks of interstellar studies. The first track comprises work that tries to scale current technology up for an interstellar mission. The second track is oriented toward examining physical laws in hopes of finding potential breakthroughs that current theory doesn't allow. No one knows if such breakthroughs are possible, but...

On Apollo 11

by Paul Gilster | Jul 20, 2009 | Culture and Society | 37 Comments

I sometimes wonder whether Neil Armstrong wrestled all the way to the Moon with what he would say when he stepped out onto the surface. The answer is probably tucked away somewhere in the abundant literature on the Moon landings. I know that if it were me, I'd be turning over the options in my mind for months in advance. What do you say upon achieving what is obviously one of the most significant accomplishments in history? Did Armstrong ponder alternatives even as he descended from the lander? In any case, the words carried a great truth. Giant leaps are made up of small steps, and not just the first step of a single astronaut leaving a footprint. It wasn't just a Saturn V that got Apollo 11 to the Moon -- it was also Einstein, and Newton, and Leibniz, and thousands of mathematicians, physicists, engineers and yes, philosophers throughout history whose work pushed the possibility forward. This is, not coincidentally, the philosophy of the Tau Zero Foundation: ad astra incrementis....

Reconfiguring the Early Solar System

by Paul Gilster | Jul 17, 2009 | Outer Solar System | 7 Comments

Other than Monday, the week here has been devoted to the outer planets, and before I leave that subject, I want to work in the findings of a team of astronomers looking at the early history of the asteroid belt. Recent numerical simulations suggest that many of the objects found in the 'main belt' between the orbits of Mars and Jupiter actually formed far out in the Solar System, moving inward during a violent spasm of planetary evolution. That points to an early system that, at particular times, underwent upheaval caused by a rearrangement of the gas giant planets. This is the so-called Nice model, so named because much of the work on it was performed at the Observatoire de la Côte d'Azur in Nice. The model proposes that the gas giant planets migrated to their present positions long after the protoplanetary gas disk had dissipated, playing a role in the Late Heavy Bombardment of the inner planets some 3.9 billion years ago, and producing many other effects, including the formation...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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