New Precursors of Life Identified in Meteorite

We know that organic compounds have been found in meteorite fragments. But are they truly extraterrestrial, or the result of contamination here on Earth? The subject, always controversial, has been given new impetus by a paper that points to the former, with interesting ramifications. Did life begin on Earth or was the Earth seeded by life from the cosmos? Or perhaps a third alternative exists, with pre-existing life influenced by infall from outer space. If we can build a viable case for the latter two possibilities, we can build one just as viable for planets around a wide variety of stars, giving the idea that granted enough time, life of some kind may become ubiquitous a most interesting boost.

Meteor shower

The scientists involved have been working with fragments of the Murchison meteorite, which fell in 1969 about 100 km north of Melbourne, Australia. Quite a bit of material — over 100 kg — could be recovered, enough for batteries of subsequent tests and the discovery of various amino acids, some common, some unusual. The most recent work finds the molecules uracil and xanthine in Murchison fragments. These are nucleobases, or precursors to the molecules that make up RNA and DNA.

Moreover, they’re found to contain a heavy form of carbon that the team believes could only have been formed in space. And that takes us to some interesting places. Here’s Mark Sephton (Imperial College London), a co-author of the paper on this work, on the possibilities:

“Because meteorites represent left over materials from the formation of the solar system, the key components for life — including nucleobases — could be widespread in the cosmos. As more and more of life’s raw materials are discovered in objects from space, the possibility of life springing forth wherever the right chemistry is present becomes more likely.”

That ‘right chemistry’ is an interesting thing indeed. Accept the idea that the first living organisms on Earth emerged as the result of the chemistry of early organic compounds. Just how that process proceeded is hidden from us by subsequent geological activity, not to mention the bombardment of the planet between 3.8 and 4.5 billion years ago. But the materials involved in the Earth’s formation can be studied in objects like the Murchison meteorite. Carbonaceous chondrites like this are a class of primitive meteorite that contains compounds conducive to life. They offer a snapshot of the organic chemistry that suggests how life began.

The effects of the heavy bombardment all those billions of years ago in jump-starting life on this planet are becoming better understood through finds like these. And they do suggest that we live in a cosmos that keeps trying to get life started wherever conditions are right. Couple that with the discovery (within a few years, surely) of Earth-mass planets in the habitable zones of other stars and the outlook for finding signs of life in future terrestrial planet hunter missions looks brighter and brighter.

The paper is Martins, et al., ““Extraterrestrial nucleobases in the Murchison meteorite”, Earth and Planetary Science Letters, Volume 270, Issues 1-2 (15 June 2008), pp. 130-136

Three ‘Super-Earths,’ One Star

The much anticipated Nantes conference on Extrasolar Super-Earths is already paying off big in the form of a triple system of such planets. Found around the star HD 40307, the planets are among the 45 candidate worlds recently identified by European scientists using the HARPS instrument, a spectrograph mounted on the European Southern Observatory’s 3.6-meter telescope at La Silla. The survey focused on F, G and K-class stars, finding 45 potential planets, all of which are below 30 Earth masses and show an orbital period shorter than fifty days.

What’s happening here testifies to the growing sophistication of our tools. While most of the 300+ positively identified exoplanets have been found around Sun-like stars, they have so far tended to be gas giants. Teasing smaller planets out of the data requires long observing runs — HD 40307, for example, has been under active study for five years — and it also requires the greater precision of instruments like HARPS. “With the advent of much more precise instruments such as the HARPS spectrograph on ESO’s 3.6-m telescope at La Silla,” says planet-hunter Stéphane Udry (Geneva Observatory), “we can now discover smaller planets, with masses between 2 and 10 times the Earth’s mass.”

Orbits around HD 40307

HD 40307 is slightly less massive than the Sun, and located 42 light years away in the southern sky, in the direction of the constellations Doradus and Pictor. The three planets turn out to have masses of 4.2, 6.7 and 9.4 times that of the Earth, and they’re in tight orbits of 4.3, 9.6, and 20.4 days, respectively. Consider how sensitive our exoplanetary studies have become: The smallest of the planets has a mass one hundred thousand times less than that of the star it circles, inducing a ‘wobble’ of only a few meters per second. But to get the big picture, bear in mind that planets in close orbits are at this point easier for our instrumentation to detect than those in wide, long-period orbits. How much are we still unable to detect?

Image: Schematic view from above of the orbits of the three super-Earths around their host star. The scale is in astronomical units (AU), the mean distance between the Earth and the Sun. All planets are thus well within the orbit of Mercury around the Sun (which has an orbital period of 88 days). Credit: European Southern Observatory.

Thus we get into some exciting quotes, this one from Michel Mayor (Geneva Observatory), a familiar name as one of the discoverers of a planet around the star 51 Pegasi in 1995. That event kicked off the exoplanet hunt, one that seems to grow in intensity with each passing day. Looking not only at the super-Earths HARPS has disclosed but at the entire HARPS sample and its 45 candidate planet result, Mayor comments:

“Clearly these planets are only the tip of the iceberg. The analysis of all the stars studied with HARPS shows that about one third of all solar-like stars have either super-Earth or Neptune-like planets with orbital periods shorter than 50 days.”

Good news indeed, especially when you follow it up with this from colleague Udry, who factors in the limitations of our instruments and currently available data:

“It is most probable that there are many other planets present: not only super-Earth and Neptune-like planets with longer periods, but also Earth-like planets that we cannot detect yet. Add to it the Jupiter-like planets already known, and you may well arrive at the conclusion that planets are ubiquitous.”

The same team also discussed two other planetary systems at the Nantes conference. One involves a 7.5 Earth-mass world around HD 181433 in a 9.5 day orbit, accompanied by a Jupiter-like planet in a three-year orbit. The other is a 22 Earth-mass planet in a system that also includes a Saturn-class world, also with a three-year period. The conference runs until the 18th and will doubtless occupy us in coming days with a series of further results. The above work from the Geneva team has been submitted in the form of two papers to Astronomy & Astrophysics. Full references here when they become available.

Science, Accuracy and the Media

This week’s Carnival of Space is up at Universe Today, and out of the mix I’ll point you to Ian O’Neill’s musings on the perceived accuracy of science. It’s a look at how tentative research findings can be misunderstood, a phenomenon that’s hardly new and often blamed on the media. But is it the media’s fault? In many cases, even a balanced newspaper or TV story can be taken out of context when given a potentially misleading headline.

Thus a 1983 story on observations by NASA’s Infrared Astronomical Satellite (IRAS) received a headline (“Possibly as Large as Jupiter; Mystery Heavenly Body Discovered”) that needlessly limited a research result that had led scientists to speculate on everything from an object near the Solar System to something of extra-galactic origin.

It’s hard to fault the Washington Post, which ran the story, for the bizarre transfiguration of this object into a proto-star or possibly a planet that was sure to collide with Earth, but this seems to have occurred in some readers’ minds. Indeed, O’Neill quotes the original story with a certain sense of disbelief at what it led to. Here’s the quote:

“So mysterious is the object that astronomers do not know if it is a planet, a giant comet, a nearby “protostar” that never got hot enough to become a star, a distant galaxy so young that it is still in the process of forming its first stars or a galaxy so shrouded in dust that none of the light cast by its stars ever gets through.”

The story seems reasonable, yet somehow ‘Mystery Heavenly Body’ became interpreted by certain readers as ‘Earth-menacing planet in the outer Solar System,’ feeding a buzz that continues to translate into various doomsday scenarios. All this was fed more fuel in the 1990’s with the discovery of objects in the Edgeworth/Kuiper belt that some determined doomsday hawkers have misconstrued as this same object. O’Neill sees part of the problem as too flamboyant a use of language:

Out here in the space blogosphere I have been guilty in using flamboyant language, especially in the titles of some of my stories (re: “Temperature Conditions of a Supernova Recreated in UK Laboratory” – I could have just said “10 Million Kelvin Achieved with Petawatt Laser”, or “Synthetic Black Hole Event Horizon Created in UK Laboratory” – Perhaps I needn’t have mentioned “black hole” in the title?), but with space blogs (or any blog for that matter), the main strength of writing in an informal, but accurate, manner is that we can be a little more expressive and more opinionated than “level-zero” news releases. The problem comes when primary sources of the media begin to base their stories on what they perceive to be accurate. Like the Washington Post article in 1983, why strongly indicate that a Jupiter-sized planet had been discovered?

Fair enough, and it’s certainly true that the use of hyperbole when dealing with scientific discovery is hardly conducive to rational thought. But the evidence suggests that if someone wants to take an idea out of context, mis-read an entire article and ignore the comments of the researchers who explained its findings, that person is going to proceed no matter what the headline. All of which is a known problem in science writing, and about the best we can do is push accurate follow-ups, especially as a story (think Gliese 581 c) plays out in ways that deflate the original exciting premise. Newspapers publish corrections that are rarely seen, but the Web offers us a more supple medium in which to report how science’s hypotheses are influenced by subsequent findings.

New Mineral Found in Cometary Dust

Does anybody remember an old science fiction movie involving an attempt to snatch meteors from space? We’re talking something made probably in the 1950’s, and all I remember is a group of one-man spaceships sent up — for reasons that escape me — to go after meteors. You can imagine the dynamics of trying to catch a meteor with a scoop on a spacecraft. All subsequent attempts to identify this film have failed, but I was reminded of it by the discovery of a new mineral in a sample of interplanetary dust. Collecting the dust wasn’t quite as terrifying as the meteor-grabbing depicted in the movie, and the motivation for it was surely sounder.

Interstellar dust particle

In any case, it’s clear that you don’t have to go into deep space to collect interesting things. It was Scott Messenger (Johnson Space Center) who suggested that interstellar dust particles (IDPs) from a particular comet could be captured in the stratosphere if scientists chose their time carefully. Messenger zeroed in on comet 26P/Grigg-Skjellerup as a source for the IDPs in question, and follow-up dust collections by NASA involved high altitude aircraft flown out of Edwards Air Force Base in 2003.

Image: Although not part of the sample gathered from comet 26P/Grigg-Skjellerup, this is a piece of interplanetary dust caught by a high-flying U2-type aircraft. It likely originates in the early days of our Solar System, being stored and later ejected by a passing comet. The particle is composed of glass, carbon, and a conglomeration of silicate mineral grains. It measures only 10 microns across, a tenth the width of a typical human hair. Credit: NASA.

Not only was the attempt successful, but 26P/Grigg-Skjellerup should turn out to be useful in future work, appearing as it does every five years. Team leader Keiko Nakamura-Messenger notes that grains of the newly identified mineral were a mere 1/10,000th of an inch in size. Fortunately, Johnson Space Center has a new electron microscope, and co-discoverer Lindsay Keller (JSC), like Nakamura-Messenger, was taken somewhat by surprise at what the instrument was able to find:

“Because of their exceedingly tiny size, we had to use state-of-the-art nano-analysis techniques in the microscope to measure the chemical composition and crystal structure of Keiko’s new mineral. This is a highly unusual material that has not been predicted either to be a cometary component or to have formed by condensation in the solar nebula.”

The new mineral is a manganese silicide now named Brownleeite, after Donald Brownlee (University of Washington, Seattle), a founder of interstellar dust particle research, and principal investigator of NASA’s Stardust mission. Turns out the trick isn’t to collect interplanetary dust — remarkably, the Earth collects about 40,000 tons of particles from space every year — but to pin down the sources of the particles. Most are assumed to come from disintegrating comets and asteroid collisions, and all are of interest because they offer information about the building blocks from which the Solar System was formed. The new mineral joins the other 4,324 minerals identified by the International Mineralogical Association, while reinforcing the case for interplanetary dust collection close to home.

Solar Sail Mission to the Sun’s High Latitudes

Every now and then, someone writes to point out that when I write about the ‘nearest star,’ I am actually talking about the Sun. True enough, and despite our interstellar focus in these pages, I don’t want to neglect the contribution of missions like SOHO, Ulysses, Hinode, STEREO and others to our understanding of how stars work. What we now need to deepen that knowledge further is a polar mission like POLARIS, which is being designed to make high-latitude studies of the Sun.

For we have no extended studies of these regions, which will set up observations impossible to make from the ecliptic. Nor does the proposed Solar Orbiter mission offer a wide enough view of the polar regions. A new study of the POLARIS mission notes its purpose: to “determine the relation between the magnetism and dynamics of the Sun’s polar regions and the solar cycle.” Indeed, the spacecraft would map the solar magnetic field in 3-D as well as helping us understand its origins.

But you knew there had to be more of an interstellar hook here. POLARIS (Polar Investigation of the Sun) would use a combination of a Venus gravity assist and solar sail propulsion to reach its 0.48 AU orbit around the Sun, with an inclination to the solar equator of 75 degrees. Two reference studies depict a sail varying in weight from 195 to 408 kilograms, with sail side length of, respectively, 153 meters or 179. Significant issues arise in considering these studies, one being the question of whether the sail should be deployed before or after the Venus gravity assist (if after, stowing the sail for six months could cause later problems).

Proposed solar sail

Paulette Liewer (JPL), Thierry Appourchaux (Institut d’Astrophysique Spatiale) and colleagues run through the options in a recent paper, with the significant note that the major challenge for the entire mission is the development and use of the sail. We need advancements in sail material, deployment, attitude and orbit control, the sail jettisoning mechanism and communications, which is why this mission catches the eye. Can an earlier GeoSail mission, a small 250-kg spacecraft with a 50 X 50 meter sail provide the essential shakedown to move some of these technologies forward?

Image: A view of the spacecraft with the sail deployed on its mast. The sail size is a square of 180 m while the spacecraft fits into a 2-m on a side cube. Credit: J.-C.Leclec’h.

Ultimately, of course, those of us who believe in sail technology hope to see sails taking us throughout the inner Solar System and used as an early boost for fast missions to the outer planets as well. Take the engineering to an extreme and we might someday envision ‘sundiver’ missions deploying a sail at close approach to the Sun for the kind of accelerations we can today only dream about. And there are, of course, those ‘lightsail’ ideas using beamed propulsion to get us to the stars.

All of which depends upon getting a sail, any kind of sail, operational in space for further study. No insurmountable difficulties stand between us and implementation of early sail missions, if we have the will to proceed with the necessary funding. So keep an eye on mission concepts like POLARIS, discussed in Appourchaux et al., “POLAR Investigation of the Sun – POLARIS,” accepted by Experimental Astronomy and now available online. Nor are we through with the Sun — I want to discuss Solar Probe+, a mission that will reach into the Sun’s corona, next week.