Having championed Webster Cash’s New Worlds Imager in earlier posts, Centauri Dreams was nonplussed yesterday to see NASA’s list of concept study selections for Discovery-class missions. Chosen for further work and 1.2 million in funding each were an asteroid sample return mission, a Venus orbiter, and a mission to produce a gravity field map of the Moon. New Worlds Imager was nowhere in sight.
NASA also chose three ‘missions of opportunity,’ meaning missions that can use existing spacecraft to produce new work. Out of these, the idea with most relevance to extrasolar work is Drake Deming’s Extrasolar Planet Observations and Characterization (EPOCh), which would use the high-resolution camera on the Deep Impact spacecraft to look for Earth-sized worlds around other stars.
Deming is a formidable player in the world of exoplanet detection (he was involved, for example, in the recent work on Upsilon Andromedae b) and we’ll be keeping an eye on EPOCh. But we’re also going to keep advocating Cash’s New Worlds Imager. The premise is to fly a starshade and separate telescope that would work in tandem (though separated by 15,000 miles) to detect planetary systems down to the terrestrial planet level. The daisy-shaped starshade could be a mere 50 meters in diameter yet capable of groundbreaking imaging, especially if the telescope using it were the James Webb Space Telescope, scheduled for launch in 2013.
That capability of double-duty for the Webb telescope should tempt NASA mission planners, who like to use existing equipment stretched into new applications. The current Discovery announcement includes another study that would use the Deep Impact spacecraft to perform a second cometary flyby, and a proposal for a flyby of comet Tempel 1 using the existing Stardust spacecraft to see what has changed since the Deep Impact mission’s visit in 2005. So Cash’s mission fits the budgetary bill (it’s a $400 million proposal) and is worthy of future consideration.
A recent Cash paper on the starshade is “Detection of Earth-like planets around nearby stars using a petal-shaped occulter,” Nature 442 (6 July 2006), pp. 51-53, with abstract available. As for the Discovery concept studies announced yesterday, one or more could be selected to move into a development stage after review; those decisions are expected next year. The budgetary benchmark for a completed mission is $425 million.
US readers should be aware of Monster of the Milky Way, a PBS program on Nova that’s scheduled to air tomorrow evening. It’s about the search for supermassive black holes in the center of galaxies and ties in nicely with this morning’s post on galactic jets. Those of you with high-definition sets are in for a treat, though you may wind up taping it if the doorbell gets active enough on Halloween. The show runs at 8:00 Eastern time.
M 87, an elliptical galaxy 50 million light years away in the constellation Virgo, houses a gigantic black hole. The object amounts to 3 billion solar masses and is apparently the source of the huge jet of particles and magnetic waves shown in the image below. That conclusion comes from work proceeding in Namibia as part of the HESS (High Energy Stereoscopic System) collaboration, where scientists have detected sudden changes in M 87’s emission of very high energy (VHE) gamma rays.
Image: The radio galaxy M 87 seen in visible light. The central region, from which the VHE gamma rays are seen, is located in the upper left part of the image and the relativistic plasma jet extends to the bottom right. Credit: Hubble Space Telescope (HST).
The variability in gamma ray emissions is interesting because it tells us about the size of the region producing the rays. There seem to be numerous ways to accelerate particles in a galaxy like M 87, but now we know that the actual source is an area about the size of our own Solar System. The conclusion seems clear: “This is not much larger than the event horizon of the super-massive black hole in the centre of M 87,” says Matthias Beilicke, a HESS scientist working at the University of Hamburg.
M 87 is a so-called radio galaxy, one that is bright in radio wavelengths and marked by powerful jets of plasma emerging from its nucleus. Exactly how the rays are produced remains enigmatic, but the process seems to be different from what we see in blazars, galaxies that are also sources of VHE gamma rays but whose jets are pointed towards Earth, their gamma rays boosted in energy and intensity by the jet particles.
In M 87, matter accreting around the black hole seems to be creating the plasma jet. The VHE gamma rays thus produced have energies a million million times that of visible light. Their association with the central black hole helps us pin down the options for the production of gamma rays in other radio galaxies.
Centauri Dreams‘ note: Blazars are tricky to study because the outflowing jet obscures astronmers’ view of the VHE gamma ray source. That makes M 87, with its jet pointed not at us but at a slant angle that allows observation, a unique testbed as we witness the violent processes of particle acceleration driven by the supermassive black hole at the galactic core.
The day the first Viking lander touched down on Mars is still fresh in my memory, particularly the early confusion about the real color of the Martian sky (which had seemed, by data misinterpretation, to be a rich blue). Then the excitement about possible life through experiments combing through the top few inches of Martian soil. Bob Schieffer announced there may be life on Mars — “no fooling”, said Schieffer with a delighted grin — on CBS news not long after, but later studies discounted the one experiment that might have detected biological activity.
Gil Levin, the scientist in charge of the disputed Viking experiment, still thinks it was successful. But other experiments could find no organic molecules in the Martian soil, an assumed prerequisite for life. Now a new paper argues that the Viking methodology was flawed. In fact, similar experiments don’t even find organic molecules in the Atacama Desert between Chile and Peru, where dry conditions seem conspicuously Mars like, and where experiments on remote life detection have continued at a robust pace. Yet updated testing reveals carbon at these sites.
And Rafael Navarro-González (National Autonomous University, Mexico) says in the new study that if the Viking scientists had known these results thirty years ago, they would have interpreted Viking’s work differently. Which is not to say that Viking detected life, but that we can’t discount organic molecules in the soil, which probably houses 1,000 times as many organic molecules as Viking data suggested.
Add to that finding Neill Reid’s recently published work on one-celled organisms from Antarctic lakes and we’re talking about living things in conditions that mimic what we should find on Mars. So let’s not rule Mars out; if bacteria can live almost two miles below the Earth in a South African gold mine, their presence tells us not to be too doctrinaire about what we consider a habitable environment.
The Wall Street Journal‘s fine science correspondent Sharon Begley goes still further in her latest entry:
Something else improves the odds that we are not alone: the building blocks of life are nearly as common in interstellar space as beer at ballparks. In August, astronomers announced they had found eight new biologically significant molecules deep in the giant clouds of gas and dust that spawn planets.
Although names like “methyl-cyano-diacetylene” might not evoke visions of whales or roses or other living things, these carbon-based molecules are the precursors to life. The new octet brings to 141 the number of different organic molecules found in interstellar space, all of which fall onto the surface of planets like seeds.
A universe seeded with life sounded preposterous not so long ago. Now the notion is gaining plausibility. It may take, as Gregory Benford reminds us, human feet on the ground on the Red Planet to conclusively make the call for Mars, but when and if we do find life there, the odds on other abodes in our own Solar System — and certainly around other stars — go up as well.
The COROT mission, to be launched in December, promises to move us to the next level of planetary detection. Devoted to studying exoplanet transits, in which a planet crosses the face of its star as seen from Earth, the space telescope will probably detect numerous ‘hot Jupiters.’ But an even more interesting possibility is rocky worlds in close orbit around their stars. And the thinking is that planets only a few times larger than Earth — and perhaps even smaller than that — will be within its reach.
Any star with a transiting planet will provide a telltale drop in light that, depending on the size of the planet and the distance of the star, may be measurable. But COROT (the acronym stands for Convection Rotation and planetary Transits) is most sensitive to rocky worlds in orbits of 50 days or less. If that sounds dismaying in terms of habitability, consider that a planet in such an orbit around a dim red dwarf could be located ideally within the star’s habitable zone. And red dwarfs comprise on the order of 70 percent of the stars in the Milky Way (excluding brown dwarfs).
Also under study is the intriguing field of asteroseismology. As sound waves ripple across a star’s surface, they produce variations in its light that help us understand the internal conditions of the star. Asteroseismology sounds exotic, but it’s already well established in the study of our own Sun. The Solar and Heliospheric Observatory (SOHO) has fine-tuned the method. Now COROT will target at least fifty stars for specific study in its examination of stellar evolution.
Launch is scheduled for the end of the year at the Soyuz-Fregat launcher at Baikonur, Kazakhstan. As we get COROT into space and anticipate the Kepler launch in October of 2008, it’s heartening to consider how far we’ve come. The earliest planetary detections were short period worlds; i.e., planets that completed their orbits in mere days. They’re easier to detect because they produce the strongest data signature, but long-period planets are a much harder catch.
Nonetheless, teams have been observing numerous stars in an attempt to build up enough data to detect such worlds, and the results are beginning to come in. That has opened up the study of multiple planets in systems already known to have one, and it begins to flesh out our picture of how planetary systems diverge. Moving into the era of small, rocky worlds has big implications as we hunt out possible havens for life. The bet here is that red dwarfs are going to prove fertile hunting grounds for planets of the right distance, size and composition. But finding an Earth-sized world around a Sun-like star remains the ultimate prize.