by Paul Gilster | Dec 31, 2004 | Outer Solar System
The dark terrain of the Cassini Regio on Iapetus will be the imaging target of the Cassini Saturn orbiter as it whisks past the moon at 2 kilometers per second later today. The Jet Propulsion Laboratory has released this map of the image coverage area. The regions Cassini will view at different imaging scales are shown within colored lines. These images were taken by Voyager in 1981; expect Cassini to deliver much better resolution, not only because of its superior optics, but also because of distance; Voyager passed Iapetus at over half a million miles, while Cassini will close to 76,700 miles (123,400 kilometers).
by Paul Gilster | Dec 31, 2004 | Astrobiology and SETI |
In The New and Improved SETI, the SETI Institute’s Seth Shostak weighs in on the Allen Telescope Array, the radio telescope installation that should give a boost to the SETI search as well as offering key research tools to more conventional astronomy. Shostak lists three advantages the ATA will offer SETI researchers, perhaps the most important being the array’s ability to make maps of the sky. “In other words,” says Shostak, “it’s like a radio camera, producing images.” Here’s his explanation of one ATA advantage:
…the ability to break up a large field of view into small (radio) pixels is also good for the SETI crowd. Consider this: you’re a radio astronomer, and your day job is mapping stuff like the Andromeda galaxy. You want your radio pixels to be in a regular, row-and-column matrix, like the members of a marching band. It’s a pixel arrangement similar to what your digital camera’s CCD has.
Fine. But for SETI purposes, you could spread the pixels around a bit, like a few grains of sand thrown onto a black piece of paper. The idea is to arrange those pixels to land on nearby stars – the very neighborhoods you wish to search for alien-generated signals. So now instead of having one soda straw to view the sky, you have a fist-full, each carefully aimed at a likely stellar system.
Another benefit of this capability is that, since these radio pixels are produced with computation, rather than being etched on silicon, you can make negative pixels – small patches of sky where you don’t pick up any signals. That’s useful not so much for blocking unsavory signals from tasteless extraterrestrials, but rather for blocking the interfering screech of our own, orbiting telecommunications satellites.
Shostak’s other points: ATA will offer an extremely wide field of view and will be far less expensive to build than a single, huge dish because the mass of steel needed to keep a big radio reflector from collapsing increases dramatically with size. Shostak says that ATA will grow to 33 dishes by spring; its first SETI assignment will be a slow scan of the inner regions of the Milky Way. “This is a test bed project certainly, but it’s also a valuable SETI experiment,” Shostak adds. “And as the ATA continues to expand, so do its speed and abilities.”
On the horizon for SETI: a new feed at the Arecibo dish will speed searches by seven times. And a Harvard instrument designed to look for extraterrestrial laser signals will soon add optical SETI to the repertoire.
by Paul Gilster | Dec 30, 2004 | Outer Solar System
Cassini’s post-Huygens separation maneuver occurred without incident on December 27. The course change was needed both to prevent Cassini from following the free-falling Huygens probe into Titan’s atmosphere and to set up the required positioning for communications between Cassini and Huygens during the latter’s atmospheric entry and descent.
Cassini will make a close pass of Iapetus on December 31, and it should be worth watching. Iapetus (pronounced eye-APP-eh-tuss) is the third-largest of Saturn’s moons, and it has already gained notoriety because of contrasts in its surface; one side is almost snow-bright, the other dark as tar. This has led to speculation that the surface is undergoing continual resurfacing due to processes that have yet to be identified.
Above: Images obtained using ultraviolet (centered at 338 nanometers), green (568 nanometers) and infrared (930 nanometers) filters were combined to produce the enhanced color views at left and center; the image at the right was obtained in visible white light. The images on the bottom row are identical to those on top, with the addition of an overlying coordinate grid. Credit: NASA/JPL/Space Science Institute
The images above are the best yet obtained for Iapetus. Note the impact craters in the bright areas and the transitional zone between bright and dark. A line of mountains appears in the images to the left (also on the eastern limb in the images at the right). According to this JPL press release, “These mountains were originally detected in Voyager images, and might compete in height with the tallest mountains on Earth, Jupiter’s moon Io and possibly even Mars. Further observations will be required to precisely determine their heights. Interestingly, the line of peaks is aligned remarkably close to the equator of Iapetus.” Current thinking at the Jet Propulsion Laboratory is that the circular feature in the southern hemisphere is an impact crater.
JPL offers a Iapetus flyby simulation here.
by Paul Gilster | Dec 29, 2004 | Astrobiology and SETI
290 miles northeast of San Francisco, the University of California at Berkeley and the SETI Institute are building an observatory for galactic and extragalactic radio astronomy at Hat Creek. The Paul Allen Telescope Array (ATA 32), named after Microsoft co-founder Paul Allen, who is a major donor for the project, is to consist of 350 networked 6.1-meter radio dishes spread out along 2.6 acres on the property. In addition to breakthrough radio astronomy, ATA 32 will enable the most comprehensive search for intelligent extraterrestrial signals (SETI) ever attempted.
According to this Lab Note by David Pescovitz at Berkeley’s College of Engineering , the Allen Telescope Array will speed up the SETI search by a factor of 100. Significantly, the system is designed so that astronomers can do other radio astronomy while the SETI search proceeds. Pescovitz quotes William “Jack” Welch, a UC Berkeley professor of electrical engineering and astronomy who holds UC Berkeley’s first Chair in the Search for Extraterrestrial Intelligence: “SETI is admittedly a long-shot…I don’t have the patience to do only that, so it appeals to me to have a steady flow of other data for us to study as well.”
Image: Three prototype radio dishes now in place at Hat Creek Observatory in northern California. By 2007, 350 of these 6.1-meter-diameter dishes will be assembled to form the Allen Telescope Array, the largest radio array in the world. Credit: Radio Astronomy Laboratory.
Which is putting the issue mildly, for the odds against a SETI detection are immense. Centauri Dreams is an advocate of SETI as long as donors with deep pockets can be found — as is the case here — and only if the instruments used are capable, as Hat Creek will be, of tandem work, expanding our knowledge of the universe through more conventional radio and optical observations. The latter is far more likely to yield substantive results, but the implications of a successful SETI hunt are significant enough to justify continuing that effort when possible.
From an astronomer’s point of view, the Hat Creek observatory offers key advantages. It will be capable of studying transient events like supernovae and gamma ray bursts through the whole sky on a nghtly basis. And the range and flexibility offered is immense. From a useful backgrounder on the project:
The telescope will have unprecedented sensitivity over a large range of wavelengths centered in the centimeter radio band, spanning the equivalent of about four and a half octaves, whereas most radio telescopes span less than half an octave and optical telescopes span perhaps one or two. The wavelength range stretches from 2 to 50 centimeters, including the important 21.1-centimeter radio emissions of cold hydrogen that have allowed astronomers to map the Milky Way galaxy’s spiral arms.
Three prototype dishes are currently in place at Hat Creek, but several dozen more should be operational by summer of 2005. The observatory’s scalable design allows serious astronomy work to begin almost immediately, though at a much lower resolution than will one day be available.
by Paul Gilster | Dec 28, 2004 | Asteroid and Comet Deflection, Outer Solar System
The possibility that a near-Earth asteroid might strike the planet in 2029 has now been ruled out. Asteroid 2004 MN4 had attained press prominence when it emerged that the 400 meter object would pass near the Earth on April 13, 2029, with the odds on impact rising to 1 in 300. That alone made for the kind of story the media love to flog, but the reality all along was that new data about the asteroid’s orbit would probably rule out the possibility of impact.
And that is just what has happened, thanks to the work of Jeff Larsen and Anne Descour of the Spacewatch Observatory near Tucson, Arizona. By studying archival images of the object, they were able to extend the observational time available to scientists, improving knowledge of the orbit of 2004 MN4 enough to fix its position in space in 2029. The final position is shown in the diagram, with alternate positions ranging through the white line that intersects the projected orbit of the asteroid. It’s a close call, but not a disastrous one. You can look at a risk analysis for 2004 MN4 at the Near Earth Object Program site.
Centauri Dreams‘ take: Near-Earth asteroids (NEAs) are unlikely short-term threats but likely long-term ones. In other words, the longer we wait, the more likely an impact will eventually occur. As an advocate of long-term thinking, Centauri Dreams would prefer to look out 100,000 years, and not rest complacent with the thought that we’re probably safe for the next hundred. In any case, these objects are tricky; the orbit of 2004 MN4 itself will be altered by its near-earth encounter, leading to less certainty about its future position post 2029.
All of this makes the development of a space-based infrastructure extending into the outer Solar System a simple matter of species survival. If 2004 MN4 had been shown to be a likely candidate for impact, could today’s technology stop it? The best place to deflect such threat is the furthest possible distance from Earth, when a small nudge can have big orbital consequences. We’ll need to be able to travel those regions in the Solar System from which stray asteroids may emerge in plenty of time to nudge them into safer orbits, and that means continuing work on advanced methods of propulsion.
Image Source: Jet Propulsion Laboratory
