Periodic Impact Events: A Critique

One of the more intriguing issues for the Wide-field Infrared Survey Explorer (WISE) satellite is the question of nearby objects that might be causing problems with the Oort Cloud. Specifically, we're interested in learning whether an object like the hypothesized 'Nemesis' -- a tiny companion star to the Sun -- or a closer gas giant ('Tyche') -- might cause disruption to cometary orbits that would create episodes in which more comets than usual make their way into the inner Solar System. Find such an object and you may be able to explain what some have been arguing, that there are periodic variations in the timing of giant impacts, a regular and revealing pattern. Of course, periodic changes in the frequency of impacts could be caused by something other than a companion star or unknown planet. Another suggested mechanism is the motion of our Solar System through the main plane of the Milky Way, causing the gravitational influence of nearby stars to tug on Oort Cloud comets on a...

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Vesta: A New World Being Revealed

Considering the nature of the Dawn spacecraft's slow, spiraling entry into orbit around Vesta, it's a little unclear precisely when orbital insertion was, but NASA is pegging an approximate time of 0447 UTC on July 16. The event is leading to closer and better imagery all the time, the example below being the first full-frame image, taken from the spacecraft's framing camera on July 24. Here we're looking at the asteroid from a distance of 5200 kilometers, seeing for the first time the kind of surface detail that has long been hidden from even the most powerful telescopes. Image: NASA's Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Dawn's principal investigator Chris Russell (UCLA) likes what he sees: "We have been calling Vesta the smallest terrestrial planet. The latest imagery provides much justification for our expectations. They show that a variety of processes were once at...

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A Swarm of Probes to the Stars

Just how big does a spacecraft have to be to do productive work? It's a provocative question in this era of CubeSats and downsized budgets, but when you start thinking interstellar, there are even more reasons to wonder how small you can make your vehicle. After all, the propulsion challenges facing interstellar missions are profound, and the more mass (including, of course, the fuel you're carrying), the greater the problem. The rocket equation is telling, and one of the many things it tells us is that trying to reach a nearby star with a conventional rocket is out of the question, at least if you're hoping to get your mission there in a reasonable century or so. Mason Peck has been pondering issues like this for a long time. Those of you who are unfamiliar with his work at Cornell can catch up by reading earlier Centauri Dreams posts, but a more current solution is the article Exploring Space with Chip-sized Satellites, which runs in the current issue of IEEE Spectrum. In it, Peck...

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Charter

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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