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Notes & Queries 12/06/08

Those of you who missed Tau Zero founder Marc Millis’ appearance on the History Channel the other day will get the chance for repeat performances on Tuesday the 9th at 8 PM EST and Wednesday the 10th at 12 AM. The show, called Light Speed, discusses the nature of light in the context of astronomical history, and goes on to consider it in relation to travel — will we ever break the light ‘barrier,’ or is c the ultimate constraint on our space journeys? Here’s the channel’s description:

According to the laws of physics we can never travel faster than the speed of light…or can we? Light speed allows us to see things instantly here on Earth, and shows us the entire history of the universe going back nearly 14 billion years. Learn all about light speed, the ultimate constant in the universe and discover ways scientists envision breaking the “light barrier” which may be the only way the star travel of our imaginations ever comes to reality.

We could have wished to see more of Marc, whose interview was squeezed into the end of the show, but what a pleasure to view the Tau Zero logo on-screen as we continue to tune up the TZF site.


Also intriguing for interstellar mavens is Journey to the Edge of the Universe, running Sunday December 7 at 8 PM EST on the National Geographic Channel. This one is a tour of the cosmos using spectacular animation to take you places — newly forming stars, black holes, distant galaxies — that science is helping us to understand in greater detail than ever before. Check the remarkable trip to the surface of Venus, for example, and the view of Triton’s surface. This YouTube video offers an interview with director Yavar Abbas on the challenges of integrating computer effects with the data from our telescopes to create the journey. Wisely, I think, the decision was to go with straight animation coupled with rigorous adherence to current theory.


Do we have a visitor from another star in our own Solar System? That’s one possible explanation for comet 96P/Machholz 1, whose chemistry sets it apart from the 150 other comets studied by Lowell Observatory astronomer David Schleicher. The molecule cyanogen (CN) is off the cometary average by a large amount, only one percent of what we would have expected. Machholz 1 is also depleted in C2 and C3 carbon, but the CN depletion is striking. No other comet has exhibited any CN depletion at all, much less this amount.

Says Schleicher:

“A large fraction of comets in our own Solar System have escaped into interstellar space, so we expect that many comets formed around other stars would also have escaped. Some of these will have crossed paths with the sun, and Machholz 1 could be an interstellar interloper.”

Other explanations are plausible, including the idea that the comet formed much further from the Sun than any other comet we’ve studied. Another possibility: Machholz 1 saw its chemistry altered by extreme heat. Because its orbit takes it well within the orbit of Mercury, and every five years at that, the repeated and frequent temperature changes could contribute to its composition. “However,” adds Schleicher, “the only other comet to show depletion in the abundance of CN did not reach such high temperatures. This implies that CN depletion does not require the chemical reactions associated with extreme heat.”

Bear in mind that before Machholz 1 revealed its secrets, we were working with two classes of comets based on their composition. The typical comet is thought to have come out of the Oort Cloud to move into the inner system, but to have been formed in the region of the giant planets, with some members of the group coming from the Kuiper Belt. But a second class of comets is known as ‘carbon-chain depleted’ — depleted in C2 and C3 like Machholz 1 — with orbits consistent with arrival from the Kuiper Belt. So the depletion may be the result of conditions in the places where the comets formed, perhaps farther out in the Kuiper Belt. Machholz 1’s unusual CN depletion sets it apart from either class, leaving us to wonder about celestial interlopers and the frequency of their journeys between the stars.

The paper is Schleicher, “The Extremely Anomalous Molecular Abundances of Comet 96P/Machholz 1 from Narrowband Photometry,” The Astronomical Journal 136 (November, 2008), pp. 2204-2213 (abstract).

Comments on this entry are closed.

  • andy December 6, 2008, 16:46

    Regarding interstellar comets, what are the predictions about the number of comets on hyperbolic orbits we should have seen by now?

    As for matter from other star systems making its way to the solar system, you might be interested in the Beta Pictoris dust stream, which is apparently the main source of interstellar meteoroids in our solar system. There are several papers about this, the discovery paper being Baggaley (2000), Journal of Geophysical Research vol. 105, pp 10353-10362.

  • Administrator December 6, 2008, 17:17

    Thanks for this tip! Baggaley’s paper is completely new to me; I’ll check right into it.

  • djlactin December 6, 2008, 21:52

    The observation that this comet appears to have originated in the Kuiper belt leaves me skeptical that interstellar origin is plausible. I would think that an interstellar interloper would be on a hyperbolic (or at least, parabolic) trajectory and at an inclination unrelated to the ecliptic. Interstellar origin means that we must postulate that it was first captured by Sol and entered an orbit within the Kuiper belt, then later perturbed into a short-period orbit (at least twice: once into an ellipse with its aphelion in the belt, and then again into a 5?-year orbit). This series of events is very unlikely. (I understand that all events are ‘unlikely’!)

    I think that a more mundane origin will be shown to be more plausible.

  • Usman December 8, 2008, 8:15

    With the exception of Michio Kaku, the people interviewed in “light speed” were totally irrelevant. It seems as if it was your typical relativity class where emphasis was on teaching the constancy of speed of light than any proper discussion of how to circumvent it. The program also concluded in a pessimistic way, laying emphasis on preserving earth rather than pushing the limits of possible and if purpose was to educate people about the connection between space travel and speed of light, the conclusion they would come to is, “forget it kid”.