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Slow spaceships and neck bones galore

Q: How long would it take earth's fastest space ship to reach Proxima Centauri? (Jeff, Cedar Rapids, Iowa)

How our Sun would appear looking back (through a high-powered telescope) from the night skies of our nearest star. [Scott Tucker, Dark Sky Images]

A: Traveling at her top speed (38,000 mph, 17,000 m/s) the Voyager 1 space probe, our fastest interstellar spacecraft, would reach our next nearest (after Sol) star in 74,000 years.

However, in 2010, we plan to launch a space sail  that will zoom five times faster than the Voyager probe. A rain of solar photons pelts the sail to give it a steady acceleration and faster speeds eventually. Still slow, though, relative to star travel.

Light, hurtling at 600 million mph (1.1 billion km/h), zips to Proxima Centauri in 4.2 years.

Voyager, our fastest spaceship, goes about 1000 times faster than the fastest horse. Humans went from horse speed to Voyager speed in about 200 years. The speed of light is 16,000 times the Voyager’s speed. Of course, we can never reach the speed of light but maybe 50% is doable. At that speed, it would take 8.4 years to reach Proxima Centauri. Maybe, someday...

Four of our probes are heading toward stars now, says Jeff Scott, aerospace engineer of aerospaceweb.org. Pioneer 10 will pass close to the star Aldebaran in the constellation Taurus in about 2 million years. Pioneer 11 heads toward the constellation Aquila and will near it in 4 million years. Voyager 2 zooms towards the brightest star in our skies, Sirius, and will get there in about 300,000 years.

The Voyager space probes splitting for the stars. [NASA]

Voyager 1 now is the farthest human-made object from the Sun. Both Voyager probes will continue to transmit signals until about 2020 when their power runs out. By then they will be 10 billion miles away — nearing the end of solar wind, the beginning of interstellar wind, and crossing the final frontier to interstellar space.

Further Surfing:

AerospaceWeb.org: Interstellar spacecraft: shows our four probes shooting off to the stars

NASA: Voyager approaching the end of our solar system, animations, still photos, discussion

NASA: Voyager interstellar mission

The Electronic Sky: Alpha Centauri

Q: In a recent question, you stated that almost all mammals have only seven neck bones. What about non-mammals? Do they have seven, too? (Bob, Marietta, Georgia)

A: Not necessarily seven. A swan has 22 to 25 neck bones, a duck 16, and a fish none.

These young trumpeter swans stretch their 23-bone necks. [US Fish & Wildlife Services]

Apparently, though, the jury is still out about the number of fish neck bones. "Some people think there are two cervical vertebrae," says Frietson Galis, biologist at the Institute of Biology of Leiden University in The Netherlands. "Other people think they don’t have any."

All amphibians have only one. As fish evolved to a land animal, the first bone in their spine changed to allow their heads to move up and down. This vertebra supports a one-bone neck. Modern toads and frogs still have only one neck bone.

Some reptile species always have the same number of neck bones. Others not.

A turtle always has eight and can bend its neck into an S-shape for pulling its head into its shell. Crocodiles always have nine. Reptiles, in general, have various numbers, depending on their life-styles. Lizards are "quite variable" and so were dinosaurs, says Galis. The plesiosaur and sauropod dinosaurs had 30 to 50 neck bones!

Pythons have only one neck vertebra out of a total of over 300 vertebrae. All the rest have attached ribs and form an unusual trunk — one long, skinny rib cage.

Reptiles and birds do have a Hox gene that controls neck bone development in the embryo. In mammals, this gene, if changed, can mess up the nervous system or cause cancer. But, apparently changes in the Hox gene don’t harm birds and reptiles. From zoo studies, we know that cancer rates in birds and reptiles are low, compared with mammals.

Reptiles have a slow metabolism rate, which might explain why their cancer rate is low since metabolic wastes can damage DNA and cause cancer. Birds, with their high metabolic rate, are a different story. Apparently, they catch cancer mainly through viruses, so changes in the Hox gene are irrelevant.

Further Reading:

WonderQuest: Only 7 mammalian neck bones

(Answered April 29, 2005)