Wednesday, June 30, 2004

Putting on the Brakes...

We're only hours away from the riskiest part of the Cassini-Huygens mission to Saturn -- braking! The Cassini probe has been slowing down naturally for quite some time as it approaches aphelion in its solar orbit. All that's required now is a successful 96-minute main engine burn to reduce its speed enough to be captured into Saturn orbit. If all goes well, we'll have a treasure trove of science beamed back from Saturn during the next four years.

In the meantime, here is more of what Cassini has treated us to so far:
Rotating view of Titan
Titan! Saturn's largest moon is seen here in an animation of its rotation. This will be the destination of the Huygens probe when it detaches from Cassini in six months -- parachuting down into the atmosphere of one of the largest moons in the solar system.

And at this site, you can listen to Saturn's rotation as recorded by Cassini. Here are the radio emissions of charged particles interacting with Saturn's magnetic field, shifted into the frequency range detectable by the human ear. Using this method, scientists have determined the average rotation period of Saturn to be about 10 hours and 45 minutes. Strangely, this is six minutes slower than the measurements of the Voyager flybys over twenty years ago. Is Saturn slowing down?

Tuesday, June 29, 2004

Look homeward, angel.

Tom has us looking at Saturn from the Cassini spacecraft as it approaches the ringed planet. How about a look back our way.

The Sun is far and away the brightest non-Saturnian object in the sky, although nearly a hundred times less bright than it appears from Earth and ten times smaller. It blazes in a star-sprinkled sky in the constellation Sagittarius, near the edge of the Milky Way.

Earth is visible about a finger-span of your outstretched arm from the Sun's disk, a bit brighter than the stars of Orion's belt. Earth is presently on the opposite side of the Sun from Saturn, so we're looking upon its almost fully illuminated face.

Venus glows several times brighter than the Earth, even closer to the Sun.

Mercury -- barely visible to the eye -- appears farther from the Sun than Earth or Venus, but that is because of the alignments of the planets in their orbits on this particular day.

Mars floats in the Milky Way, on the edge of naked-eye visibility. We are seeing mostly its dark side.

Jupiter is brightest of all, about as bright as the brightest stars, about three handspans away from the Sun.

If you were aboard Cassini, looking back you'd surely feel a pang of separation anxiety.

Monday, June 28, 2004

Saturn Roundup

Chet's newest musing on the Cassini-Huygens mission to Saturn has been posted.

The Cassini probe begins its Saturn Orbit Insertion burn on July 1st -- a 96-minute firing of its main engine that will place Cassini in orbit around Saturn. This will be the first Earth spacecraft to make more than a passing visit to the Saturnian system.

One of the neat features of the Cassini website is the "Where is Cassini now?" page. I find the "overhead" image particularly striking. It gives you a hint of the majesty of Saturn and her many moons.

These images are generated by the Jet Propulsion Laboratory's Solar System Simulator. This is a terrific web app that can accurately simulate the view of any solar system body from anywhere else at any time. Be sure to check out the samples page as well. Tucked away there is a terrific animation of Cassini's arrival at Saturn.

China's Century

Wait'll you see the amenities the Chinese put on for the 2008 Summer Olympics, including the stunning Beijing stadium designed by Swiss architects Herzog & de Meuron. The Olympics will be an eye-opener for Americans, many of whom can't imagine that we might ever lose our place as the world's premier economy and scientific powerhouse.

When I was a kid we saved our pennies for the missions in China. When we wasted food our parents exhorted us to "remember the starving children in China." A far cry from the gleaming skyscrapers and traffic jams of present day Shanghai.

The 19th was Britain's century in science and technology. The 20th century belonged to America. Don't be surprised if the 21st century is dominated by China.

Friday, June 25, 2004

Little Worlds

Antoine de Saint-Exupery's Little Prince lived on an world so small he could watch a dozen sunsets in a single evening just by moving his chair westward around the circumference of his tiny planet. His planet had a few weeds and three volcanoes, two active, one extinct; the Little Prince kept the active volcanoes placid by periodic cleaning with a Q-tip sort of swab.

Cassini's photo of Saturn's outermost moon Phoebe (see below) reminds me a bit of the Little Prince's world, although Phoebe is rather larger.

It would be cruel to turn the cold eye of science on so charming a tale as that of the Little Prince. So I will not point out that his tiny planet would have too little gravity to retain an atmosphere, or for that matter a Prince. Or that so small a world would have insufficient internal heat to stoke a volcano.

Likewise Phoebe is a cold, stark, airless place, and we must wait till Cassini's Huygens probe descends into the atmosphere of Saturn's largest moon Titan before we start fantasizing about possible domiciles for extraterrestrial life.

Thursday, June 24, 2004

Phoebe Update

The initial analysis from Cassini's Phoebe flyby is in. As suspected by astronomers, Phoebe appears to be a Kuiper Belt Object, one of the "leftover bits" from the earliest period of solar system formation. Most of these small planetoids were flung out beyond the orbit of Neptune by gravitational interaction with the larger planets.

Phoebe, however, managed to stick around. She got herself stuck in a distant and eccentric orbit of Saturn and stayed there unheeded and undisturbed for billions of years. Last week, Cassini became the first Earth spacecraft to observe one of these planetary "oddballs" close up. Phoebe did not disappoint.

Wednesday, June 23, 2004

Mongo or Bust! -- Part 2

Speaking of Princess Aura and Ming the Merciless of Mongo, here are the three Laws of Alien Life I learned from the comics:

Law 1: All women on other planets are young, beautiful, and scantily clad, and all men are beastly, misshapen, or otherwise unattractive.

Law 2: The dominant creatures on other planets are always at a stage of evolution approximately the same as our own.

Law 3: All intelligent extraterrestrials speak English.

All three Laws have implications for researchers in the SETI (Search for Extraterrestrial Intelligence) project. No kidding! See my Intimate Look at the Night Sky, Chapter 11, in Books.

Tuesday, June 22, 2004

Mongo or Bust!

The comparison of Burt Rutan's spaceship to Flash Gordon's is an apt one. Flash Gordon first appeared in newspapers in 1934, at the height of what is now called the "Golden Age of Aviation." This was the era of Lindbergh and Earhart. It was the time where powered flight left its infancy and the possibilities of the future seemed limitless. The rickety canvas-covered biplanes of the First World War gave way to the sleek metal-skinned air racers of the 30s. The look of the Flash Gordon comics and serials was a futuristic reflection of this. Flash Gordon rocketed to the planet Mongo in a ship designed by the eccentric Doctor Zarkov. Yesterday, Mike Melvill rocketed to the edge of space in a ship designed by the eccentric Burt Rutan, hopefully ushering in a new "Golden Age."

It also should be noted that whereas many of the pioneers of spaceflight where sometimes nothing more than cargo aboard giant rockets, Melvill piloted his ship into space. SpaceShipOne was not computer controlled nor flying a preset course. Melvill was in control of the ship the whole way up and down. Even the control surfaces of the craft were triggered by simple cables rather than more sophisticated hydraulic systems. Back to the Future indeed...

Back To the Future -- Earth's Newest Astronaut, Part 2

What I love about Burt Rutan's space ship, the first private vehicle to escape the Earth's atmosphere, is the way it evokes the space ships of the old Flash Gordon comics. I grew up with Flash, before I ever heard of Robert Goddard or Werner von Braun. To me, Rutan's SpaceShipOne and the White Knight mother ship bear an uncanny resemblance to the craft that carried Flash to the planet Mongo, more so than to the monstrous Roman-candlelike rockets and tin-can modules that took Apollo astronauts to the moon.

This old Flash Gordon fan now has renewed hope that somewhere out there among the stars my first true love, the lovely Princess Aura, daughter of Ming the Merciless, awaits my coming. Rutan, save me a seat.

Earth's Newest Astronaut

Civilian test-pilot Michael Melvill made history today as the world's first privately funded astronaut. Melvill piloted the Burt Rutan designed SpaceShipOne to an altitude of 62.2 miles officially crossing the border into space. His sub-orbital flight is certainly a significant achievement in opening up public access to space. Within the next 50 years, adventurers will surely be traveling to the moon and back in much the same way today's thrill-seekers risk their lives on the summit of Everest.

Friday, June 18, 2004

How Far the Pleiades?

Tom's view of Saturn from Phoebe (thanks, Starry Night Pro) is gorgeous! It raises the question: Just how far away are the Pleiades, the most famous, and almost the nearest, cluster of stars.

The most direct way of measuring the distance to a star is the so-called method of parallax: the tiny shift in the apparent position of a star (against the background of more distant stars) when seen from different places in the Earth's orbit. Hold up you finger in front of your nose and look first with one eye, then the other. Notice the shift. The nearer your finger, the greater the shift. Ditto for stars.

However, stars are so far away compared to the size of Earth's orbit that this method traditionally worked only for some thousands of the nearest stars. At greater distances the parallax is too small to measure even with the best Earth-based telescopes, due to atmospheric blurring.

Enter the Hipparcos satellite telescope, launched in 1989 to measure stellar parallaxes from above the atmosphere. Hipparcos has obtained the distances of more than a million stars with unprecedented precision, including a distance for the Pleiades -- 385 plus or minus 13 light-years.

Alas, this is in conflict with another standard method for measuring distances to stellar clusters, called main-sequence fitting. This method uses the well-established relation between the color of a star in the prime of its life and the star's absolute or true brightness. A comparison of the absolute brightness of a star and its apparent brightness yields distance.

For the Pleiades, main-sequence fitting gives a distance of 430 plus or minus 13 light-years. Uh, oh!

If Hipparcos is right, and main-sequence fitting wrong, then our estimate for the size of the universe (which depends on main-sequence fitting for distant clusters) is in error, perhaps by as much as ten percent.

If Hipparcos suffers from some sort of systematic error, then its wealth of data is called into question.

Sorting out this discrepancy involves -- you got it! -- devising ever more exact and clever ways to measure the distance to the Pleiades. That little group of stars, which has fascinated stargazers from time immemorial, has a yet bigger role to play in our quest to measure the universe.

See Bohdan Paczynski, A Problem of Distance: Nature, 22 January, 2004.

Thursday, June 17, 2004

A Moon with a View

We've been enjoying the view from Cassini the past week looking in at Saturn's moon Phoebe. But what about the view from Phoebe? With the help of the sky simulation program Starry Night Pro, I created this view of Saturn from the surface of Phoebe. On this day, looking out into the Phoebean sky, Saturn is within 5 degrees of the Pleiades with Titan delightfully nestled nearby.
Saturn near Pleiades

Wow! -- Part 3

The Cassini space craft has sent back photographs showing boulders on Saturn's moon Phoebe!

These days Saturn is lost in the Sun's light, setting soon after the Sun. But it's out there, on the other side of the Sun from Earth and ten times farther from the Sun than Earth.

Almost every school room has a solar system poster with the planets lined up like soldiers on parade, or a dangling mobile with the planets jostling each other in the breeze. These illustrations do little to help a student comprehend the scale of the solar system or the emptiness of space.

To get a better idea of Cassini's feat, imagine the Sun -- our blazing star, nearly a million miles in diameter -- as a smallish grapefruit on the goal line of a football field. On this scale, Earth is a salt grain on the 10 yard line, and Saturn is a pea at the far end of the field.

In our football-field sized solar system, the Cassini spacecraft is infinitesimally small. (In real life, it is about the size and weight of a school bus.) It was not possible with existing rocketry to make Cassini move fast enough to travel directly to Saturn, at least not without taking decades to get there. So NASA engineers used a little orbital magic. Instead of directing the craft toward Saturn at launch in October 1997, they aimed for Venus -- in the opposite direction! The craft darted around Venus in April 1998 and got a gravitational boost of energy at the expense of that planet, like a stone whirled in a sling. It coasted out past the orbit of Earth, then fell towards Venus again, where it got another kick. By this time the spacecraft had made nearly two orbits of the Sun. It climbed again, away from the Sun, meeting Earth on the 10-yard line for another gravitational boost, then to Jupiter out there on the 50-yard line for one more increment of energy.

And on to Saturn.

The photos of Phoebe are spectacular, but equally spectacular is the finesse with which navigational engineers take advantage of gravitational assists to speed their craft on their way, looping and darting like swallows through the vast emptiness of the solar system. In the case of Cassini, the early flybys of Venus and the Earth provided the equivalent of 75 tons of fuel. After the initial launch towards Venus, only small adjustments to the trajectory were necessary to direct the craft towards its next rendezvous!

(See a NASA animation of Cassini's journey here. - 1.3MB MPEG file)

Give that dog a bone -- Part 2

OK, so a border collie named Rico can identify 200 toys by spoken word, or roughly the vocabulary of a 3 year-old human. Tom rightly wonders why a dog needs 200 toys. You might ask the same thing about three-year old humans -- my grandchildren, for example.

Does Rico's feat mean dogs are smarter than cats? As far as I know, no cat has demonstrated language responses remotely as numerous as Rico's. But as the bumper sticker says: Dogs have owners, cats have staff. What self-respecting cat would humiliate itself by running to fetch one of 200 toys to please some "owner's" ego?

With so little access to the inner lives of animals, it is exceedingly difficult to access language ability. Rico's talent is more than matched by chimps, and equaled by "bird-brained" parrots. Researchers have a long way to go before we understand fully even how human children acquire language.

Scientists spend a lot of time teaching experimental animals to run mazes and and other tricks of pseudo-human behavior; we force the animals into a human template, rewarding them with food when they conform or zapping them with an electric charge when they fail. It may be that we have more to learn from them than they have to learn from us.

For my money, one of the most engaging books I have ever read about animal communication is Alan Powers' Bird Talk: Conversations With Birds. Powers teaches English at Bristol Community College in Fall River, Massachusetts. He is an avid birder, scholar, poet, and knowledgeable musician, all of which he brings to bear on his topic. His little book doesn't provide answers to the deepest questions about animal communication, but it leaves the reader in little doubt that real, two-way communication is possible with other species.

Tuesday, June 15, 2004

Give that dog a bone

This is a story that's been getting a lot of play in the media lately. A border collie who can recognize the names of up to 200 different toys. Of course the question that scientists are unable to answer is why the dog needs 200 toys to begin with.

Monday, June 14, 2004

Wow! - Part 2

Close enough to see boulders on the surface of Phoebe.

Sunday, June 13, 2004

Voyager vs. Cassini

The last time Phoebe was imaged by an Earth spacecraft was Voyager 2 in 1981 from a distance of 2.2 million kilometers. The photo yesterday was taken at a distance of 77,441 kilometers. (Compare the two below) Cassini's closest approach of Phoebe was 2,068 kilometers. Those photos are yet to be released...

Saturday, June 12, 2004


Saturn's outermost moon, Phoebe, close up.

Thursday, June 10, 2004

Closing in...

Cassini is due to zip past Saturn's outermost moon, Pheobe, tomorrow afternoon. Perhaps a chance to view a Kuiper Belt object close up...