The Beagle 2 lander carried a suite of instruments to search for evidence of past life on Mars. Here's an artist's idea of how it would look in action.

European Space Agency (ESA)

Europeans used the honkin-huge Jodrell Bank Observatory in the UK to listen for the bark of their stray Beagle.

European Space Agency (ESA)

The dog in question is Beagle 2, a Mars lander that jumped off Mars Express, the mother spaceship, and began sniffing its way down toward to the Red Planet. Beagle 2 is named for Beagle, the ship that carried Charles Darwin on his epochal voyage of discovery in the 1840s.

While Mars Express remains healthy, a thunderous silence continues on the radio frequency that should be carrying Beagle 2's whimpering: "I'm staying, like you told me, boss. But I ate that whole box of dog biscuits in the back seat on the drive over here. What am I supposed to do now?"

Ambitious science goals
What Beagle 2 is supposed to do is look for signs of past life on Mars, such as the presence of water (necessary for all known forms of life) and carbonate minerals or organic compounds, which are often made by organisms. The long-distance hound was also going to measure chemicals in the atmosphere, and temperature, pressure, wind and dust.

A record of failure
If Beagle 2 proves to be a dog of a spacecraft, it will join a long line of Martian mishaps. Two-thirds of Mars missions have flopped, according to the New York Times, which pointed out that, "Only one of the six attempts by Russia to land there made it, and that craft ceased transmissions 20 seconds later."

The United States succeed in with two Viking landers, (1976) and the robotic breadbox Sojourner, which rolled across the planet in 1997. But in 1999, Mars Polar Lander and Mars Climate Orbiter both croaked. Just two weeks ago, Japanese controllers quit trying to redirect a straying spacecraft that was supposed to study Mars and two small moons.

The scent of a failure
What, we wonder, could be dogging Beagle 2, the mutt on Mars? The Why Files asked Sanjay Limaye, a senior scientist at the University of Wisconsin-Madison Space Science and Engineering Center, to speculate on the source of Beagle 2's blues. He focused on the landing system, complexity and communications.

Like Sojourner, Beagle 2 was supposed to bounce down to a landing inside protective airbags. While that sounds simpler than slowing the descent with rockets, it's tricky. Limaye says he heard from an aerospace contact that Sojourner had 28 "single-point failure modes."

To understand this concept, consider your car. If the brakes go bad, the failure will probably affect only one of two separate braking lines, leaving half the normal braking power (plus the parking brake) intact. But if you yank off the steering wheel, your goose is cooked. There is no substitute for this single-point failure mode.

Problems can also arise from complexity. As the masters of Beagle 2 liked to brag, their craft had an extraordinary ratio of science instruments to mass. "It had a greater density of scientific instruments than other spacecraft, suggesting that it was extremely ambitious," says Limaye. "I'm totally bewildered by the descriptions of instrumentation, a drill, spectrometers, a corer. It looks way too complicated... I think Beagle 2 was a long shot to begin with."

Complexity can matter most during descent, when things suddenly start to happen in a hurry after a long, languid cruise through space. The doomed Polar Pathfinder, he notes, tried to control 12 rockets during descent. "It was so crazy to process that kind of information in real time, it requires a lot of gumption, brute force computing, and I don't think it had it." A spike in the incoming data rate may have confused the computer, which shut down the rockets too soon, Limaye says. "It basically fell like a rock."

Barking mad!
The malignant record of mangled Martian missions has caused changes in American spacefaring techniques, Limaye says:

• Better knowledge of spacecraft position, produced by triangulating from two giant radio telescopes, should improve the odds of landing. The doomed Mars Climate Observer crashed because it came in too low, Limaye says, probably because engineers didn't know its true position.
• Precise positioning should also simplify communications: Because Mars is moving relative to Earth, radio waves are altered by the Doppler shift. "You know what frequency you want to use to transmit and listen," says Limaye, "but you must account for the Doppler shift caused by the rotation of planet, and that depends on where it lands."
• Future landers' low-gain antennas will transmit during entry, helping engineers track events in case of a flub-up.
• Automatic analysis of photos will enable landers to slow their speed across the landscape, helping them land on target, locations chosen (no surprise) for their flat, non-threatening terrain.

In the meantime, as the Brits listen for the bark of their Beagle, Mars Express, the spacecraft that carried the leashed hound to Mars, is healthy enough. And that's good news to Limaye and others who are working on Venus Explorer, which will use similar technology while orbiting the planet named for the Greek goddess of love.

Hot planet of love
Venus is a strange place. With a surface temperature of 950 degrees F, it's much hotter than its distance from the sun would suggest. Credit the cooking to a runaway greenhouse effect: As the planets rocks warmed, they released carbon dioxide, which in turn caused further warming.

Studying Venus could shed light on a doomsday greenhouse scenario on Earth: If warming causes the release of methane and carbon dioxide from soil, seabed and tundra, the gases could intensify the greenhouse effect, causing the release of yet more greenhouse gas.

"I'm not suggesting we are going to get that hot," says Limaye, "but there is a warning here." Venus Express, scheduled for launch in 2005, will not carry dogs - or any other landing craft. Given the current situation on Mars, that may be just as well.

For now, we'll just hope that the dog days on Mars are a temporary setback, and that the baying of a tiny spacecraft will soon be transmitted across millions of miles of empty space.

Read more about spacecraft snafus.