- News Home
5 December 2013 11:26 am ,
Vol. 342 ,
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
- 5 December 2013 11:26 am , Vol. 342 , #6163
- About Us
On Mars, No One Can Hear You Scream
12 June 2006 (All day)
Sound dies quickly in the cold, thin air of Mars. Researchers have modeled a sound wave traveling through the Martian atmosphere and report that it doesn't go far--even a lawn mower's roar dies after a hundred meters or so. The model presents an unusually detailed picture of how sound travels in an alien atmosphere and hints at what it would take to communicate on the Red Planet.
The shriek of a baby, an ambulance's siren, or a violin sonata are all essentially the same thing: waves of pressure traveling through the air. Sound can also travel through water, or a solid like the ground, but because molecules must bump into each other to propagate the pressure wave, the denser the medium the better. Hoofbeats or footsteps travel farther through the ground than through the air, for example, because the molecules in air have to travel further to bump into one another than those in soil, thus losing energy more quickly.
The Martian atmosphere is mostly carbon dioxide and only 7% as dense as Earth's is, so sound should fade more quickly. But the details of how sound waves travel in the Martian atmosphere were unclear and could be important to future Mars missions.
Now, a computer model has given a molecule-by-molecule map of how sound moves on Mars. Graduate student Amanda Hanford and physicist Lyle Long of Pennsylvania State University in State College presented the model last week at a meeting of the Acoustical Society of America meeting in Providence, Rhode Island. The model is unusual in its molecular approach; most acoustical models of sound treat the medium it travels through as a continuous block with average properties. Such models are fine for dense atmospheres like Earth's, but treating the air like a loose bunch of freewheeling molecules is more realistic for Mars' rarefied atmosphere, say the researchers.
Hanford and Long first set up a virtual "box" filled with about 10 million carbon dioxide molecules floating about randomly, at the same density as the Martian atmosphere. A sound wave then appeared on one side of the box, and the model calculated its progress across to the other side, computing nanosecond by nanosecond exactly how the carbon dioxide molecules bumped and moved. The results show that a noise that would travel several kilometers on Earth would die after a few tens of meters on Mars. Quieter sounds would travel far shorter distances, making eavesdropping on a quiet conversation nearly impossible.
Henry Bass, a physicist at the University of Mississippi in Oxford, notes that if people ever go to Mars and want to communicate audibly, they'll need to design devices that can work with the lower frequencies transmitted by the Martian atmosphere.