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10.24.2005

Ice Beneath Mars Is Asking, "Can You Hear Me Now?"

This picture shows a close-up view of an antenna that is a circular apparatus made out of intricate wiring that looks like a gigantic industrial fan. The camera angle is from the ground looking up, and the far right and far left curves of the antenna are not visible in the picture. Three 6-meter (20-foot) long, white metal beams jut off of the middle of the antenna in a tepee shape, pointing out and up to the sky. The triangular beams intersect at a point at the top center of the image right where the midday sun beams brightly in a white, glowing circle the size of a quarter. A clean, blue sky covers the background of the entire image and can be seen through the wire mesh antenna.
Nestled in the foothills of Stanford University, SRI International's 46-meter (150-foot) radio telescope works in tandem with the Odyssey spacecraft to study the subsurface of Mars.
Image credit: NASA/JPL
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In August 2003, as the twin Mars Exploration Rovers were barreling toward Mars in their flying saucers, scientists and engineers sent a radio signal disguised as the rovers’ "voice" to the Odyssey orbiter at Mars. The call to Odyssey was what Dr. John Callas, Mars Exploration Rover Science Manager, defines as a "can-you-hear-me-now?" test. Scientists and engineers wanted to ensure the UHF (ultra-high frequency) radio system on Odyssey, a primary communications relay between the rovers and Earth, would work. Odyssey responded with a resounding yes, and something else from Mars responded too….

Hearing Unexpected Echoes In The Noise

When the first, clear "I-can-hear-you" reply beamed back from Odyssey, modest high-fives and conservative cheers were exchanged amongst the small team of PhDs huddled around a computer near a 46-meter (150-foot) antenna at Stanford University known locally as the "Dish." SRI International manages the radio telescope, the only deep space antenna near the Jet Propulsion Laboratory that can send UHF radio waves from Earth to Mars. As each new line of relay test data streamed down to the computer screen at the Dish, Stanford University's Dr. Ivan Linscott began to mutter, "Huh…what's that?…that's strange."

This graphic shows a technical chart with a thick straight vertical red line outlined in yellow in the first third of a fuzzy green and blue square. A very faint yellow line curves to the left of the red line. To the right of the chart is a color key, with signal strength numbers noted in decibels (dB) and corresponding with colors (red equals high, blue equals low).

The solid red line in this data stream indicated Odyssey would be able to hear the rovers loud and clear and that the orbiter successfully passed the relay communications test to SRI's antenna, which sent a rover-like signal to Odyssey. The faint, curved yellow line later became known as the "Lucky Stripe."

Image credit: NASA/JPL

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A peculiar stripe on the data-return-screen was arcing underneath the straight line that represented the primary communications from Odyssey. The mysterious curve then intersected the primary line, and stopped sending data at the same time the main signal disappeared. The team initially dismissed the strange line as signal noise that engineers term "radio frequency interference" (RFI). But the curved line of data has now earned the title, "Lucky Stripe," and the so-called static has become the subject of the "Mars Bi-Static UHF Radar Experiment."

Experiment Is Like A Fun House Mirror

This picture shows a man smiling at the camera, tilting his head, and leaning his arm on a high shelf next to a globe of Mars. John is about 40-years-old, trim, has short dark brown hair, and is clean-shaven. He wears a grey dress shirt with a rover logo above the right pocket.

Dr. John Callas, Mars Exploration Rover Science Manager and Mars Bi-Static UHF Radar Experiment Principal Investigator.
Image credit: NASA/JPL

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After a week of studying the stripe, the team discovered that the extra data was actually a reflection from the surface of Mars. "Anyone who's used rabbit ears to pick up a television signal has probably seen a ghosting effect - a signal echo," explains Callas.

The ghosted image arrives off-center and is more transparent because the source signal hit some neighboring wall or structure and then bounced back to the TV receiver a little later and more scattered. The Lucky Stripe is a reflection of the martian surface, and the stripe is curved because the Odyssey spacecraft was traveling in an arcing orbit over the planet as the echo from the surface of Mars reverberated back to Earth.

"Just like a distorted reflection in a fun house mirror tells you something about the mirror's shape, radar reads an echo of the surface of Mars that tells us about the shape of the surface it's reflecting," explains Callas. The team later confirmed multiple reflections, which suggests they are seeing "echoes" of material beneath the surface of Mars.

This image shows three people in an industrial-looking room, with floor to ceiling computers, wires, and machine racks. Dr. Cousins stands behind Dr. Ivan Linscott and Hrefna Gunnarsdottir who are both sitting. Dr. Cousins is smiling as he looks at a computer screen in from of Dr. Linscott. Dr. Cousins has dark brown hair and wears a green and white plaid short-sleeved shirt and black jeans. Dr. Linscott has bushy grey hair, a grey mustache, and wears a light blue dress shirt and tan slacks. Dr. Linscott is moving a mouse as he looks intently at a computer screen. Hrefna smiles brightly into the camera as she sits holding her own black camera that is strapped around her neck. Hrefna has blond hair pulled back and wears a light turquoise sweater and light tan pants.

SRI team members operating "The Dish" in northern California. From left to right, Dr. Mike Cousins, Dr. Ivan Linscott, and Stanford graduate student Hrefna Gunnarsdottir.

Image credit: NASA/JPL

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Expanding Science Using Current Resources

Fast-forward to October, 2005. The bi-static radar experiment team, led by Callas, is now using the Odyssey UHF radio system and SRI's antenna to hunt for subsurface water ice – a key component to understanding the history or future of life on Mars. Timing is best now as Earth and Mars merge toward a close approach on October 29, 2005 and UHF radio signals become stronger and take less time to travel between the planets. Scientists are hoping to find unexpected treats in the form of "noisy" radar tricks from now until just past Halloween.

This bonus science is possible because the communications team didn't disregard the "noise" from the original test and later NASA support for the discovery. "This simple, inexpensive technique utilizes resources that are already in place," explains Callas. The NASA-funded experiment is a collaboration between JPL-Caltech, Stanford University, and SRI, and uses antenna-scheduling resources and communication protocols already in place to support the rover mission.


--->

This image shows Byron Jones, a 25-year-old man, wearing a yellow short-sleeved polo, jeans, and glasses. Byron has short brown hair, and he is looking and pointing at a timeline chart that is projected on a large screen. Byron uses a three-foot wooden stick to point to an area on the top of the timeline.

Byron Jones discusses resource sharing for the bi-static experiment at a Mars Relay Team meeting.

Image credit: NASA/JPL

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Rover Mission Planner Byron Jones reflects the mindset of various Mars experts who have helped the experiment succeed. “There’s a real sense of community during our Mars Relay meetings as various missions work to share memory space on Odyssey so the bi-static experiment can operate,” says Jones. When Mars is whispering, “Can you hear me now?” through cryptic radio echoes, all of the mission teams can't help but eagerly listen.

To learn more about two other radar experiments for Mars, please see:

MARSIS

SHARAD


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