New Telescope is Upside-Down at the Bottom of the Sea


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	New Telescope is Upside-Down at the Bottom of the Sea By Robert Roy Britt Senior Science Writer posted: 07:00 am ET 19 March 2003

On Monday, a submarine in the Meditexxx Sea attached the first of 10 strings to a fiber optic cable on the sea floor, beginning construction of an underwater "telescope" that will study mysterious particles that originate in deep space

Construction got serious this week on a newfangled telescope that wafts in the currents near the bottom of the Mediterranean Sea and points downward.

It is no accident. The telescope's array of detectors, strung along 1.5 miles (2,400 meters) of seafloor, will search for particles so physically inconsequential they pass right through the Earth, yet so theoretically important they could reveal what's going on in the hearts of the most energetic objects in the far corners of time and space.

The project, called ANTARES (Astronomy with a Neutrino Telescope and Abyss environmental RESearch), will hunt for evidence of elusive neutrinos crossing space and passing right through the planet. These elementary particles are thought to originate in supernovae, gamma-ray bursts and the activity surrounding black holes.

Images

An artist's rendering of the completed ANTARES telescope array.

Some neutrinos (red) are converted to a shower of muons, which emit blue light that ANTARES will look for.

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On Monday, March 17, a submarine attached the first of a series of heavy-duty "strings," packing multiple devices, to a fiber optic cable on the sea floor.

Testing and deployment of ANTARES equipment has been underway since the late 1990s in a complex construction project whose engineers have had to figure out how to track the exact positions of the array's sensors in ever-shifting currents.

Elusive quarry

Most elusive are the neutrinos themselves. Neutrinos have been studied before: A low-energy variety emanates from the core of the Sun and allows scientists to better understand how the star works. High-energy neutrinos, the quarry of ANTARES, are extremely difficult to detect. But the clues they provide could add to a basic understanding of the universe's structure and evolution.

Physicists theorize that high-energy neutrino sources could also be places where mysterious dark matter interacts. Dark matter, known to exist because of its gravitational effects, comprises 23 of the universe. But no one has seen any and nobody knows exactly what it is.

Neutrinos are almost as mysterious. They have no electric charge, almost no mass and rarely interact with matter. Even magnetic fields in space cannot divert them. Importantly, this means neutrinos travel in a straight line -- across space and through all objects -- and can therefore serve as pointers back to energetic cosmic phenomena.

However, rock or seawater will stop a neutrino now and then, creating a shower of elementary particles called muons.

Muons are similar to electrons but heavier. When they travel through water, muons give off blue light, which the telescope will look for.

"By following the path of the muons we will be able to determine where the neutrinos came from and discover the source of their creation," said ANTARES project leader Lee Thompson of the University of Sheffield in the UK.

Complex setup

When completed, the telescope will have 10 strings, each 1,575 feet (480 meters) long, all affixed to the seabed with a weight and supported by a buoy at the other end. Each string is actually two sturdy cables spaced 7.5 feet (2.3 meters) apart. Along the length of the cables are about 30 light-detection devices, all pointing downward.

Because the strings are suspended in the sea, each detection device is constantly monitored for position. Tiltmeters and compasses measure angles and orientations on the string. A separate and complimentary system uses rangemeters placed on the string to send acoustic signals to transponders on the sea floor.

The detectors and associated electronics are all housed in pressure-resistant glass spheres.

A 25-mile (40 kilometer) fiber optic cable is already in place to relay data to a base station on the south coast of France. Some muon tracks have been successfully recorded using test equipment.

Things are looking down

Why are the detectors near the seafloor and looking down? Because cosmic rays constantly bombard Earth and its atmosphere, and these interactions generate muons, too, in great quantity.

"The water prevents muons from cosmic rays in the atmosphere from contaminating our study," Thompson explained. "By looking down, the Earth also acts as a filter, as muons that haven't been created from a neutrino will be absorbed before they can get into the study area."

When muons are detected, their trajectories will be mapped, and researchers expect to pinpoint the direction in the universe from which the neutrino came. This will, in turn, allow astronomers to figure out what the sources of neutrinos are by surveying the patch of sky with standard telescopes or reviewing archived observations.

Another neutrino telescope, called AMANDA, detects muons a mile (1.5 kilometers) below the frozen surface of Antarctica. AMANDA broke ground in the field by proving that neutrinos could be effectively studied by these offbeat telescopes. The two projects together cover the entire sky with some overlap that will allow researchers to crosscheck some findings.

Other neutrino detectors have been built in abandoned mines, but are typically limited in scope compared to ANTARES. Scientists have also proposed using the Moon as a giant neutrino detector.