American scientists have found evidence that the surface （表面） of the planet （行星） Mars （火星） once moved like that of present-day Earth. The evidence comes from a new map of magnetic forces on Mars.
The map was put together from observations （觀測） by an American space vehicle, the Mars Global Surveyor. The American space agency sent the Mars Global Surveyor into orbit around Mars in nineteen ninety-seven. The spacecraft （太空船） spent nearly four years studying the planet, its atmosphere and what lies under its surface. The spacecraft is now on an extended trip to gather more information.
The space agency says the new magnetic field map of Mars is the first of its kind. The map （地圖） provides images of the full surface of the planet.
Scientists say the map shows that the surface of Mars was created in much the same way as Earth's. On both planets, the outer surface is broken up into large pieces, or plates. These plates are moving over areas of hot liquid （液體） rock, called the mantle. As the mantle rises up and breaks through the surface of the planet, the plates push apart. The mantle reaches the surface and cools into hard rock.
The magnetic （磁場） field on the planet pulls the rock in one direction. More material pushes from under the planet's surface, building a new rock surface on top of the old. Sometimes different levels of rock will be pulled in different directions. This happens when the magnetic field changes several times every million years.
The planet Mars also has a series of mountains called the Tharsis volcanoes. They lie in a straight line. Volcanoes on Mars are ten to a hundred times larger than those on Earth. Scientists have wondered why this is so. With the help of the map, scientists can now see that the mountains were formed in a very hot area between two plates. On Earth, this kind of volcanic activity formed the Hawaiian Islands.
The Mars Global Surveyor also examined an extremely deep hole. It is called the Valley （峽谷） Marineris. It is six times as long and eight times as deep as the Grand Canyon in the western United States.
The spacecraft also found that the magnetic field on Mars did not cover the planet. Magnetic fields protect planets from some kinds of radiation （輻射） from space. Scientists think the presence of even a partial magnetic field around Mars may mean that living organisms were able to exist on the planet. Medical researchers may have found a cause of prostate （前列腺的） cancer. They say the finding could lead to more effective treatments and a possible cure for the disease.
The researchers said they identified a way of organizing chromosomes that causes two genes to combine, or fuse. This unusual gene activity is found only in prostate cancer. The researchers said they found the gene activity in most of the prostate cancer tissue they studied. The genes did not combine in prostate tissue free of the disease.
Arul Chinnaiyan of the University of Michigan Medical School led the study. The research team included scientists from the United States and Germany （德國）. Science magazine reported their findings. America's National Cancer Institute provided support for the study.
The two genes involved are called ETV-One and ERG. They are normally separate. But each fused with another gene, known as TMPRSS-Two. This gene is directly linked to the prostate gland in men.
The researchers developed a step-by-step process for identifying （鑒別） genes commonly linked to cancer. The process searches for unusual genetic activity in prostate cancer tissues.
Laboratories at the University of Michigan （密歇根州） tested twenty-two pieces of prostate cancer tissue. The process found the unusual gene activity in ninety-one percent of the tissue studied.
No one knows what caused the genes to fuse. Researchers say similar gene fusions are likely to be seen in most prostate cancers. But they say other unknown gene combinations （組合） may be the cause for the other prostate cancers.
The presence of these gene combinations may one day be used to test for prostate cancer. Doctors now test men for levels of prostate-specific antigen, or P.S.A. P.S.A. is found in the blood or liquid wastes. But experts say P.S.A. tests are not always dependable （可靠的）. Doctors often need tissue to confirm prostate cancer. Experts say better tests would reduce the need for such invasive methods.
The map was put together from observations （觀測） by an American space vehicle, the Mars Global Surveyor. The American space agency sent the Mars Global Surveyor into orbit around Mars in nineteen ninety-seven. The spacecraft （太空船） spent nearly four years studying the planet, its atmosphere and what lies under its surface. The spacecraft is now on an extended trip to gather more information.
The space agency says the new magnetic field map of Mars is the first of its kind. The map （地圖） provides images of the full surface of the planet.
Scientists say the map shows that the surface of Mars was created in much the same way as Earth's. On both planets, the outer surface is broken up into large pieces, or plates. These plates are moving over areas of hot liquid （液體） rock, called the mantle. As the mantle rises up and breaks through the surface of the planet, the plates push apart. The mantle reaches the surface and cools into hard rock.
The magnetic （磁場） field on the planet pulls the rock in one direction. More material pushes from under the planet's surface, building a new rock surface on top of the old. Sometimes different levels of rock will be pulled in different directions. This happens when the magnetic field changes several times every million years.
The planet Mars also has a series of mountains called the Tharsis volcanoes. They lie in a straight line. Volcanoes on Mars are ten to a hundred times larger than those on Earth. Scientists have wondered why this is so. With the help of the map, scientists can now see that the mountains were formed in a very hot area between two plates. On Earth, this kind of volcanic activity formed the Hawaiian Islands.
The Mars Global Surveyor also examined an extremely deep hole. It is called the Valley （峽谷） Marineris. It is six times as long and eight times as deep as the Grand Canyon in the western United States.
The spacecraft also found that the magnetic field on Mars did not cover the planet. Magnetic fields protect planets from some kinds of radiation （輻射） from space. Scientists think the presence of even a partial magnetic field around Mars may mean that living organisms were able to exist on the planet. Medical researchers may have found a cause of prostate （前列腺的） cancer. They say the finding could lead to more effective treatments and a possible cure for the disease.
The researchers said they identified a way of organizing chromosomes that causes two genes to combine, or fuse. This unusual gene activity is found only in prostate cancer. The researchers said they found the gene activity in most of the prostate cancer tissue they studied. The genes did not combine in prostate tissue free of the disease.
Arul Chinnaiyan of the University of Michigan Medical School led the study. The research team included scientists from the United States and Germany （德國）. Science magazine reported their findings. America's National Cancer Institute provided support for the study.
The two genes involved are called ETV-One and ERG. They are normally separate. But each fused with another gene, known as TMPRSS-Two. This gene is directly linked to the prostate gland in men.
The researchers developed a step-by-step process for identifying （鑒別） genes commonly linked to cancer. The process searches for unusual genetic activity in prostate cancer tissues.
Laboratories at the University of Michigan （密歇根州） tested twenty-two pieces of prostate cancer tissue. The process found the unusual gene activity in ninety-one percent of the tissue studied.
No one knows what caused the genes to fuse. Researchers say similar gene fusions are likely to be seen in most prostate cancers. But they say other unknown gene combinations （組合） may be the cause for the other prostate cancers.
The presence of these gene combinations may one day be used to test for prostate cancer. Doctors now test men for levels of prostate-specific antigen, or P.S.A. P.S.A. is found in the blood or liquid wastes. But experts say P.S.A. tests are not always dependable （可靠的）. Doctors often need tissue to confirm prostate cancer. Experts say better tests would reduce the need for such invasive methods.