Scientists studying data Galileo returned from its close flyby of Jupiter's moon Io last December have concluded the large moon has a giant iron core and may possess its own magnetic field.
The results, published in the journal Science earlier this month, were based on the trajectory of the spacecraft as it passed within 900 km (560 mi) of Io on December 7, as well as data returned from the spacecraft's magnetic fields experiments.
According to Dr. John Anderson of JPL, team leader of the spacecraft's celestial mechanics experiment, the Galileo data shows Io has a core made of iron or iron sulfide up to 900 km (560 mi) in diameter. A mantle of partially molten rock overlays the core.
The core may have been formed by the intense tidal heating of the moon caused by its close location to Jupiter. Such heating may have melted much of rock and metal in the moon and allowed the denser iron to fall to the center, creating the core.
Galileo's magnetic field instruments detected a sudden, unexpected drop of up to 30 percent of the strength of Jupiter's magnetic field in the vicinity of Io. "The data suggest that something around Io -- possibly a magnetic field generated by Io itself -- is creating a bubble or hole in Jupiter's own powerful magnetic field," said Dr. Margaret Kivelson of UCLA, who heads the project's magnetic fields investigations.
Galileo is on course for its first flyby of Jupiter's largest moon, Ganymede, on June 27. The spacecraft will pass within 850 km (530 mi) of the moon at that time.
Two teams of astronomers using the Hubble Space Telescope to measure the rate of expansion, and the age, of the universe found results that were in rough agreement with one another, but may still conflict with the ages of the oldest stars.
The two teams announced ages of the universe ranging from 9-12 billion years for one and 11-14 billion years for the other.
One Hubble team, led by Wendy Freedman of the Carnegie Observatories, Robert Kennicutt of the University of Arizona, and Jeremy Mould of the Mount Stromlo and Siding Springs Observatory in Australia, found values for the Hubble constant of 68 to 78 km/sec/megaparsec. Another team, led by Allan Sandage of Carnegie, used different data to find a value of 57 km/sec/Mpc.
Freedman and her group use a type of variable star known as Cepehids to determine the distance of neighboring galaxies. The period of a Cepheid variable star is a function of its intrinsic brightness. Sandage and his team look for type Ia supernovae which, according to Sandage, serve as a "standard candle" to calibrate the distances to galaxies.
The Hubble constant is a measure of the expansion of the universe. It shows that objects at greater distances from us are moving away at faster speeds. Higher Hubble constants are correlated with younger ages of the universe.
At the same time, evidence from globular clusters show that some of the stars may yet be older than these age estimates. Dr. Don VandenBerg of the University of Victoria, Canada, presented research at a conference earlier this month that showed that some stars in the cluster M92 may be up to 15 billion years old, and certainly no younger than 12-13 billion years. Such a discrepancy may require revisions to the Big Bang theory of the origin of the universe.
Scientists dedicated the second giant telescope at the W. M. Keck Observatory atop Mauna Kea, Hawaii, in ceremonies at the observatory on May 8.
Like the first Keck telescope, Keck II is a 10-meter (394-inch) telescope, the largest telescope in the world. Its mirror consists of 36 hexagonal sections which are precisely controlled by computer to create a single flat surface.
The Keck II also has "adaptive optics" controls which allow the telescope mirror to change shape to remove much of the image distortion caused by atmospheric turbulence. This system will allow Keck images to approach and even exceed the quality of images from the Hubble Space Telescope.
While the W. M. Keck Foundation picked up most of the costs of the two telescopes, to the tune of over $150 million, NASA contributed $44 million and will provide $2 million a year for operations. In return, NASA will get a fraction of the time on the two telescopes.
NASA plans to use Keck primarily in its program to look for planetary systems around other stars. Plans call for combining the two telescopes into a single optical interferometer to greatly improve the resolution of images taken by the two telescopes simultaneously, making it possible to directly image planets around other stars.
"We'll be looking primarily for Jupiter-like planets because Jupiters are so much easier to detect than much smaller Earth-like planets," said Dr. Edward Stone, director of the Jet Propulsion Laboratory and chairman of the California Association for Research in Astronomy, the organization that manages the Keck telescopes.
The Keck II telescope is slated to undergo a series of tests over the next several months, and will begin full operation in October.
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