Compiled and written by Daniel Fischer, Skyweek - older "Mirrors" in the Archive - and find out what the future might bring!

HST Key Project final report:
The Hubble Constant is 70 +/- 7!

Although Cepheids are rare, they provide a very reliable "standard candle" for estimating intergalactic distances. The team used the stars to calibrate many different methods for measuring distances that reach much further into the distant Universe than the Cepheids do. Four of these methods (involving the brightnesses and sizes of certain types of galaxies, Type Ia supernovae and the resolvability of the oldest stellar populations) were then used to arrive at the "final value" of Ho. More than 400 hours of Hubble observing time spread over the past 8 years have gone into the project that some thing was once essential in "selling" the HST to the U.S. Congress.

All the details about the tremendous work (that has led to 23 scientific papers in the Astrophysical Journal so far, with 11 more submitted or in preparation by summer) will be presented next week at the AAS Chicago meeting. Other groups using Cepheid distances and solely Ia supernovae continue to arrive at 60 and 64 respectively, but the error bars of their results and the Key Project analysis already overlap. And what does Ho=70 mean? Perhaps an age of the Universe of 12 billion years, that is if the other fundamental parameters are estimated at conservative values. (NASA News Conference on May 25 at 15:00 UTC, broadcast live via telephone)

Another orbit revision for asteroid 1999 AN10

New measurements of 1999 AN10, made over the last week and a half by amateur astronomer Frank Zoltowksi in Australia, have permitted more improved orbital calculations that confirm a close approach to Earth on Aug. 7, 2027. The orbital motions of the Earth and the asteroid do not permit a collision then, but the close approach will certainly change the asteroid's orbital path. If the asteroid passes through certain narrow "keyholes" in the uncertainty ellipse, its changed orbit will bring it back for another Earth close approach in a later year. The 2039 impacting scenario identified last month actually required passage through two keyholes, one in the 2027 ellipse, and one in the 2034 ellipse, which explains why it was so unlikely (about one chance in a billion).

This week's new observations have now moved the uncertainty ellipse completely off the 2039 keyhole, which indicates that this impacting scenario is no longer possible. The newly identified impacting possibilities for August 6, 2044 and August 7, 2046 each require passage through only a single keyhole in the 2027 ellipse, and the probabilities of impact for these cases are correspondingly larger, on the order of one chance in 500 000 for 2044, and one chance in five million for 2046. These odds of collision are larger than those for any other object, but they are still less than 1/100 the chance of an undiscovered asteroid of equivalent size striking the Earth sometime before 2044.

The difference in elevation between the hemispheres results in a slope from the South Pole to North Pole that was the major influence on the global-scale flow of water early in martian history. Scientific models of watersheds using the new elevation map show that the Northern Hemisphere lowlands would have drained three-quarters of the martian surface. During the ongoing Mars Global Surveyor mission, the MOLA instrument is collecting about 900 000 measurements of elevation every day. These data will further improve the global model, help engineers assess the area where NASA's Mars Polar Lander mission will set down on Dec. 3, and aid the selection of future landing sites.