The M.A.S. Newsletter 25

The annual general meeting has been postponed for Friday 31st of March at 7:30 pm at the Saint Esprit College, Quatre Bornes, due to lack of quorum. A slide show about the planets is scheduled at the above meeting.

At dawn on the 28th, Mercury rises at 04:19 in the constellation of Aquarius. It is at its greatest western elongation. Closer to the horizon lies Venus, which rises at 04:54. On the 2nd of April, the Moon is close to Mercury at dawn. On the 6th of April, the planets Mars, Jupiter, Saturn and the Moon clustered close to the western horizon after sunset.

An international team of astronomers has released what it calls the first map of giant structures of "dark matter" that make up most of the mass in the Universe. The maps, released Tuesday by a team of European, Canadian and American astronomers, show giant, intricate filaments of invisible dark matter that may make up 90% of the mass of the Universe. To make the map, astronomers took images of 200,000 galaxies in a two-square-degree region of the sky using a wide-field camera attached to the Canada-France-Haiwaii Telescope (CFHT), a 3.6-meter telescope located atop Mauna Kea, Hawaii. The images were than analyzed at the TERAPIX data processing centre in Paris, where a sophisticated computer program look for evidence of minute distortions in the shape of the galaxies. Such distortions, called cosmic astigmatism or cosmic shear, are caused by gravitational lensing as the light bends around dark matter structures between the galaxy and Earth. These observations allowed astronomers to map out for the first time the structures of dark matter in that region of the sky, revealing a complex, interconnected web of filaments. The maps don't provide any insights into the composition of the dark matter itself, but may help astronomers better understand the nature of the Universe, including why many galaxies appear grouped together in giant sheets and filaments, with corresponding large regions of the Universe that are devoid of any visible galaxies. "To build cosmological models we need to have an idea of the total matter content of the Universe," said Dr Yannick Mellier of the Institut d'Astrophysique de Paris and the Observastoire de Paris, the team's leader. "Also, to test our models, to see if they accurately describe the Universe, we need to look at the results of our simulations against what is actually out there, what astronomers really see." The results, which have been submitted for publication in the journal Astronomy and Astrophysics, cover only a small portion of the sky. However, a new wide-field camera that will be installed at the CFHT in 2002 will be able to cover three times the area of the current camera, making efforts to map the entire dark-matter structure of the visible sky more feasible. "This new instrument will greatly enhance our ability to map the cosmic distribution of dark matter," said CFHT director Greg Fahlman. "Our goal is to help create the first distribution maps of dark matter across the sky, similar to the distribution maps you currently see for galaxies.

Hot Gases and Dark Matter

Credit: R. Mushotzky, ROSAT, NASA Goddard Space Flight Center, ESA

Is the gravity of these galaxies high enough to contain the glowing hot gas? Superposed on an optical picture of a group of galaxies is an image taken in X-ray light. The X-ray picture, taken by ROSAT, shows confined hot gas highlighted in false red color, and provides clear evidence that the gravity exerted in groups and clusters of galaxies exceeds all the individual component galaxies combined. The extra gravity is attributed to dark matter, the nature and abundance of which is the biggest mystery in astronomy today.

Two flybys of Ganymede and joint observations of Jupiter with the Cassini spacecraft are in store for the Cassini spacecraft this year, project officials announced Wednesday, March 8. Thoses events are part of the Galileo Millennium Mission, the latest mission extension which started last month and has already included a flyby of the moon Io. Galileo will fly by Ganymede May 20 and December 28 and study Jupiter's magnetosphere with Cassini as it flies by Jupiter December 30 en route to Saturn. The extended mission runs through April 2001, although the project is considering possible additional flybys of Io or Callisto if the spacecraft remains healthy.

The terrain of the north and south polar caps on Mars is markedly different, scientists reported last Wednesday. High-resolution MGS images of the north polar cap of Mars show a relatively flat, pitted terrain - reminescent of cottage cheese - while the south polar cap features larger pits, troughs, and mesas that scientists compared to Swiss cheese. The difference may be linked to composition: the residual, or year-long, north polar cap is mostly water ice, while the south cap is mostly carbon dioxide "dry ice". "The unusual shapes of the landforms on the north and south polar caps suggest that these regions have had different climates and histories for thousands or perhaps even millions of years," said Cornell University's Peter Thomas.