The M.A.S. Newsletter
Journal of the Mauritius Astronomical Society
April 2000
The Next Meeting:
The next meeting will be held on Friday 28th April at 7:30 pm at the Saint Esprit College, Quatre Bornes, for the observation of the Virgo Cluster. Members are kindly informed that if they do not pay their yearly contribution by 31st May 2000, their membership will lapse.
The new committee for the year 2000/2001 is as follows:
President
Mr R. Auckbur
Vice President
Mr B. Sobha
Treasurer
Mr B. Desai
Assistant Treasurer Mr F.M.
Robert
Secretary
Mr S. Florens
Assistant Secretary Mr G.
Ferré
Member
Mr H. Ramkhelawon
The sky this month:
Mars and Saturn are at their closest on the 16th. As from the 21st, try to observe the Lyrids meteor shower in early morning in the north east, then on the 6th of May the Eta Aquarids meteor shower.
Mars Polar Lander:
The premature shutdown of the descent engine on the Mars Polar Lander (MPL) spacecraft is the mostly likely cause for the failure of the mission, a NASA report released Tuesday concluded.
Astronomers find Saturn-sized Extrasolar Planets:
A team of veteran planet hunters has for the first time discovered extrasolar planets with masses that might be less than that of Saturn.
Astronomers G. Marcy, P.Butler and S. Vogt announced Wednesday 29th March the discovery of a pair of extrasolar planets orbiting Sun-like stars, each with a minimum mass less than that of Saturn. By carefully measuring shifts in the wavelength of spectral lines from these stars (Doppler shifts), a technique known as the radial velocity method, astronomers are able to detect the "wobble" induced in the motion of a star by a planet as it rotates around the star. Measuring the magnitude and period of the shifts allows the determination of the mass, period, and orbital distance of the pertubing planets. A drawback of the radial velocity method is that without knowledge of the inclination of the planet's orbit as seen from Earth, the exact mass of the planet cannot be determined. A planet whose orbit is nearly face-on to to the Earth would have to be very massive to generate the same wobble as one in an edge-on orbit. Thus, the mass determined by the radial velocity method is usually just a minimum mass, leading some critics to wonder if the objects being detected are not, in fact, much more massive brown dwarfs, or "failed stars". The discovery of these worlds with even smaller minimum masses should go on a long way towards convincing astronomers that these are planets and not brown dwarfs. Another key aspect of this discovery is that the wobble velocity of these stars is about 11 m s-1: less than the wobble velocity of our own Sun generated by Jupiter. This makes it possible for astronomers to eventually discover "Jupiter analogues", extrasolar planets the mass of Jupiter orbiting in distant, circular orbits, rather than the very close or eccentric orbits in which extrasolar planets to date have been discovered. Such Jupiter analogues are the "Holy Grail" of planet searches, said Alan Boss of the Carnegie Institution of Washington. Stars with Jupiter-like worlds in Jupiter-like orbits would be good places to look for even smaller Earth-like planets in orbits that could support life.
Discovery of terrestrial worlds will have to wait for future spacecraft missions, like the Space Interferometry Mission. That spacecraft, scheduled for launch in 2006, will combine light from two or more widely-separated telescopes to create a large "virtual" mirror that may be able to resolve smaller worlds around other stars i.e. visually detect extrasolar planets. Another future mission, the Terrestrial Planet Finder (TPF), would fly several large telescopes in interplanetary space that would be able to take pictures and spectra of terrestrial worlds, allowing astronomers to determine which worlds might be able to support life.
New Black Hole images:
Astronomers have combined images from two cameras on the HST to provide the first close look at spirals of dust in the center of galaxies that may feed black holes. Using images from visible and infrared cameras, astronomers revealed dust formations that appeared to be spiraling into supermassive black holes in the center of 20 active galaxies. The existence of such spirals of dust may be the key difference between active galaxies and "normal" ones, like the Milky Way, which have black holes but do not emit the large amount of energy that active galaxies do. "Before black holes become active, you have to feed them," said astronomer Richard Pogge.
Serge Florens, Secretary