Mississauga Centre RASC

122nd Meeting

                                                      Speaker’s Night

           

 Day:                Friday March 6, 2009

 

Speaker: Ivan Semeniuk

                     

 The Astronomy of the Invisible

 

Ivan Semeniuk, Staff Astronomer at the Ontario Science Centre has just started as the new Science Journalist at the U of T Dunlop Institute. A popularizer of astronomy for years, he has worked for the Discovery Channel and New Scientist magazine. He has a blog and weekly podcast “The Universe in Mind” at http://www.di.utoronto.ca/journalist/ .  Ivan spoke of various aspects of the invisible in astronomy.  He began by playing his first podcast where he called professional astronomers to find out what they were doing at that time.  The podcast is Ivan’s IYA project.  He spoke of Galileo and his discovery of Jupiter’s moon – the Medicean stars and the “handles” of Saturn. 

Until 1609, all things known in the universe could be studied only with the naked eye and all thinkers were working with the same database.  Then, in the next 50 years, an enormous number of discoveries were made due to people using telescopes.  Afterwards, most astronomers had personal observatories until 1911 when national observatories (Paris, Greenwich) came into being.   What next?  Ivan discussed four recent discoveries having to do with the invisible in astronomy. 

 

Is Mars dead or alive?  Mars is in the news. In the past 5 years rovers have told us that in the past Mars was more hospitable than now.  There was surface water in the distant past, the best evidence being sedimentary channels in the Opportunity site.  More recently, the Phoenix Lander dug a few cm. until it found ice-water present.  In the Phoenix area, the pH is 8 like seawater whereas in the Opportunity site it is acidic.  One month ago, a small amount of methane was detected near Syrtis Major.  Methane was observed from Earth and by the Mars Express spacecraft.  Some longitudes had more methane than others.  As well, there is more methane during the summer season.  Methane is broken down rapidly and needs to be replenished. It is localized and may be vented by volcanoes. Or, perhaps, bacteria through chemical reactions are breaking other molecules into methane as some do on Earth.  Perhaps methane was made long ago and is being released locally.  This discovery was made by telescopes on the Earth and not by spacecraft.  To distinguish between the geologic or biologic origin of the methane, it is necessary to go to Mars itself, check isotopes (biologic processes tend to use more carbon-12 rather than carbon-13). 

 

The exoplanet revolution began in 1995 when the first one was discovered. Now more than 300 exoplanets are known.  This year has been the most exciting one so far.  Just as stars are seen in both the day and night but are not noticed in daytime due to the brilliance of the sky, so planets are not easily noticed because of the brilliance of the star.  So far, planets have been found either by transiting the star or by the Doppler shift in the star’s spectrum.  Now we have a third method of detecting planets – by direct imaging.  For example, in September 2008, U of T astronomers, using the Gemini telescope,  blanked out the star HR 9799 and used infrared to see planets.  In 1998, the Hubble Space Telescope imaged HR 9799 but the planets weren’t seen then.  The U of T team looked at other HST stars, subtracted the light from HR 9799 and saw the planet.  There are at least 100 stars in the HST database where this could be done and creative mathematics can tease out the planets.  

In the last month, the COROT satellite has been looking for transits of planets that are maybe like Earth.  In February 2009, a star with an estimated mass of 5 to 11 earths and a diameter 1.7 earth was found.  The density is too great to be gas, so it is either metal or less dense.  What is it? A super-earth?  A hot Ganymede? Supercritical water (hotter than the boiling point but under pressure)?  The next step for exoplanet searching will be the Kepler spacecraft due for launch on this night. 

 

Has dark matter been discovered?  Discussions of dark matter are suddenly reaching a fever pitch.  The computer simulation, Via Lactea, of a billion particles shows a huge halo  of matter around the galaxy – a lump of dark matter. The satellite PAMELA and the ATIC balloon experiment show many positrons.  WMAP shows excessive photons from the centre of the galaxy which could be caused by dark matter.  WIMPS (weakly interacting massive particles) could be colliding with each other producing positrons and gamma rays as the annihilation products.  The Fermi space telescope will give us the best view of the gamma ray sky, scanning the sky every 2 days.  It is hypothesized that neutralino dark matter annihilation causes the gamma rays but there is a great deal of noise. We want to see the dark matter signal stand out against the strong signal from the galaxy.  In August, data from Fermi will be available to the public.  The underground DAMA experiment in Italy claims to detect more light flashes from purported WIMP interactions at one time of the year supposedly caused by Earth going through a “dark matter wind”.   The biggest Canadian dark matter detector is being planned at the SNO.  The Large Hadron Collider may be online again in the autumn and may produce neutralinos. So, in the next 5 years we may know what dark matter is.   

 

What was before the beginning?  In the next month, the Herschel spacecraft may measure the microwave background.  Microwaves started soon after the Big Bang which is as far back as we can see.  We look at the microwave background and infer the state of the universe, that it is 74% dark energy.  Planck (launch scheduled for April 16) will see the background in much finer resolution as well as its polarization.  Events before the microwave background may be leaving their fingerprints on it i.e. inflation would cause ripples due to gravity waves.  The fine elements would help distinguish between competing models such as inflation vs. higher dimension spaces or membranes which can come together to for a Big Bang.  The mission can distinguish between the two theories.

 

Chris Malicki, Secretary