MadSci Network: Astronomy

Re: What types of studies are investigating planetary systems?

Date: Fri Oct 6 14:54:18 2000
Posted By: Angelle Tanner, Grad student, Astronomy, UCLA
Area of science: Astronomy
ID: 970284173.As

Planetary systems are a hot topic right now in astronomy! 
So you could keep reading my summary of planetary systems OR feel
free to go to - - for all the information you 
could possible want on the topic. 

It was only very recently in 1992 that a group of astronomers discovered 
a planet orbiting the neutron star, PSR 1257+12. Then the field began 
exploding with new discoveries of Jupiter-like planets around more normal
stars like our own Sun. The total number of extrasolar planetary systems
has risen to over 50!! 

Before these new discoveries, our only idea of what a planetary system
might be like came from our own back yard - nine planets, some rocky, 
some gaseous, orbiting one, fairly average star. So classically, a 
planetary system consists of a group of terrestrial (Earth-like) 
and/or gas giant (Jupiter-like) planets orbiting around a star. 
While we have always assumed that if other planetary systems exist apart
from our around the Sun they would have to be much like our own. 
This has proven to not be the case. 

There are a variety of different methods which can be used to identify
extrasolar planetary systems - pulsar timing, radial Doppler shifts, 
direct imaging and transits - to name a few. 

Pulsar timing uses the outrageously accurate period of the radio pulses of
a neutron star as it spins rapidly on its axis. The gravitational pull of
an orbiting planet will disturb the pattern of the signals enough to be 
measured and then astronomers can use the physics of spinning bodies to
determine the distance and mass of the otherwise invisible planet. This
method was the first to detect any type of planet outside our own solar
system and was a very significant result since it implied that our solar
system is not unique. 

Even though pulsar timing was the first method to detect planets, 
it has not proven to be the most effective. 
That honor goes to a technique which uses the wobble of a normal 
star in the presence of a massive Jupiter-like planet. The light from 
the star undergoes a Doppler shift (like the change in the pitch of
a car horn as it passed by you) as it wiggles toward and away from us 
due to gravitational pull of the massive planet. 
Most of the discoveries planetary systems using this method
have been done by Geoff Marcy, Paul Butler, Michel Mayor and Didier Queloz.
This type of planet search is good at finding massive planets near their 
parent stars since that results in a large enough wobble for us to 
detect at the Earth with present day large telescopes. The fact that so 
many gas giants exist so near their star (much closer than the Earth-Sun
distance!) has surprised scientists since its so different than our solar 
system (Jupiter is 5 times further from the Sun than the Earth). Our ideas
about how planetary systems are created and evolve has had to change to 
explain these observations. 

Another method of planet detection which is in its infancy involves
seeing a planet block out the light from its parent star as it
orbits around or "transits" the star. Since the planet does not 
produce that much light, the light from the star will dip as the planet
orbits in front of it. This type of planet detection is tricky because
it requires the orbit of the planet to be such that the planet travels
between us and the star. Also, we need to be looking at the right star 
at the right time since the "event" might occur over a small percentage
of the total orbit of the planet. Finally, we need to have telescopes
which are sensitive enough to detect the ever so slight decrease in the
star's light during the transit. This type of planet detection will become
more common with bigger telescopes and more telescopes are being devoted to
looking for such transit events. 

One simple method for finding planets is taking their picture or 
"direct imaging". This type of detection is not yet possible 
for even Jupiter-like planets due to the fact that a star is so much 
brighter than a gas planet that its light overwhelms any 
light from a planet close to the star. Even if the planet were far away
from the star, our telescopes just don't presently have the light
gathering power to see them. This will improve dramatically with 
bigger, more sensitive telescopes. 

There is a bright future for finding many more planetary systems
as NASA is focusing a lot of resources on this endeavor through 
future space telescopes and present programs like the Doppler 
studies. One telescope, called the Terrestrial 
Planet Finder, has the goal of finding Earth-sized planets around
neighboring stars using a special kind of telescope know as
an interferometer. This is definitely a topic of astronomy to keep and
eye on. I can guarantee you'll see many future stories of discovery 
on the news. 
Thanks for your question! I wish to pursue this type of research in the
future so this was a great chance for me to review the topic. 

				Angelle Tanner
				UCLA Astronomy

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