PHYS 182 Lecture Notes - Lecture 6: Radial Velocity, Direct Image Functor, Wide Field Infrared Survey Telescope
PHYS182: Our Evolving Universe
2017-09-21 LEC 6: Exoplanets
Guest Lecture: Lisa Dang
What is an Exoplanet
• Also referred to as exosolar planets or extrasolar planets
• They are planets outside of the solar system
o They are either orbiting another star (1) or free floating planets (2)
• Planets don’t create their own energy and are difficult to find
Is Our Sun Special?
• No, it is an average star
o 10% of all stars are Sun-like stars
o 20B stars in our Galaxy are just like our sun
• The largest star is 24,000x bigger and 315x more massive than our sun
• The smallest star is 2000x smaller and 13x less massive
What makes our sun different?
• It was the only known planetary system for centuries
• Still the only system hosting 9 significantly diverse planets
Finding Planets is Difficult
• They are small and far
• They are dim compared to their host star
o Planets appear dark, the only way to see them is if they reflect energy of their star
o The glow of a star masks any brightness the planet could have
Finding Planets Start with 51 Peg b (aka Dimidium)
• 51 Peg c is a star in the sky, and it was discovered that it had a companion with ~ the mass of
Jupiter
• 1995: Group of French Scientists found the first planet
• 51 Pegasi b: “Hot Jupiter”
o 0.5x Jupiter’s mass (Dimidium is “half” in latin)
o Takes 4.23 days to orbit around the star (very close to the sun)
o Temperature over 1300 K (Venus is ~700K)
o We don’t expect life as we know it on this planet
• We have 4 rocky planets: Me V E Ma
• We have 4 gas giants: J, S, …
o Things that are metal and rocky are closer to the sun because the temperature is hotter,
and things that condensate at colder temperatures are farther out
o We would not expect gaseous planets as close to the star as Hot Jupiter, but it has roughly
the same composition
Exoplanets
• As of Sep 19/17:
o 3510 confirmed
o 4496 candidates
o 2615 systems
o 366 terrestrial (rocky)
Document Summary
It was the only known planetary system for centuries: still the only system hosting 9 significantly diverse planets. Finding planets start with 51 peg b (aka dimidium: 51 peg c is a star in the sky, and it was discovered that it had a companion with ~ the mass of. Exoplanets: as of sep 19/17, 3510 confirmed, 4496 candidates, 2615 systems, 366 terrestrial (rocky, number have exoplanets has grown exponentially over the past few years, found via measuring radial velocity and transits mostly. In the presence of another body of mass orbiting a star, the star will also orbit about their common center of mass: centre of mass: mean location of distribution of mass in space. I. e. the heavier the star is compared to the planet, the closer the center of the mass is to the star: the closer the center of mass is to the star, the smaller the orbit of the star.
