Planet Transits Lecture Thirty, Apr. 16, 2003

Projects due April 25 Background papers have been graded (out of 15 points). Background papers have been graded (out of 15 points). Happy to offer suggestions or answer questions for your project. Happy to offer suggestions or answer questions for your project.

Extrasolar Planets We have now found about 100 planets around other sun like stars by observing small Doppler shifts in the star light. We have now found about 100 planets around other sun like stars by observing small Doppler shifts in the star light. Planets not seen directly. Only have information on planets masses and orbits. Planets not seen directly. Only have information on planets masses and orbits. Doppler method most sensitive to close in massive planets. Doppler method most sensitive to close in massive planets. New methods and instruments will allow the discovery of many more planets. New methods and instruments will allow the discovery of many more planets.

Artist guess for planet close to 51 Peg

Who lives on these planets?

From 1950s SF movie “The Day The Earth Stood Still”

New Methods to find Planets One can observe transits of extrasolar planets with quit small telescopes

Transit of Venus in 1769

The Size of the Solar System Johannes Kepler and Edmund Halley in 1716 predicted that Venus would traverse across the sun in 1761 and Johannes Kepler and Edmund Halley in 1716 predicted that Venus would traverse across the sun in 1761 and Timing these transits from different places on earth could allow measurement of the astronomical unit (earth sun distance). Timing these transits from different places on earth could allow measurement of the astronomical unit (earth sun distance). Note transits occur in pairs about every century. The next transits will occur June 8, 2004 and June 5, Note transits occur in pairs about every century. The next transits will occur June 8, 2004 and June 5, Bad weather spoiled observations of the 1761 transit. Bad weather spoiled observations of the 1761 transit.

Measuring solar system Sun London Tahiti Venus Deduce parallax angle from time difference of transit viewed at Tahiti and viewed at London. Allows one to calculate AU in terms of diameter of earth Angle AU

The Results Observations allowed the AU to be determined to within 3% of its modern value. Observations allowed the AU to be determined to within 3% of its modern value. Secret orders had ship going on after transit and exploring mysterious southern continent (Australia and New Zealand). Secret orders had ship going on after transit and exploring mysterious southern continent (Australia and New Zealand). AU was measured more accurately in modern times from parallax measurement during a close approach of asteroid Eros to earth. AU was measured more accurately in modern times from parallax measurement during a close approach of asteroid Eros to earth. AU is now known very accurately from radar measurements of distances to Mars and Venus. AU is now known very accurately from radar measurements of distances to Mars and Venus.

Extrasolar Transits If plane of extrasolar planet’s orbit happens to be exactly aligned with us. IE by chance we happen to observe the system edge on. Then we can observe a transit. If plane of extrasolar planet’s orbit happens to be exactly aligned with us. IE by chance we happen to observe the system edge on. Then we can observe a transit. Star’s light will drop slightly because a small amount of it is blocked by planet. Star’s light will drop slightly because a small amount of it is blocked by planet. Need to very carefully observe brightness of star as a function of time looking for a small dip. Need to very carefully observe brightness of star as a function of time looking for a small dip.

The Hubble measurements are so accurate they set strong limits on moons

Want telescopes all around world to monitor a star 24 hours a day.

Results since 1995 We have found about 100 massive planets around sun like stars. Some of them orbit close in. Some orbit at larger distances up to the 5AU of our Jupiter. We have found about 100 massive planets around sun like stars. Some of them orbit close in. Some orbit at larger distances up to the 5AU of our Jupiter. Doppler shift method sensitive to massive planets relatively close to star. Doppler shift method sensitive to massive planets relatively close to star. About 10% of stars have a massive planet within about 5 AU. About 10% of stars have a massive planet within about 5 AU. We are not yet sensitive to earth mass planets. The induced velocity of the star is to small to measure. We are not yet sensitive to earth mass planets. The induced velocity of the star is to small to measure.

“Jupiters” can be good and bad Our Jupiter out at 5 AU helps shield earth from impacts (for example Shoemaker Levy 9 was removed as a threat to earth). Our Jupiter out at 5 AU helps shield earth from impacts (for example Shoemaker Levy 9 was removed as a threat to earth). A “Jupiter” near a small planet’s orbit or a Jupiter in an elliptical orbit can eject “earth’s” after a while. A “Jupiter” near a small planet’s orbit or a Jupiter in an elliptical orbit can eject “earth’s” after a while. The massive planets we have discovered prove that planets are common in the galaxy! The massive planets we have discovered prove that planets are common in the galaxy!

To find other Jupiters is interesting. To find other earths would be exciting! Talk about new technology for finding low mass planets next time.