Why is still technically challenging to be able to detect planets with the prope

Question

Why is still technically challenging to be able to detect planets with the properties of Earth orbiting stars like the Sun? (Think of two particular techniques we discussed in class to detect planets, the Doppler or velocity method, and the transit method. It is hard for both cases. Explain for both cases why it is hard.

Thinking about the masses of stars, is it easier to detect planets that orbit around stars with less mass than the Sun or around stars with more mass than the Sun? Explain your answer.

Explanation / Answer

planets have been used using several different techniques:
(i) Between 1995-2011 majority of planets discovered via Radial Velocity Method: Detects orbital motion by searching for slight shifts in the positions of spectral lines in a star's spectrum (from red to blue). - studies star's spectrum to find signs that star is moving around a center of mass (which would mean there's a planet pulling it!) - BEST FOR: big planets, small orbit, nearby star, EDGE-ON orbit. - COMPLICATIONS: current tech allows it to be applied to only one star at a time, so only a few stars can be studied. - has found more than 90% of extrasolar planets

(ii) In 2011-present, the majority of planets have been discovered via the Transit Method due to launch of Kepler satellite:Relies on searching for slight changes in a star's brightness caused by a planet passing in front of it. - planets seen as a small black dot in front of the star they are passing because they are blocking a tiny amount of star's brightness (which allows us calculate planet's radius. - repeated dimming must be seen & if it occurs with a regular period, it's likely telling us the orbital period of a transiting planet. we can then calculate the planet's orbital distance and mass - BEST FOR: big planets, close to their star.

With Doppler shifting, we can only measure the radial velocity, which is less than the true velocity. Since mass is proportionate to the velocity, the mass we measure is less than the true mass.

It would take a planet several times more massive than its parent star to see a star orbit around a planet.The vast difference in mass between a star and planet is what shifts the point of orbit (aka barycentre) to be located far closer to the stars point of orbit than the planets.

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