"Learning More about Outer System Planets" Topic

"What kind of planets are most common in the outer reaches of a planetary system? It's a tricky question because most of the data we've gathered on exoplanets has to do with the inner regions. Both transit and radial velocity studies work best with large planets near their stars. But a new gravitational microlensing study looks hard at outer system planets, finding that planets of Neptune's mass are those most likely to be found in these icy regions.

It should be no surprise that gravitational microlensing has produced few planets, about 50 so far, compared to the thousands detected through transit studies and radial velocity methods. After all, microlensing relies upon alignments that are far more unusual than even the transit method, in which a planet crosses the face of its star as seen from Earth. In microlensing, astronomers look for rare alignments between a distant star and one much nearer.

Given the right alignment, the ‘bending' of spacetime caused by the nearer star's mass allows researchers to study changes in the brightness of the background star, which can be clues to the existence of a planet. Microlensing can see not just planets close to their host stars but those far distant from the primary. Moreover, as the new work points out, we can use microlensing to figure out the mass ratio of the planet to the host star, and in about 40 percent of events, we can measure the mass of the host star and planet themselves…"
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