One of the methods of detecting an exoplanet is checking for dips in the brightness of the host star. But sunspots also cause a dip, so how do scientists differentiate between the two? How do they differentiate between a ‘hot Jupiter’ closely orbiting and a sunspot?
The dip in light from a transiting planet would happen on a regular orbital period. If you saw that dip exactly every 174.31 days or whatever, it’s a pretty good indication that it’s a planet. I think they wait for 3 orbits to declare an exoplanet discovered. The odds of transient events creating such events randomly are rather small.
It would take a very extreme starspot to produce as much of a dip in luminosity as a planet, and any star that’s volatile enough to produce such extreme starspots would show its volatility clearly enough to eliminate it from consideration.
There’s also the matter of the time profile. For a typical star, a spot will remain visible for days or weeks, but a transit will be over in hours. The change in luminosity due to a spot, meanwhile, will vary over the entire time its visible, while a transit will leave the luminosity constant for most of the duration of the event, with the drop at the beginning and rise at the end following a very particular pattern.
Yes, just like the rotational period of the star…
Doesn’t that depend upon how fast the star rotates and the presumed location of the presumed planet? The sun has a rotational period of 25 days or so at its equator; the Earth has a rotational period of 1 day.
The Earth’s rotational period is irrelevant; it’s the orbital period (1 year) that matters here. And any Earthlike planet is certainly going to have a period somewhere around that. The rotational periods of stars can vary somewhat, but so far as we know not enough to overlap with that.
Sadly, the latest from the Kepler mission, that was the best in finding exoplanets, is that its planet hunting days are over.