Gravitational microlensing

They noted that the 5-10 Earth mass requirement needed to explain the ETNO anomalies perfectly overlaps with an unexpected excess of microlensing events observed in a five-year dataset by the Optical Gravitational Lensing Experiment, or OGLE.

Micro-lensing is when a dark, invisible object passes in front of a distant background star, and its gravity acts like a magnifying glass, bending the starlight and making it temporarily brighter, right?

Exactly.

These OGLE micro-lensing events are traditionally attributed to those free-floating rogue planets we discussed earlier drifting through the galaxy.

And that means that these two methods- Transits is a great method for looking at the closer in planets.

Microlensing focuses on the further out planets around their host star.

So these two methods will allow us to span the entire demographic range of planetary distances from their host.

And microlensing will even be able to find planets that aren't bound to any host star.

Okay, great.

So we have a number for the number of stars, but how many planets are there around these stars? Thanks to a planet-hunting technique called gravitational microlensing, which is really sensitive to cold, distant exoplanets, we've determined that every star, on average, has one cold planet.

Looking at another planet-hunting technique called transits, which looks at close-in warm planets around their star, we find on average, one warm planet per star.

Now, remember the way this averaging is working out is that there could be some stars out there which have no planets, and there could be some stars which are chocked full of them.