Microlensing & Exoplanets

A planet does not have to shine to be detected. It does not even have to orbit a star. Free-floating planets, sometimes called rogue planets, travel through the Milky Way without being gravitationally bound to a host star. That makes them extraordinarily difficult to find. There is no parent star for the planet to transit, … Read more

In gravitational microlensing, astronomers often begin with a convenient simplification: they treat the distant source star as a single point of light. Usually, that approximation works remarkably well. But when the lens passes extremely close to the source, the star’s actual angular size can no longer be ignored. The resulting change in the observed light … Read more

A caustic crossing occurs when the apparent path of a background star crosses a boundary in the magnification pattern of a two-body gravitational lens. The star does not travel through a foreground planet or collide with a lens. The changing alignment produces a rapid, finite feature in the measured brightness. This article separates three things … Read more

Chromatic microlensing means that the measured color changes during a gravitational magnification event. In the usual geometric-optics description, gravity is not separating colors like a prism. The color signal comes from the source’s wavelength-dependent structure, or from light mixed into the measurement. Separate the lens from the measured image An isolated point source, magnified achromatically, … Read more

Starspots distort exoplanet transits because the planet blocks one strip of a star while the telescope measures light from the entire visible disk. If that strip differs from the disk average, a transit can give a biased radius or spectrum even when its light curve looks smooth. Crossed and uncrossed spots do different things When … Read more

A change in measured transit depth does not necessarily mean an exoplanet changed size. Depth is the blocked light divided by a measured baseline. Both quantities depend on the star, neighboring light, wavelength and analysis. The first task is to establish whether two observations measure the same thing. Compare like with like Check passband, aperture, … Read more

An asymmetric transit has an ingress, egress or internal shape that fails to mirror the other side of the event. The cause may lie in the star, material around the planet, orbital motion or the measurement process. The shape is a clue to investigate, not a unique diagnosis. First define the expected symmetry A spherical … Read more

Transit duration variations measure changes in how long a planet takes to cross its star. Another planet can produce them by perturbing the orbit, including its orientation. A changing duration is therefore a possible dynamical clue, but it does not identify a hidden planet by itself. Define which duration was measured The full transit duration, … Read more

Transit timing variations, or TTVs, are departures of measured transit midpoints from a constant-period schedule. Gravitational interactions between planets can produce them, allowing astronomers to constrain planetary masses and sometimes infer a companion that does not transit. A late transit alone is not a planet discovery. Build the reference clock first For transit number E, … Read more