→ Widely unknown Exoplanet Astronomer

An artists impression of ultracool dwarfs, and how they might look like to the naked eye, should you ever travel out into space to have a look at them directly. The hotter ultracool dwarf is on the left. Credit: NASA/JPL-Caltech

The direct imaging method, whereby the exoplanet is photographed directly, is one of the most difficult methods for studying exoplanets. To date, less than 30 exoplanets have been studied this way. The type of exoplanets studied using the direct imaging technique are usually big, bright planets with big orbits. Exoplanets too close to the host star simply get lost in the glare of the star, a bit like looking at a firefly really close to the sun on a bright summers day. One way in which we astronomers can learn something about the exoplanet is by performing what is known as photometry. That is, observing how the amount of light from the planet varies over a period of time. This can give ut some hints as to what the upper visible atmosphere is like.

The ultracool approach

By studying ultracool dwarfs (really cool “small” stars) it will be possible to learn more about the atmospheres of exoplanets. These ultracool dwarfs are similar in temperature to the exoplanets discovered by direct imaging method and also have the advantage of not having a great big blinding star close by. Studying their atmospheres might give us a hint as to what conditions give dusty or clear atmospheres. It is an interesting field of study as it might give us a better understanding of cloud formations in cool atmospheres. Our own solar system show banding and persistent storm systems. How common it is for planets to have these features is something astronomers are trying to figure out.

The Red Spot of Jupiter.

To be able to find the radius of an exoplanet, astronomers study the lighcurve. The lightcurve is made by plotting the flux form the host star as a function of time. Here is an example of a light curve:

The depth of the light curve will depend on a number of things such as the radius of the exoplanet and the distance of the exoplanet  from the host star. However, it is not only the properties of the exoplanet which matter. Imagine a star-planet system where we now double the radius of the host star whilst keeping the radius of the planet the same. In this case the exoplanet will block out the same amount of light, but the dip in the light curve will be smaller, since the host star has a greater flux.

Thus, from the transit method astronomers are only able to derive the radius of the exoplanet relative to the radius of the host star.  The unit used is the radius of the planet over the radius of the host star, Rp/R*.