• What is this site all about?
This site is based upon the work of Stephen Kane & Dawn Gelino on the topic of Habitable Zones, particularly for planets in eccentric orbits. This work in turn is based upon numerous other references.
• What is a "Habitable Zone"?
The Habitable Zone (HZ) is defined as the range of circumstellar distances from a star within which a planet could have liquid water on its surface, given a dense enough atmosphere. This is depicted by the green annulus in each of the figures in the Gallery.
• What are the light green and dark green regions shown in the Gallery figures?
The boundaries are calculated using the methodology of Kopparapu et al. (2013) and Kopparapu et al. (2014). These boundaries allow for both conservative and optimistic scenarios depending on how long it is presumed that Venus and Mars were able to retain liquid water on their surfaces. The conservative model (shown in light green) uses the ``Runaway Greenhouse'' and ``Maximum Greenhouse'' criteria for the inner and outer Habitable Zone boundaries respectively. The optimistic model (shown in dark green) extends the inner/outer boundaries by using the ``Recent Venus'' and ``Early Mars'' criteria. The Table shows the percentage of the planetary orbital phase spent in the Habitable Zone for each of these models.
• How are the number of Habitable Zone Planets reported on the front page determined?
These are the planets whose orbits lie entirely within the optimistic Habitable Zone around their respective stars. To locate these planets, go to the Table then sort by clicking on the "tHZo (%)" column header twice. This will bring those planets that spend 100% of their orbital phase in the optimistic Habitable Zone to the top of the table.
• Where do the stellar/planetary parameters originate?
The stellar and planetary parameters used to calculate the orbits and locations of the Habitable Zone are regularly extracted from the Exoplanet Data Explorer.
• How are the calculations performed?
The figures, movies, and tables are generated using FORTRAN code (yes ... FORTRAN) that utilizes the above parameters. The actual calculations performed and technical descriptions thereof are contained in the linked article by Kane & Gelino as well as numerous other references.
• What assumptions are made?
The planetary temperature calculations are based upon parameters that aren't available in all cases, and thus assumptions are occasionally made. For example, planetary radii are only known for the transiting planets. In all other cases we apply a power law model as a first order approximation. We also assume zero albedo such that the planets absorb all of the incident flux from the host star.
• Are planets in the Habitable Zone habitable?
This is unknown since there are a variety of planetary properties that contribute towards habitability as well as the flux received from the host star. For example, many of the planets described here are giant planets that may not even have a rocky surface. Moons of those planets may have conditions more suitable for sustaining life however.
• Why aren't all planets listed?
Including planets in the list relies on having both a complete orbital solution and sufficient information regarding the host star properties. Since this list is drawn primarily from radial velocity and transiting planets, it is normally the latter that impedes inclusion in the list. Also, there can sometimes be a delay from when new information is published to when it appears in the archives that this service draws upon.
• How do I reference this site?
Links to this site are always welcome. If the site is used for research leading to a publication, it can be acknowledged as follows: "This research has made use of the Habitable Zone Gallery at hzgallery.org." Please also cite the associated Kane & Gelino article.
• Who can I contact about this site?