The Habitable Exoplanets Catalog

The Habitable Exoplanet Catalog (HEC), a project by University of Puerto Rico (UPR) at Arecibo, went online on the 5th of December and after a brief peruse I felt compelled to express my approval and appreciation in blog form as soon as possible! A brief description, taken from the UPR Acecibo site:

The HEC is the first extensive catalog on the number, diversity, and characteristics of habitable exoplanets in the universe. It uses new developments by the PHL [Planetary Habitability Laboratory] like the Earth Similarity Index (ESI), the Habitable Zones Distance (HZD), classification systems, and comparisons with Earth past and present, to help assess the habitability of exoplanets.

The project uses three habitability metrics as well as two classification systems to assess the relative similarity and potential habitability of a number of exoplanets that have been announced and proposed but awaiting confirmation. These indices are built from observational data, but also from model output. The results, which at the moment outline 16 possibly habitable exoplanets, are presented via awesome individual graphics, thus:

KOI 736.01

This is exoplanet KOI 736.01 (as always, a wonderfully enigmatic name), a Kepler candidate considered to be ‘most similar’ to Earth based on the new habitability rating system. Awesome, right? Along with general planetary characteristics (part observational, part modelled) there are also some interesting classifications (mesoplanet, terran etc.) and some unusual indices (ESI, SPH, HZD) on the right. Let’s explore these in some detail, using KOI 736.01 as our case study. The classification methodology is described by the authors here.

Firstly, the classifications. The Planetary Class (pClass) sorts planets according to three thermal divisions (hot, warm, cold) and seven mass divisions, which are, in ascending order: asteroidan, mercurian, subterran, terran, superterran, neptunian, and jovian. KOI 736.01 is a warm terran planet, meaning that it is within the habitable zone of its star and of a comparable mass to Earth. Class M (mesoplanet) alludes to the fact that KOI 736.01 has a surface temperature of between 0 – 50 °C according to the Habitable Class classification (hClass). Other divisions in hClass range from extremely cold hypopsychroplanets through to very hot hyperthermoplanets.

Great so far, now lets turn our attention to the habitability metrics on the right. ESI or the Earth Similarity Index uses several planetary characteristics, namely radius, density, escape velocity, and surface temperature to determine the relative similarity of the planet to Earth on a scale from 0 (completely dissimilar) to 1 (identical). Our chosen planet has an ESI of 0.98, making it very like Earth and therefore likely to harbour a rocky interior and terrestrial atmosphere. This shouldn’t come as too much of a surprise; based on the general characteristics (mass, radius, gravity and period) included in the graphic it is fairly easy to ascertain that this is a planet very similar to our own, with the exception of a very brief orbital period. SPH, or the Standard Primary Habitability is a measure, calculated from surface temperature and humidity, of the ability of the planet to support terrestrial primary producers and in turn estimate the net primary productivity that would be expected. 0 is very unproductive and 1 is more so. With a SPH of 0.63, KOI 736.01 is moderately productive and very similar to the Earth at 0.65. SPH makes the assumption that water would be present, given a surface temperature of between 0 and 100 °C but in my opinion this may not always be the case. The final metric, HZD stands for Habitable Zone Distance, and describes the position of the planet within the habitable zone: +1 is on the very outer edge, 0 in the middle and planets with a HZD of -1 are straddling the inner edge. Accordingly, with a HZD of -0.59, KOI 736.01 is about half-way between the very centre of habitable zone and its inner edge.

All in all, the Habitable Planet Catalog is a wonderful resource with the potential to increase the accessibility of exoplanet science substantially. It also provides an excellent standardisation methodology that I hope will be readily adopted by other scientists for coherence and comparison. Bearing in mind my analysis was only based on one small area of the site dedicated to Earth-similarity, I suggest that anyone interested in the habitability of extra-solar planets takes the time to wonder around this great site and explore it in more detail.


Follow Professor Abel Mendez, the principal investigator at the PHL, on Twitter here.


25 comments on “The Habitable Exoplanets Catalog

  1. One crucial info seems to be missing, and that is the distance of each of these exoplanet with the earth. I would in particular like to know if there would be a potential for radio communication at the speed of light within the next 50 years… after that I’ll probably be dead haha… (not sure that’s funny).

  2. With an orbital period of just 19 days this is going to be a tidally locked planet, unless it has a highly eccentric orbit which would create other problems for habitability, and as it is also orbiting a dim red dwarf star, surely it is very optimistic to claim that this planet will be at all habitable, well habitable as in a human being could live/survive there for more than five seconds without donning a spacesuit.

    • There has been a reasonable amount of research conducted recently (chiefly by Jill Tarter et al.) that suggests that M-class ‘red dwarf’ stars may be able to host habitable planets, given the optimal orbital distances. They are also incredibly long-lived which extends their habitable period several orders of magnitude relative to G-type Sun-like stars. As for tidal locking, there is still more work that needs to be done in this area but I feel you’re probably right about this being an inhibitory orbital configuration for life. It is possible that the ‘terminator’ zone between the permanently lit and permanently dark hemispheres may be able to support microbial life, but I think that the temperature gradients (and therefore wind speed) would be too great. Also, we should avoid placing too much of an anthropic bias on habitability; the discovery of any form of exobiology, including prokaryote-like ‘simple’ organisms, would still be an important and monumental discovery to help us garner some perspective on our existence.

    • While you make a good point people also thought that witches where real and that flying machines wern’t possible to create and so far bot of these have happened therefore from what I have read about this planet I would take my chances there it sounds interesting and there is only one true way to determine if a place is hospitipal and that is to put people there.
      (Hope I’m one)

    • I’ve readrecently about the possibility that a well developed cloud system could transport heat from the ever ligth zone to the ever dark ones, making the overall temperature much more pleasant.

      • I agree. If the atmosphere can shift this kind of heat around the planet, then great. Still, the temperature differential between the day and night surfaces will be huge and the winds across the terminator would be beyond hurricane force.

  3. I love the new system too. Only, I cannot for the life of me figure out why they used the prefix psychro- instead of the much more common and recognised cryo-. They’re both Greek for cold! Any thoughts on why they did that?

  4. well i think wat most people forget is that we r not the only type of spicies out in the universe. just like animals adapt to their surroundings wouldnt be a posibility that their is other species unknow to humans that are able to adapt to diferent conditions… so it would be ignorent from us to think that that planet is or may not be habitable

  5. These planets are bs. Stop wasting tax dollars because we have equipment to bs. Can’t believe how much they make to commit fraud w/looking for “new planets”. This is a mocary of intelligence.

    • Dude you are sad our sun is going to engulf the planet in about 5 billion years and that’s after it’s gotten very very very very very cold for quite a long while and that’s if we don’t nuke ourselfs out of extinction first of if we don’t pollute or starve out first so just shut up and go back to your right wing nut job republican or democrat hole that you live in and leave us free of your bsing and misspelling’s

  6. So, is the term “habitable” referring to anything that qualifies as a life form, no matter how small or simple? Ya know, if we found a planet with a thriving civilization of humanoid inhabitants out there, the vast distances preclude any fruitful communication (let alone actual visitation), so other than satisfying the big “wonder if” question, there’s no real practical reason why we’d spend the money to find out “if”. Remember, if light from an object that far way takes that long to reach our position, that’s how old that image is. The fastest form of communication we have is dependant upon our being here to retrieve and discern any response to that communication (that’s if there’s a reason to suspect anything out there could discern it for what it is and reciprocate it). I guess money spent on deep space research is better than seeing it wasted on a giant military industrial complex, but still, we’ve bigger fish to fry. Lets make sure that our planet is still habitable a thousand years from now.

    • Won’t be over popullation, poor polotics, right wing nut jobs and plain human stupididy will rain supreme
      Sorry I wish it wasn’t true but it most likly will be I hope to god that I’m wrong

  7. I coudnt really care less about this planet. why dont we just stop wasting money on that new planet and start using it for OUR planet.(earth)

    • Our planet is pretty much going to be dead anyway… Maybe looking for a new home planet might be worth doing. Ever read time riders? The author does a pretty realistic interpretation of the future.

  8. Is there any oxygen on this planet? Also, for people who know so much about science, did any of you take spelling in school?

  9. Dreamers dream and move us forward. Success is born from knowing that failure on risky ventures will come 90% of the time. Its the 10% that make it all worth while. The capitalistic philosophy, “you must spend money to make money” also fits with research. You must invest in what may be a stretch if you are ever going to leap forward.

    When black-hole (or other) time travel acceleration is mastered, the investment made now wont seem so foolish. We just need to look past the trees to see the forest.

    Good luck dreamers, we are all counting on you…

    • Thanks for this comment, very nice sentiment and much appreciated. Amongst the unintelligible ranting and dreary moaning about ‘tax dollars’, it’s good to see that there’s still some people with at least a modicum of foresight floating around the web.

  10. Another issue is that is there any way to see what sort of magnetic field it generates? Earth is lucky because it had that collision with Thea, adding its core to the Earth’s own.

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