Islands of Life Across Space and Time

Oct 06, 2009
This image shows a comparison of the potential habitable space available on Earth, Mars, Europa, Titan, and Enceladus. The green spheres represent the global volume with the right physical environment for most terrestrial microorganisms. On Earth, the biosphere includes parts of the atmosphere, oceans, and subsurface. The potential global habitats of the other planetary bodies are deep below their surface. Enceladus has the smallest volume but the highest habitat-planet size ratio followed by Europa. Surprisingly, it also has the highest mean habitability H, in the Solar System, although too deep for direct exploration. Mars and Europa are the best compromise between potential for life and accessibility. Credit: UPR Arecibo, NASA Photojournal

A new study by the University of Puerto Rico at Arecibo shows the first quantitative evaluation of planetary habitability. The study identifies some potential habitats in the solar system and also shows how the habitability of our planet has changed in the past, with some periods being even better than today.

Abel Mendez presented his results on Monday, October 5, at the 41st Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society in Fajardo, Puerto Rico.

The study of planetary habitability has become more important with climate change and so has the search for habitable environments in the solar system and beyond. Many environmental factors control the habitability of a planet in complex ways, but a direct assessment of the habitability of a planet has been a continuous problem in planetary sciences.

“It is surprising that there is no agreement on a quantitative definition of habitability. There are well-established measures of habitability in ecology since the 1970s, but only a few recent studies have proposed better alternatives for the astrobiology field, which is more oriented to microbial life. However, none of the existing alternatives from the fields of ecology to astrobiology has demonstrated a practical approach at planetary scales,” said Mendez, a biophysicist from the Department of Physics and Chemistry.

Mendez’s approach to the study of planetary habitability started with the development of a Quantitative Habitability Theory (QH Theory) to assess the current state of terrestrial habitability and to establish a baseline for relevant comparisons with past or future climate scenarios and other planetary bodies including extrasolar planets.

“QH Theory is based on two new biophysical parameters: the habitability H, as a relative measure of the potential for life of an environment, or habitat quality, and the habitation M, as a relative measure of biodensity, or occupancy. Both parameters are related to other physiological and environmental variables and can be used to make predictions about the distribution, abundance, and productivity of primary producers, such as plants and phytoplankton, and microbial life in general. Initially, habitability was modeled from the environment’s temperature and humidity because they are easier to measure at planetary scales with ground or orbital instruments. Global habitability and habitations maps were constructed of terrestrial land and ocean areas with data gridded at various spatial and temporal resolutions. Preliminary work shows that the QH Theory is comparable to existing models in predicting terrestrial primary productivity,” said Mendez.

“This work is important because it provides a quantitative measure for comparing habitability,” said Chris McKay, of NASA Ames Research Center. “It provides an objective way to compare different climate and planetary systems.”

Studies about the effects of climate change on life are of special interest to the scientific community and to the general public. One of the goals of Mendez’s studies is to trace the evolution of terrestrial habitability from paleoclimates to global warming.

“The biophysical quantity Standard Primary Habitability (SPH) was defined as a base for comparison of the global surface habitability for primary producers. The SPH is always an upper limit for the habitability of a planet but other factors can contribute to lower its value. The current SPH of our planet is close to 0.7, but it has been up to 0.9 during various paleoclimates, such as during the late Cretaceous period when the dinosaurs went extinct. I’m now working on how the SPH could change under global warming,” said Mendez.

“This methodology could also be extended to studies of planets around other stars that may be found during the next two decades,” said geoscientist James Kasting at Penn State University.

The search for habitable environments in the universe is one of the priorities of the NASA Astrobiology Institute and other international organizations. The studies of Mendez also focus on the search for life in the solar system including extrasolar planets.

“Various planetary models were used to calculate and compare the habitability of Mars, Venus, Europa, Titan, and Enceladus. Interestingly, Enceladus resulted as the object with the highest subsurface habitability in the solar system, but too deep for direct exploration. Mars and Europa resulted as the best compromise between habitability and accessibility. In addition, it is also possible to evaluate the global habitability of any detected terrestrial-size extrasolar planet in the future. Further studies will expand the habitability definition to include other environmental variables such as light, carbon dioxide, oxygen, and nutrients concentrations. This will help expand the models, especially at local scales, and thus improve its application in assessing habitable zones on Earth and beyond,” said Mendez.

“I was pleased to see Enceladus come out the winner,” McKay stated. “I’ve thought for some time that it was the most interesting world for astrobiology in the .”

Mendez is currently starting collaborative efforts in this line of research with other scientists from the University of Puerto Rico at Rio Piedras and Mayaguez, NASA Ames, the SETI Institute, and other national and international institutions. His studies were supported by the University of Puerto Rico at Arecibo and NASA Astrobiology Institute MIRS Program.

Source: Astrobio.net/University of Puerto Rico at Arecibo

Explore further: Comet Siding Spring whizzes past Mars (Update)

add to favorites email to friend print save as pdf

Related Stories

Tides Have Major Impact on Planet Habitability

Oct 13, 2008

(PhysOrg.com) -- Astronomers searching for rocky planets that could support life in other solar systems should look outside, as well as within, the so-called "habitable zone," University of Arizona planetary ...

New Drake equation to quantify habitability?

Sep 17, 2009

Researchers from the Open University are laying the groundwork for a new equation that could mathematically quantify a habitat's potential for hosting life, in a similar way to how the Drake equation estimates ...

Deciphering Mars: Follow The Water

Sep 13, 2005

Why do we have such a longstanding fascination with Mars? Very simply put, it's about life. The search for life elsewhere in our solar system has been a major driver for exploring Mars, pretty much since we ...

NASA Selects Science Teams for Astrobiology Institute

Oct 03, 2008

(PhysOrg.com) -- NASA has awarded five-year grants, averaging $7 million each, to 10 research teams from across the country, including two from NASA's Jet Propulsion Laboratory in Pasadena, to study the origins, ...

Gliese 581: one planet might indeed be habitable

Dec 13, 2007

More than 10 years after the discovery of the first extrasolar planet, astronomers have now discovered more than 250 of these planets. Until a few years ago, most of the newly discovered exoplanets were Jupiter-mass, ...

Recommended for you

Europe secures new generation of weather satellites

15 minutes ago

Contracts were signed today to build three pairs of MetOp Second Generation satellites, ensuring the continuity of essential information for global weather forecasting and climate monitoring for decades to ...

Comet Siding Spring whizzes past Mars (Update)

12 hours ago

A comet the size of a small mountain and about as solid as a pile of talcum powder whizzed past Mars on Sunday, dazzling space enthusiasts with the once-in-a-million-years encounter.

NASA investigating deep-space hibernation technology

Oct 17, 2014

Manned missions to deep space present numerous challenges. In addition to the sheer amount of food, water and air necessary to keep a crew alive for months (or years) at a time, there's also the question ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

frajo
1 / 5 (1) Oct 06, 2009
If only they would be more precise with the difference between "life as we know it on the local planet" and "life that is not possible on the local planet". Sigh :(
Secundum datur, I assume. And those who think otherwise are in for a few surprises.