A United States federal agency is not necessarily the first place you think of when it comes to answering some of the deepest existential questions for our species. Yet over the last half-century this is precisely where some of the greatest practical progress has been made. It is also where some of the deepest conceptual shifts about our cosmic status have had their genesis.
From Apollo 17′s archetypal view of the Earth as a ‘blue marble’, to vistas of the surface of Mars and the frigidly serene outskirts of our solar system, to the temperature noise of remnant microwaves from the young universe, and to a catalog of more than 4,000 candidate planets orbiting other stars. NASA’s been there, done that.
Of course, as a government agency NASA’s got its fair share of problems, from being bounced around as a political pawn to its own often creaky and Byzantine bureaucracy. But when it gets stuff right, it really is the right stuff.
So it’s very exciting that a big new effort has been announced to draw together the exoplanetary science community across the US. In full disclosure – I’ve known about this for several months now, and I’m directly involved as the institutional PI for Columbia University and the Columbia Astrobiology Center as part of a contributing team led by the Goddard Institute for Space Studies in New York and partnered with the Goddard Space Flight Center as well as some other institutions such as U. Washington, Weber State, and NASA Ames. Phew, and that kind of mouthful is precisely why the whole thing is being called NExSS (Nexus for Exoplanet System Science).
The official description can be read here. In a nutshell, it is a bold scheme to bring structure to the many and varied threads of exoplanetary science that NASA supports, and the search for life on new worlds. The ‘system science’ part of this arises from the recognition that we need to understand how planets and life inter-operate, how planets and stars inter-operate, and how the whole astrophysical, geophysical, geochemical, climatological, biochemical kit-and-kaboodle works together.
I’ll brag about the work of my colleagues because I’m hugely biased and think that it’s one of the most exciting pieces of all this. Our scientific contribution to NExSS centers around the development of what we’re calling ROCKE3D. This will be, we think, one of the world’s best three-dimensional supercomputer models of the surface environment of rocky planets. It’s being built out of a generalized version of an Earth climate model, known as a general circulation model, or GCM.
A huge computer program like this models a planet’s atmosphere as a fluid, where energy is transported by winds, where there are oceans and ice, there is atmospheric chemistry and electromagnetic radiation transfer, clouds form and dissipate, and ultimately the biosphere is involved.
But you can’t just reset the parameters to ask about, for example, the nature of climate on Mars or a distant exoplanet. Earth-based GCM’s are notoriously highly tuned to accurately reproduce modern Earth climate conditions and sensitivities – as they should be in order to help answer our most pressing questions about climate change. If you need to ask about new worlds, or even the Earth as it was across the past 4 billion years, you need to rewrite lots of code.
And in order to test that the model is actually accurate you need to properly calibrate it. That’s what we’re going to do with ROCKE3D – by using what we know about the ‘habitability’ of the solar system across the past 4.5 billion years to try to pin down the right physics and mechanics in the simulations. Some very early results are on display here.
Left to right you’re looking at the surface temperature of Mars during its northern winter, the surface air temperature of a slow-rotating (tidally locked) Earth as a proxy for a young Venus, and the Neoproterozoic Earth (perhaps a billion years ago, note the continents are different) during a cold ‘snowball’ episode, showing low-level cloud coverage (white), and the surface level wind speeds and directions (green).
My own small role in this project is to help with some of the model inputs. Specifically the spin-orbit history of the planets, because if you don’t know the orientation and orbit of a planet you don’t know the proper input of solar power – the ‘insolation’ of a world – that drives climate. We need to figure out the plausible spin-orbit states of planets like Venus, Earth, and Mars at various key epochs across the last 4.5 billion years – not a particularly easy task – so we’re coming up with some novel ways to tackle this, many of which will involve throwing gobs of computer time at the problem.
Along the way we’re going to be figuring out the possibilities for exoplanets, especially those worlds that could sustain a temperate climate for billions of years, and the planets that upcoming and future generations of telescopes will be able to probe.
In this case the solar system really is the stepping stone to the stars.