Space Friday: Pluto Skies, Neutrinos, and Habitability

Building on Mars

With the opening of The Martian last week, NASA is seizing on the excitement of human exploration of the (relatively) nearby Red Planet. In fact, the agency launched a challenge this week for innovative ideas to use Mars’s natural resources when astronauts arrive.

The challenge comes with cash prizes totaling $15,000—fairly inexpensive when you consider the price tag of taking materials into Low Earth Orbit (around $10,000 per kilogram). So how might you use Mars’s native materials for human exploration? The challenge website has suggestions: “One could use surface-based materials such as regolith or basalt to produce structural elements that can be interconnected to create launch/landing pads; blast protection berms; roads and walkways; radiation, thermal, and micro-meteorite shielding insulation and structures; equipment shelters; pressure vessels for fluids storage; ablative atmospheric entry heat shields; construction foundations; and other useful structures.”

“We are looking for creative and novel solutions from all types of people,” says Robert Mueller of NASA’s Swamp Works. So get crackin’! The deadline is December 3. –Molly Michelson

Sunshine and Sweden

Big news this week about the Nobel Prize in physics! The Royal Swedish Academy of Sciences awarded the 2015 prize to Takaaki Kajita (Super-Kamiokande Collaboration, University of Tokyo) and Arthur B. McDonald (Sudbury Neutrino Observatory Collaboration, Queen’s University) for their experimental evidence showing that neutrinos have mass.

Lawrence Krauss wrote an elegant description of the discovery for the New Yorker, but here’s a shorter, Science Today summary…

Kajita and McDonald led teams that, in the 1990s, resolved a nagging concern about the number of neutrinos measured coming from the Sun. Neutrinos are slippery little particles interacting rarely with ordinary matter like us (indeed, trillions of the little fellas are zipping through your body every second), so they proved challenging for physicists to find. Nonetheless, experiments as early as the 1960s had succeeded in detecting neutrinos that originated in the heart of the Sun, zipping unimpeded from the center of our star.

Or so we thought. Neutrinos come in a few different flavors, and the early experiments were sensitive to only a single variety. And far fewer of those neutrinos were detected than the finest theories predicted. After decades of astrophysicists banging their heads against the problem, couldn’t resolve the disparity, giving rise to the solar neutrino problem. What was going wrong?

Turns out that neutrinos are even slipperier than we imagined! The earliest models assumed that neutrinos had no mass, so they could never change flavor. A neutrino with mass, however, could “oscillate” between flavors faster than a Bertie Bott jelly bean. A simple solution to the solar neutrino problem! The neutrinos changed flavors en route from the center of the Sun to our detectors on Earth (mostly near the center of the Sun, by the way, and not in the cool, uneventful vacuum of space).

The extensive experimental efforts of Kajita—installing a 50,000-ton tank of ultrapure water a kilometer (0.6 miles) underground—and McDonald—building a separate, 1,000-ton tank of heavy water twice as far underground—led to the confirmation of massy, flavor-changing neutrinos and the resolution of the solar neutrino problem.

The dirty secret of all this? The Standard Model of particle physics doesn’t really know how to handle a neutrino with mass. So there’s more physics (in the form of theory and experiments) to be done! –Ryan Wyatt

Pluto: Blue Skies and Water Ice

Thursday, NASA’s New Horizons mission team had yet another big announcement about Pluto—well, two actually—the discovery of a blue-ish hazy glow in its upper atmosphere and confirmation of water ice on its surface.

The color of an atmosphere tells us about its composition. “A blue sky often results from scattering of sunlight by very small particles” explains Carly Howett of Southwest Research Institute (SwRI). “On Earth, those particles are very tiny nitrogen molecules. On Pluto they appear to be larger—but still relatively small—soot-like particles we call tholins.” They appear high in Pluto’s atmosphere as UV light from the Sun breaks apart and ionizes nitrogen and methane molecules, which then react to form complex macromolecules—similar to the process first observed on Saturn’s moon Titan.

The discovery of water ice has only given the team more questions, mostly about its color and its distribution. Large patches of the ice (along with the rest of Pluto) are distinctly reddish, and the relationship between the ice and its color is not yet understood. Explaining the where we see water ice on the surface also poses a challenge. “Large expanses of Pluto don’t show exposed water ice,” says Jason Cook of SwRI, “because it’s apparently masked by other, more volatile ices across most of the planet. Understanding why water appears exactly where it does, and not in other places, is a challenge that we are digging into.”

These latest announcements add to the long list of features and properties now identified on the dwarf planet. With only about 10 percent of the data back from New Horizons, plenty more discoveries and announcements await us. –Elise Ricard

Exoplanet Habitability Index

There are nearly 2,000 confirmed exoplanets beyond our solar system, thousands more candidates yet to be confirmed, and almost 100 deemed potentially habitable. But how exactly do we define a habitable world and what makes one exoplanet more worthy of our attention than another? This week, University of Washington’s Virtual Planetary Laboratory published in the Astrophysical Journal their habitability index for transiting planets as a way to rank and compare exoplanets that have been observed with the transit method.

“Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme, so that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with,” says Roy Barnes of University of Washington.

While other such indexes have been developed previously, this new one is considered more nuanced. Factors include the estimated rockiness of a planet, its albedo (the amount of starlight it reflects), and the eccentricity of the exoplanet’s orbit. According to this measure, the best candidates for life are planets they receive 60 to 90 percent of the solar radiation that the Earth receives from the Sun, which is inline with scientist’s current thinking about habitable zones around stars.

So which worlds topped the list? Not Earth. Kepler-442b and a yet-to-be confirmed planet known as KOI 3456.02 both ranked higher than our home world, with a 0.955 for KOI 3456.02 and 0.836 for Kepler-442b, compared with 0.829 for Earth. –Elise Ricard

Image: Pluto's atmospheric haze, NASA/JHUAPL/SwRI