BLOGS

Heat trap The proposed nanoparticle warming method. (Courtesy: Aaron M. Geller, Northwestern Center for Interdisciplinary Exploration and Research in Astrophysics)

Topics: Aerogels, Exoplanets, Mars, Materials Science, Nanomaterials, NASA, Planetary Science. Thermodynamics

Suffice it to say, Mr. Musk's nuking the Martian planet idea is impractical, and a nonstarter, but to show that he's mature about it, he has T-shirts, because that always makes bad ideas palatable, like a spoon [full] of sugar to help bitter medicine go down (Mary Poppins thought so). The "real-life Tony Stark" he's not.

If humans released enough engineered nanoparticles into the atmosphere of Mars, the planet could become more than 30 K warmer – enough to support some forms of microbial life. This finding is based on theoretical calculations by researchers in the US, and it suggests that “terraforming” Mars to support temperatures that allow for liquid water may not be as difficult as previously thought.

“Our finding represents a significant leap forward in our ability to modify the Martian environment,” says team member Edwin Kite, a planetary scientist at the University of Chicago.

Today, Mars is far too cold for life as we know it to thrive there. But it may not have always been this way. Indeed, streams may have flowed on the red planet as recently as 600,000 years ago. The idea of returning Mars to this former, warmer state – terraforming – has long kindled imagination, and scientists have proposed several ways of doing it.

One possibility would be to increase the levels of artificial greenhouse gases, such as chlorofluorocarbons, in Mars’ currently thin atmosphere. However, this would require volatilizing roughly 100,000 megatons of fluorine, an element that is scarce on the red planet’s surface. This means that essentially all the fluorine required would need to be transported to Mars from somewhere else – something that is not really feasible.

An alternative would be to use materials already present on Mars’ surface, such as those in aerosolized dust. Natural Martian dust is mainly made of iron-rich minerals distributed in particles roughly 1.5 microns in radius, which are easily lofted to altitudes of 60 km and more. In its current form, this dust actually lowers daytime surface temperatures by attenuating infrared solar radiation. A modified form of dust might, however, experience different interactions. Could this modified dust make the planet warmer?

Nanoparticles designed to trap escaping heat and scatter sunlight

In a proof-of-concept study, Kite and colleagues at the University of Chicago, the University of Central Florida, and Northwestern University analyzed the atmospheric effects of nanoparticles shaped like short rods about nine microns long, which is about the same size as commercially available glitter. These particles have an aspect ratio of around 60:1, and Kite says they could be made from readily available Martian materials such as iron or aluminum.

To make Mars warmer, just add nanorods, Isabelle Dumé, Physics World

That isn't tea, but the paradox still applies: Dispersing gold nanoparticles in an aqueous chlorine solution. (Courtesy: Ai Du)

Topics: Aerogels, Einstein, Materials Science, Nanomaterials, Soft Materials

If you stir a colloidal solution containing nanoparticles, you might expect the particles to disperse evenly through the liquid. But that’s not what happens. Instead, the particles end up concentrated in a specific region and may even clump together. This unexpected result is an example of Einstein’s tea leaf paradox, and the researchers at Tongji University in China who discovered it – quite by accident – say it could be used to collect particles or molecules for detection in a dilute solution. Importantly, it could also be used to make aerogels for technological applications.

We usually stir a liquid to evenly disperse the substances in it. The phenomenon known as Einstein’s tea leaf paradox describes a reverse effect in which the leaves in a well-stirred cup of tea instead become concentrated in a doughnut-shaped area and gather at the bottom center of the cup once stirring ceases. While this paradox has been known about for more than 100 years and is understood to be caused by a secondary flow effect, there are few studies on how it manifests for nanoparticles in a stirred solution.

Liquid "squeezing"

Researchers led by Ai Du of the School of Physics, Science, and Engineering at Tongji University in Shanghai have now simulated how gold nanoparticle spheres dispersed in water move when the solution is stirred. When they calculated the flow velocity distribution of the fluid, they found that the rate at which the particles moved appeared to follow the fluid’s flow velocity.

“Interestingly, by dividing the whole container into several sectors, we also observed that the high-velocity region driven by the stirrer was also the region in which the particles aggregated,” explains Du. “We think that this phenomenon is probably due to direct ‘squeezing’ of the liquid created by the stirrer and comes from the mass differences between the nanoparticles and the liquid phase.”

Einstein’s tea leaf paradox could help make aerogels, Isabelle Dumé, Physics World.