by Gen Ito
What are worlds outside of Earth like?
Many readers today probably can imagine some kind of extraterrestrial scene when asked this question. You might have seen a photo of a landscape of Mars captured by the recent rover, Curiosity, or perhaps astronauts walking on the Moon from Apollo missions. Others might recall images from science fiction books and movies, such as the recent film Interstellar. We live in a society now where basic space and planetary knowledge has become part of common life.
This was not always true; much of the universe was unknown. For example, we did not know much about the water content of Mars, number of near-Earth asteroids, or methane on Titan. Scientists in the space and planetary field have been working to
understand more about the universe in which we live. They use a variety of methods to
study space and planets, including a technique called remote sensing, which looks at (“senses”) something from far away (a “remote” place). The power of remote sensing lies in the fact that it canbe used to study places on a global scalewithout physically going to those places, and is therefore widely used for studying the planets in our Solar System. A research group at Stony Brook University, headed by Dr. Timothy Glotch, builds models that enhance the remote sensing application to areas of Mars that have been difficult to understand in the past. These models could pave the way for more efficient exploration of planetary bodies in the future.
Instruments used in remote sensing are frequently carried on satellites. These instruments contain optical devices similar to telescopes that look down at the ground instead of up at the stars, and the optical devices are combined with sensors that detect light. The type of light detected is not just normal light that we can see with our naked eye, but rather infrared light. Infrared light, although we cannot see it directly, is actually all around us. One example of visualizing this form of light is the use of night vision cameras. Night vision cameras work by detecting infrared light that is emitted as heat (e.g. body heat released from humans and animals). The same physics behind night vision cameras are also understood by remote sensing scientists, and they can use infrared light to study physical and chemical properties of materials. Remote sensing scientists analyze infrared and visible light that comes from the planetary surfaces to understand what the planets are made of, what they looked like in the past, questions about the existence of life, or where a safe and scientifically interesting place to send the next rover may be.
Remote sensing is a useful tool to study distant planets, but it is not perfect. One major limitation is accurate detection of planetary surfaces that are covered by fine particles, like dust on Mars. The interaction of infrared light with fine particles is complicated and makes accurate data interpretation difficult. This is problematic because Mars has many dusty regions. When trying to analyze the composition of an area that may be tied to past water activity, for example, remote sensing cannot provide accurate results if the area is covered by dust. Dr. Glotch’s group at Stony Brook University tries to push this limit by building light scattering models of the interaction of infrared light with fine particles. These models provide firm understanding of the pattern of infrared light affected by fine particles. The models are based on one of the most fundamental concepts in physics, Maxwell’s equations. Maxwell’s equations mathematically describe the behavior of electric and magnetic fields. By solving Maxwell’s equations, the models simulate the paths of infrared light as it goes through clusters of particles that resemble a dusty planetary surface. The outputs from these models provide detailed parameters that describe the behavior of infrared light as it interacts with fine particles, and this leads to better understanding of data acquired by remote sensing. From the scattering parameters, we will be able to understand how much of the infrared pattern was caused by fine particles and how much was caused by the composition of the surface itself. This understanding is important because having accurate compositional interpretationwill help answer big questions like whether life on Mars is possible. Building light scattering models enhances remote sensing application to areas of Mars that have been difficult to study, and with more accurate remote sensing capabilities, we will be able to more efficiently explore planetary bodies.
Issue 1, October 2015