As millions looked skyward last month for the total solar eclipse, including those in the path of totality in Cleveland, we were reminded of the mysteries and challenges that lie beyond our atmosphere. Among the vast expanse of the cosmos, questions still linger—questions that push the boundaries of our understanding, and fuel the relentless pursuit of knowledge by scientists worldwide.
In honor of National Space Day (May 3), The Daily sat down with Ralph Harvey to learn more about what experts still don’t know about outer space. Harvey is a professor in the Department of Earth, Environmental and Planetary Sciences at Case Western Reserve University, where most of his research involves the geochemical study of planetary materials.
Read on to learn Harvey’s thoughts on big questions that still linger about our universe—and beyond.
1. What is Dark Matter (and the equally invisible Dark Energy?)
Gravity is the most relatable of the fundamental forces of nature, operating on scales that humans can understand, whether we’re talking about an apple falling from a tree or a planet circling the sun. We also understand gravity really, really precisely, at least for distances from the width of a hair to trillions of kilometers. But when you start looking at things on really big scales, say the size of galaxies (100,000 light-years across) or larger, gravity seems to misbehave. Beautiful spiral galaxies should spin fluidly, like water down a drain—instead they often behave more like rigid disks; clusters of galaxies bend light around them as if they contain 20 times more mass than we can see in the form of stars, gas and dust. Those problems go away if we hypothesize the presence of Dark Matter, an invisible “missing mass” that interacts with normal matter only through gravity.
Even more elusive is an invisible “push” labeled Dark Energy; on the very largest scale, looking out over billions of light years, there’s clear evidence that not only is gravity (Dark Matter included) not holding the universe together; but as a whole it is expanding at changing speeds. Of course it’s also possible that our understanding of gravity is alarmingly, fundamentally wrong at longer distances. Whatever’s going on, resolving the nature of these invisible components of our cosmos is one of the biggest challenges in the space sciences.
2. Is life sustainable on other planets—or is Earth really that rare?
Our planet has hosted life for nearly 4 billion years, if not longer, and through all that time, organisms and the Earth have co-evolved. Planetary processes like plate tectonics, volcanism, and climate swings have dramatic effects on the Earth’s biosphere, while metabolic processes and their waste products in huge volumes have returned the favor. As a result, it’s very difficult to say precisely what allowed life to take root and thrive on Earth; was it pure geology, suggesting worlds are destined to host life if all the ingredients are in place? Or is life on Earth due to a chain of myriad improbable things that happened in just the right way at just the right time (lucky us)? People of faith, philosophers, artists and others have studied this as extensively, as have scientists, but unfortunately, with our planet being the sole example for study, it’s very hard to objectively explore the uniqueness of the Earth.
Amazingly, the situation is changing rapidly. In the past few decades exoplanets (planets around other stars) have gone from theoretical maybes to being confirmed by the thousands. As detection limits have dropped, more and more exoplanets are being discovered whose first-order characteristics (size, density, distance from their parent stars, etc.) suggest they could be tantalizing “other-Earths.” Exoplanet research is itself transforming into habitability science, seeking and sometimes finding tantalizing hints within their atmospheres and compositions. Is the Earth just another habitable planet amongst millions, or something much much rarer? Regardless of the answer, it will fundamentally alter how we view our planet.
3. How concerned should we be about asteroids and other cosmic threats?
Our very habitable Earth can make life seem eternal, but the scarred face of the moon and our own planet’s history of impacts remind us that one good asteroid collision can ruin everything (just ask the dinosaurs). The Shoemaker-Levy impact into Jupiter of 1994 and the meteorite explosion over Chelyabinsk, Russia, in 2013 are just two of the more recent reminders of doom arriving from space.
NASA (as well as other space agencies around the world) takes these threats very seriously. A baseline mission of NASA (written into federal law) is the detection and characterization of 100% of the potentially-hazardous Near Earth Objects (NEOs) 100 meters across or bigger by 2033. Spearheading these efforts is NASA’s Planetary Defense Initiative, a little-known but incredible organization that includes our planet’s foremost experts on dealing with the threat of asteroid impact. Not only do they detect potential impactors but they also continually track and characterize them to model their behavior. They don’t skimp on the human implications, either; Planetary Defense extensively war-games impact scenarios to fine-tune a detailed, coordinated communication structure to manage responses. Not all of their responses will be passive; NASA’s recent DART mission successfully modified the orbit of a small asteroid as the starting point for future threat mitigation studies. The Planetary Defense Initiative is a great example of how science can be a direct effort to save the world.