I just finished reading Donald Yeomans’ excellent new book “Earth-Approaching Asteroids: Finding Them Before They Find Us” and figured many of you might enjoy hearing about it. The book is published by Princeton University Press and available from Amazon for $15.73.
Author Donald Yeomans might be known to some of you already for his youtube video debunking 2012 doomsday predictions. He works as a senior research scientist at the Jet Propulsion Lab, where he manages NASA’s Near-Earth Object Program Office. His book offers an excellent introduction to the layperson on near-Earth asteroids (NEAs), those objects that can potentially pass within about 29 million miles of Earth as they orbit around the sun.
Yeomans’ primary focus is on a smaller group within the NEAs called the PHAs or potentially hazardous asteroids. These pass within 4.65 million miles of the planet and span at least 500 feet across, large enough to cause significant destruction should they impact Earth. Close-approaching comets are also discussed.
The book is 161 pages long and divided into 10 chapters, starting with asteroid and comet basics and moving on to how astronomers calculate orbits and name names. Next is an overview of the new Nice model (developed in Nice, France) of the solar system’s evolution, where we learn that the giant planets did not form where they now reside.
Gravitational interactions of Jupiter, Saturn, Uranus and Neptune with each other and the small asteroid-like building blocks of the solar system called planetesimals caused the outer planets to migrate over time. As they moved to their current locations, they scattered planetesimals hither and yon to form the current main asteroid belt between Mars and Jupiter and the distant Kuiper Belt beyond Neptune. It’s a fascinating read and goes far in explaining the present-day layout of the solar system.
With the Nice model as background, Yeomans delves into how asteroids from the main belt – the origin of nearly all NEAs – are delivered into Earth-crossing orbits through a combination of the Yarkovsky effect and gravitational nudges from Jupiter and Saturn. Heat absorbed by a rotating asteroid from the sun radiates back into space, giving it a little push and causing the asteroid to spiral toward or away from the sun – this is the Yarkovsky effect. Once the asteroid crosses into a “resonance” point with Jupiter or Saturn, it can then get tossed into the near-Earth neighborhood.
Because near-Earth objects, both comets and asteroids, are composed of primitive materials from early days of the solar system’s history, Yeomans believes they’re critical to understanding our origins. These small bodies may well have delivered much of the water and organic (carbon-containing) compounds necessarily for life to have evolved on Earth.
The first near-Earth asteroid, 433 Eros, was discovered in 1898, while the first dedicated survey to hunt for them didn’t begin until 1973, when Gene Shoemaker and Eleanor Helin used the 18-inch Schmidt telescope on Mt. Palomar to search for small, fast-moving asteroids.
Yeomans describes accelerating efforts to find and track NEAs in the 1980s and 1990s thanks to workshops and papers by asteroid researchers, the discovery of the dinosaur extinction-asteroid connection and introduction of CCD technology (electronic cameras) that allowed for much more rapid and efficient surveys.
As scientists and legislators realized the potential destruction power of near-Earth objects, part of NASA’s budget was directed toward creating the Near-Earth Objects Observations Program in 1998. Its goal: to detect, track and characterize 90 percent of near-Earth asteroids 1 km and larger. The lower limit for an asteroid or comet to cause a global disaster is 0.9 miles (1.5 km).
Especially interesting is how the notification system works should a potential threat be detected during a survey run. I’ll leave it for you to read, but let’s just say, there are many checks before an announcement would be made.
Yeomans describes asteroids’ and comets’ compositions and how we might mine near-Earth asteroids for materials to build space ports and rockets. Much of our planet’s metal content long ago sank to the core or is otherwise deep beneath the surface. Asteroids wear their metals on their sleeves so to speak, with abundant iron, nickel and precious metals like platinum and rhodium much more easily available.
Later chapters go into detail about the potential threats of near-Earth objects, how orbits are refined through continued observation and the protocols in place should an alert need to be issued. Already about 90 percent of NEAs 0.9 mile and larger have been discovered; no known asteroids of this size will impact Earth for at least the next 100 years.
The final chapter describes what we’d do to deflect a potentially threatening asteroid. The slow-pull gravity tractor method (changing its trajectory by “towing” into a safer orbit via gravity from a neighboring spacecraft) and detonating a nuclear device on or near an asteroid are explored.
I highly recommend the book. Since it covers so many aspects of these fascinating asteroids, I found it comprehensive and a great read. While Yeoman covers a topic that some of us worry about, he provides the facts needed to stay cool yet informed. One very small criticism – a list of web resources on the topic in the index would have been nice addition.
I liked the occasional touches of humor, such as when the author wondered why there wasn’t a “rhodium” credit card yet, since that metal’s even more precious than the vaunted “platinum”. We’ll finish with the book’s final sentence:
“Near-Earth objects are among the smallest members of the solar system, but their diminutive size is in no way proportional to their importance. When it comes to their role in the development and future of humankind, next to the sun itself, theirs is the most important realm.”