Asteroid Hunters

Carrie Nugent

• Publisher: Simon & Schuster UK
• Year: 2017
• Print ISBN: 9781471162398
• eBook ISBN: 9781471162404
• Topic: Physical Sciences
• Subtopic: Space Science

Dr Carrie Nugent is an asteroid hunter - one of the select group of scientists working diligently to map our cosmic neighbourhood. For the first time ever we are reaching the point where we may be able to prevent a natural disaster resulting from an asteroid collision. Nugent will delve into the impact asteroids have had in the past: the extinction of the dinosaurs, the earth-sized hole Shoemaker-Levy 9 left in Jupiter just a few years ago, how the surprise hit on Chelyabinsk in Russia could have started a war and unlucky Ms Anne Hodges - the only person (that we know of) in modern history to be the victim of a direct hit.
Nugent will alsoreveal the cutting-edge work that she is part of - using NASA's NEOWISE telescope to track down near-Earth asteroids. NEOWISE has seen over 158, 000 asteroids and discovered over 30, 000. We will alsoget a rare glimpse into the work of this band of asteroid hunters and their techniques.
Asteroid orbits are chaotic which means a small early change has a big impact later on. The successful hunt and mapping of asteroids could mean nothing less than saving life on Earth.

1

A Wild Frontier

I want you to imagine the solar system. I bet you’re trying to recall an image from a childhood textbook: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The planets are stately spheres, in a neat line leading away from the Sun.

Viewed this way, our cosmic neighborhood looks orderly and uncomplicated: a simple place that a child could draw. It seems thoroughly explored; after all, spacecraft have traveled to every planet. Each world has been measured and photographed. The solar system has been visited, explored, and mapped. Any remaining mystery must lie farther out, for future generations to discover.

I’m here to tell you that is not so. Our solar system is actually a wild frontier, teeming with different, diverse places: planets and moons, millions of objects of ice and rock. It is absolutely enormous; billions of kilometers (miles) across, so vast that we are only just beginning to figure out exactly where the solar system ends and interstellar space begins.

But even in our cosmic backyard, close to Earth, discoveries await us. I am talking about asteroids; the small, mysterious bodies that travel between the planets.

Every night, teams of scientists scour the sky for these objects. Every night, they discover new ones. It is a quiet effort, a steady accumulation of data over decades, a task that rewards coordinated teamwork. I am one of these asteroid hunters. It’s a pretty cool job, and I love telling people about it.

When I tell people I’m a space scientist studying asteroids, they sometimes assume I’m a super-smart math whiz. The kind of person who skipped a bunch of grades and went to college when they were sixteen. Although I am good at math, school was difficult for me, and I didn’t get straight As. But I was willing to work hard to satisfy my curiosity; I wanted to understand how things worked. As children, humans are naturally inquisitive about the world, and I was lucky to have encouraging parents. When I was five, my mom gave me a packet of litmus papers, chemical strips that change color when they are dipped in acids and bases. I ran around the house testing everything I could, trying to assemble a rainbow of results. So I was pretty young when I learned that science let you understand—and even better, predict!—the workings of the universe. By the time I got to college, I knew I wanted to study physics.

Becoming a scientist is a long journey, and at every step I found projects that were exciting, motivating me to continue. My path was not straightforward—when I began studying physics in college, I had no idea I would end up studying asteroids; in fact, I never took an astronomy class. But as it happened, my physics degree led me to study geophysics in graduate school, and that led me to study asteroids today. I love studying asteroids because they are relatively simple, just rocks in space. They can be understood with physics and described with elegant equations. For the most part, they are serene celestial bodies.

But for many people the word asteroid is synonymous with destruction; it brings to mind the extinction of the dinosaurs, or images from disaster movies of shattering buildings and cartwheeling cars. But large asteroid impacts are exceedingly rare. And as it turns out, there are actually things we can do now to lower the chance that someday one may harm us.

The idea that an asteroid impact can be prepared for, like one might prepare for a big winter storm, can come as a surprise. Metaphorically, asteroids seem to embody our lack of control over the universe. In literature, art, and popular culture, they are acts of God, cosmic phenomena that highlight our own powerlessness.

But the reality is quite different. As a species, we have the scientific understanding and technological prowess to actually do something about this particular problem. And it all starts with mapping the asteroids in our cosmic neighborhood.

Thanks to the hard work of generations of asteroid hunters, we have found almost all of the biggest, most hazardous objects. By the end of 2011, we had found over 90 percent of asteroids bigger than one kilometer across that get close to Earth; that is, those capable of massive destruction. And because the hunt for these objects has continued since then, that percentage is even higher today.

It is crucial we keep searching the skies. Not only would we like to find all the asteroids bigger than one kilometer across, it is also a good idea to find the slightly smaller, but still pretty big asteroids that are out there. Asteroid hunters are currently working toward a second target: finding 90 percent of the sasteroids bigger than 140 meters across that get close to Earth. These objects are big enough to decimate a medium-sized country, and so far, only about thirty percent of these have been found.

Asteroid hunting is our responsibility to the rest of the planet. We are the only species able to understand calculus or build telescopes; the poor dinosaurs didn’t stand a chance, but we do. If we found a hazardous asteroid with enough early warning, we could nudge it out of the way. Unlike earthquakes, hurricanes, or volcanic eruptions, asteroid impacts are a natural disaster that can be precisely predicted and, with enough time, entirely prevented.

As you will see, finding asteroids is a complex task that requires teamwork and patience. Asteroid hunters spend long nights on remote mountains, with only skunks and owls to keep them company. We use a robotic telescope that orbits Earth, diligently imaging the sky every eleven seconds. We send data to a centralized archive called the Minor Planet Center. And all this work is managed from a nondescript building in Washington, DC, by NASA’s Planetary Defense Coordination Office, an unusual place that combines the futuristic work of defending Earth from asteroids with the bureaucratic reality of operating within the US government.

•  •  •

But let’s back up a bit. What exactly is an asteroid?

Asteroids are commonly thought of as the rocky and metallic leftovers of the planet-building phase of our solar system. There are millions of them. The biggest are hundreds of kilometers across, while the smallest tracked ones are mere meters wide. Even smaller ones than that certainly exist, but are too tiny to see with today’s telescopes. To the causal eye, asteroids are gray or brown; some are light in color, and some are so dark they look black. Most asteroids travel around the Sun alone, but some have asteroid moons. A few have two moons. So far, we’ve never seen one with three moons, but that doesn’t mean we never will.

There are beautiful images of asteroids taken by spacecraft or radar imaging. Asteroids are generally lumpy. Like a Rorschach test, what you think an asteroid looks like often says more about you than the asteroid. Americans often default to “potato shaped”; in fact, asteroid 88705 is named Potato. After the Chinese spacecraft Chang’e-2 took photographs of one asteroid, the mission scientists published a paper called “The Ginger-shaped Asteroid 4179 Toutatis.” After the Japanese spacecraft Hayabusa imaged asteroid 25143 Itokawa, mission scientists compared its shape to a “sea otter,” describing a distinct “head” and “body.”

Where do asteroids live?

Most asteroids reside in the “main belt” between Mars and Jupiter, and never get close to Earth. Their orbits around the Sun haven’t changed much over billions of years. Small in astronomical terms, they are quite large when viewed from a human perspective. One of the biggest is a main-belt object called Vesta, and it is 525 kilometers (326 miles) across. It’s got roughly the same surface area as Pakistan.

Although it contains millions of asteroids, the main belt isn’t at all the crowded place that you are probably picturing. I blame that misconception on that scene from The Empire Strikes Back where Han Solo plunges the Millennium Falcon into an “asteroid field” to evade the pursuing Empire. Princess Leia exclaims, “You’re not actually going into an asteroid field?” Han Solo replies, “They’d be crazy to follow us, wouldn’t they?”

Our heroes are dodging asteroids, which are flying in every direction, and the pursuing bad guys are being taken out one by one by collisions. C-3PO says, “Sir, the possibility of successfully navigating an asteroid field is approximately 3,720 to 1!” And Han, who is really selling these lines, says, “Never tell me the odds.”

Clearly I love that scene.¹ But the real odds of safely navigating the asteroid belt in our solar system are a whole lot better.² It’s pretty much 1:1. NASA has done this successfully many times, starting with Pioneer 10 (which launched in 1972) to the Juno mission, which reached Jupiter in 2016.

Although there are millions of asteroids in the main belt, the fact is that each one is very small compared to the enormity of space. If you were to take all the known asteroids and squash them together to form a giant ball, that giant ball would still be smaller than our Moon. And the region in space where they orbit is so vast that if you were to stand on the surface of any one asteroid and look around, any other asteroids you could see would appear to be faint points of light.

The main belt isn’t the only place in the solar system where you can find asteroids. There’s a class of asteroids called trojans that hangs out along Jupiter’s orbit, clustering a little before and a little after that planet as it orbits the Sun. Some of the moons of Jupiter and Saturn are probably asteroids that have gotten caught by the gravity of those giant planets. There are tens of thousands of rocky, icy objects beyond the orbit of Neptune in a region called the “Kuiper Belt,” and perhaps many more beyond that in a region called the “Oort Cloud. ”

There are also comets. Comets, which occasionally light up the sky with their spectacular tails, have been known to humanity as long as the stars have. Traditionally, comets and asteroids were thought to be totally different types of objects—asteroids were made of rock or metal, and comets were made of rock and ice. As comets get close to the Sun, their ices—frozen CO₂ and water—sublimate, changing from a solid straight to a gas, leaving the surface. The departing gas brings dust with it, creating the beautiful tails we see.

New discoveries have blurred the line between comets and asteroids. Things we thought were asteroids have unexpectedly started to look like comets, and some asteroids may actually be “dead comets”: comets whose ices have been burned off after many orbits around the Sun.

Several asteroids and comets have been visited by robotic explorers. As I write this, NASA’s Dawn is orbiting Ceres. The European Space Agency’s Rosetta orbits the comet Churyumov–Gerasimenko. The Japan Aerospace Exploration Agency launched Hayabusa2 in 2014; it is on its way to the asteroid 162173 Ryugu to grab and return a sample of surface material. NASA has its own mission to an asteroid to grab and return surface material: OSIRIS-REx is slated to launch in September 2016 and will visit the asteroid 101955 Bennu.

Asteroids, and comets, offer an incredible opportunity to a space-faring species. With their diversity of orbits, many asteroids are much easier to get to than Mars but more difficult to get to than the Moon; stepping stones for astronauts as we venture ever farther from our home planet. Working on an asteroid would, of course, be technologically challenging. There would likely be large amounts of dust, and the barely-there gravity means that you can’t walk around on the surface. As scientist Michael Busch described it to me³, “It’s not really landing on the surface. Because if you try to stand, the pressure from your legs is likely to throw you up off the surface again. And if you push too hard you fly off into space completely. . . . You can jump, and then spend two hours orbiting around and then land on the surface again. But it’s not entirely clear what happens even when you touch the surface.”

I am particularly interested in a class of asteroids called “near-Earth asteroids.” These are often targets for spacecraft, and are often mentioned as potential targets for future crewed missions. Near-Earth is a broad term; it means only that the asteroid gets within 1.3 astronomical units of the Sun, where an astronomical unit is the distance between Earth and the Sun. So, many near-Earth asteroids spend most of their time out beyond the orbit of Mars, and plenty of near-Earth asteroids don’t even get within 40 million kilometers (25 million miles) of Earth’s orbit.

Astronomers are just beginning to map the population of near-Earth asteroids; quite simply, there are a lot of them. When I wrote this chapter, exactly 14,445 near-Earth asteroids had been discovered, but with over 100 being discovered every month, by the time you read this, that number is probably several thousand too small.

Finding asteroids is a challenging but solvable problem. Much like building a giant bridge, it’s a problem that can be solved with math, hard work, and logic. It’s not an easy task, but it’s one well within our grasp.

2

Things that Hit the Earth

You might be surprised to learn that rocks from space hit Earth every day. Most of them are very small. In fact, the bigger the space rock, the less likely it is to hit Earth. Let’s take a quick tour of a few notable impacts.

On any given day, about 90,000 kilograms (100 tons)⁴ of dust and small rocks hit Earth. That seems like quite a lot to small creatures like us, but it’s only 0.000000000000000001 percent of Earth’s mass. Put another way, that’s less than one percent of the total weight of coffee consumed by humans each day. A scientist would say that’s pretty negligible.

A couple of times a year, Earth passes through a region of space where a comet has previously been. The surface of the comet was warmed by the Sun, causing the water ice and frozen CO₂ on the surface to turn to gas, taking dust and tiny rocks with it. The comet left behind this cloud of tiny rocks, which gets pushed around a bit by sunlight and gravity. When the Earth passes through the cloud, those rocks burn up in our atmosphere, causing a beautiful display known as a meteor shower.

The best thing about meteor showers, in my opinion, is that they aren’t fussy. They last several days, which allows you some flexibility in case the weather is poor. If you can find a really dark part of the world to watch from, you’ll see more, but you can be in the middle of a big city and still see a few. I spotted a couple of the Geminid meteors one year from a backyard party in the middle of Los Angeles, which has pretty awful light pollution.

If you haven’t seen a meteor shower, let me tell you, you are missing out. And to see one, you don’t need a telescope or any fancy equipment. You just need a clear night at the right time of year, and you can easily find the dates of upcoming showers on the Internet. Grab a friend, a blanket, and some hot chocolate (or a beer, if that’s your style), and lie on your back. Don’t look at your phone—it will ruin your night vision. Look up, wait, and just shoot the breeze. Pretty soon you’ll see flashes of light streak across the sky.

These streaks of lig...

Table of contents

• Cover
• Dedication
• Chapter 1: A Wild Frontier
• Chapter 2: Things That Hit the Earth
• Chapter 3: Rules of Asteroid Hunting
• Chapter 4: The First Asteroid
• Chapter 5: Terrestrial Asteroid Hunting
• Chapter 6: My Favorite Telescope
• Chapter 7: The Giggle Factor
• Chapter 8: The Planetary Defense Coordination Office
• Epilogue
• Acknowledgments
• Further Reading
• About Carrie Nugent
• Watch Carrie Nugent’s TED Talk
• Related Talks on TED.com
• More from TED Books
• About TED Books
• About TED
• Notes
• Copyright