Tracking killer comets before they strike

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• JUDY WOODRUFF:

  Now a different kind of space mission, finding asteroids and other large objects before they get close to Earth.

  This Sunday, a comet will be making an unusually close fly-by near Mars. In fact, it will be coming closer to Mars than any other comet has come near Earth in recorded history. It's also a moment when scientists are assessing our own risk from such objects.

  Science correspondent Miles O'Brien has our report.

• MILES O’BRIEN:

  Traveling 40 times faster than a speeding bullet, it is a menacing messenger from the very distant past. The comet known as Siding Spring, a dirty snowball packed with four-billion-year-old leftovers from the dawn of our solar system, will streak ever so close to Mars and NASA's armada of spacecraft, for scientists, an unprecedented bonanza, for all of us, a stark reminder.

  Jim Green is the space agency's director of planetary science.

• JIM GREEN, NASA:

  There's not only the scientific interest of where these objects fit in, in the origin and evolution of our solar system, but indeed ignorance is not bliss. We can't, in all consciousness, expect us to ignore the near-Earth population.

• MILES O’BRIEN:

  By that, he means the millions of comets and asteroids that come close enough to Earth that they could collide with the planet.

  Don Yeomans runs the Near-Earth Object Program at NASA's Jet Propulsion Laboratory.

• DON YEOMANS, NASA:

  It's just a matter of time before a large one is on an Earth-threatening trajectory. The only question then is, will we discover it well ahead of time and do something about it?

• MILES O’BRIEN:

  We humans got a stunning shot across the bow in February of 2013, when a 60-foot-wide asteroid exploded over Chelyabinsk, Russia. Equivalent to 30 atomic bombs, it shattered windows, injuring about 1,500.

• DON YEOMANS:

  I think we have gotten over that stage where people dismissed this with a Chicken Little-type attitude and a giggle factor.

• MILES O’BRIEN:

  The Mount Lemmon Observatory near Tucson is one of three facilities funded by NASA to tackle the problem by searching the night sky for asteroids and comets that might be a threat.

• ERIC CHRISTENSEN, Catalina Sky Survey:

  Yes. So, on an average night, we'll find two or three new near-Earth objects. It's almost like a fisherman going out to the lake and spending the day, and maybe you catch something, maybe you don't, but there's always the chance that you're going to find something.

• MILES O’BRIEN:

  Astronomer Eric Christensen showed me how he trolls for trouble using a 60-inch telescope built in the 1970s, now outmoded for more distant discoveries.

• ERIC CHRISTENSEN:

  So we might take four visits to the same field within about half-an-hour or 45 minutes. And then we have software that processes these images and compares each of the visits and identifies the stationary objects, the stars and galaxies, and identifies objects that are potentially transients.

  So, this is a near-Earth object. It is moving in a different direction at a much faster rate. That's because it is much closer to the Earth.

• MILES O’BRIEN:

  Collectively, near-Earth object surveys have catalogued about 12,000 asteroids and comets, including 1,000 that are six-tenths-of-a-mile in diameter and larger, big enough to cause a global catastrophe. They have found 95 percent of them.

  Now they are looking for objects down to 450-feet wide, which could take out a region. NASA's congressionally mandated goal is to find 90 percent of those by 2020. Operating on old, small telescopes and a budget of $40 million a year, the survey has found only 10 percent of those objects and will come nowhere near to that goal.

  In September, NASA's Inspector General's Office released a report critical of the agency's efforts to identify near-Earth objects and mitigate hazards. It concludes the effort lacks structure, has limited resources, needs to improve oversight and grants and forge partnerships inside the federal government and internationally as well.

• JIM GREEN:

  You know, we were in the middle of the program. Yes, it's sort of walking into a car factory and say, how come you don't have fenders on the car? Well, we're getting in the process of putting them on. And if the I.G. came back even within a year, I think they would see a much more methodical and solid program operating under a well-defined plan.

• MILES O’BRIEN:

  But as the search homes in on smaller objects, the size of the task grows exponentially.

• ED LU, Sentinel Mission:

  If you want to find a million asteroids, finding 1,000 a year doesn't cut it, right?

• MILES O’BRIEN:

  Ed Lu is a former NASA astronaut, now CEO of the nonprofit B612 Foundation. The organization hopes to raise $450 million to build launch and operate an infrared space based telescope designed to find a few hundred thousand asteroids in its first year of operation alone.

• ED LU:

  And this is all being done by a private organization, because NASA simply doesn't have the money to do this. And it's within the capability of individuals to solve that problem, because NASA simply isn't doing it.

• MILES O’BRIEN:

  The magnitude of the problem became a reality in July of 1994 with the comet Shoemaker-Levy 9. Jupiter's gravity broke it into 21 fragments. It then plowed into the giant planet over the course of a week.

• ROBERT MACNEIL, Anchor:

  Jupiter's collision with a giant comet is next.

  Mrs. Shoemaker, thank you for joining us. Are you satisfied with the splash your little comet is making?

• CAROLYN SHOEMAKER, Astronomer:

  Oh, Robin, I'm thrilled with the splash my comet is making.

  (LAUGHTER)

• MILES O’BRIEN:

  The whole world was watching, thanks to the eagle eyes of Carolyn Shoemaker.

  I caught up with her recently at the Lowell Observatory, near her home in Flagstaff.

  You knew it was real. You saw it with your own eyes.

• CAROLYN SHOEMAKER:

  That's right.

• MILES O’BRIEN:

  Who saw the comet 16 months before impact week began.

• CAROLYN SHOEMAKER:

  That thrilled us, in part because so many people had said, you're not going to see anything at all; it's just going to break up and nothing will be seen.

• MILES O’BRIEN:

  She, her late husband, geologist Gene Shoemaker , and amateur astronomer David Levy were conducting an early survey of near-Earth objects at California's Palomar Observatory when they had the eureka moment.

• DAVID LEVY, Astronomer:

  Shoemaker-Levy 9 was famous not because of what it was, but because of what it did. It was the first time we saw the process of collision.

• MILES O’BRIEN:

  Could something like that happen to Earth? Just one look at the moon offers case in point. We orbit the sun in a rough neighborhood; 65 million years ago, an asteroid six miles' wide hit what is now Mexico, wiping out the dinosaurs. The evidence of this and other impacts is mostly buried, but not Arizona's Meteor Crater.

  In the 19th century, geologists thought this might have been caused by some sort of volcanic explosion. There was a lot of debate over this in the first half of the 20th century, but then in 1960, Gene Shoemaker settled it once and for all. He found minerals here that are smoking gun proof that was a high-powered impact and an explosion.

  So what can we do to defend our planet against this inevitable threat? Surprisingly, scientists say that is the easy part. The method considered simplest, crashing a spacecraft into the asteroid with enough force to knock an it off of its collision course with Earth. In fact, it is something NASA has already done. In 2005, the Deep Impact spacecraft plowed into comet Tempel 1, changing its orbit.

• DON YEOMANS:

  There's three important ingredients for asteroid or comet impact mitigation. We need to find them early, we need to find them early, and we need to find them early.

• MILES O’BRIEN:

  Meanwhile, the scientists in charge of the NASA research satellites that orbit Mars have gradually changed their orbits, so that they will be shielded from the hazards posed by the whizzing debris in Siding Spring's tail.

  Still, they will try to gather as much data as they safely can.

  Rich Zurek is the chief scientist for the Mars program at JPL.

• RICH ZUREK, NASA:

  Our instruments, our cameras and such, aren't really designed to look at a diffuse object. However, we have a ringside seat. If we knew a comet was coming, we might have done something different.

• MILES O’BRIEN:

  Backyard astronomers will also be out in force. At David Levy's home and observatory near Tucson, where the sky is big and beautiful by day and night, he will be on the lookout as Siding Spring slides by the Red Planet.

• DAVID LEVY:

  Comets are not your Facebook activity. Comets are a reminder that the universe is all about time. And it takes its time about showing us things.

• MILES O’BRIEN:

  Levy reminds us the ancients viewed comets as bad omens. If we moderns don't tackle the threat posed by near-Earth objects, we may prove our ancestors right.