Earth's geological history could have a lot to say about our future in space. Every time we investigate a huge crater like Chicxulub, the Yucatan impact site that may have played a role in the demise of the dinosaurs, we're reminded that the Solar System is an active and dangerous place. And the evidence multiplies. The Wilkes Land crater in east Antarctica may bear witness to the Permian-Triassic extinction that destroyed almost all life on Earth some 250 million years ago. A defensive system in space with the capability of deflecting dangerous Earth-crossing objects is vital for species survival, whether the next strike occurs in ten or a hundred thousand years. But it's a hard concept to sell because Earth's major strikes, unlike those on the Moon, for example, tend to be obscured over time. Absent a visible historical context, a relatively minor strike like the 1908 Tunguska event can come to be seen as a quirky accident rather than evidence of a larger threat. Now comes word of...

The potential threat from near-Earth asteroids can sometimes seem purely theoretical, an academic exercise in how orbits are calculated and refined. But when we start quantifying possible damage from an asteroid strike, the issue becomes a little more vivid. Modeling potential impact points all over the planet, a University of Southampton (UK) team has worked out some stark numbers. The University's Nick Bailey presented the results at the recent Planetary Defense Conference in Washington. The researchers put a software package called NEOimpactor to work on asteroids under one kilometer in diameter and assumed an impact speed of 20 kilometers per second. Obviously, larger objects are out there and the impact velocity is arbitary, but asteroids in this size range seem to hit the Earth every 10,000 years, frequent enough that the next one that does hit will probably fit this description. Says Bailey: 'The consequences for human populations and infrastructure as a result of an impact...

A little bit of asteroid 1999 RQ36 may wind up on Earth in 2017. That's assuming that NASA's OSIRIS mission launches in 2011, with the aim of investigating the properties of such Earth-crossing bodies. And while an asteroid sample may help us understand much about the early Solar System, OSIRIS offers a potentially greater benefit. It can help us sharpen our tracking skills so we can plot asteroid orbits with much greater precision. How? You'll recall that we recently discussed the the Yarkovsky Yarkovsky-O'Keefe-Radzievskii-Paddack effect. YORP is the minute push that an asteroid receives over time as it absorbs sunlight and emits heat -- let's call it the Yarkovsky Effect for short. It's a tricky thing to measure because of the uneven nature of asteroidal surfaces, and the varying wobble and rotation of each. Trying to predict an asteroid's orbit as it approaches Earth demands that we take the Yarkovsky Effect into account. And OSIRIS is tasked with measuring the effect for the...

NASA's March report to Congress on deflecting Near-Earth Objects offers some startling assessments. Specifically, the report says this: "Nuclear standoff explosions are assessed to be 10-100 times more effective than the non-nuclear alternatives analyzed in this study. Other techniques involving the surface or subsurface use of nuclear explosives may be more efficient, but they run an increased risk of fracturing the target NEO. They also carry higher development and operations risks." Fair enough re setting off a nuke on the surface of an asteroid. But aren't we jumping the gun on other nuclear options when alternatives seem available? That's certainly the view of Rusty Schweickart, founder of the B612 Foundation, which is all about spreading the word on the threat these objects may pose to Earth. Alan Boyle discussed these matters with Schweickart in a recent post, from which this on the non-nuclear option: Schweickart argues that the so-called "nuclear standoff" option should be...

OK, we sometimes encounter scientific terms with large numbers of syllables, but how about this one, perhaps the prize winner: the Yarkovsky-O'Keefe-Radzievskii-Paddack Effect. This multicultural monicker -- drawn on the names of a Russian engineer, an American scientist, a Russian astronomer and a NASA aerospace engineer -- has something interesting to say about sunlight. As solar radiation heats and cools an asteroid, released energy can change its rotation. In the case of the asteroid 2000 PH5, the effect increases the spin rate to the point where the asteroid may eventually come to spin faster than any asteroid known. This complicated study used a variety of telescopes to make the case that the asteroid's rotation period decreases by 1 millisecond every year. That's a long and slow effect, but the results build over time, and they're more readily observable because 2000 PH5 approaches Earth every year. The cause is the heating of the asteroid's surface by the Sun. Stephen Lowry...

NASA is putting the number of potentially hazardous asteroids and comets at 20,000 in a report that will be released later this week, according to an AP story now circulating. And the report, reviewed at a Planetary Defense Conference in Washington yesterday, pegs the cost of finding 90 percent of these objects at $1 billion. That's bad news for those worried about Earth-crossers. For AP quotes NASA Ames director Simon Worden: "We know what to do; we just don't have the money." And as Larry Klaes wrote me this morning, "But just imagine the bill after a big space rock hits Earth." NASA is already tracking some 769 objects in a search now described as behind schedule. From the story: One solution would be to build a new ground telescope solely for the asteroid hunt, and piggyback that use with other agencies' telescopes for a total of $800 million. Another would be to launch a space infrared telescope that could do the job faster for $1.1 billion. But NASA program scientist Lindley...

At the University of Alabama at Huntsville, a team of scientists and engineers is looking into the possibility of identifying and deflecting Earth-endangering asteroids with lasers. Blake Anderton, an engineer at Raytheon Corp., wrote his thesis on the topic. From a UAH news release: Anderton said his thesis discusses "a way to look at asteroids at maximum range, which means early detection." According to his calculations, an asteroid could be characterized up to 1 AU away (1.5 x 10 to the 11 meters). Arecibo and other radar observatories can only detect objects up to 0.1 AU away, so in theory a laser would represent a vast improvement over radar. The laser the group is working on may one day evolve into a system with asteroid-nudging capabilities. UAH's Richard Fork, who has compiled forty years of experience with lasers, says the work goes back to research he and others performed in the 1980s at AT&T Bell Laboratories. Remote sensing is a short-term goal, but Fork says "My vision...

What would happen if asteroid 99942 Apophis ever hit the Earth? It's about 1200 feet in diameter, and according to David Morrison (NASA Ames), that's large enough to obliterate an area the size of England. The subject was under discussion at the recent American Association for the Advancement of Science meeting, and is reported capably in this Columbus Dispatch story, which quotes others on their own conclusions. Jay Melosh, a geophysicist at the University of Arizona's Lunar and Planetary Laboratory, said that if Apophis struck Earth, it would produce a 40-megaton blast, almost eight times larger than the most powerful nuclear bomb ever detonated. The explosion would create a crater more than 2 miles wide and obliterate buildings and bridges in a 4-mile radius. Melosh said everything around it would be buried beneath 20 inches of debris. Nice to see a sober article discussing asteroid deflection in the popular press. Apophis probably isn't going to make this kind of history, but the...