Photons streaming outward from the Sun can impart momentum, which is how a solar sail works. But even more subtle effects produced by the warming of irregular objects may have visible results. A new study of asteroid moons and how they form invokes the tongue-twister known as the Yarkovsky, O'Keefe, Radzievskii, Paddack effect, mercifully shortened to 'YORP effect' by those who study it. A body warmed by the Sun gives off infrared radiation, which carries momentum as well as heat. An asteroid's spin can thus be speeded or slowed by sunlight. Add plenty of time and things get interesting. Start with the kind of asteroid that is little more than a pile of rocky rubble held together by gravity, then spin that rubble pile up slowly over a period of millions of years and eventually material will be slung off from the asteroid's equator. Colliding materials of this nature can eventually coalesce into the satellite we see orbiting its parent, says Patrick Michel (Cote d'Azur Observatory,...

As America celebrates its Independence Day, I'm thinking not only of the fireworks in store for tonight but also those that may have lit up northern Canada almost 13,000 years ago. The case for an asteroid or comet impact there has been strengthened by work in Ohio and Indiana that examines an unusual fact: Gold, diamonds and silver found in the region owe their origins to the diamond fields of Canada. Did glaciers bring these deposits, which evidently arrived in the same period as the supposed impact, much further south? Or is geophysicist Allen West correct in flagging them as the signs of an ancient catastrophe? Ken Tankersley, an anthropologist at the University of Cincinnati, doubted West's notion and opted for the glacier theory until his recent work on the deposits. Says Tankersley: "My smoking gun to disprove (West) was going to be the gold, silver and diamonds. But what I didn't know at that point was a conclusion he had reached that he had not yet made public -- that the...

By Larry Klaes "Suddenly in the north sky… the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire… At that moment there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing. The earth trembled." So wrote a witness -- fully forty miles away from the event -- of the Tunguska impact of 1908, whose 100th anniversary is today. As Larry Klaes notes, small bodies still undetected by astronomers could pose the threat of another Tunguska, making the hunt for Earth-crossing objects a matter of high importance not just for science but planetary security. Across the many billions of miles of space that our Solar System occupies in its small piece of the vaster Milky Way galaxy, the most numerous members of our celestial neighborhood by far are the comets, planetoids, and meteoroids. Although much smaller than the Sun, the major planets, and...

With the 100th anniversary of the Tunguska impact in Siberia coming up on Monday (and we'll look at it closely then), several items seem germane to the topic of asteroid deflection. Yesterday, a technical briefing at the University of Calgary outlined the Canadian NEOSSat (Near Earth Orbit Surveillance Satellite) mission, a space telescope designed to track small objects near Earth, some of which may pose a collision threat. The suitcase-sized NEOSSat (launch date 2010) capitalizes on technology developed for Canada's MOST (Microvariability and Oscillation of STars) satellite, which was designed to measure stellar ages in our galaxy. While NEOSSat's asteroid-hunting capabilities draw most media attention, the satellite is also going to act as a monitor on other satellites orbiting the Earth, contributing to the worldwide Space Surveillance Network. Satellite-tracking tests using the MOST instrument have proven that a microsatellite can track other satellites, but tuning the...

Asteroid and comet impacts seem to be obvious culprits in mass extinctions on Earth. The heavily cratered Moon reminds us how severe earlier bombardments have been, and it's an easy segue to note that 23 extinction events are now thought to have occurred since the beginnings of life on our planet. In the past 540 million years (the period during which abundant animal life has existed), we can identify five mass extinctions, with huge losses in particular to marine plants and animals. The Chicxulub crater in the Yucatan is a striking piece of evidence for this scenario, but massive volcanic activity may well have played a role, and perhaps a major one. And what of the other extinctions? A new theory published in Nature seems to put a damper on the easy correlation of extinctions with impacts. Indeed, Shanan Peters (University of Wisconsin-Madison) argues that the largest factor may have been changes in ocean environments related to sea level. Says Rich Lane (National Science...