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 technology for asteroids takes another leap. David Cooper, general manager of Ontario-based Dynacon, the prime contractor for NEOSSat and the manufacturer and operator of MOST, puts the issue this way:
“NEOSSat requires remarkable agility and pointing stability that has never before been achieved by a microsatellite. It must rapidly spin to point at new locations hundreds of times per day, each time screeching to a halt to hold rock steady on a distant target, or precisely track a satellite along its orbit, and image-on-the-run.”
‘Rock steady’ is an exquisitely apt phrase for an asteroid hunter. And while the mission’s telescope, at 15-centimeters, is an instrument smaller than that used by many amateurs, placing it 700 kilometers about the atmosphere should offer great advantages. In a fifty minute polar orbit, the satellite will, according to team members, be able to detect asteroids delivering as few as 50 photons in a 100-second explosure. The more asteroid cataloging we can do, the better, and NEOSSat’s unique vantage point also offers the possibility of identifying non-threatening, slow-moving asteroids close to Earth for possible rendezvous missions.
Although it demands a sunshade for the satellite, NEOSSat’s polar orbit will allow it to search the sky to within 45 degrees of the Sun, a region hard to observe from the ground but the place where near-Earth asteroids are concentrated, and the only part of the sky where asteroids that orbit entirely inside Earth’s orbit can be discovered. With current estimates of 100,000 asteroids greater than 140 meters in diameter in near-Earth space, finding those on Earth-crossing orbits should be a high priority for a space-capable civilization, one to which even a small aperture telescope can make a contribution.
Add to this the new analyses of Martian terrain published this week in Nature, three letters that examine the Borealis basin, which covers about forty percent of the planet’s surface, and find it to be the remains of a huge impact early in the Solar System’s formation. Mars is home to abundant testimony of the effect of collisions, but the 5300-mile width of the Borealis basin is four times that of the Hellas basin, also on Mars, that had been the largest impact crater identified in the Solar System before now. Every sign points to the Borealis event having been caused by an object larger than Pluto, with an impact at least 3.9 billion years ago.
The early Solar System was rife with such impacts, but we have seen in our own time that much smaller objects (think Comet Shoemaker-Levy on Jupiter in 1994, or Tunguska in 1908) continue to pose a threat to our planet. Every battered landscape we see on the moons of the outer planets, not to mention our own Moon, bears witness to the violent history of our surroundings. Ensuring planetary security will lead us not only to improved asteroid cataloging but, inevitably, to missions to nearby asteroids as we develop the technology needed to adjust a threatening trajectory. Defense alone pushes us deep into the Solar System, from which point we should have the infrastructure needed to stay.