Mar 12 2007, 12:01 PM
A dedicated space-based telescope is needed to achieve a congressionally mandated goal of discovering 90% of all near-Earth asteroids down to a size of 140 metres by the year 2020, says a report NASA sent to the US Congress on Thursday. Asteroids of that size are large enough to destroy a major city or region if they strike the planet – but NASA says it does not have the money to pay for the project.
- Could Venus watch for Earth-bound asteroids?
Mar 12 2007, 05:36 PM
It might be that a telescope orbiting the Sun near the distance of Venus would be the most efficient at detecting NEOs, but the cost would be huge, compared to an Earth-based system. I would rather have a less efficient, but operational, Earth-based effort than a 'better' but far more expensive system that is never built.
Mar 13 2007, 08:52 AM
Earth-based and Earth-orbit-based searches have low sensativity to asteroids with aphelions close to Earth's orbit. They spend most of their time near the Sun in the sky and you mostly see their nightsides when they're near Earth, with low brightness crescent illumination.
Move a spacecraft with a 1 meter infrared telescope (thermal IR, I think) in somewhere near Venus' orbit and look out toward Earth's orbit, and you see them in full phase, well illuminated, and thermally hot. Much more detectable.
Also... Some asteroids are in nearly synchronous orbits with the Earth, doing 3 solar orbits while Earth does 2, or 2 orbits while Earth does 3, etc.. (and all the other small number resonances that are relevant) Earthbased searches may miss them for decades, as various bad phasing and viewing geometries can "conspire" to hide them. A near-Venus-orbit mission can't be fooled by such "antics" and will "gotcha" that population as easily as any others in similar orbits.
Mar 24 2007, 11:39 PM