Should the Cluttered Skies Demote Earth?

If you want to be a purist, the plethora of nearby asteroids suggests that Earth is just a dwarf planet, like its distant cousin Pluto.

Like planes zipping in and out of Chicago's O'Hare airport, in just one night (Jan. 29) 16 near-Earth asteroids whizzing across the sky were discovered by the prototype Panoramic Survey Telescope & Rapid Response System (Pan-STARRS), PS1, on Haleakala, Maui.

The wide-field telescope observes the entire night sky several times each month and stores away huge quantities of data. This yields a "movie" of the sky where moving objects like faint asteroids can be caught. Enhancement of Pan-STARRS software and multiple observation techniques have minimized the risk for false detections since it started operation last year.

Pan-STARRS is now the most sensitive system dedicated to discovering potentially hazardous asteroids, say its builders.

This latest observation reminds us that we live in a dangerously cluttered region of the solar system. Over 1,200 potentially hazardous asteroids have been cataloged in sky surveys so far. These pass within 4 million miles of Earth. There could be as many as 20,000 such objects according to some estimates.

The Blue Dwarf

This leads me to my next point. If you want to be a purist, the plethora of nearby asteroids suggests that Earth is just a dwarf planet, like its distant cousin Pluto.

That is, at least by the definition the International Astronomical Union hobbled together in 2006. Let me quote from one of their qualifications: " (a planet) has cleared the neighborhood around its orbit."

Well, sorry, but one look at the diagram above, from just one night of Pan-STARRS observations, shows that Earth has not accomplished this.

In fact, the density of objects per cubic volume of space in the Kuiper belt is likely much lower than here in the inner solar system. If one want to impose the IAU's dynamical rule for the definition of a planet, Earth fails the test.

Asteroid Hunters

PS1 and its bigger brother, PS4, which will be operational later this decade, are expected to discover a million or more asteroids in total. In addition, the planned Large Synoptic Survey Telescope will be able to find 90 percent of the Earth-threatening asteroids over 400 feet in diameter.

Last summer, a NASA advisory task force recommended that the space agency build and launch an infrared survey telescope that would orbit closer to the sun than Earth. Looking outwards toward Earth's orbit, the telescope would have a truly panoramic view of asteroids in Earth-crossing orbits. This would catch the asteroids that ground-based telescopes might miss.

The photo below shows the panoramic view you get of the planets as viewed by looking outward from near the sun. It was taken by NASA's Mercury Messenger spacecraft. The planets are, from left to right Venus, Earth-moon, Jupiter, Uranus, Neptune, Mars, Mercury, Saturn.

An infrared telescope with this view sure would be useful!

Photo credit: Smithsonian Institution/Rob Ratkowski/NASA