Naked Eye Visible Comet Pann-Starrs, The Dangers Of Comets And NEOs

 

 

This is Comet Pan-STARRS’s first visit to the inner solar system, so surprises are possible as its virgin ices are exposed to intense solar heating.

Pan-STARRS, the observatory that found the new comet, is designed to be an advance to the next level in NEO survey work. This new system will have 3-16 times the collecting power of the current NEO survey telescopes and a massive array of state-of-the-art CCD detectors in the focal plane. They will enable the Pan-STARRS survey to reach about 5 magnitudes (a factor of 100) fainter objects than observed by current NEO surveys. Further, Pan-STARRS’ large field of view (7 deg2 per exposure) is larger than that of any of the current NEO survey programs. This will allow us to observe the available sky faster and more frequently than any of the current programs. Finally, Pan-STARRS will have higher spatial resolution than the existing survey systems, allowing us to work in the parts of the sky where the ecliptic plane overlaps with the Milky Way, often too crowded with stars for the current surveys to observe effectively.

The Pan-STARRS system consists of more than just the telescope and CCD cameras. Backing up the observing equipment will be a powerful computing environment that will process the observations, calibrate the astrometric and photometric (position and brightness) properties of individual observations, and detect the “moving” objects such as asteroids, comets, and trans-Neptunian objects (TNOs). The system will also track all objects already known (or discovered by itself), so that on future nights when an object is reobserved it can be rapidly identified and if necessary, its orbit updated to include the new data. There are currently about 100,000 known moving objects in our solar system that are tracked by professional astronomers. With Pan-STARRS, we estimate that we will catalog up to 10 million main-belt asteroids and tens of thousands of NEOs and TNOs.

By reaching objects 100 times fainter than those currently observed in the NEO surveys, Pan-STARRS should quickly help finish off the Congressional mandate to find and determine orbits for the 1-km (and larger) threatening NEOs. Further, we will be able to push the detection limit for a complete (99%) sample down to objects as small as 300 meters in diameter. Such objects, while not capable of wiping out life on Earth, would cause considerable local and/or regional damage should one collide with our planet.

 

(Please allow time for animation to load) Animation of asteroids in the solar system. The central white object is the Sun; the others are Mercury, Venus, Earth, Mars and Jupiter respectively. Blue dots are asteroids whose orbits do not cross the Earth’s orbit, and yellow dots are Earth-crossing asteroids. Animation by Nick Kaiser

Since it formed over 4.5 billion years ago, Earth has been hit many times by asteroids and comets whose orbits bring them into the inner solar system. These objects, collectively known as Near Earth Objects or NEOs, still pose a danger to Earth today. Depending on the size of the impacting object, such a collision can cause massive damage on local to global scales. There is no doubt that sometime in the future Earth will suffer another cosmic impact; the only question is “when?”. 

 

 

There is strong scientific evidence that cosmic collisions have played a major role in the mass extinctions documented in Earth’s fossil record. That such cosmic collisions can still occur today was demonstrated graphically in 1994 when Comet Shoemaker-Levy 9 broke apart and 21 fragments, some as large as 2 km in diameter, crashed into the atmosphere of Jupiter. If these fragments had hit Earth instead, we would have suffered global catastrophes of the kind that inspire science fiction movies:

Shoemaker-Levy 9
Asteroid threats in science fiction movies

The dangers posed by these intruders in the inner solar system are now the subject of serious scientific investigation. Excellent introductions to the NEOs and the threat they pose to our planet can be found at the following websites:
NEO website at NASA’s Jet Propulsion Laboratory
Asteroid Impact website at NASA’s Ames Research Center
The asteroid/comet connection news page
“Eyes wide shut”: Nature article by David Jewitt

Most of the asteroids and comets in our solar system pose no danger to our planet. But, for every thousand or so of those objects, there is one with an orbit crosses that of Earth, raising the possibility of a future collision. In 1991 the U.S. Congress directed NASA to conduct workshops on how potentially threatening asteroids could be detected, and how they could be deflected or destroyed. This mandate led to theSpaceguard Survey Report in 1992. In 1994 the House Committee on Science and Technology directed NASA, in coordination with the DOD, to work with the space agencies of other countries to identify and catalogue within 10 years the orbital characteristics of 90% of all comets and asteroids larger than 1 km and in orbits that cross the orbit of Earth.

Following the 2003 NASA report from the Near-Earth Object Science Definition Team, Congress went even further and in 2005 assigned NASA the task of detecting 90% of near-Earth objects with a size greater than 140 meters in diameter by the year 2020.

In response to these mandates from Congress, several programs have been undertaken to map the orbits of large NEOs that might pose a danger to Earth. These include the following projects:
Lincoln Near Earth Asteroid Research (LINEAR)
Lowell Near Earth Object Search (LONEOS)
Near-Earth Asteroid Tracking (NEAT)
Spacewatch
Catalina Sky Survey

These search programs have discovered hundreds of thousands of main-belt asteroids, and have identified thousands of NEOs. They have made great progress toward meeting the Congressional mandate and have cataloged most, but not all, of the 1-km and larger NEOs — the ones that are most likely to produce a global catastrophe, such as a mass extinction should they collide with Earth. Pan-STARRS will complete the survey of all 1-km diameter objects, and will detect most of the dangerous objects down to 300 meters in diameter — objects that can cause major regional catastrophes should they hit the Earth.

What can be done if one of these surveys finds an asteroid on a collision course with the Earth? Scientists and engineers at theB612 foundation are looking at ways of using a spacecraft to gently change the orbit of an asteroid. One promising approach is the “gravity tractor” invented by NASA astronauts Ed Lu and Stan Love.