A consortium of astronomers from universities around the world have started a project to patrol the night skies for intruders. Their targets aren’t alien spacecraft looking for a dry patch of Earth on which to set down. These scientists are mapping asteroids and other objects in Earth’s vicinity that could one day strike our planet.
Our solar system contains a number of asteroids and other debris that orbit the sun, sometimes in meandering patterns that can bring them in close proximity to larger objects, like planets. In those cases, a planet’s stronger gravitational pull can draw the wandering asteroid closer until it collides with the planet. All of the solar system’s planets have been hit by comets, asteroids, or even larger bodies countless times over the past 4.6 billion years of our solar system’s existence. In fact, some 4.5 billion years ago, a very young Earth was hit by an object roughly the size of Mars, leading to the formation of our beloved Moon. Some 65 million years ago, an asteroid hit Earth just off of Mexico’s Yucatan Peninsula, contributing to the mass extinction even that (among other things) robbed Earth of its dinosaurs. In 1994, Comet Shoemaker-Levy 9 broke apart and collided with Jupiter. More recently, another mysterious object (probably an asteroid) hit Jupiter near one of its poles.
These impacts don’t occur very often. Most of the time, the asteroids and comets of the solar system coexist peacefully with their larger planet (and dwarf planet) neighbors. And even when comets hit Jupiter, for example, life on Earth continues unabated. The problem is that — sometimes — asteroids and comets hit Earth. Smaller versions of these objects burn up in our atmosphere, creating beautiful shooting stars for us to glance at as they dance across the night sky. Larger objects, however, can punch through the atmosphere, hitting the surface. The damage they can cause depends on the size: smaller impactors cause less damage.
Recognizing these realities, in the early 1990s the U.S. Congress directed NASA to investigate methods to find asteroids and comets in Earth’s vicinity, and to divert or destroy large objects that may impact the planet. In 1994, the House of Representatives gave NASA ten years to form strategic partnerships with other space agencies and institutions to identify 90% of asteroids and comets with a diameter greater than 1km which have orbital patterns crossing Earth’s own orbit. Thus, NASA began to foster relationships with universities and space agencies around the world, utilizing ground-based telescopes to painstakingly catalog our local skies for these “larger” threats (an object over 1km in diameter could devastate life on our planet if it hit us). In 2003, NASA delivered its report and catalog of 1km (or larger) objects to Congress, and two years later Congress expanded on that original mission: by 2020, NASA and its partners must identify 90% of objects near Earth with a diameter greater than 140m. The 140m guidepost is not a random target: astronomers have repeatedly warned that even asteroids or comets with a diameter as small as 150m could cause massive local devastation if they hit Earth.
Given this substantial mandate, NASA has extended and expanded its international partnerships to map the skies for near-Earth threats. The large telescope pictured above is a new addition to this sky-watching party. The telescope resides near the summit of Haleakalā on the Maui Island in the State of Hawaii. Termed Pan-STARRS 1 (for Panoramic Survey Telescope And Rapid Response System), this telescope is the first of four to be constructed on either Maui Island or nearby Mauna Kea on the Island of Hawaii. When all four Pan-STARRS telescopes are completed at a cost of over $100 million, they will work together to peer into the deepest reaches of the universe to chart the evolution of galaxies and search for elusive dark matter. For now, only Pan-STARRS 1 is up and running, and one of its first missions is to help map near-Earth objects in the night sky.
The Pan-STARRS 1 mission consortium includes scientists from eight universities and organizations in the U.K., Taiwan, Germany, and the U.S. While Pan-STARRS 1 has been operating full-time for the past month, now the telescope will begin a dusk-to-dawn scan of the night sky, taking repeated images with its high-powered cameras. Computers will monitor the orbits of known near-Earth objects to see if anything looks amiss, and identify and track new near-Earth objects. The Pan-STARRS 1 consortium would like to identify all near-Earth objects with a diameter of 300m or more using this night-scan method.
Pan-STARRS 1 is much more powerful than other ground-based telescopes, both in terms of the amount of sky it can observe and the resolution it can offer. In one month, Pan-STARRS 1 can survey one-sixth of the sky, and can complete two full surveys of the night sky in a year. This is a much faster and accurate rate than previous surveys, and will permit repeated observations of near-Earth asteroids and comets even within the span of a few months. In addition, Pan-STARRS 1 has the resolution to identify smaller objects. It can also accurately view those portions of our night sky that lie against the backdrop of the Milky Way, one of the arms of our galaxy which has obstructed ground-based telescopes in the past. Thus, Pan-STARRS 1 is a vast improvement on our ability to track near-Earth comets and asteroids.
The launch of the Pan-STARRS 1 program should give NASA hope that it can indeed meet its goals to map and track near-Earth comets and asteroids by 2020, paying special attention to those larger objects which could threaten life on this planet. However, tracking is one thing. Once we identify an object that may threaten us, what should we do? That, unfortunately, is a problem we’re still working on.
Image provided courtesy of the Pan-STARRS 1 Science Consortium and Rob Patkowski.