Astro Bob blog: A new impact hazard in our future?Spanish astronomers make an uncomfortable prediction about an asteroid discovered in 1999. News on the Mars Spirit Rover
By: Bob King, Duluth News Tribune
A new impact hazard in our future?
A wedge of twilit sky is reflected in Horse Lake in the Boundary Waters two nights ago. Below right are Indian pictographs of a pelican and a canoe (with paddlers and prayer flag) on a cliff overhang on the Basswood River. Photos: Bob King
I've spent the past few days with my friend Glenn in the Boundary Water Canoe Area in northern Minnesota paddling through bogs and lakes, studying the rich array of pictographs on the Basswood River along the international border and eating very well. Mosquitoes were everywhere but 100% Deet and occasional gusty winds helped to allay their full force.
I see while I was away that an asteroid was found to have a 1 in 1000 chance of hitting the Earth in 2182. Maybe you've already heard of this bad boy, which goes by the name of 1999 RQ36. At 1,837 feet across, it's a mighty big rock, and if it did strike Earth would cause an enormous amount of destruction. The University of Pisa's Andrea Milani examined the asteroid's orbit using information from telescopic and radar studies and modeled its future whereabouts. The odds for an impact increase after 2080 as 1999 RQ36's orbit brings it closer to Earth. Although Milani's paper appeared in a noted astronomy journal last year, the story just surfaced this week in the mainstream media.
Artist impression of a good-sized asteroid striking the Earth. Smaller objects like meteorites either burn up or break up and are greatly slowed by their passage through the atmosphere before they hit the ground. A larger object like 1999 RQ36, discovered in 1999, would come crashing to Earth at close to its orbital speed and cause widespread destruction. Credit: AP
There are always uncertainties in pinning down an asteroid's precise orbit. After a number of observations, astronomers determine a preliminary orbit or set of possible orbits for an asteroid. If one or more of those orbits indicate a close pass by Earth, they may assign a certain probability of impact. The only way to know for sure is to make additional observations and refine the orbit. As the data come in, the number of possible orbits drops from many to several and finally to one very good one. No orbit is set in stone, however. Gravitational effects from the planets and other asteroids, and even the pressure of light from the sun -- the Yarkovsky Effect -- can push an asteroid farther from or closer into harm's way.
209 telescopic observations and 13 radar surveys were used to determine the current best-fit orbit for 1999 RQ36. Based on that data, there's a small chance for a hit 172 years from now. Since this asteroid is now an "object of interest", astronomers will continue to observe it and adjust impact probabilities along the way. In the few earlier cases when asteroids were forecast to make dangerously close passes to Earth, probabilities have always been revised way downward the more data points astronomers have added to their orbits. There's a lot of time between now and 2182 for revision. If you'd like to keep up with all this scary stuff, check out NASA's current impact risks website.
Spirit took this self-portrait when its became stuck in the sand last spring on Mars. It hasn't been able to move since. Photo: NASA
Meanwhile NASA scientists haven't heard from the Mars Spirit Rover since March 22. It's now the middle of winter where Spirit sits stuck in the sand on the Red Planet. Its internal temperature has dropped as low as 67 below Fahrenheit. This winter is the toughest yet for the robotic explorer since it couldn't get into position to aim its solar panels at the sun to recharge its batteries. Batteries operate a heater that keeps the electronics running inside the craft. Spirit is likely in low-power hibernation mode hanging on for dear life. NASA usually listens for a regular signal beamed out by the rover, but since that's not been forthcoming, they're now trying to wake it up by sending commands to reply. So far, there's been no response. Could this be the end of the line for the little explorer? For more on the story, please see this press release.
Darkness has returned to the evening sky with the late rising of the last quarter moon. While paddling on the lakes, I enjoyed seeing the moon still up in the blue sky after sunrise. The contrast between its dry, sun-baked surface and the wet pliancy of the water dramatically illustrated how strikingly different our two worlds are. The moon's departure points the way to dark skies for the annual Perseid meteor shower next month. I am so looking forward to kicking back in a lawn chair and watching meteors streak by. I bet you are, too. We'll be taking a closer look at the shower and how to get the most out of watching it in about a week.