Podcaster: Dr. Al Grauer
Title: Travelers in the Night Eps. 177E & 178E: That’s 2 & EX Most Dangerous
Organization: Travelers in The Night
Description: Today’s 2 topics:
- Gennady Borisov’s new asteroid, 2015 RH2, has a diameter about one and a half times the size of a football field.
- 2015 PU228 was thought to be the asteroid most likely to collide with Earth in this century.
Bio: Dr. Al Grauer is currently an observing member of the Catalina Sky Survey Team at the University of Arizona. This group has discovered nearly half of the Earth approaching objects known to exist. He received a PhD in Physics in 1971 and has been an observational Astronomer for 43 years. He retired as a University Professor after 39 years of interacting with students. He has conducted research projects using telescopes in Arizona, Chile, Australia, Hawaii, Louisiana, and Georgia with funding from NSF and NASA.
He is noted as Co-discoverer of comet P/2010 TO20 Linear-Grauer, Discoverer of comet C/2009 U5 Grauer and has asteroid 18871 Grauer named for him.
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177E: That’s 2
Gennadii Borisov has done it again. In a stretch of less than six weeks this talented observer and telescope maker discovered two interesting Earth approaching objects. In this age of big science it is gratifying to see that an individual with relatively modest equipment can make scientific discoveries. In this case Borisov beat my team the Catalina Sky Survey and the Pan-STARRS group in Hawaii with our large telescopes and powerful computer systems to the discovery of a significant object.
Borisov discovered his new asteroid using a half meter telescope and an electronic camera. After posting his observations on a Minor Planet Center website this object was tracked by 11 different observatories around the world.
Gennady Borisov’s new asteroid, 2015 RH2, has a diameter about one and a half times the size of a football field. It crosses the orbits of the Earth and Mars as it orbits the Sun every once every 489 days. In October of 2011, nobody spotted it as it passed the Earth about 50 times the Moon’s distance from us at a speed of 6 miles per second. At its closest 2015 RH2 can come to within 4.4 times the distance to the Moon from us. The current data indicates that 2015 RH2 will make a particularly close approach to planet Earth in February of 2024. As the asteroid hunting community continues to track this object our knowledge of its orbit will continue to improve. Not to worry, there is no chance that 2015 RH2 will collide with the Earth in the foreseeable future.
178E: EX Most Dangerous
For a week or so after its discovery by the 3.5 meter Space Surveillance Telescope, 2015 PU228 was thought to be the asteroid most likely to collide with Earth in this century. Calculations based on limited data indicated that this asteroid had a one in 23,000 chance of colliding with our planet in January of 2081. As the length of 2015 PU228’s observed path in the sky grew its chances of a collision with Earth decreased. More than a month’s observations has made us sure that it will completely miss planet the Earth in 2081.
How could such a dramatic change in our prediction of a possible collision occur? We know the Earth’s orbit with great precision and can calculate exactly where it will be far into the future. A recently discovered asteroid is a different story. In this case, 2015 PU228 takes more than 1200 days to orbit the Sun. If we have only a week or so’s worth of data it’s orbit is very poorly know.
Typically, as the length of a newly discovered close approaching asteroid’s measured path around the Sun increases its impact probability grows until it suddenly drops to zero indicating a complete miss of our planet.
Against enormous odds, perhaps one day, perhaps even tonight, asteroid hunters will discover an object for which every new observation makes it appear more likely that it will collide with planet Earth. Hopefully, if a large threatening object is ever discovered there will be sufficient lead time so that humans can take steps to mitigate the damage an impacting asteroid could cause.
For Travelers in the Night this is Dr. Al Grauer.
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