It's no trick, but certainly a treat that on 31 October 2015 at 10:00 am PDT the near-Earth object (NEO) 2015 TB145 (nicknamed “spooky” by some) will pass within ~490,000 km or ~305,000 miles from Earth (roughly 1.3 times farther away than the Moon). Using our global network of telescopes at LCOGT, we have been monitoring 2015 TB145 for the past 2.5 weeks since shortly after it was discovered by the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) survey in Haleakala, Maui, Hawaii on 10 October 2015. Using our 1.0-m telescope in Cerro Tololo, Chile, we were one of the first groups to provide follow-up observations of 2015 TB145. These observations helped to improve the NEO's orbit and confirm that it will be whizzing past the Earth on Halloween.
The movie shows images taken from our 1.0-m telescopes in Southerland, South Africa and Cerro Tololo, Chile taken during seven 15 minute windows spaced roughly 1 hour apart. During this time, roughly 7 hours altogether, 2015 TB145 travels a distance across the sky of about 2.3 times the diameter of the Moon.
2015 TB145 is about 400 m in diameter (roughly 0.25 mile). At this size, if you were to skewer 2015 TB145 with the empire state building, only a small portion of the spire on top would stick out! It is roughly twenty times as large as the asteroid that hit Chelyabinsk, Russia on 15 February 2013. 2015 TB145 has a zero probability of hitting the Earth on Halloween, but keeping a watchful eye on all NEOs that come close to the Earth is important for determining the probability that future asteroids and comets could strike us and is an integral part of the work we do at LCOGT. Our ability to use multiple sites allows us to watch multiple objects at a time, and when keeping a close eye on one particular object these sites provide multiple opportunities to observe the object should one site develop bad weather or need to be used by another observing group.
2015 TB145 has a high eccentricity (highly elliptical) orbit with a three year orbital period that makes this Earth close approach quite rare since the NEO and Earth are rarely in the same place at the same time, making this a unique opportunity for astronomers to study this object. The observations from LCOGT telescopes will aid astronomers at NASA in aiming their Goldstone radio antennas at 2015 TB145, which will allow them to determine the object's shape using detailed radar images.
2015 TB145's unusual orbit also has astronomers curious as to whether it is an asteroid or a comet. Its highly elliptical orbit appears more like that of a comet, but 2015 TB145 does not show any signs of a bright coma or tail as it gets closer to the Sun as comets typically do. This could mean 2015 TB145 is an 'extinct' comet that has already lost all of its volatile material and now looks more like an asteroid. Its close proximity to the Earth will allow astronomers to take a closer look and hopefully answer this question. Overall, 2015 TB145 is proving to be quite a Halloween treat for astronomers!
Happy Halloween!
This work is supported in part by a NASA Near Earth Object Observations (NEOO) Grant (NNX14AM98G) to LCOGT.