Asteroid 2015 TB145 – Close Approach to Earth on 31 October

Discovered by Pan-STARRS on 2015 October 10, this Apollo-type object probably measures 300-600 metres across and is in a short-period (3.07 yr) comet-like orbit tilted 40 deg to the ecliptic.  It is due to reach perihelion 0.29 au from the Sun on 2015 December 11. To date, the object appears to be only asteroidal in nature and will pass within 1.27 lunar-distances of the Earth on October 31 17:01 UT.

Observers in the UK have their best views on the night of Friday, October 30/31 when it will attain 11th magnitude and be located between the Hyades and Orion. Unfortunately, its path remains close to a bright Moon and so a medium-size or larger telescope will be required to see it in the glare of our nearest neighbour in space. The following table lists the periods of visibility, etc. for UK-based observers during the run-up to closest approach.

Date / Time (UT)            Magn. (V)  Motion (“/min) Moon illum. Dist.(deg)
Oct. 27/28 23:00-05:00   15.8-15.6    1.5-1.8       100-99%       29-26
Oct. 28/29 22:00-05:20   15.2-14.9    2.8-3.6        97-96%        20-17
Oct. 29/30 21:45-05:30   14.2-13.7      7-10          92-90%        16-16
Oct. 30/31 21:30-05:30   12.5-11.4     32-96         85-82%        17-13

Due to its relative proximity, observers will need to look up an ephemeris of its positions for a location or observatory near them to avoid parallax effects. A good source is available from the Minor Planet Ephemeris Service at:

Make sure you enter a suitable location by clicking on ‘Observatory Code’ and choosing from the list then entering the IAU Code in the box provided halfway down the webpage. For England, I suggest using the code ‘456’.

Radar observations of 2015 TB145 have been scheduled and these, it is hoped, will show the object in unprecedented detail (2-m resolution). An informative article can be found on NASA’s Jet Propulsion Laboratory’s website at:

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