Summary of the 2017 Apparition

UPDATE!! 2012 TC4 has been recovered by VLT observers!

2017 Aug 06: Owing to the latest VLT observations by O. Hainaut, D. Koschny, and M. Micheli, 2012 TC4 is now recovered! Initial observations of a potential object found on July 27, 2017 were confirmed on July 31 and August 5, 2017.

Astrometry from these new observations improved the orbital solution, indicating that the nominal close approach distance, at 0.000335 AU (~50100 km) is closer than was thought from the previous solution, and will occur 1 hour an 47 minutes earlier, at 5:41 on Oct 12. The object's H-magnitude value is near 26.7, corresponding to a diameter of around 15 meters for an object with an albedo of about 15%. A copy of the Minor Planet Electronic Circular that reported the recovery can be found here.

2012 TC4 is a near-Earth asteroid

  • Makes a very close approach to the Earth on Oct 12, 2017 05:40:55 UT
    • Passes within the Moon's orbit
  • Geocentric Distance (current best value - JPL#34)
    • 0.000335 AU
    • 7.9 Earth Radii
    • 0.13 Lunar distances
    • 50,168 km
    • 31,173 miles


  • Not very well constrained
  • Current estimates suggest it should peak around mag 13 at closest approach
  • Only brighter than mag 20 for the week before close approach

Observing conditions (for observations at visible wavelengths)

  • Conditions are fairly good for the asteroid's approach
    • Near opposition
    • Earth-facing surface is mostly illuminated
    • Visible for many (6+) hours per night, for months before close approach
    • Its orbit is within 1° of the ecliptic, so it is observable from both hemispheres.
  • Within ~12 hrs of close approach, conditions change rapidly
    • Declination decreases from -9° (@-12 hrs) to -46° (@close approach) then rises again to +6 deg (@+12 hr).
    • Solar elongation decreases from 138° (@-12 hr) to 53° (@close approach) to a minimum at 16° (@+5 hr) and then slowly rises again to 39° (@+12 hr).
    • Brightness increases rapidly, peaking shortly before close approach, then even more rapidly drops to become very faint.
    • Radio and IR studies, which may be able to observe during the day, may be more successful in post-close approach time period than visible wavelength observations.
    • The example values listed here are given relative to a geocentric observer, but because the close approach distance is small, the specific geometric conditions will be strongly dependent on the observer's actual location.
  • Locations for observing around closest approach
    • At the time of closest approach, 2012 TC4 will be over a point in the ocean south of Australia. Unfortunately, this occurs several hours before local sunset, so Australia is a poor location for observing any part of the closest approach phase of the encounter.
    • Because the south Pacific extends to the East of the close approach point, there are no large ground-based telescopes that will be able to observe the asteroid at close approach when the Sun is below the horizon. However, there should be significant coverage when the asteroid is at its brightest shortly before closest approach.
    • South America is likely to offer the best geometric conditions for ground-based observing. Although the asteroid will set shortly before closest approach, South America offers the longest baseline for observations leading up to the event.
    • Mauna Kea is well positioned for observing the approach and peak brightness, but the asteroid never rises above an altitude of 26° and the sun rises and the asteroid sets before closest approach.
    • The U.S. southwest is well positioned for observing the lead-in to closest approach, though the asteroid never rises above an altitude of 27° and sets before closest approach.
  • Conditions are very poor for the asteroid's departure
    • After close approach, the solar elongation is small
    • Earth-facing surface is mostly in shadow
    • Brightness drops very quickly

Opportunity to characterize this NEA

  • Astrometry - Pin down its orbit
  • Photometry - Derive size, shape, rotation
  • Spectroscopy - Derive composition, taxonomy
  • Radar - Resolved echoes of the surface