Why was 2015 TB145 detected just weeks before its closest approach, while so many other asteroids (which will make closer approach or farther approach) are detected years before? What made this asteroid difficult to detect?

  • $\begingroup$ Can anybody explain why it is difficult to detect the asteroids based on the @LocalFluff orbital inclination histogram and to which angle of inclination does this asteroid belong? $\endgroup$
    – r2_d2
    Oct 27, 2015 at 12:01

2 Answers 2


2015 TB145 had an apparent magnitude of 20 when it was discovered. This is pretty faint and may account for it not being found earlier.

Most asteroids have a small inclination (angle relative to the ecliptic plane). Some of the early asteroid surveys didn't look at high inclinations, because it can take a long time to do a survey of the entire sky. These programs need to look at the same area of sky several times per year to detect which objects have moved, so they made a decision to limit the area they looked at. With increasing computing power and better CCDs it became possible to do full-sky surveys. These detection programs tend to get hardware upgrades every few years.

Pan-STARRS (which discovered 2015 TB145) does full-sky surveys and has been operational since 2010. So even with this inclination, Pan-STARRS has looked at the region of sky where 2015 TB145 was several times already without detecting it.

  • $\begingroup$ Does not checking the entire sky makes us vulnerable to those faint high inclination asteroids? $\endgroup$
    – r2_d2
    Oct 27, 2015 at 14:33
  • $\begingroup$ Yes, but most programs are entire-sky surveys by now. $\endgroup$
    – Hobbes
    Oct 27, 2015 at 14:43

I bet that the high inclination, 40 degrees, is the explanation. Very few asteroids are, or have been found, at such high inclination. But I don't specifically know how asteroid searches work with inclinations.

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  • $\begingroup$ with respect to which plane? $\endgroup$
    – r2_d2
    Oct 27, 2015 at 11:51
  • $\begingroup$ @r2_d2 I would assume the ecliptic. That's usually the plane of reference in this context. $\endgroup$
    – called2voyage
    Oct 27, 2015 at 13:23

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