16974 Iphthime (/ɪfˈθaɪmiː/; provisional designation 1998 WR21) is a Jupiter trojan and a binary system from the Greek camp, approximately 57 kilometers (35 miles) in diameter.

It was discovered on 18 November 1998, by astronomers with the Lincoln Near-Earth Asteroid Research at the ETS Test Site in Socorro, New Mexico.

[10] Its V–I color index of 0.96 is typical for D-type asteroids, the most common spectral type among the larger Jupiter trojans.

[10] In October 2009, a rotational lightcurve of Iphthime was obtained for the first time by Stefano Mottola from photometric observations during seven nights at the Calar Alto Observatory in Spain.

[6][7][8] The Collaborative Asteroid Lightcurve Link adopts the results obtained by IRAS, that is an albedo of 0.0691 and a diameter of 55.43 kilometers based on an absolute magnitude of 9.8.