  In the outer Solar system, primordial Trojan asteroids may have remained
dynamically stable for billions of years. Several thousands of them accompany
Jupiter in its journey around the Sun and a similarly large population may be
hosted by Neptune. In addition, recently captured or transient Jovian and
Neptunian Trojans are not uncommon. In contrast, no Trojans of Saturn have been
found yet and just one Uranian Trojan is known, 2011 QF99. Here, we discuss the
identification of a second Trojan of Uranus: 2014 YX49. Like 2011 QF99, 2014
YX49 is a transient L4 Trojan although it orbits at higher inclination (25.55
degrees versus 10.83 degrees), is larger (absolute magnitude of 8.5 versus 9.7)
and its libration period is slightly shorter (5.1 versus 5.9 kyr); contrary to
2011 QF99, its discovery was not the result of a targeted survey. It is less
stable than 2011 QF99; our extensive N-body simulations show that 2014 YX49 may
have been following a tadpole trajectory ahead of Uranus for about 60 kyr and
it can continue doing so for another 80 kyr. Our analysis suggests that it may
remain as co-orbital for nearly 1 Myr. As in the case of 2011 QF99, the
long-term stability of 2014 YX49 is controlled by Jupiter and Neptune, but it
is currently trapped in the 7:20 mean motion resonance with Saturn.
Consistently, the dynamical mechanism leading to the capture into and the
ejection from the Trojan state involves ephemeral multibody mean motion
resonances.
