Measuring the Spins of Trans-Neptunian Objects

Figure 1: Artist’s impression of a trans-Neptunian object. Credit: NASA/JPL-Caltech/T. Pyle (SSC).

Using the exquisite photometric precision of NASA’s repurposed Kepler space telescope as part of the K2 mission, A. Pál et al. (2015) present the first K2 observations of two trans-Neptunian objects (TNOs). As an object rotates, its shape and surface albedo variations can cause its observed brightness to vary. This variation in brightness is known as the rotational light curve and its periodicity gives a direct measurement of the object’s rotational period.

The two TNOs observed by K2 are 2007 JJ43 and 2002 GV31. From the observed rotational lightcurves, 2007 JJ43 and 2002 GV31 are found to have rotational periods of 12.097 hours and 29.2 hours, respectively. 2007 JJ43 is a relatively large object located near the outer edge of the Kuiper belt. Its diameter is estimated to be ~600 km. At this size, its self-gravity is certainly strong enough for it to be a round object. The other TNO, 2002 GV31, is much smaller with an estimated diameter of less than 200 km.

Figure 2: Rotational light curve of 2007 JJ43 (red points). The bold symbols with the error bars are binned values. A. Pál et al. (2015).

Figure 3: Rotational light curve of 2002 GV31 (red points). The bold symbols with the error bars are binned values. A. Pál et al. (2015).

Reference:
A. Pál et al. (2015), “Pushing the limits: K2 observations of the trans-Neptunian objects 2002 GV31 and (278331) 2007 JJ43”, arXiv:1504.03671 [astro-ph.EP]