Science - USA (2020-04-10)

and their pulse widths. This approach yields
a period range of 1.751 to 1.765 hours. Folding
the radio data by different periods (Fig. 4)
shows that pulses align in phase for periods
in the range 1.751 to 1.765 hours but are not
well aligned for periods outside that range.
For an IR period ofTatmosphere= 1.741 ±
0.007 hours, a uniformly distributed radio period
ofTinterior= 1.751 to 1.765 hours, and a radius
of 67,200 km ( 24 ), Eq. 1 gives a wind speed

for 2MASS J1047+21 of 650 ± 310 m s−^1. This

assumes that the IR variability originates in

the equatorial region, but Eq. 1 can be adapted

to other latitudes by scaling by the cosine of the

latitude. The inclination of 2MASS J1047+21’s

rotation is unknown, but all other radio-

bursting brown dwarfs with known inclinations

are viewed nearly equator-on ( 18 ). Photometric

variability most commonly originates at equa-

torial to mid-latitudes of less than 35° ( 21 , 27 ).

Thus, latitudinal or viewing-angle effects would

likely change the result by less than the uncer-

tainty. The measured wind speed is that of

the (unknown) atmospheric inhomogeneity

that dominates the photometric variability.

If this atmospheric feature occurs between

bands of zonal wind having alternating wind

direction, our measured wind speed would

underestimate the true zonal wind speeds.

Some of Jupiter’s atmospheric features are

SCIENCEsciencemag.org 10 APRIL 2020•VOL 368 ISSUE 6487 171

Fig. 3. Radio light curve of 2MASS J1047+21 from VLA observations.
(AtoC) Left-circularly polarized radio flux in microjanskys (points) on three
consecutive nights of observations, each lasting about 10 hours. 1suncertainties
are plotted as vertical lines for each data point. Radio pulses of varying intensity

are evident. Thin vertical dashed lines indicate pulse TOAs ( 23 ). Thick vertical

solid lines indicate TOAs from the best-fitting period derived from these data,

labeled with the number of rotations since the start of the observation. The data

cover about 18 rotations out of 34 that occurred in this period.

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