Correction to: Nature Astronomy https://doi.org/10.1038/s41550-019-0772-5, published online 20 May 2019.

In the version of Letter originally published, there was an error in the units shown Fig. 4. Specifically, the color bar labels in Fig. 4a, now reading as ± “0.014 mT yr–1”, originally read ± “0.015 nT yr–1.” Further, there was an error in the color bar units at center-bottom of Fig. 4, where ± “1.5 mT” has been changed to read ± “1.4 mT”.

The errors have been corrected in the online version of the article.