So was a data collaboration with NASA, the first cooperation since a 2011 law banned such activity without congressional approval. With the government shutdown, it remains unclear whether Capitol Hill gave its okay..

Chinese space agency’s deputy director, Wu Yanhua, and NASA exchanged information to help better monitor the landing, according to the Associated Press. NASA provided information about its lunar orbiter satellite and China shared the time and coordinates of the intended landing. NASA was able to take pictures that it shared after the probe was on the moon’s surface.

The Chinese probe, named Chang’e 4, launched on Dec. 7, 2018, and landed on Jan. 2, 2019, according to The Verge.

The dark side of the moon is a challenge to explore because it faces away from the Earth, making direct radio contact and control of a remote device impossible. China used a combination of an exploratory vehicle and orbiting satellite that related signals back and forth.

Unless previously authorized by Congress, the collaboration could have violated U.S. law. As part of a spending bill passed in 2011, a two-sentence addition prohibited NASA or the White House Office of Science and Technology Policy from using federal funds “to develop, design, plan, promulgate, implement, or execute a bilateral policy, program, order, or contract of any kind to participate, collaborate, or coordinate bilaterally in any way with China or any Chinese-owned company,” according to Forbes.

Fortune has called NASA for a comment and is seeking congressional comment.