Nine days ago, a stream of photons exploded off the sun’s corona and flew 93-million miles, to the blue, wave-wrinkled surface of the southern Atlantic ocean. The dark waters swallowed some of these photons, but others ricocheted back into space, where they traveled nearly 900-million miles more. A few concluded this long journey by threading a cosmic needle. They approached Saturn at the perfect angle to pass between two of its rings, and into a camera attached to Cassini, a space probe that has circled the sixth planet since 2004.
Cassini beamed the resulting snapshot back to NASA’s Jet Propulsion Laboratory in Los Angeles. After some spiffing up at the Space Science Institute in Boulder, Colorado, it was converted into light pulses, and sent out into the messy snarl of fiber-optic tubes that spans our planet, so that anyone with a networked screen could admire this singular image, of the only world in the cosmos known to host life. Call it an early Earth Day present, from a robot on the far side of the solar system.
Tomorrow, tens of thousands of people will mark that vaguely pagan holiday by taking to the streets, in protest of a Trump administration they perceive as hostile to science. Many will hold up signs mocking the administration’s proposed budget, which, among other research cuts, defunds several of NASA’s Earth Science missions, including the Deep Space Climate Observatory, and new satellites that monitor cloud systems and plankton blooms.