NASA's James Webb Space Telescope will see the first galaxies to form after the Big Bang, but to do that, its instruments first need to get cold—really cold. On April 7, Webb's Mid-Infrared Instrument (MIRI)—a joint development by NASA and ESA (European Space Agency)—reached its final operating temperature below 7 kelvins (minus 447 degrees Fahrenheit, or minus 266 degrees Celsius).