NASA's New Horizons probe just woke up after 321 days—with Kuiper Belt data in hand

The New Horizons probe—currently 5.9 billion miles away—was awakened on June 23 after a 321-day hibernation period, NASA confirmed Tuesday. The spacecraft had been gathering data in the distant Kuiper Belt beyond Pluto during this period and is now ready to transmit it to Earth.

Because of New Horizons' extreme distance, the radio signals confirming the successful wake-up call took 8 hours and 52 minutes to reach Johns Hopkins APL (Applied Physics Laboratory) Mission Operations Center via NASA's Deep Space Network station located near Madrid, Spain. During such phases when New Horizons is placed into this resource-saving hibernation, controllers do not send any commands or retrieve data, but its heliospheric plasma sensors—Solar Wind at Pluto and the Pluto Energetic Particle Spectrometer Science Investigation—and its space dust detector—the Venetia Burney Student Dust Counter—stay online. 

During the nearly year-long silence, which was New Horizons' longest hibernation period, the spacecraft was not entirely cut off from its handlers. Alice Bowman, the New Horizons mission operations manager at APL, explained that the spacecraft regularly reported back to Earth with a weekly status beacon. “Every status report through this hibernation period was ‘green,’ meaning all was well aboard New Horizons each and every week," she said. In about three weeks, the onboard Alice ultraviolet spectrograph will be activated to study the distribution of hydrogen gas in the outer heliosphere—a bubble created by solar wind that protects the planets in our solar system from cosmic radiation. The other three instruments mentioned above will also continue their measurements. The team will begin retrieving data from these three instruments after they have downlinked the health and safety data of the spacecraft.

The ground-system software is also set to undergo upgrades that will help maintain the spacecraft's operations, with tests already underway. Designed for operations farther from the Sun, the updated autonomy logic that New Horizon is running on accommodates the reduction in power and the increase in radio-signal travel time.

Launched by NASA in January 2006, the probe holds the distinction of being the first to explore Pluto up close, flying by the dwarf planet and its moons in 2015. In 2019, New Horizons broke another record by flying by the Kuiper Belt object Arrokoth, making the latter the most distant object ever observed up close.

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