Checking out the Kuiper Belt

This week’s green light signal from the Kuiper Belt-bound New Horizons came when the spacecraft was more than 436 million kilometers from Earth. It was traveling a speed (with respect to the Sun) of 14.2 meters per second. At the rate it’s going, NH will encounter object MU69 on the first day of January 2019. The Voyager and Pioneer spacecraft are much farther away and have sent back information about the interplanetary medium at their locations. They’re moving in other directions, no longer seeking out new worlds. New Horizons is still an active planetary exploration mission, extending our gaze to the Kuiper Belt. You can follow its progress on the mission website.

Reasons For Kuiper Belt Explorations

As NH and other spacecraft move out through these distant reaches, the question comes up: what do we expect to learn out there? Of course, the obvious answer is that we want to find and study other worlds. It’s not likely that NH will find more distant places. However, it is on track to study at least one more. MU69 is its next target. This tiny worldlet was found by the Hubble Space Telescope and has been studied from Earth through occultation tracking. That means astronomers have watched it via telescopes as it passed between us and a star. Those observations helped them determine a rough shape for MU69.

Of course, there are other worlds in the Kuiper Belt, such as Eris and Quaoar. No spacecraft is headed toward them. New Horizons’s study of Pluto, its moons, and MU69, is likely the best “close-up” look we’re going to get of places in the Kuiper Belt.

It’s not just worlds out there that beckon our interest. The solar wind still has an influence on the distant solar system, and interplanetary space in the region contains a fair amount of dust and gas. Those are important to measure. As well, cosmic rays and other radiation from beyond the solar system can be detected and measured. It’s as important to know all of the components of the outer solar system—from planets and their moons to magnetic fields, solar wind particles, and cosmic rays.

What Green Beacons from the Kuiper Belt Mean

Every Monday, the spacecraft team for the New Horizons mission “listens” for a signal from their fast-moving spacecraft. This grand-piano-sized probe is on its way to another object in the Kuiper Belt, called MU69. These beacons are important because they are the only signal the team gets while New Horizons is in hibernation. That means most (if not all) of its systems are powered down or in very limited-use mode. It conserves energy, equipment, and wear and tear on the electronics on the spacecraft while it’s en route to its next target.

Once the beacon is received, the team can get back to work on their planning. Alan Stern, PI of the team, usually tweets a “green beacon” announcement, letting the rest of the world know all is well. He described the beacon process in a “PI’s Perspective” blog entry in 2008.

What New Horizons Beacon Tones Mean

There are several beacon tones that New Horizons could send. Green is the best—it means that everything’s right on the nominal, that nothing is wrong with the sleeping spacecraft. It’s the equivalent of a text message saying, “Doing good, talk next week”. Anything not-green, particularly if it’s a red beacon tone, means there is (or could be) a problem. Luckily, throughout the mission, the green beacons outnumber the reddish ones. Right now the spacecraft is sleeping happily and will do so until mid-year 2018 when flyby operations start up again.

In the meantime, while New Horizons may be slumbering its way across the inner limits of the Kuiper Belt, its scientists and technical support staff members are busy rehearsing the next flyby, which will take place January 1, 2019. At that point, Earth and the spacecraft will be in the neighborhood of 43 astronomical units apart. That’s 6,432,708,440 kilometers, or 3,997,099,712 miles. Signals from the flyby will take six hours to get to Earth, making round-trip communication a 12-hour-long “conversation”.