This weekend, a team of scientists who sent the first spacecraft to Pluto caught a brief glimpse of their vehicle’s next destination: a tiny, primitive space rock at the edge of the Solar System. Members of the mission team trekked down to a remote part of Argentina and spotted the distant object with numerous telescopes as it passed in front of a background star, blocking out the star’s light. It was a momentary eclipse — known as an occultation — and though it lasted just seconds, the sighting will provide useful information about the shape and size of the object that the spacecraft will visit next year.
That spacecraft is New Horizons, which famously flew within 8,000 miles of Pluto in July 2015. The vehicle was never meant to stop at the dwarf planet, though. Instead it zoomed by Pluto at more than 30,000 miles an hour and has been journeying farther outward in the Solar System ever since. New Horizons was designed to last for years after the flyby, and the vehicle is still fully operational. So rather than let a functioning spacecraft go to waste, NASA decided to extend the New Horizons’ mission and send it on to another object at the Solar System’s edge.
Now, New Horizons is on its way to meet up with an object in the Kuiper Belt — the large cloud of small, icy bodies that orbit beyond Neptune. The object in question is called 2014 MU69, and it’s thought to be an incredibly old space rock that’s remained relatively unchanged since the Solar System first formed 4.6 billion years ago. But tracking 2014 MU69 has been pretty tough. It’s only about 30 miles wide, and it orbits over 4 billion miles from Earth. That makes it incredibly faint and hard to see. Up until now, the Hubble Space Telescope has been the only observatory that could spot 2014 MU69, and it still couldn’t tell scientists the exact shape and size of the object.
That’s why the New Horizons team set out to see 2014 MU69 with an occultation. “The only thing we have to navigate to this target is our Hubble-based orbit,” Alex Parker, a senior research scientist at the Southwest Research Institute in Colorado and member of the New Horizons mission team, tells The Verge. “We were really trying to understand what we do and don’t know.” Using the Hubble data, along with precise star positions measured by Europe’s Gaia satellite, the team predicted various times when 2014 MU69 might pass directly in front of a star.
However, the first two times the scientists tried to see the occultation, they didn’t see the object’s shadow. The first attempt was on June 3rd, with two separate teams looking in Argentina and South Africa, and the scientists tried again on July 10th with NASA’s SOFIA airplane — a flying observatory — as it flew over the Pacific Ocean. It wasn’t until this weekend, just before midnight Eastern Time on Sunday, that the mission team finally caught the occultation while huddled around telescopes in Chubut and Santa Cruz, Argentina. Amanda Zangari, a co-investigator on New Horizons and scientist at the Southwest Research Institute, was the first to spot the event after looking through data collected over the weekend. “We nailed it spectacularly,” she said in a statement.
In fact, up to five different telescopes were able to spot the occultation in Argentina, giving the New Horizons team five different angles of the event. All of these measurements will help them to better measure how big 2014 MU69 is, the object’s shape, and its brightness. For instance, they can figure out if the space rock is shaped more like a peanut or if it’s mostly round. “It’s exciting to get our first look at what this thing looks like,” says Parker. “It’s the first time we have the physical properties of that target revealed. It’s going to be really exciting to see that as the data gets cleaned up.”
Knowing the size, shape, and brightness of 2014 MU69 will definitely help the team better plan New Horizons’ flyby of the target, which is supposed to happen on New Year’s Day in 2019. If the object turns out to be relatively big and dark, then the spacecraft will need to increase its camera’s exposure to get better images, for instance. All these details and measurements will allow the New Horizons team to figure out the best sequence of events for the flyby and ensure that the spacecraft’s instruments get the best data it can of 2014 MU69.
Plus, the occultation has also served as a check on the team’s work up until now. Being able to predict when the occultation would occur — and then see it — means the New Horizons scientists have accurately figured out the orbit of 2014 MU69. And they can now go back and figure out why they didn’t see the occultation during the first two attempts. “It’s a really good sign we do actually know what’s going on,” says Parker. “It’s a load off. We do know what we’re doing and we’ll be able to navigate there as we need to.”