New adventures for New Horizons

Space probe heads for distant object that might not exist.

The New Horizons space probe, which in 2015 beamed back humanity’s best-ever views of Pluto, is hurtling through the outer reaches of the solar system on its way to rendezvous with a lump of ice known as 2014 MU69.

It won’t get there for more than a year – the fly-by is expected on 31 December 2018 or 1 January 2019 – so the spacecraft is hibernating to conserve energy Meanwhile, scientists are doing everything they can to find out as much as possible about its target before it gets there.

2014 MU69 sits in the Kuiper belt, a broad disc of small floating bodies way beyond Neptune, four to six billion kilometres from the Sun. In some ways it mirrors the asteroid belt between Mars and Jupiter, though Kuiper belt objects are on the whole much icier.

Very little is known about 2014 MU69: it was only discovered in 2014, when astronomers used the Hubble Space Telescope to look for something interesting beyond Pluto that New Horizons might be able to manoeuvre itself towards. Because it is so tiny and distant it’s hard to get a good look.

Astronomers have been watching very closely when MU69 passes in front of a background star. On these occasions, known as stellar occultations, observing changes to the image of the star reveals information about the size of the lump, and also whether any debris near it might pose a navigation hazard.

The first occultation occurred on 3 June. More than 50 observers set up telescopes in South Africa and Argentina to observe it. Although the event lasted only two seconds, the telescopes captured more than 100,000 images.

The observers did see the background star dimming but were unable to make any direct observations of 2014 MU69 itself, which suggests it is smaller than thought. It is also possible it is actually a swarm of objects, rather than a single entity.

Two other occultations in July were observed by NASA’S airborne Stratospheric Observatory for Infrared Astronomy and the Hubble Space Telescope.

When all the data has been analysed, the New Horizons team should have everything they need to make sure that when the probe wakes up on its journey through the void, it will have the best information possible to guide it on its way.

See the future of space missions, page 72.